ArticlePDF Available

Effects Of Caffeine And Ethanolic Extract Of Kolanut On Glucose Uptake In The Canine Hindlimb At Rest And During Contraction

Authors:

Abstract and Figures

The study investigated the effects of caffeine and ethanolic extract of kolanut (EEK) on glucose uptake in the canine hindlimb at rest and during contraction. Thirty male anaesthetized Mongrel dogs (11 - 13kg) were divided into six groups (5dogs/group). Caffeine (6mg/kg), EEK (5mg/kg), or normal saline (control) was administered intravenously to each group at rest. Arterial and venous blood samples were collected at 0, 5, 10, 15, 20, 25, 30, 45, 60, 75 and 90 minutes after drug administration. Blood glucose was measured by glucose oxidase method. Arterio-venous (A-V) glucose difference was calculated and venous blood flow (VBF) was measured during the sampling period. Hindlimb Glucose Uptake (HGU) was calculated as the product of (A-V) glucose and blood flow. After sampling at rest, the experiments were repeated with the right femoral nerve stimulated using electrical stimulator at 5Hz. At rest, (A-V) glucose increased significantly (P<0.05) from 4.2±0.2mg/dl to 29.8 ± 8.6, and 24.4±2.6 for caffeine and EEK respectively. VBF decreased to 2.0±0.9 and 6.0±0.6ml/min for caffeine and EEK respectively. However, HGU significantly increased from 34.8±0.1mg/min to 74.5±3.2mg/min and 175.8±3.4mg/min for caffeine and EEK, respectively. Contraction of the hindlimb muscle alone significantly increased the (A-V) glucose (68%), VBF (26%) and HGU (120%) when compared with the control. During contraction, (A-V) glucose increased from 4.3±1.5mg/dl to 35.6±3.0mg/dl, and 27.0±2.2mg/dl for caffeine and EEK respectively. VBF also increased from 8.4±0.3ml/min to 12.8±0.3ml/min for EEK. Although, contraction improves VBF (7.3±0.5ml/min) to the hindlimb in response to caffeine, the value was significantly (P<0.05) lower than that of control (8.4±0.5ml/min). Contraction also significantly increased HGU from 35.8±3.6mg/min to 249.0±3.3 and 286.72±2.0mg/min for caffeine and EEK, respectively. The results showed that caffeine and EEK significantly increased HGU and that these effects are due to the increases in glucose extraction ((A-V) glucose) caused by caffeine and EEK.
Content may be subject to copyright.
33
EFFECTS OF CAFFEINE AND ETHANOLIC EXTRACT OF KOLANUT ON
GLUCOSE UPTAKE IN THE CANINE HINDLIMB AT REST AND DURING
CONTRACTION
H. M. SALAHDEEN AND A. R. A. ALADA
Department of Physiology, College of Medicine, University of Ibadan, Ibadan, Oyo State, Nigeria
E-mail: dralada@yahoo.com
Summary: The study investigated the effects of caffeine and ethanolic extract of kolanut (EEK) on glucose
uptake in the canine hindlimb at rest and during contraction. Thirty male anaesthetized Mongrel dogs (11
- 13kg) were divided into six groups (5dogs/group). Caffeine (6mg/kg), EEK (5mg/kg), or normal saline
(control) was administered intravenously to each group at rest. Arterial and venous blood samples were
collected at 0, 5, 10, 15, 20, 25, 30, 45, 60, 75 and 90 minutes after drug administration. Blood glucose was
measured by glucose oxidase method. Arterio-venous (A-V) glucose difference was calculated and venous
blood flow (VBF) was measured during the sampling period. Hindlimb Glucose Uptake (HGU) was
calculated as the product of (A-V) glucose and blood flow. After sampling at rest, the experiments were
repeated with the right femoral nerve stimulated using electrical stimulator at 5Hz. At rest, (A-V) glucose
increased significantly (P<0.05) from 4.2±0.2mg/dl to 29.8 ± 8.6, and 24.4±2.6 for caffeine and EEK
respectively. VBF decreased to 2.0±0.9 and 6.0±0.6ml/min for caffeine and EEK respectively. However,
HGU significantly increased from 34.8±0.1mg/min to 74.5±3.2mg/min and 175.8±3.4mg/min for caffeine
and EEK, respectively. Contraction of the hindlimb muscle alone significantly increased the (A-V) glucose
(68%), VBF (26%) and HGU (120%) when compared with the control. During contraction, (A-V) glucose
increased from 4.3±1.5mg/dl to 35.6±3.0mg/dl, and 27.0±2.2mg/dl for caffeine and EEK respectively. VBF
also increased from 8.4±0.3ml/min to 12.8±0.3ml/min for EEK. Although, contraction improves VBF
(7.3±0.5ml/min) to the hindlimb in response to caffeine, the value was significantly (P<0.05) lower than
that of control (8.4±0.5ml/min). Contraction also significantly increased HGU from 35.8±3.6mg/min to
249.0±3.3 and 286.72±2.0mg/min for caffeine and EEK, respectively. The results showed that caffeine and
EEK significantly increased HGU and that these effects are due to the increases in glucose extraction ((A-
V) glucose) caused by caffeine and EEK.
Key words: Caffeine, kolanut, dog, glucose uptake, hindlimb
Introduction
Administration of caffeine has been
demonstrated to cause a transient impairment of
glucose tolerance in able-bodied human (Graham
et al, 2001; Petrie et al, 2004; Robinson et al,
2004; Thong and Graham 2002). During an oral
glucose tolerance test (OGTT) caffeine ingestion
results in elevated insulin and C-peptide
responses without a subsequent lowering of the
glucose response (Graham et al, 2001; Thong
and Graham 2002), suggesting a caffeine-
induced impediment to the action of insulin. This
impediment in the action of insulin is further
demonstrated by studies employing the
euglycaemic-hyperinsulinemic clamp technique
that reported a 15-25% decrease in whole body
insulin-mediated glucose disposal following
caffeine ingestion (Thong and Graham 2002;
Keijzers et al, 2002; Thong et al., 2002).
Furthermore, Thong et al, (2002) demonstrated a
50% decrease in skeletal muscle (leg) glucose
uptake, which is the predominant tissue
responsible for whole body glucose disposal in
humans.
The mechanism by which caffeine decreases
glucose tolerance and/or glucose disposal
remains undetermined. Although caffeine is a
known adenosine receptor antagonist (Biaggioni
et al, 1991; Smits et al, 1987), it remains unclear
as to whether or not adenosine contributes
significantly to insulin-mediated glucose uptake
with skeletal muscle. Within adipose tissue,
adenosine has been consistently reported to
enhance insulin-mediated glucose uptake (Christ
et al, 1998; Hellsten, et al, 1998); however, the
results obtained for skeletal muscle have been
conflicting. Studies conducted on rodent muscle
have demonstrated increases (Espinal et al,
1983; Leighton et al, 1988), decreases (Han et
al, 1998) and no change (Vergauwen et al,
1994) in insulin-mediated glucose uptake
following the administration of an adenosine
receptor antagonist. In humans, the infusion of
the adenosine reuptake inhibitor dipyridamole
failed to show an enhancement of whole body
insulin-mediated glucose disposal during a
euglycaemic-hyperinsulinemic clamp, suggesting
Nigerian Journal of Physiological Sciences 24(1):33-45 ©Physiological Society of Nigeria, 2009
Available online/abstracted at http://www.biolineinternational.org.br/nps; www.ajol.info/journals.njps;
www.cas.org
34
that adenosine may not contribute significantly
to insulin action in humans (Graham et al, 2001).
Again, until recently, it was believed that the
small, albeit significant, elevation in epinephrine
concentration observed following caffeine
ingestion was most likely responsible for the
impairment in glucose tolerance (Thong and
Graham 2002; Battram et al, 2005). However,
although epinephrine is a potent antagonist of
insulin-mediated glucose disposal (Deibert and
De Fronzo 1980; Bessey et al, 1983, Baron et
al, 1987), the infusion of epinephrine in
concentrations similar to those observed
following caffeine ingestion did not significantly
impede insulin-mediated glucose disposal
(Battram et al, 2005).
Most of the literature on the relationship
between caffeine and glucose uptake in skeletal
muscle have been limited to humans and rodents
with little work done on dogs. However, a recent
report by Pencek et al, (2004) showed that
infusion of caffeine through the portal vein in
conscious dogs caused significant increases in
hepatic glucose uptake. There is no information
on how the skeletal muscle handles glucose
uptake following administration of caffeine in
the dog. The present study was therefore
designed to study the effect of intravenous
administration of caffeine on the glucose uptake
by the canine hindlimb. The second part of this
study also tried to investigate the effect of
kolanut extract on the glucose uptake by the
canine hindlimb. Kola nut contains several
organic compounds including caffeine. There are
reports that suggest that caffeine content of kola
nut could be as high as 7% (Ogutuga, 1975) and
is often considered to be the agent responsible
for the biological action of kola nut (Chukwu et
al, 2006). The question now asked is: Will kola
nut extract produce the same effect as caffeine
on the hindlimb glucose uptake?
Materials and methods
Selection of Kolanut and preparation of
ethanolic extract:
Seeds of specie Cola nitida were used in this
study. The seeds were purchased from a market
in Ibadan, Nigeria and authenticated for
identification at the Department of Botany and
Microbiology, University of Ibadan where a
sample was kept. The seeds were dried under
shade for almost two weeks and thereafter
reduced to powdered form. One kilogram of the
powdered seeds was obtained and exhaustively
extracted with ethanol. Powdered kola nut was
extracted (1kg per 2 liters) two times with
ethanol and water (80:20 V/V) for 1 h at room
temperature, under magnetic stirring. After
filtration, the solvent was evaporated at 40
0
C
under vacuum (Rotavapor), and final ethanolic
extract lyophilized. The extract solution was
prepared as suspension with 4g/100ml of saline
for the physiological and pharmacological
studies.
Toxicity study
Acute toxicity of the kolanut ethanolic
extract was evaluated using male Swiss mice
(25-35grams). An initial pilot study was
conducted to determine the dose range of the
extract to be used for the study. Fifty–five mice
were used to determine the LD
50.
The mice were
divided into 11 groups of 5mice per group. The
doses administered were selected after
preliminary experiments. The animals were then
observed for a period of 72 hours post-treatment
for clinical signs of toxicity such as movements,
weakness, sleeping and death to determine the
LD
50
.
Experimental procedure:
Male mongrel dogs weighing 11-13kg were
used for the study. Each animal was fasted for
18-24hr before the start of an experiment.
Anaesthesia was induced by i.v injection of
sodium pentobarbitone, 30mg/kg. Light
anaesthiesia was maintained with supplemental
doses of i.v. sodium pentobarbitone as necessary.
The trachea was intubated using endotracheal
tube and the animal was allowed to breath room
air (temp. 25
0
C) spontaneously.
The right femoral vein and artery were
cannulated. The cannula in the right femoral vein
was moved into an extracorporeal position and a
non-crushing clamp was applied to its free end.
The left femoral vein was cannulated for the
administration of drug and left femoral artery
was also cannulated and connected to a two-
Channel physiographic recorder through pressure
transducer model 7070 Gemini (Ugo basil) to
monitor blood pressure and heart rate.
The right femoral nerve was isolated and
muscular contraction was induced by electrical
square pulses of 0.2ms duration using electrical
student stimulator to the nerve (Brooks
Instruments, UK). The output voltage was
limited to 2.5, 5 or 10Hz for nonpainful muscle
contraction for thirty minutes (Hamada et al,
2004). At the end of surgical procedure, sodium
heparin 300unit per kg-body weight was
administered intravenously to prevent blood
clotting. After all surgical procedures were
completed, a 60-90 minutes stabilization period
H. M. Salahdeen and A. R. A. Alada
35
was observed. The blood flow to the hindlimb
was measured by time collection of the blood
from the right femoral vein as previously
described by (Alada and Oyebola, 1996).
Arterial and venous blood samples for glucose
estimation were obtained from the cannula
placed in the right femoral artery and vein
respectively. After stabilization, basal
measurements of the femoral venous blood flow,
arterial and venous glucose were determined.
The experiments were carried out in six groups
(with 5dogs per group). In each group, blood
samples for basal glucose measurements were
obtained and basal blood pressure and blood
flow were also monitored.
Group I (Control)
A bolus injection of normal saline (0.1ml/kg)
was given through the femoral vein. Blood
pressure and hindlimb blood flow measurements
were continuously monitored, while the arterial
and venous blood samples for glucose estimation
were obtained at 5min, 10min, 15min, 20min,
25min, 30min, 45min, 60min, 75min, and 90min
post-injection.
Group II (Normal saline and hindlimb muscle
contraction)
A bolus injection of normal saline (0.1ml/kg)
was given through a cannula in the femoral vein
during which the femoral nerve was electrically
stimulated at 5Hz for thirty minutes using
student stimulator (Brooks Instruments, UK) to
produce contraction of the hindlimb muscles.
The procedures for blood pressure recording,
blood flow rate measurement, and blood sample
collection for glucose estimation from arterial
and venous ends during hindlimb muscle
contractions were repeated as in group I.
Group III (Caffeine)
A bolus injection of caffeine at a dose of 3, 6
or 9mg/kg, was given i.v to three separate
subgroups of dogs, each subgroup containing
5dogs. The procedure for blood pressure
recording, blood flow rate measurement, and
blood samples collection from the femoral artery
and vein were repeated as in group I.
Group IV (Caffeine and hindlimb muscle
contraction)
A bolus injection of caffeine at a dose of
(6mg/kg), was given i.v. through the femoral
vein followed by stimulation of femoral nerve to
produced hindlimb contraction for thirty
minutes. The procedures for blood pressure, and
blood flow monitoring, arterial and venous blood
sampling were carried out as in group I during
the hindlimb contraction and after stimulation of
the nerve.
Group V (Kolanut extract)
A bolus injection of kolanut extract in a dose
of 2.5mg/kg or 5mg/kg), was given i.v. through
the femoral vein to two separate subgroups with
5dogs per subgroup.. The procedure for blood
pressure recording, blood flow rate measurement
and blood sample collection from femoral artery
and vein were repeated as in-group I.
Group VI (Kolanut and hindlimb muscle
contraction)
A bolus injection of kolanut extract at a dose
of (5mg/kg), was given i.v. through the femoral
vein followed by stimulation of femoral nerve to
produced hindlimb contraction for thirty
minutes. The procedures for blood pressure, and
blood flow monitoring, arterial and venous blood
sampling were carried out as in group I during
the hindlimb contraction and after stimulation of
the nerve.
Blood glucose measurement
Blood glucose was determined with one
touch basic-plus glucometer. The meter was
checked against the standard glucose solution at
regular interval to ensure accuracy. Result of
blood glucose measurement using glucometer
correlates excellently with the results obtained
from standard laboratory methods (Ajala et al,
2003; Devreese and Leroux-Roels 1993).
Glucose uptake was computed as the product of
the (A-V) glucose and blood flow (Alada and
Oyabola 1997).
Data were analyzed using Microsoft Excel
statistical package. All values given are the mean
±S.E of the variables measured. Significance was
assessed by the analysis of variance (ANOVA)
followed by a post hoc Fisher’s PLSD test for
multiple comparisons. P values of 0.05 or less
were taken as statistically significant.
Table 1: Effect of ethanolic extract of kolanut on
acute toxicity in mice
Groups
Doses
mg/kg
No of
Death Percentage
I 1 0 0
II 100 0 0
III 1000 0 0
IV 2000 0 0
V 3000 0 0
VI 6000 0 0
Caffeine and kolanut extract on canine hindlimb glucose uptake
36
Results
Acute toxicity tests in mice:
Table 1 shows the acute toxicity results after
administration of graded doses of ethanolic
extract of kolanut in mice. The results showed
that there were no deaths caused by graded doses
of the extract even at very high doses.
Effect of normal saline on blood glucose, blood
flow and Hindlimb Glucose Uptake (HGU) at
rest and during hindlimb muscle contraction
Normal Saline has no significant effect on
arterial and venous blood glucose, (A-V) blood
glucose, blood flow and hindlimb glucose uptake
by the dog. The resting arterial and venous blood
glucose levels were 99.3±1.4mg/dl and 95.2±1.5
mg/dl respectively. The resting (A-V) glucose
was 4.2±0.2mg/dl and the resting blood flow to
the skeletal muscle was 8.3 ± 0.2 ml/min. At rest,
the Hindlimb Glucose Uptake (HGU) in the dogs
was 34.8 ± 0.1 mg/min.
Contraction of hindlimb muscle caused
insignificant increases in both arterial and
venous glucose levels from 99.3±1.4mg/dl, and
95.2±1.5 mg/dl to 120±6.6 mg/dl and
98.4±3.3mg/dl at twenty and twenty-five minutes
respectively (Table 2). Figure 1a shows the
effect of hindlimb contraction on arterio-venous
glucose difference during hindlimb muscle
contraction. There was a steady rise in (A-V)
glucose, from 4.2±0.2mg/dl to 24±2.7mg/dl
which reached its peak twenty minutes into the
contraction period and thereafter gradually
returns towards the basal level. The blood flow
to the hindlimb also significantly increased from
8.3 ± 0.2 ml/min to 14.5±0.6ml/min (p< 0.01)
and was sustained throughout the contraction and
post-contraction observation periods (Figure 1b).
Glucose uptake increased steadily from 34.8 ±
0.1 mg/min to 180.7±3.3mg/min in the first
20min, reaching its peak, and thereafter started to
decrease. (Figure 1c). It is to be noted, that even
in the post-contraction observation period, (A-V)
glucose and glucose uptake did not return to the
basal level.
Effect of caffeine on blood glucose, blood
flow and Hindlimb Glucose Uptake (HGU) at
rest in dogs
The effects of different doses (3, 6, and
9mg/kg) of caffeine on blood glucose are shown
in table 3. Caffeine at 6mg/kg caused significant
increases in arterial blood glucose from
99.2±0.7mg/dl to 160.2±1.2mg/dl at fifteen
minutes post-injection. The increase in blood
glucose was immediate and sustained throughout
the 90min post-injection observation period.
Caffeine at 6mg/kg also produced significant
increase in venous blood glucose from
94.9±1.5mg/dl to 130.6±2.3mg/dl which was
sustained. The venous blood glucose levels are
however lower than the arterial glucose levels
throughout the post-injection observation period.
3mg/kg of caffeine did not produce any
significant effect on both the arterial and venous
blood glucose levels. At a higher dose of
9mg/kg, caffeine produced significant reductions
in both arterial and venous blood glucose levels
from 99.3±1.2 mg/dl and 95.2±1.5mg/dl to
88.0±5.3mg/dl and 74.6±6.1mg/dl respectively.
The different doses of caffeine produced
significant increases in the arterio-venous
glucose difference in the hindlimb (figure 2a).
While both 3mg/kg and 9mg/kg caffeine caused
slight but significant increases in glucose
extraction by the hindlimb, 6mg/kg produced a
more significant effect. The effect of 6mg/kg of
caffeine on glucose extraction by the hindlimb
was immediate and sustained throughout the
post-injection observation period. While 3mg/kg
and 9mg/kg caffeine increased (A-V) glucose
from 4.2±0.2mg/dl to 19.6±2.4mg/dl and
21.6±5.4mg/dl respectively (P<0.05), 6mg/kg
caffeine produced maximum (A-V) glucose of
29.6±8.6 mg/dl (P<0.01). Figure 2b shows that
caffeine significantly decreased blood flow to the
hindlimb. The three doses of caffeine decreased
blood flow also in a dose–dependent manner.
The effects of caffeine on the hindlimb glucose
uptake in the resting state are shown in figure 2c.
Both 3mg/kg and 6mg/kg of caffeine produced
significant increases in the glucose uptake from
35.6±1.2mg/min to 79±1.3mg/min and
75±3.2mg/min respectively (p<0.01). While,
9mg/kg of caffeine did not produce any
significant effect on the hindlimb glucose uptake.
Comparing the 3mg/kg and 6mg/kg of caffeine,
the 3mg/kg caffeine produced a more significant
(P<0.001) increase in the hindlimb glucose
uptake. The increases in hindlimb glucose uptake
in response to 3mg/kg and 6mg/kg of caffeine
were immediate and sustained throughout the
post-injection observation period.
H. M. Salahdeen and A. R. A. Alada
37
Table 2: Effect of intravenous injection of saline (0.1ml/kg) on arterial and venous blood glucose levels
(mg/dl) at rest and during hindlimb contraction in dogs. Values are expressed as Mean ± SEM. (n=5)
Table 3: Effects of intravenous injection caffeine (3, 6, 9 mg/kg) on arterial and venous blood glucose levels (mg/dl) in
dogs Values are expressed as mean ± SEM. (n=5) (*P<0.05; **P<0.01)
Effect of caffeine on blood glucose (A-V) glucose
and glucose uptake during hindlimb contraction
in dogs
The effect 6mg/kg of caffeine on blood
glucose during hindlimb contraction is shown in
table 4. Contraction of hindlimb did not affect
caffeine influence on arterial blood glucose
levels although a slight reduction in venous
glucose levels was obtained. The effect of
caffeine on the (A-V) glucose in a contracting
hind limb is shown in figure 3a. While caffeine
increased glucose extraction from 4.2mg/dl to
26.2mg/dl at rest, it also increased (A-V) glucose
from 4.2mg/dl to 35.6mg/dl during contraction
of the hindlimb. That is, contraction of hindlimb
potentiated the glucose extraction effect of
caffeine by the hindlimb (p<0.01).
The effects caffeine on blood flow during
hindlimb contraction is shown in figure 3b.
Although, caffeine caused significant
reduction in blood flow at rest, it however,
caused a slight but significant increase in the first
10mins and returned to basal level during the
contraction of the hindlimb. It must also be
added that the blood flow to the hindlimb was
significantly higher during the contraction of the
hindlimb than at rest throughout the post-
injection observation period.
The effect of caffeine on hindlimb glucose
uptake (HGU) during muscular contraction of
the canine hindlimb is shown in figure 3c.
Caffeine at rest increased hindlimb glucose
uptake (HGU) by about 272%. It further
increased HGU by about 411%, during
contraction of the hindlimb. That is, contraction
of hindlimb potentiated the action of caffeine on
the hindlimb glucose uptake in the dog.
Treatment
Time
(min) 0 5 10 15 20 25 30 45 60 75 90
Normal
Saline
(Rest)
Arterial
100
±1.4
97.4
±0.9
98
±0.8
98.2
±1.9
97.6
±1.2
98.4
±1.0
98.2
±1.4
97.6
±0.9
97.8
±0.8
97.6
±1.0
98.2
±0.4
Venous
95
±1.5
93.2
±1.7
92
±1.1
94
±1.2
93.2
±1.5
93.4
±1.4
92.2
±1.2
93.4
±1.6
92.2
±1.4
93.6
±1.6
92.2
±1.7
Normal
saline
hindlimb
contraction)
Arterial
99
±1.4
109
±5.4
115
±5.7
118
±6.5
120
±6.6
116
±6.1
117
±7.1
114
±5.6
115
±4.2
116
±5.5
115
±5.8
Venous
95
±6.0
94.2
±5.2
94
±6.2
95.6
±2.1
97.6
±2.1
98.4
±3.3
92.2
±4.2
93.6
±4.7
93.4
±5.1
93
±5.6
93
±5.6
Treatment
(min) 0 5 10 15 20 25 30
60 75 90
Caffeine
(3mg/kg)
Arterial
99.4
±0.7
103.
8
±3.2
96.2
±0.8
97
±2.5
97.4
±2.0
104
±3.5
101.4
±4.8
102
±4.0
102.2
±7.8
104.4
±6.4
107.2
±4.1
Venous
95.1
±1.5
86
±2.6
85.4
±2.6
85.6
±1.7
82.2
±4.7
84.4
±3.2
82.2
±4.3
±1.1
82.6
±5.2
85.4
±2.9
90.6
±2.0
Caffeine
(6mg/kg)
Arterial
99.2
±1.4
156.8
±1.9**
160.2
±1.2**
159.8
±1.9**
157.8
±1.6**
159.4
±2.4**
154.4
±3.5**
151.8
±2.8**
144.2
±1.2**
146.4
±3.5**
137
±5.3*
Venous
94.9
±1.5
140.4
±3.3**
133.8
±3.7**
137.6
±2.3**
133
±3.9**
129.6
±3.0**
132.6
±3.4**
128.4
±4.5*
127.6
±4.5*
115.2
±3.6*
124
±1.3**
Caffeine
(9mg/Kg)
Arterial
99.3
±1.2
93.4
±4.2
92.2
±5.9
89.6
±4.9*
88
±5.3*
92.6
±3.7
85.4
±5.3*
±3.0
92.8
±5.1
90.8
±6.0
93.2
±5.2
Venous
95.2
±1.5
83
±3.9
77.6
±3.6
77
±5.2
76.6
±4.3*
76
±5.2*
74.6
±6.1
68.4
±7.5*
74.6
±6.1*
73.4
±4.4*
72.8
±6.1*
Caffeine and kolanut extract on canine hindlimb glucose uptake
38
Table 4: Effects of intravenous injection of caffeine (6mg/kg) on arterial and venous blood glucose levels (mg/dl) during rest and
hindlimb contraction in dogs. Values are expressed as Mean ± SEM. (n=5) (*p<0.05; ** p<0.01)
Treatment (min) 0 5 10 15 20 25 30 45 60 75 90
Contraction
of Hindlimb Arterial
99
±1.4
109
±1.4
115
±5.4
118
±5.7
120
±6.5
116
±6.6
117
±6.1
114
±7.1
115
±5.6
116
±4.2
115
±5.5
Venous
95
±6.0
94
±5.2
94
±6.2
96
±2.1
98
±2.1
98
±3.3
92
±4.2
94
±4.7
93
±5.1
93
±5.6
93
±5.6
Caffeine
Contraction Arterial
99.3
±1.2
131
±3.7
154
±3.8*
160
±3.7**
156
±5.1**
151
±3.6**
156
±4.1*
148
±3.4*
149
±2.1*
149
±2.1*
148
±4.2*
Venous
95.4
±4.9
115
±5.4*
126
±4.0
132
±4.3*
123
±4.9
121
±3.1
121
±2.1
120
±2.1*
126
±3.2*
120
±2.3
118
±2.2*
Table 5: Effects of intravenous injection of ethanol extract of kolanut (EEK) (2.5 and 5 mg/kg) on arterial and venous blood
glucose levels (mg/dl) at rest in dogs. Values are expressed as Mean ± SEM. (n=5) (*p<0.05; ** p<0.01)
Treatment (min) 0 5 10 15 20 25 30 45 60 75 90
EEK
(2.5mg/kg) Arterial
99
±1.1
116
±3.7**
96.2
±4.8
91
±4.1
86.2
±3.8*
82.2
±4.6*
78.4
±4.5*
74.8
±3.5**
76.6
±5.8*
82
±7.0
83
±8.2
Venous
96
±1.7
86.2
±3.1
77.6
±4.0*
75
±3.9**
68.4
±3.9***
67.4
±4.7***
63
±4.9***
60.4
±4.3***
69.2
±4.6***
73
±6.1*
76
±7.3
EEK
(5mg/kg) Arterial
99
±1.2
115
±1.9**
130
±5.7***
121
±6.2**
118
±5.3**
114
±5.3**
109
±3.6
106
±3.6
110
±4.6
105
±3.8
109
±6.7
Venous
96
±1.4
92.4
±3.3
106
±6.8
100
±6.2
101
±5.6
98.6
±4.9
92.8
±4.2
93.6
±4.4
91
±1.9
90
±1.9*
96
±7.8
Table 6: Effects of intravenous injection of kolanut ethanolic extract (KEE) (5mg/kg) on arterial and venous glucose (mg/dl)
during rest and during hindlimb muscles contraction in dogs. Values are expressed as Mean ± SEM. (n=5) (*p<0.05;
** p<0.01)
Time
(min)
0
5
10
15
20
25
30
45
60
75
90
Contraction
of Hindlimb Arterial
99
±1.4
109
±1.4
115
±1.4
118
±5.4
120
±5.7
116
±6.5
117
±6.6
114±6
.1
115
±7.1
116
±5.6
115
±4.2
Venous
95
±6.0
94
±5.2
94
±6.2
96
±2.1
98
±2.1
98
±3.3
92
±4.2
94
±4.7
93
±5.1
93
±5.6
93
±5.6
EEK
Contraction Arterial
99
±1.1
115
±1.9
**
130
±5.7*
**
123
±5***
123
±3.4
***
120
±3.1*
**
112
±3.0*
*
108
±3.2*
109
±4.8*
105
±4*
109
±7*
Venous
94
±1.7
104
±1.1
110
±4.9*
107
±2.5*
105
±4.3
*
104
±2.8*
98
±1.0
93
±2.2
95
±2.3
91
±1.1
96
±7.3
Effect of ethanolic extract kolanut (EEK) on
blood glucose, (A-V) glucose and hindlimb
glucose uptake (HGU) in the resting dog
The two doses of EEK (2.5mg/kg and
5mg/kg) produced slightly different pattern of
responses (Table 5). While 2.5mg/kg EEK
caused an immediate but significant rise in both
arterial and venous blood glucose levels from
99.3±1.4mg/dl and 93.2±1.5 mg/dl to
116±6.8mg/dl and 96±5.7mg/dl followed by
slight reduction to hypoglyceamic levels
throughout the remaining post-injection
observation period (P<0.05), 5mg/kg EEK
caused immediate increases in arterial blood
glucose, 99.3±1.4mg/dl and 95.2±1.5 mg/dl to
106±6.8mg/dl and 130±5.7mg/dl which lasted
for between 25min to 30min and thereafter
returned to near basal levels during the
remaining post-injection observation period
(P<0.01).
H. M. Salahdeen and A. R. A. Alada
39
0
5
10
15
20
25
30
Aterio-venous glucose differences (A-V)
(mg/dl) (mean ± SE)
Normal saline (rest) Normal saline (contraction)
**
**
**
**
**
**
(a)
4
6
8
10
12
14
16
18
Blood flow (ml/min)
(mean ± SE)
**
**
**
*
*
*
**
**
*
*
(b)
0
50
100
150
200
250
0 5 10 15 20 25 30 45 60 75 90
Time (min)
Glucose uptake (mg/min)
(mean ± SE)
***
***
***
**
***
***
*
*
*
*
( c)
Fig. 1: Effect of intravenous injection of normal saline
on (a) arterio-venous (b) blood flow (c) glucose
uptake at rest and during hindlimb muscle
contractions in dogs (n=5) *P<0.05; ** P<0.01; ***
P<0.01). Arrow shows point of drug injection.
Figure 4a shows that 2.5mg/kg of EEK
produced a significant increase in (A-V) glucose
from 4.2±1.3mg/dl to 16±2.6mg/dl followed by a
gradual returned to basal level (P<0.01), at
5mg/kg EEK produced a more sustained increase
in (A-V) glucose to 19±1.9mg/dl which lasted
for about 30min before returning to the basal
levels (P<0.001).
Figure 4b shows that the two doses of EEK
produced significant decrease (P< 0.05) in blood
flow to the hindlimb, from resting value of
8.3±0.2 ml/min to 7.9±0.2ml/min and
6.2±0.7ml/min for both 2.5 and 5mg/kg
respectively. However, 5mg/kg of EEK caused a
greater decrease in blood flow than 2.5mg/kg of
EEK. The two doses (2.5 mg/kg and 5mg/kg)
produced different patterns of response in
hindlimb glucose uptake (Figure 4c). While
2.5mg/kg of EEK caused a sharp increase in
HGU, which lasted for 10min, and followed by
return to basal level, the higher dose (5mg/kg)
produced a more sustained significant increase in
HGU which lasted for about 30min. The lower
dose of EEK, however, produced a higher HGU
within the short period than the high dose of
EEK. The maximum HGU in response to
2.5mg/kg EEK is 402% and 511% in response to
5mg/kg of EEK.
Effect of ethanolic extract kolanut (EEK) on
blood glucose, (A-V) and glucose uptake during
hindlimb contraction in dogs
During contraction of the hindlimb, EEK
produced a significant effect on the blood
glucose levels. Administration of 5mg/kg EEK
during contraction of the hindlimb increased
significantly both the arterial and venous glucose
levels from 99.2±1.1mg/dl and 93.8±1.7mg/dl
to135±5.7mg/dl and 110±4.9mg/dl respectively.
The arterial and venous glucose levels were
sustainably higher throughout the post-injection
observation period. The arterial blood glucose
levels were also higher than the venous glucose
levels (Table 6). The effect of EEK on (A-V)
glucose during contraction of the hindlimb of the
dog is shown in figure 5a. Following hindlimb
contraction, (A-V) glucose increased from
4.2±0.2mg/dl to 42.1±0.9mg/dl. The increase in
(A-V) glucose produced by contraction was
significantly higher than the (A-V) glucose of
23±2.6mg/dl produced by EEK at rest. There
was however, no significant difference in the
effect of EEK during contraction of the hindlimb
compared with the effect of contraction without
EEK. The effect of EEK on blood flow is shown
in figure 5b. During contraction of hindlimb,
ethanolic extract of kolanut increased blood flow
significantly to the hindlimb from 8.3±0.3ml/min
to 13±0.3ml/min. This result is in contrast to the
reduction in blood flow caused by EEK in non-
contracting state. The effect of EEK on HGU
during contraction of the hindlimb is shown in
figure 5c. Contraction of the hindlimb increased
HGU by 354%. Administration of EEK resulted
in a more significant increase in HGU. EEK
caused 611% increase in HGU following
contraction of the hindlimb.
Caffeine and kolanut extract on canine hindlimb glucose uptake
40
0
5
10
15
20
25
30
35
Arterio-venous
glucose (mg/dl)
Caffeine (3mg/kg) Caffeine (6mg/kg) Caffeine (9mg/kg)
**
**
**
*
*
*
(a)
**
** ** **
**
*
*
*
** **
0
1
2
3
4
5
6
7
8
9
10
Blood flow (ml/min
(mean ± SE)
***
*
*
*
*
*
*
****
**
**
**
**
**
***
***
***
***
*** *** *** *** *** ***
(b)
0
20
40
60
80
100
0 5 10 15 20 25 30 45 60 75 90
Time (min)
Glucose uptake (mg/min)
***
***
***
***
**
**
**
**
**
**
**
**
**
**
**
**
**
**
**
(c)
Fig.2: Effects of intravenous injection of caffeine (3, 6
and 9mg/kg) on (a) arterio-venous glucose
difference (b) blood flow (c) glucose uptake at
rest in dogs (N=5) (*p<0.05; **p<0.01;
***p<0.001). Arrow shows point of drug
injection.
Fig.3: Effects of intravenous injection of caffeine
(6mg/kg) on (a) arterio-Venous glucose
difference (b) blood flow (c) glucose uptake at
rest and during hindlimb contraction in dogs.
(N=5) (*p<0.05; **p<0.01; ***p<0.001).
Arrow shows point of drug injection.
Discussion
The observed increase in blood glucose
level following administration of caffeine in
dogs in this study agrees with the report of
Pencek et al., (2004). It is also consistent with
previous reports (Graham et al, 2000) whereby
caffeine was reported to impair insulin mediated
glucose disposal probably through release of
adrenaline from adrenal medulla. Adrenaline is a
well known hyperglycemic agent (Deibert and
De Fronzo 1980; Alada and Oyebola 1997).
Adrenaline increases blood glucose level through
the process of hepatic glycogenolysis and
gluconeogenesis (Akiba et al, 2004). There are
also several reports that showed that caffeine
decreases insulin sensitivity (Greer et al, 2001;
Robinson et al, 2004) through blockade of
adenosine receptors (Thong and Graham 2002;
Akiba et al, 2004). The observed increase in
arterio-venous (A-V) glucose difference and
hindlimb glucose uptake following
0
5
10
15
20
25
30
35
40
45
A- V gluc ose diff erence (mg/dl)
(mea n SE)
Caffeine (rest) Caffeine (contraction)
***
*** ***
***
***
***
*** ***
*** ***
***
***
***
***
**
**
*
(a)
0
2
4
6
8
10
12
B lo o d flo w ( m l/m in )
(m e a n ±S E )
***
***
*** ***
**
***
***
***
***
***
(b)
0
50
100
150
200
250
300
0 5 10 15 20 2 5 30 45 60 75 90
Time (min)
Glucose uptake (mg/min)
(mean ± SE)
***
***
***
**
**
***
***
**
*
**
**
**
**
**
**** **
**
( c)
H. M. Salahdeen and A. R. A. Alada
41
administration of caffeine is consistent with the
reports of many workers in humans (Lee et al,
2005; Greer et al, 2001; Battram et al, 2005) and
animals (Pencek et al, 2004). The increase in (A-
V) glucose observed in the present study showed
that caffeine actually increased glucose
extraction by the canine hindlimb despite the
decrease in blood flow. The observed increase in
glucose extraction by the hindlimb following
administration of caffeine is probably a response
to the increase in blood glucose levels, since
both occur at about the same time.
Fig.4: Effects of intravenous injection of ethanolic
extract of kolanut (2.5 and 5mg/kg) on (a)
arterio-venous glucose difference (b) blood
flow (c) glucose uptake at rest in dogs (N=5)
(*p<0.05 **p<0.01, ***p<0.001). Arrow
shows point of drug injection.
Fig. 5: Effect of intravenous injection of ethanolic
extract of kolanut (5 mg/kg) on (a) arterio-
venous glucose difference (b) blood flow (c)
glucose uptake at rest and during hindlimb
contraction in dogs. (N=5) (*p<0.05;
**p<0.01; ***p<0.00). Arrow shows point of
drug injection.
0
5
10
15
20
25
30
35
A-V glucose (mg/dl)
(mean ± SE)
EEK (2.5mg/kg) EEK (5mg/kg)
***
**
**
**
***
*** ***
**
**
**
*
*
*
(a)
0
50
100
150
200
250
0 5 10 15 20 25 30 45 60 75 90
Time (min)
Glucose uptake (mg/min)
(mean± SE)
***
***
*** ***
***
**
***
**
** ** **
*
**
*
( c)
5.5
6
6.5
7
7.5
8
8.5
9
Bl oo d fl ow (m l/m in)
*
**
*
*
*
*
**
**
***
(b)
0
50
100
150
200
250
300
350
0 5 10 15 20 25 30 45 60 75 90
Time (min)
Glucose uptake (mg/min)
(mean± SE)
**
***
***
* *
**
**
***
*** ***
***
**
**
*
**
( C )
4
5
6
7
8
9
10
11
12
13
14
15
Blood flow ml/min)
(mean ± SE)
**
**
**
*
(b)
0
5
10
15
20
25
30
35
A rte rio- Ven oue gl ucos e di ffer enc e (m g/ dl)
(m ean + SE )
EEK (rest) EEK (contraction)
**
**
**
** ** **
**
**
**
**
**
(a)
Caffeine and kolanut extract on canine hindlimb glucose uptake
42
Previous studies have shown that glucose
transport across skeletal muscle cell membrane is
enhanced during hyperglyceamia (Battram et al,
2005; Zierler, 1999) irrespective of its causes.
There are also reports, which showed that
caffeine-induced increases in skeletal muscle
glucose uptake are through the release of calcium
ions into the cytoplasm (Hardie and Sakamoto,
2006). Studies in which frog sartorius muscle
was incubated with caffeine resulted in several
fold increase in glucose transport due to release
of calcium ion into the myoplasm (Hardie and
Sakamoto, 2006; Rose and Richter 2005). In rat
epitrochlearis muscle, raising intracellular
calcium ions by treatment with caffeine in-vitro
also increased glucose transport (Hardie and
Sakamoto, 2006).
The significant reduction in hindlimb blood
flow following caffeine administrations observed
in this study is also consistent with the reported
vasoconstriction effect of caffeine (Pincomb et
al., 1985; 1991; Smits et al., 1986; Sung et al.,
1994). The possible explanation for the
vasoconstriction effect of caffeine is the
blockade of vasodilatory actions of adenosine
(Fredholm, 1995). Acute intake of caffeine has
also been reported to increase vascular resistance
(Smits et al., 1990). The reported increase in
vascular resistance is consistence with the
present report. The absence of any significant
effect of caffeine on arterial blood glucose levels
during contraction of hindlimb in this study
seems to suggest that the hyperglyceamia
produced by caffeine at rest has been removed
during contraction of the hindlimb probably as a
result of increased demand for glucose by the
exercising muscles (Richter, 1996; Rose and
Richter, 2005). Although few workers have
reported a slight increase in blood glucose levels
during exercise (Andersen and Saltin, 1985),
most workers however, have reported no change
in blood glucose during exercise (Rose and
Richter, 2005). The greater increase in glucose
extraction and hindlimb glucose uptake due to
caffeine during contraction of the hindlimb
muscles in this study is of great interest. It is
well established that glucose uptake by skeletal
muscle increases many folds during muscular
exercise (Rose and Richter, 2005; Hardie and
Sakamoto, 2006). Skeletal muscle is therefore a
major sink for disposal of glucose in
postprandial state. The higher increase in glucose
extraction and glucose uptake due to caffeine
during contraction of the hindlimb in the dog
observed in this study seems to suggest that
during hindlimb contraction, caffeine acts to
argument the glucose uptake by the hindlimb.
The mechanisms by which caffeine arguments
glucose uptake by the canine hindlimb during
exercise are not known. However, several
mechanisms have been postulated to explain the
effect of caffeine on glucose uptake during
exercise.
Previous studies have shown that increasing
glucose supply to the working muscle by raising
glucose concentrations during contractions in-
vitro (Richter et al, 1988; Petersen et al, 2003) or
during exercise in-vivo (Richter, 1996) increases
skeletal muscle glucose uptake during exercise
even when insulin levels are prevented from
rising (Rose and Richter, 2005; Akiba et al,
2004). Conversely, during prolonged exercise
when insulin in blood decreases, glucose uptake
decreases as well (Ahlborg et al, 1974). It is
noteworthy, that within physiological range of
glucose concentrations, the relationship between
glucose concentration and insulin is also linear,
indicating that changes in plasma glucose level
translate in all proportionality to changes in
glucose uptake by muscle (Rose and Richter,
2005), whereas the increase in muscle blood
flow seems to match the glucose uptake demands
of the contracting muscle (Anderson and Saltin,
1985) and does not pose any obvious limitation
to glucose uptake in healthy individuals. The
blood glucose concentration is an important
limiting factor during muscular exercise (Rose
and Richter, 2005).
Again, there are reports that caffeine
induced glucose uptake through release of
calcium ions into the myoplasm (Hardie and
Sakamoto, 2006). An increase in calcium
concentration in the myoplasm results in muscle
contraction and alteration in the permeability of
glucose. In this study, the significant reduction in
blood flow to the hindlimb observed with EEK is
similar to the observation on caffeine in the
present study. The slight increase in blood
glucose level produced by administration of EEk
is of interest. After an extensive search of
literature, there was no reported work on the
effects of kolanut on blood glucose. Since the
pattern and the magnitude of hyperglycemia
induced by the ethanolic extract of kolanut are
similar to that of caffeine, it will therefore be
difficult not to conclude that the effect of
ethanolic extract of kolanut on blood glucose is
not due to caffeine. It is also true that caffeine is
not the only active substance in EEK. Other
active ingredients may also contribute to the
various effects of kolanut. Further studies using
other active ingredients of kolanut may shed
H. M. Salahdeen and A. R. A. Alada
43
more light on this. There is however, no doubt
that caffeine is a major contributor to the action
of kolanut. The possible mechanism by which
caffeine increases glucose level in this study had
earlier been explained. The increase in hindlimb
glucose extraction and glucose uptake observed
in this study is consistent with the action of
caffeine on other parameters measured in this
study. Ethanolic extract of kolanut increased
hindlimb glucose uptake by about 44% while
caffeine 6mg/kg produced about 700% increase.
The difference in the magnitude of hindlimb
glucose uptake by the two substances is probably
due to the different concentrations of caffeine in
circulation. Higher levels of caffeine in
circulation have been reported to produce greater
effects, for instance in blood pressure monitoring
(Nurminen et al, 1999).
The potentiating effect of ethanolic extract of
kolanut on hindlimb glucose uptake during
contraction was also similar to the effect of
caffeine under similar conditions. Contraction of
the hindlimb muscle also tend to abolish the
effect of ethanolic extract of Kolanut on blood
flow, since in non-exercising animal ethanolic
extract of kolanut produced an increase in
vascular resistance and a decrease in blood flow.
This is also similar to the effect of caffeine on
blood flow and vascular resistance in the dog.
Generally, caffeine and ethanolic extract of
kolanut seem to exhibit the same pattern of
response with different magnitudes in all
parameters measured in the present study. The
difference in the effects of caffeine and EEK is
only in the magnitude of the response and
duration of the event. Since the concentration of
caffeine in EEK used in this study was not
determined, it will therefore be difficult to expect
that the concentration of pure caffeine and
caffeine in EEK will be the same. A
pharmacodynamic study on the metabolism of
kolanut may be necessary to throw more light on
metabolic pathway of EEK. In similar studies
using decaffeinated products of coffee, the
significant role of caffeine in coffee, chocolate,
cocoa and other food substances containing
caffeine were highlighted (Nurminen et al,
1999). Most of the physiological effects of cola
nitida are said to be due to caffeine. Although,
the quantity of caffeine in the cola nitida was not
determined in this study, the fact that ethanolic
extract of kolanut increased mean arterial blood
pressure (unpublished observation) supports the
hypothesis that the pressor effect of kolanut is
due to caffeine. Similar observation has been
made with other food products such as coffee,
cocoa, which contain caffeine (Khee and
Jaworski, 1987). In actual fact, in some studies
using decaffeinated coffee, there was no increase
in blood pressure. An earlier worker (Somorin,
1973) found that cola nitida contains 0.16-gram
caffeine per 100g powder of kola nut. The
concentration of caffeine used in this study is far
less than the amount stated above. Since the
effects of EEK on blood flow, and hindlimb
glucose uptake are essentially similar to that of
caffeine in this study, it will therefore be difficult
not to conclude that the effects of EEK was
being carried out by the presence of caffeine in
it. Further studies whereby caffeine and other
active substances in EEK will be isolated will
throw more light on the mechanisms of action of
EEK in the dog.
References
Ahlborg G, Felig P, Hagenfeldt L, Hendler R,
and Wahren J. (1974). Substrate turnover
during prolonged exercise in man.
Splanchnic and leg metabolism of glucose,
free fatty acids, and amino acids. J Clin
Invest , 53: 1080–1090.
Ajala M.O, Oladipo O.O, Fasanmade O and
Adewole T.A. (2003). Laboratory assessment
of three glucometers. Afri. J. Med. med. Sci.
32: 279-282.
Akiba T, Yaguchi K, Tsutsumi K, Nishioka T,
Koyama I, Nomura M, Yokogawa K,
Moritani S and Miyamoto K. (2004).
Inhibitory mechanism of caffeine on insulin-
stimulated glucose uptake in adipose cells.
Biochem Pharm; 68: 1929–1937.
Alada, A.R.A. and Oyebola D.D.O (1996).
Evidence that the gastrointestinal tract is
involved in glucose homeostasis. Afr Med
med Sci. 25:243-249
Alada, A.R.A. and Oyebola D.O.O. (1997). The
role of adrenergic receptors in the increased
glucose uptake by canine gut. Afr. J. Med.
med. Sci: 26: 75-78.
Andersen, P. and Saltin, B. (1985). Maximal
perfusion of skeletal muscle in man. J
Physiol 366: 233-249.
Baron A.D, Wallace P, and Olefsky J.M. (1987).
In vivo regulation of non-insulin mediated
and insulin mediated glucose up take by
epinephrine J. Clin Endo. Metab 64: 889
895.
Battram D.S, Bugaresti J, Gusba J and Graham
T.E. (2007). Acute caffeine ingestion does
not impair glucose tolerance in persons with
tetraplegia. J. Appl. Physiol. 102: 374–381.
Battram D.S, Graham T.E, Richter E.A and Dela
F. (2005). The effect of caffeine on glucose
Caffeine and kolanut extract on canine hindlimb glucose uptake
44
kinetics in humans – influence of adrenaline.
J. Physiol; 569: 347–355.
Bessey P.Q, Brooks D.C, Black P.R, Aoki T.T
and Wilmore D.W. (1983). Epinephrine
acutely mediates skeletal muscle insulin
resistance. Surgery; 94: 172–179.
Biaggioni I, Paul S, Puckett A, and Arzubiaga C.
(1991). Caffeine and theophylline as
adenosine receptor antagonists in humans. J
Pharm Exper Thera; 258: 588–593.
Christ G.H. Xu B. LaNoue K.F. Lang C.H.
(1998). Tissue specific effects of in vivo
adenosine receptor blockade on glucose
uptake in Zucker rats. FASEB ; 12: 1301
1308.
Chukwu L.O., Odiete W.O., and Briggs, L.S.
(2006). Basal metabolic regulatory responses
and rhythmic activity of mammalian heart to
aqueous kolanut extracts. Afr. J. Biotech. 5:
484-486.
Deibert D.C and De Fronzo R.A. (1980).
Epinephrine – induced insulin resistance in
man J Clin Invest. 65: 717 – 721.
Devreese K and Leroux-Roels G. (1993).
Laboratory assessment of five glucose meters
designed for self monitoring of blood glucose
concentration. Eur. J. Clin. Biochem. 12:829-
837
Espinal J, Challiss R.A and Newsholme E.A.
(1983). Effect of adenosine deaminase and
an adenosine analogue on insulin sensitivity
in soleus muscle of the rat. FASEB. 158:
103–106.
Fredholm B.B. (1995). Astra Award Lecture.
Adenosine, adenosine receptors and the
actions of caffeine. Pharm Toxicol. 76: 93–
101.
Graham T.E, Sathasivam P, Rowland M, Marko
N, Greer F, and Battram D. (2001). Caffeine
ingestion elevates plasma insulin response in
humans during an oral glucose tolerance test.
Can. J. Physiol. Pharmacol. 79: 559–565
Graham, T. E., Helge, J. W., and Maclean, D. A.
(2000). Caffeine ingestion does not alter
carbohydrate or fat metabolism in human
skeletal muscle during exercise. J Physiol
(Lond). 529: 837-847.
Greer F. Hudson R, Ross R and Graham T.E.
(2001). Caffeine decreases glucose disposal
during an euglycemic hyperinsulinemic
clamp in sedentary males. Diabetes ; 50:
2349 – 2354.
Hamada T, Hayashi T., Kimura T., Nakao K, and
Moritani T. (2004). Electrical stimulation of
human lower extremities enhances energy
consumption, carbohydrate oxidation, and
whole body glucose uptake. J. Appl. Physiol.
96: 911-916.
Han D.H. Hansen P.A. Nolte L. A. Holloszy J.
O. (1998). Removal of adenosine decreases
the responsiveness of muscle decrease
transport to insulin and contractions
Diabetes; 47: 1671 – 1675.
Hardie D.G. and Sakamoto, K. (2006). AMPK:
A key sensor of fuel and energy status in
skeletal muscle. Physiol. 21: 48-60.
Hellsten, Y., MacLean, D.A., RaÊdegran, G.,
Saltin, B. and Bangsbo, J. (1998). Adenosine
concentrations in the interstitium of resting
and contracting human skeletal muscle.
Circulation. 98: 6-8.
Keijzers G.B, De Galan B.E, Jack G, and Smits
P. (2002). Caffeine can decrease insulin
sensitivity in humans. Diabetes care 25: 364
– 369.
Lee S, Hudson R, Kilpatrick K, Graham T.E and
Ross R. (2005). Caffeine ingestion is
associated with reductions in glucose uptake
independent of obesity and type 2 diabetes
before and after exercise training. Diabetes
Care. 28: 566–572.
Leighton B, Lozeman F. Viachonikolis (1988).
Effects of dipyridamole on the sensitivity of
glucose transport, glycolysis and glycogen
synthesis to insulin in muscles of the rat. Int.
J Biochem. 20: 23 – 27.
Nurminen M.L., Niittynenl, Korpela R.,
Vapaatalo H., (1999). Coffee, caffeine and
blood pressure: a critical review. Eur. J Clin
Nutr. 53: 831-839.
Ogutuga, D.B.A. (1975). Chemical composition
and potential commercial uses of kolanuts,
Cola nitida vent Cachott and Endlisher) Gh.
J. Agri. Sci. 8: 121-125.
Pencek R.R, Battram D, Shearer J, James F.D,
Lacy D.B. Jabbour K,Williams P.E, Graham
T.E and Wasserman D.H (2004). Portal vein
caffeine infusion enhances net hepatic
glucose uptake during a glucose load in
conscious dogs. J Nutr 134: 3042–3046.
Petersen HA, Fueger PT, Bracy DP, Wasserman
DH, Halseth AE. (2003). Fiber type-specific
determinants of Vmax for insulin-stimulated
muscle glucose uptake in vivo. Am J.l
of Physiol . 284; E541–E548.
Petrie H.J, Chown S.E, Belfie L.M, Duncan
A.M, McLaren D.H, Conquer J.A and
Graham T.E (2004). Caffeine ingestion
increases the insulin response to an oral-
glucose-tolerance test in obese men before
and after weight loss. Am. J Clin. Nutr. 80:
22–28.
H. M. Salahdeen and A. R. A. Alada
45
Pincomb G.A, Lovallo W.R, Passey R.B,
Whitesett T.L, Silverstein S.M and Wilson
M.F. (1985). Effects of caffeine on vascular
resistance, cardiac output and myocardial
contractility in young men. Am. J Cardiol.
56: 119 – 122.
Pincomb G. A, Wilson M. F. Sund B. H, Passey
R. B and Lovallo W.R. (1991). Effect of
caffeine on pressor regulation during rest and
exercise in men at risk for hypertension. Am.
Heart. J. 122: 1107 – 1115.
Richter E.A, Hansen S.A and Hansen B.F
(1988). Mechanisms limiting glycogen
storage in muscle during prolonged insulin
stimulation. Am. J. Physiol 255: E621–E628.
Richter E.A. (1996). Glucose utilization. In:
Handbook of Physiology. Exercise:
Regulation and Integration of Multiple
Systems. Bethesda, MD. Sect. 12, pp. 913–
951.
Robinson L.E, Savani S, Battram D.S, McLaren
D.H, Sathasivam P and Graham T.E. (2004).
Caffeine ingestion before an oral glucose
tolerance test impairs blood glucose
management in men with type 2 diabetes. J.
Nutr 134: 2528–2533.
Rose A.J and Richter E. A. (2005). Skeletal
muscle glucose uptake during exercise: How
is it Regulated? Physiology 20: 260-270.
Smits P, Boekema P, De Abreu R, Thien T and
van’t Laar A (1987). Evidence for an
antagonism between caffeine and adenosine
in the human cardiovascular system. J.
Cardiovasc. Pharmacol. 10: 136–143.
Smits P, Lenders J.W and Thien T. (1990).
Caffeine and theophylline attenuate
adenosine- induced vasodilation in humans.
Clin. Pharmacol. Ther. 48: 410–418.
Smits P. Pieters G. Thien T. (1986). The role of
epinephrine in the circulatory effects of
coffee. Clin Pharmacol. Ther. 40: 431 – 437
Somorin O. (1973).Spectrometric determination
of caffeine in Nigeria kolanuts. J .Food Sci.
381: 911-913.
Sung B.H, Whitsett T.L, Lovallo W.R, al’Absi
M, Pincomb GA and Wilson MF (1994).
Prolonged increases in blood pressure by a
single oral dose of caffeine in mildly
hypertensive men. Am. J. Hypertens 7: 755-
758.
Thong F.S, Derave W, Kiens B, Graham T.E,
Urso B, Wojtaszewski JF, Hansen BF and
Richter EA. (2002). Caffeine-induced
impairment of insulin action but not insulin
signaling in human skeletal muscle is
reduced by exercise. Diabetes 51: 583–590.
Thong F.S, Graham T.E. (2002). Caffeine
induced impairment of glucose tolerance of
glucose is abolished. J Appl Physiol; 92:
2347 – 52.
Vergauwen L, Hespel P, Richeter E.A. (1994).
Adenosine receptors mediate synergistic.
Stimulation of glucose uptake and transport
by insulin and by contractive in rat skeletal
muscle. J. Clin. Invest. 93: 974 – 981.
Zierler K. (1999). Whole body glucose
metabolism. Am. J. Physiol. E409-E426.
Caffeine and kolanut extract on canine hindlimb glucose uptake
... Each animal was fasted for 16-18 h before the start of each experiment with access to water only. [24,25] This was to ensure that the blood glucose measured was only the fasting one and not a result of recently absorbed food. Anesthesia was induced by an intraperitoneal injection of 0.6 ml/100g body weight of 25% urethane. ...
... Group III (caffeine and adenosine, n = 5): Caffeine (Alfa Aeser, Avocado, US) dissolved in normal saline was first given to the rats intravenously (6 mg/kg) [24,25] through the femoral vein after measuring the basal blood glucose. Thirty minutes after caffeine injection, another basal glucose measurement was obtained from the carotid artery. ...
... These observations convincingly showed that stimulation of adenosine receptors reduces blood glucose, while their antagonism/blockade increases blood glucose. The observed hyperglycemic effect of caffeine in this study in rats is similar to previous reports in dogs [24,25] and humans. [29] Is adenosine-induced reduction in blood glucose-dependent on endogenous insulin? ...
Article
Full-text available
Background: Reports from previous studies on the effects of adenosine and caffeine on blood glucose are controversial and inconclusive. The present study sought to investigate the effect of acute adenosine infusion and caffeine injection on blood glucose level in rats. Materials and Methods: Thirty-four male albino rats (300-400 g) were randomly divided in a blinded-fashion into six groups, namely, Group I (n = 6) received normal saline (0.1-0.2 ml), Group II (n = 6) received adenosine (347.8 µg/kg/min), Group III (n = 5) received caffeine (6 mg/kg), followed by adenosine (347.8 µg/kg/min), Group IV (n = 5) were diabetic rats that received adenosine (347.8 µg/kg/min), Group V (n = 6) received caffeine (6 mg/kg), and Group VI (n = 6) received nifedipine (300µg/kg), followed by caffeine (6 mg/kg). Administrations were done through the femoral vein, while blood samples were taken from the carotid artery for glucose measurement. Results: Adenosine caused a reduction in blood glucose level in normal and diabetic rats, though the reduction was more noticeable in diabetic rats. Pretreatment of rats with caffeine completely abolished the adenosine-induced reduction in blood glucose and produced an exaggerated increase in blood glucose comparable to the level seen in rats that received caffeine alone. Pretreatment of rats with nifedipine reduced the caffeine-induced hyperglycemia by two-third. Conclusion: This study suggests that adenosine receptors could be of therapeutic target in the treatment of Type 1 diabetes due to its blood glucose-lowering potential in both diabetic and normal rats. It also suggests that intracellular calcium mobilization is more implicated in caffeine-induced hyperglycemia than adenosine receptor antagonism, even though other unidentified mechanism(s) remain to be explored.
... Previous reports have shown that administration of kolanut extract stimulates the central nervous system activities (Scotto et al., 1987), increases the cardiac muscle contraction (Chukwu et al., 2006), increases gastric acid secretion (Osim et al., 1991), increases glucose uptake in skeletal muscle in dogs (Salahdeen and Alada, 2009) and causes relaxation of smooth muscle (Salahdeen et al., 2014). The biological effects of the kolanut extract have been attributed to its caffeine content (Osim et al., 1991) even when the caffeine content in the kolanut extract has not been characterized. ...
... The solvent was evaporated at 40°C under vacuum (Rotavapor), and final ethanolic extract lyophilized (kolanut extract yield 15.7%). The stock solution was prepared as suspension with 4 g/100 ml of saline for this study (Salahdeen and Alada, 2009). ...
... The lower concentration (11.9, 7.5, 6 mg/kg/body weight) of crude kolanut extract, caffeine isolated from kolanut and synthetic caffeine used in this study were equivalent to three cups of coffee per day in human when the conversion is based on the metabolic body weight (70 kg) and one cup is equivalent to drinking 227 g of regular coffee, which contains 137 mg of caffeine (Donovan and De Vane, 2001). The dose was based on our previous study (Salahdeen and Alada, 2009). ...
Article
Full-text available
In this study, gas chromatography-mass spectrometry (GC/MS) was used to analyse the isolated caffeine from kolanut and deternine the acute and chronic toxicity of the extract and the isolated caffeine. In chronic toxicity test, rats were divided into five groups (10 rats per group). Each rat was administered with normal saline (control group), crude kolanut extract (11.9 mg/kg), isolated caffeine (7.5 mg/kg), synthetic caffeine (6 mg/kg) or (6 mg/kg) decaffeinated kolanut extract orally for 90 days. Biochemical assessment and body weight of the rats were determined. In acute test, the limit test dose of 2000 mg/kg was administered to the rat and observed for 48 h post treatment. This dose caused behavioural changes but did not cause mortality in the rats tested. The results of the chronic administration showed that caffeine significantly (P < 0.05) decreased body weight. Liver enzymes were significantly (P < 0.05) increase, total plasma protein levels, creatinine, bilirubin, very low density lipoprotein (VLDL), low density lipoprotein (LDL) and total serum cholesterol levels were also significantly (P < 0.05) higher. However, urea was significantly (P < 0.05) lower in the caffeine treated groups. The results of the GC-MS analysis showed that the isolated caffeine from kolanut extract contains 82.69% pure caffeine with 96% in quality. Our results showed that the kolanut extract is rich in high quality caffeine and chronic consumption of it is associated with significant toxic effects as shown by elevated biochemical parameters, and reduction in body weight.
... Results of the previous studies have consistently shown adverse effects of Cola nitida consumption to include increase contraction of cardiac muscle, increased secretion of gastric acid, and increased uptake of glucose in the skeletal muscles of dog [7][8][9][10]. Many researchers have attributed the biological and physiological effects of Cola nitida to it caffeine content [9]. ...
Article
Full-text available
The effect of Cola nitida consumption on melatonin production in albino male Wistar rats was investigated. Wistar rats weighing 150-220 g were fed for 30 days with different percentages of powdered Cola nitida (5%, 10%, 20%, 30% and 0% w/w). Serum concentrations of melatonin, ascorbic acid (AA), glutathione (GSH), serum alkaline phosphatase (ALP), serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) of albino rats were determined using standard methods. Results show that melatonin level increased in the range of 14.8-23.8 ng/ml. As the concentration of Cola nitida in the exposed groups increased there was a decrease in melatonin concentration (9.3 ng/ml). There was a significant decrease (p<0.05) in the level of ascorbic acid (0.0085 to 0.0057 mg/dl) and glutathione (5.7 to 2.5 mg/dl) compared to the control group which showed 8.9 mg/dl and 6.7 mg/dl respectively. Similarly, aspartate aminotransferase (56.7 to 24.8 U/l) and alkaline phosphatase activities (54.5 to 25.3 Ul) decreased significantly (p<0.05) as the concentration of Cola nitida increased compared to control. However, alanine aminotransferase activity increased as the concentrations of Cola nitida increased between 20% to 30%. This study shows that Cola nitida reduce the levels of melatonin production in exposed rats and may consequently cause sleeping related disorders among consumers or exposed groups.
... Previous studies have reported that the administration of kola nut extract may stimulates the central nervous system activities [10], increases cardiac muscle contraction, increases glucose uptake in skeletal muscle in dogs, and causes relaxation of smooth muscle [11][12][13]. Caffeine is the major component of the kola nut extract that elicits its biological effects [14]. ...
Article
Full-text available
Aim: This study investigated the effects of sub-chronic administration of crude ethanol extract of Cola nitida mucosa epithelial lining and liver function enzymes in albino rats. Place and Duration of Study: Department of Biochemistry and Molecular Biology and Chemical Pathology Usmanu Danfodiyo University, Sokoto, between March 2017 and January 2018. Methodology: Twenty (20) albino rats have randomly divided into five (5) groups of A, B, C, D, and E of four rats each and were fed with an equal volume of ethanol extract of Cola nitida of 600, 1200, 1800 and 2400 mg/kg body weight of the rats by oral administration for 28 days, while group A serves as a control, respectively. Results: Result indicates the LD50 was above 5000 mg/kg B.W., serum aspartate transaminase (AST) and alanine transaminase (ALT) activity revealed a significant increase (P = .05) for AST (31.23 ± 9.39), (40.44 ± 12.24), (44.59 ± 8.69), and (36.30 ± 13.18) in rats fed with 600, 1200, 1800 and 2400 mg/kg, and ALT (33.66 ± 7.94) for group fed with 2400 mg/kg B.W as compared against the control group (16.97 ± 6.58) and (20.11 ± 4.39). The serum alkaline phosphatase (ALP) also showed a significant increase (P = .05) (7.99 ± 2.89), (7.07 ± 2.21), and (5.49 ± 1.28) in the group fed with 1200, 1800, and 2400 mg/kg as compared to the control (2.34 ±0.84). Histological studies on the mucosa epithelial lining showed an eroded epithelium and vacuolations at a dose above 1200 mg/kg as compared to the control group. Conclusion: This study was able to establish that crude ethanol extract of Cola nitida have some deleterious effects on mucosa epithelial lining, and liver function enzymes.
... C affeine, a trimethyl xanthine, alters cardiovascular function acutely with increases in blood pressure, 1-3 catecholamine levels, 4-6 vascular resistance, 7 blood glucose, [8][9][10] lipids, 11,12 and a dichotomous effect on heart rate (HR). [13][14][15] Whether chronic intake of caffeine will have similar effects still remains unclear due to paucity of reports in this area and the fact that the few available reports in this area have involved animal models such as rats and mice, which have a lot of cardiovascular variations when compared with humans. ...
... Results of the previous studies have consistently shown adverse effects of Cola nitida consumption to include increase contraction of cardiac muscle, increased secretion of gastric acid, and increased uptake of glucose in the skeletal muscles of dog [7][8][9][10]. Many researchers have attributed the biological and physiological effects of Cola nitida to it caffeine content [9]. ...
Article
Full-text available
The effect of Cola nitida consumption on melatonin production in albino male Wistar rats was investigated. Wistar rats weighing 150-220 g were fed for 30 days with different percentages of powdered Cola nitida (5%, 10%, 20%, 30% and 0% w/w). Serum concentrations of melatonin, ascorbic acid (AA), glutathione (GSH), serum alkaline phosphatase (ALP), serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) of albino rats were determined using standard methods. Results show that melatonin level increased in the range of 14.8-23.8 ng/ml. As the concentration of Cola nitida in the exposed groups increased there was a decrease in melatonin concentration (9.3 ng/ml). There was a significant decrease (p<0.05) in the level of ascorbic acid (0.0085 to 0.0057 mg/dl) and glutathione (5.7 to 2.5 mg/dl) compared to the control group which showed 8.9 mg/dl and 6.7 mg/dl respectively. Similarly, aspartate aminotransferase (56.7 to 24.8 U/l) and alkaline phosphatase activities (54.5 to 25.3 Ul) decreased significantly (p<0.05) as the concentration of Cola nitida increased compared to control. However, alanine aminotransferase activity increased as the concentrations of Cola nitida increased between 20% to 30%. This study shows that Cola nitida reduce the levels of melatonin production in exposed rats and may consequently cause sleeping related disorders among consumers or exposed groups.
... A significant portion of the NIRS signal is passing through the scalp, skull and cerebrospinal fluid (Gagnon et al. 2011), which will contribute to the NIRS values. Since caffeine decreases blood flow to skeletal muscle (Salahdeen and Alada 2009), it is possible that it will also cause a decline in blood flow within the skull and scalp, thus contaminating the NIRS signal coming from the brain. However, because the NIRS probe is tightly pressed against the forehead, there should be very little blood in the skin and scalp, which will lessen their impact. ...
Article
Full-text available
Caffeine is one of the most widely consumed psycho-stimulants in the world, yet little is known about its effects on brain oxygenation and metabolism. Using a double-blind, placebo-controlled, randomized cross-over study design, we combined transcranial Doppler ultrasound (TCD) and near-infrared spectroscopy (NIRS) to study caffeine's effect on middle cerebral artery peak blood flow velocity (Vp), brain tissue oxygenation (StO2), total hemoglobin (tHb), and cerebral oxygen metabolism (CMRO2) in five subjects. Hyperventilation-induced hypocapnia served as a control to verify the sensitivity of our measurements. During hypocapnia (~16 mmHg below resting values), Vp decreased by 40.0 ± 2.4% (95% CI, P < 0.001), while StO2 and tHb decreased by 2.9 ± 0.3% and 2.6 ± 0.4%, respectively (P = 0.003 and P = 0.002, respectively). CMRO2, calculated using the Fick equation, was reduced by 29.3 ± 9% compared to the isocapnic-euoxia baseline (P < 0.001). In the pharmacological experiments, there was a significant decrease in Vp, StO2, and tHb after ingestion of 200 mg of caffeine compared with placebo. There was no significant difference in CMRO2 between caffeine and placebo. Both showed a CMRO2 decline compared to baseline showing the importance of a placebo control. In conclusion, this study showed that profound hypocapnia impairs cerebral oxidative metabolism. We provide new insight into the effects of caffeine on cerebral hemodynamics. Moreover, this study showed that multimodal NIRS/TCD is an excellent tool for studying brain hemodynamic responses to pharmacological interventions and physiological challenges. © 2015 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.
... The powdered form (500 g) was then macerated in 1 L ethanol at room temperature for a period of 72 h. The solvent was evaporated at 40 ° C under vacuum (Rotavapor), and the fi nal ethanolic extract was lyophilized (yield 11.7%) [14] . The extract solution was prepared as a solution with 20 mg/mL of distilled water for this study. ...
Article
Full-text available
Background: The effect of Tridax procumbens aqueous ethanolic extract on the rat corpus cavernosum smooth muscles was evaluated in the present study. Method: Corpus cavernosum strips obtained from healthy, young, adult male Wistar albino rats (250-300 g) were precontracted with phenylephrine (10-7 M) or KCl (60 mM) and then treated with various concentrations of T. procumbens extract (0.15-1.05 mg/mL). The change in corpus cavernosum strip tension was recorded. The interactions between T. procumbens extract with acetylcholine and with sodium nitroprusside were also evaluated. Results: The results indicated that corpus cavernosum strips relaxation induced by T. procumbens extract was concentration-dependent and this was significant (p<0.5). Pre-treatment with a nitric oxide synthase (NOS) inhibitor (N(1) nitro-L-arginine-methyl ester, l-NAME), did not completely inhibit the relaxation. However, T. procumbens extract (0.6 mg/mL) significantly (p<0.5) enhanced both acetylcholine- and sodium nitroprusside-induced corpus cavernosum strips relaxation. Conclusions: RESULTS suggest that T. procumbens extract has a concentration-dependent relaxant effect on the isolated rat corpus cavernosum. The mechanism of action of T. procumbens extract is complex. A part of its relaxing effect is mediated directly by the release of NO from endothelium which may improve erectile dysfunction.
Article
Full-text available
Previous studies on the ability of caffeine to enhance endurance and boost performance have focused on theenergy substrates that are utilized by the skeletal muscle and the brain but nothing of such has been reported on cardiactissue. This study was designed to investigate the effect of caffeine on cardiac tissue metabolism in the rabbit. The study wascarried out on adult male New Zealand rabbits divided into 3 groups (n=5). Group I rabbits served as control and were given0.5ml/Kg of normal saline while group II and III rabbits were administered with 2mg/Kg and 6mg/kg of caffeine respectivelyfor 28 days. Blood samples were collected by retro orbital puncture for biochemical analysis. Animals were sacrificed bycervical dislocation and cardiac tissue biopsies were collected for biochemical and immunohistochemical analysis. Cardiactissue glycogen concentration was determined by anthrone reagent method. Cardiac tissue CPT 1 activity and cAMPconcentration were determined by immunohistochemistry and colorimetry techniques respectively, with assay kits obtainedfrom Biovision Inc. The results showed that Caffeine at 2 and 6 mg/kg significantly inhibited MPO activity from 0.72±0.05to 0.164±0.045 and 0.46±0.12 U/L respectively (p<0.05). Caffeine at 2mg/kg had no effect on serum nitric oxide but at6mg/Kg, it significantly increased serum nitric oxide form 28.01±6.53 to 45.25±3.88µM of nitrite (p<0.05). Also, Caffeineat 2 and 6mg/kg increased cardiac tissue glycogen from 15.62±0.73 to 40.69±6.35 and 38.82±6.91mg/100g respectively andcarnitine palmytol transferase 1 activity from 18.3 to 20 and 25.2% respectively. In conclusion, the study showed that caffeineconsumption increased CPT 1 activity suggesting increased utilization of free fatty acids for energy metabolism and sparingof cardiac tissue glycogen by mechanism(s) which probably involved blockade of A1 adenosine receptors and cAMPsignaling pathway.
Article
Full-text available
We determined whether intraportal caffeine infusion, at rates designed to create concentrations similar to that seen with normal dietary intake, would enhance net hepatic glucose uptake (NHGU) during a glucose load. Dogs (n = 15) were implanted with sampling and infusion catheters as well as flow probes >16 d before the studies. After a basal sampling period, dogs were administered a somatostatin infusion (0-150 min) as well as intraportal infusions of glucose [18 micromol/(kg . min)], basal glucagon [0.5 ng/(kg . min)], and insulin [8.3 pmol/(kg . min)] to establish mild hyperinsulinemia. Arterial glucose was clamped at 10 mmol/L with a peripheral glucose infusion. At 80 min, either saline (Control; n = 7) or caffeine [1.5 micromol/(kg . min); n = 8] was infused into the portal vein. Arterial insulin, glucagon, norepinephrine, and glucose did not differ between groups. In dogs infused with caffeine, NHGU was significantly higher than in controls [21.2 +/- 4.3 vs. 11.2 +/- 1.6 micromol/(kg . min)]. Caffeine increased net hepatic lactate output compared with controls [12.5 +/- 3.8 vs. 5.5 +/- 1.5 micromol/(kg . min)]. These findings indicate that physiologic circulating levels of caffeine can enhance NHGU during a glucose load, and the added glucose consumed by the liver is in part converted to lactate.
Article
Studies in recent years have demonstrated an important role for glucose in the supply of oxidizable substrate to exercising skeletal muscle in man. Glucose uptake by muscle rises 20–35 fold above the basal level after 40–60 min of work [13, 27]. If oxidized, the glucose taken up may account for as much as 30–50% of the total metabolism of the muscle. The blood glucose pool is replenished continuously during exercise, the major part being derived from accelerated hepatic glycogenolysis [1, 11, 23, 27]. Quantitative considerations indicate that the rates of hepatic glycogenolysis reached during exercise can be maintained only for a limited period of time. Maintenance of glucose homeostasis in prolonged exercise will thus necessitate an increase in gluconeogenesis, a diminution of glucose uptake by muscle or a combination of these mechanisms.
Article
Preliminary investigation on the effect of aqueous extracts of three species of kola nut; Cola acuminata (P. Beav), C. nitida subsp. rubra and C. nitida subsp. alba (Vent), on the rhythmic activity of mammalian heart and metabolic rate was carried out using male albino rats, Rattus sp. Low concentrations of kola nut extract stimulated the heart by increasing rate and force of contraction as well as metabolic rate. Higher concentrations reduced rate and amplitude of beat resulting, at still higher concentrations in heart failure.
Article
A randomized, double-blind and placebo-eon-trolled study was performed in 10 normotensive male subjects to analyze a possible antagonism between caffeine and adenosine with respect to their effects on the cardiovascular system in humans. Caffeine alone. 250 mg intravenously (i.v.). increased blood pressure by 9/12 mm Hg. and resulted in a fall of heart rate (HR) of 3 beats/ min. Plasma epinephrine (E) rose by 1149? after caffeine. Adenosine alone, in an increasing dose of 0.04-0.16 mg/kg/min, induced an increase in systolic blood pressure (SBP) (17 mm Hg). and HR (33 beats/min). a moderate fall in diastolic blood pressure (DBP) (-4 mm Hg). and no change of mean arterial pressure (MAP). At the highest adenosine infusion rate, forearm blood How. Skin temperature (ST), and transcutaneous oxygen tension were lowered, whereas plasma (nor)epinephrine was increased 227.2 and 215.9%, respectively. Adenosine infusion after caffeine induced comparable effects, but the fractional adenosine-induced changes of SBP. HR, plasma catecholamines, plasma renin activity (PRA), and aldosterone all were significantly reduced by previous administration of caffeine. Our results indicate an antagonism between caffeine and adenosine in humans, which may support the suggestion that some circulatory effects of caffeine are caused by an interaction with endogenous adenosine. (C) Lippincott-Raven Publishers.
Article
1.1. Zoleus, extensor digitorum longus (EDL) or hemi-diaphragm muscles of the rat were incubated in the presence of insulin and rates of the processes of glycolysis and glycogen synthesis were measured.2.2. The concentrations of insulin required to cause half-maximal stimulation of glycolysis in both soleus and EDL preparations were significantly decreased by the presence of adenosine deaminase in the medium.3.3. Adenosine deaminase increased the sensitivity of the process of hexose transport to insulin (in an identical manner to the change in sensitivity of glycolysis) in the EDL preparation.4.4. None of the adenosine mediated effects on insulin-stimulated rates of glycolysis were observed in the hemi-diaphragm preparation or on the rates of glycogen synthesis in any of the three muscle preparations.5.5. Therefore, changes in the adenosine system in skeletal muscle influence insulin sensitivity regardless of fibre type composition of the muscle.
Article
Preliminary investigation on the effect of aqueous extracts of three species of kola nut; Cola acuminata (P. Beav), C. nitida subsp. rubra and C. nitida subsp. alba (Vent), on the rhythmic activity of mammalian heart and metabolic rate was carried out using male albino rats, Rattus sp. Low concentrations of kola nut extract stimulated the heart by increasing rate and force of contraction as well as metabolic rate. Higher concentrations reduced rate and amplitude of beat resulting, at still higher concentrations in heart failure.
Article
Substantial in vitro and animal data suggest that methylxanthines, such as caffeine and theophylline, act as adenosine receptor antagonists. To test this hypothesis in humans, we first determined if theophylline would antagonize the effects of adenosine. Intravenous administration of adenosine, 80 micrograms/kg/min, increased heart rate 28 +/- 6 bpm, systolic blood pressure 19 +/- 5 mm Hg and minute ventilation 6.1 +/- 2.2 liters/min. All these changes were significantly attenuated during theophylline administration (17 +/- 3 bpm and 1 +/- 2 mm Hg and 1.6 +/- 0.6 liters/min, respectively, P less than .05), at a dose (10 mg/kg over 1 hr, followed by 1.8 micrograms/kg/min i.v.) that produced plasma theophylline levels of 17 +/- 2 micrograms/ml (94 microM). We then determined if chronic caffeine consumption resulted in upregulation of platelet adenosine receptors in eight normal volunteers. After 7 days of caffeine abstinence, the adenosine analog 5'-N-ethylcarboxamidoadenosine produced a dose-dependent inhibition of thrombin-induced aggregation (EC50 = 69 nM). Subjects then were given caffeine, 250 mg p.o. 3 times a day for 7 days. Actual caffeine withdrawal, that is, virtual disappearance of caffeine in plasma, was apparent 60 hr after the last dose of caffeine. Caffeine withdrawal produced a significant shift to the left of 5'-N-ethylcarboxamidoadenosine inhibition of aggregation (EC50 = 49 nM, P less than .01), implying sensitization and/or upregulation of adenosine receptors as seen after chronic exposure to an antagonist. These results suggest that methylxanthines act as adenosine receptor antagonists in humans.(ABSTRACT TRUNCATED AT 250 WORDS)