Blueberry Tea Enhances Insulin Sensitivity by Augmenting Insulin-Mediated Metabolic and Microvascular Responses in Skeletal Muscle of High Fat Fed Rats

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International Journal of Diabetology & Vascular Disease Research, 2013 © 29
Keske MA et al,. (2013) Blueberry Tea Enhances Insulin Sensitivity by Augmenting Insulin- Mediated Metabolic and Microvascular Responses in Skeletal Muscle of High Fat Fed Rats.
Int J Diabetol Vasc Dis Res. 1(5), 29-36
International Journal of Diabetology & Vascular Disease Research(IJDVR)
ISSN 2328-353X
Blueberry Tea Enhances Insulin Sensitivity by Augmenting Insulin-Mediated Metabolic and Microvascular
Responses in Skeletal Muscle of High Fat Fed Rats
Research Article
Premilovac D1, Roberts-Thomson KM1, Ng HL1, Bradley EA1, Richards SM1, Rattigan S1, Keske MA1*
Menzies Research Institute Tasmania, University of Tasmania, Hobart, Australia.
Abstract
Background: The aim of the current study was to determine whether a unique blueberry tea (BT) ameliorates insulin resistance by improv-
ing metabolic and vascular actions of insulin in skeletal muscle.
Methods: Male Sprague Dawley rats were fed normal (4.8% fat wt/wt, ND) or high (22.6% fat wt/wt, HFD) fat diets for 4 weeks. A second
group of HFD rats was provided BT (4.0% wt/vol) in the drinking water during the nal 2 weeks. Animals were subjected to an intraperi-
toneal glucose tolerance test (1g glucose/kg IPGTT) or euglycaemic hyperinsulinaemic clamp (10mU/min/kg x 2hr).
Results: HFD rats displayed signicantly (p<0.05) higher plasma glucose levels at 15 and 30 mins following the IPGTT compared to ND,
and this increase was completely abolished by BT treatment. Glucose infusion rate, muscle glucose uptake, and microvascular perfusion in
muscle were signicantly (p<0.05) impaired during clamps in HFD and all markedly improved (p<0.05) with BT treatment. Insulin-mediated
changes in femoral artery blood ow were unaffected by HFD or BT treatment.
Conclusions: We conclude that BT treatment ameliorates glucose intolerance and insulin resistance by restoring both metabolic and mi-
crovascular insulin sensitivity in high fat-fed rats. Therefore, BT consumption may have therapeutic implications for insulin resistance and
type 2 diabetes.
Key Words: Insulin Sensitivity; Glucose Tolerance; High Fat Diet; Blueberry Tea; Microvascular Perfusion; Muscle Glucose Uptake.
*Corresponding Author:
Michelle A. Keske
Menzies Research Institute Tasmania, University of Tasmania, Hobart,
Australia.
Tel: (03) 62 26 2669; Fax: (03) 62 26 7704
E-mail: Michelle.Keske@utas.edu.au
Received: November 21, 2013
Accepted: December 16, 2013
Published: December 18, 2013
Citation: Keske MA et al,. (2013) Blueberry Tea Enhances Insulin Sensi-
tivity by Augmenting Insulin- Mediated Metabolic and Microvascular Re-
sponses in Skeletal Muscle of High Fat Fed Rats. Int J Diabetol Vasc Dis
Res. 1(5), 29-36. doi: http://dx.doi.org/10.19070/2328-353X-130006
Copyright: Keske MA© 2013 This is an open-access article distributed
under the terms of the Creative Commons Attribution License, which
permits unrestricted use, distribution and reproduction in any medium,
provided the original author and source are credited.
Introduction
Insulin resistance plays a key role in the pathogenesis of type-2
diabetes (T2D). While the root causes of insulin resistance are
multifactorial, two of the major contributors are increased dietary
fat and a sedentary lifestyle [1-4]. A dening feature of insulin re-
sistance is impaired glucose disposal by the skeletal muscle, which
is normally responsible for ~80% of insulin-mediated glucose
uptake in the post-prandial state [5].
In addition to the classical metabolic actions of insulin to stimu-
late glucose uptake in skeletal muscle, insulin also has important
vascular actions [6-13]. Our research implicates vascular dysfunc-
tion in skeletal muscle as one major cause of muscle insulin resist-
ance. Insulin stimulates both total blood ow to skeletal muscle
[11-13] and increases microvascular perfusion of the myocytes
[6-10]. However insulin’s actions on microvascular perfusion and
total muscle blood ow are separate events and insulin-mediated
glucose uptake is altered by changes in microvascular perfusion
and not total muscle blood ow [7,14].
We have demonstrated that insulin infusion or the ingestion of a
mixed meal stimulate microvascular blood ow in skeletal muscle
in both experimental animals [6-10] and humans [15-17]. Insu-
lin stimulates microvascular recruitment to facilitate delivery of
glucose and insulin to the myocyte to enhance glucose disposal
[6-10,18]. Insulin resistant rats [3] and obese humans [15,16] also
display marked reductions in insulin-mediated microvascular re-
cruitment and insulin-mediated muscle glucose uptake suggesting
that the loss of muscle perfusion may contribute to the insulin re-
sistance. Recently, we reported that high fat-induced insulin resist-
ance can originate from impaired microvascular insulin responses
and that this microvascular defect precedes the development of
myocyte insulin resistance [14].
Current treatments for T2D are limited, have unwanted side ef-
fects, and lose effectiveness over time. Finding novel therapeutic
treatments that act by improving microvascular and metabolic in-
sulin responses in skeletal muscle may aid in the prevention of
insulin resistance and T2D or potentially enhance the action of
current treatments. There is a growing public interest in the use
of complementary and alternative approaches for treating insulin
resistance and T2D. Blueberries and blueberry leaves have been
reported to have anti-diabetic actions [19-21] and have been used
as a traditional medicine for glycaemic control [22,23]. Here we

International Journal of Diabetology & Vascular Disease Research, 2013 © 30
Keske MA et al,. (2013) Blueberry Tea Enhances Insulin Sensitivity by Augmenting Insulin- Mediated Metabolic and Microvascular Responses in Skeletal Muscle of High Fat Fed Rats.
Int J Diabetol Vasc Dis Res. 1(5), 29-36
report on novel ndings demonstrating that a unique blueberry
tea blend (BT) restores metabolic and microvascular insulin sensi-
tivity in muscle of the high fat-fed rat model.
Methods
Animal Care
Male Sprague-Dawley rats (4 weeks of age) were obtained from
the University of Tasmania Central Animal Facility. On arrival,
the rats were divided into two groups and provided either a nor-
mal (4.8% fat wt/wt; ND, Specialty Feeds, Glen Forrest, WA,
Australia) or high (22.6% fat wt/wt; HFD, Specialty Feeds) fat
diet ad libitum for 4 weeks. The macronutrients in these diets are
shown in Table 1. A second group of HFD rats were supplement-
ed with blueberry tea (HFD+BT; 4% wt/vol) during the nal two
weeks of HFD feeding. The blueberry tea, Blueberry Boost™,
was a kind donation from Dromana Blueberries (Oyster Cove,
Tasmania, Australia) which contains a propriety blend of dried
blueberries, blueberry leaves, spearmint leaves, raspberry leaves
and cinnamon. BT was brewed at the rate of 4g of loose leaves
per 100ml of boiling water, allowed to infuse for 10 minutes, then
strained through a 0.75mm mesh to remove particulate matter
and cooled. Animals in the HFD+BT group were provided with
both normal drinking water and BT in separate drinking bottles
ad libitum. The tea was replaced every two days. All animals were
housed at 21±2°C with a 12h-12h light-dark cycle. All experi-
mental procedures were approved by the University of Tasmania
Animal Ethics Committee and performed in accordance with the
Australian Code of Practice for the Care and Use of Animals for
Scientic Purposes – 2013, 8th Edition.
Surgical Preparation
Rats were anaesthetised with an intraperitoneal injection of
aqueous pentobarbital sodium (50mg/kg body wt.) and surgery
performed as previously described [6-10]. Animals were main-
tained under anaesthesia for the duration of the experiment by
an intravenous infusion of pentobarbital sodium (0.6 mg/min/
kg body wt.), and mean arterial blood pressure (MAP) and heart
rate continuously recorded. Following surgical preparation, 1 hr
was allowed for the animal’s cardiovascular parameters to stabilise.
Subsequently, animals were then subjected to either an intraperi-
toneal glucose tolerance test (protocol 1), or a euglycaemic hyper-
insulinaemic clamp (protocol 2).
•
Protocol 1 - Intraperitoneal glucose tolerance test
Animals were subjected to a 90 min glucose tolerance test (1g
glucose/kg IPGTT). Arterial blood was sampled from the carotid
artery at baseline (0 min) and at 15, 30, 45, 60 and 90 min fol-
lowing the glucose injection. Blood samples were centrifuged and
plasma glucose levels were assessed using a glucose analyser (YSI
2300, Yellow Springs Instruments, OH, USA).
•
Protocol 2- Euglycaemic hyperinsulinaemic clamp
Following an overnight fast a 2 hr infusion of insulin (10mU/
min/kg; Humulin, Eli Lilly, West Ryde, NSW, Australia) was initi-
ated through the jugular vein. A 30% glucose solution (wt/vol)
was infused at a variable rate to maintain fasting blood glucose
concentrations over the course of the experiment. Arterial blood
glucose levels were assessed from the carotid artery every 10-15
min using a glucose analyser (YSI 2300) and the glucose infusion
rate (GIR) was adjusted accordingly.
Fasting and clamp plasma insulin concentrations were determined
by ELISA (Mercodia AB, Uppsala, Sweden). Fasting plasma non
esteried fatty acid (NEFA) levels were determined using an en-
zymatic assay kit (Wako Pure Chemical Industries, Osaka, Japan).
Muscle-specic glucose uptake was assessed by uptake of 2-de-
oxy-D-[1-14C]glucose (2DG; 0.1mCi/mL; American Radiolabeled
Chemicals, Inc., MO, USA) as described previously [3,14]. Briey,
45 min prior to the conclusion of the experiment an i.v. bolus
of 2DG was given (20μCi). Arterial plasma samples (25μL) were
collected 5, 10, 15, 30 and 45 min after the 2DG bolus to assess
plasma specic activity of 2DG. At the end of the experiment the
calf muscle group (gastrocnemius, plantaris, soleus) was excised,
immediately freeze clamped and stored at -80°C until analysed.
The frozen muscle was ground under liquid nitrogen and ~100mg
was homogenised with 1.5mL of distilled water. The homogenate
was centrifuged and 1mL of supernatant was separated for free
and phosphorylated 2DG using an anion exchange column (AG-
1X8; Bio-Rad Laboratories, CA, USA). Biodegradable counting
scintillant (Amersham, Arlington Heights, IL, USA) was added
to each sample and radioactivity was measured using a scintilla-
tion counter (Tri-Carb 2800TR, Perkin Elmer, IL, USA). From
this measurement and the specic activity of 2DG in plasma, the
rate of muscle glucose uptake (R’g) was calculated as previously
described [24].
Femoral artery blood ow (FBF) was continuously measured by
an ultrasonic ow probe positioned around the femoral artery
(Transonic, Ithica, NY, USA). Microvascular perfusion in muscle
was assessed from metabolism of exogenously infused 1-methyl
xanthine (1-MX; Sigma Aldrich, St. Louis, MO, USA) as previ-
ously published [3,6,8,14,25-29]. Briey, a bolus of allopurinol
Table 1. Macronutrient composition of the ND and HFD diets expressed as % total weight.
ND HFD
Protein 19.4% 19.0%
Carbohydrate 70.7% 49.0%
Fat 4.8% 22.6%
Monounsaturated (% total fat) 39% 39%
Polyunsaturated (% total fat) 44% 9%
Saturated (% total fat) 17% 52%

International Journal of Diabetology & Vascular Disease Research, 2013 © 31
Keske MA et al,. (2013) Blueberry Tea Enhances Insulin Sensitivity by Augmenting Insulin- Mediated Metabolic and Microvascular Responses in Skeletal Muscle of High Fat Fed Rats.
Int J Diabetol Vasc Dis Res. 1(5), 29-36
(10μmol/kg; Sigma Aldrich) was given 5 min prior to 1-MX infu-
sion to partially inhibit the activity of xanthine oxidase and ensure
a constant saturating arterial level of 1-MX. 1-MX (0.4mg/min/
kg) was infused intravenously during the nal 60min of the ex-
periment. At the end of the experiment 100μL of arterial plasma
was added to 20μL of perchloric acid (2M) to precipitate pro-
teins. Hindleg venous plasma, obtained from the femoral vein us-
ing a 29G needle, was collected and 100μL was mixed with 20μL
of perchloric acid (2M). The arterial and venous samples were
centrifuged and the supernatant assessed for 1-MX and oxypuri-
nol concentrations using reverse-phase high-performance liquid
chromatography as previously described [6]. The metabolism of
1-MX was calculated from the plasma arterio-venous 1-MX dif-
ference multiplied by FBF and expressed as nmol/min.
Statistical Methods
Data are presented as the means ± SEM and statistics were per-
formed using SigmaStat (Systat Software, San Jose, CA, USA).
Comparisons between groups were made using One-way ANO-
VA. Comparison of time-series measurements in each group was
performed by two-way repeated measures ANOVA. When a sig-
nicant difference of p<0.05 was detected, pairwise comparisons
by Student-Newman-Keuls test was used to assess treatment dif-
ferences.
Results
Physical and biochemical characteristics of rats
At the conclusion of the dietary intervention, there were no
differences in body weight (Figure 1A) or energy intake from
food (Table 2) between ND, HFD or HFD+BT groups. Water
intake was the same between ND and HFD groups. However
the HFD+BT group consumed more uids as they were given
both water and BT ad libitum (Table 2). At the end of the dietary
intervention, there were no differences in plasma glucose con-
centrations between ND, HFD and HFD+BT rats (Figure 2A
and B). As expected, HFD rats had signicantly (p<0.05) elevated
epididymal fat pad weights (Figure 1B), fasting plasma insulin
(Figure 3A), and fasting plasma NEFA (Figure 3B) concentra-
tions when compared to ND. These outcomes were unaffected
by BT treatment, however there was a trend (p=0.07) for fasting
plasma NEFA concentrations to be lower in the HFD+BT when
compared to HFD.
•
Protocol 1 - Intraperitoneal glucose tolerance test:
Table 2. Food, water and BT intake in ND (4.8% fat wt/wt), HFD (22.6% fat wt/wt) and HFD+BT (4% wt/vol blueberry
tea) rats.
ND HFD HFD+BT
Food intake (kJ/day/kg body wt) 1410 ± 46 1339 ± 42 1418 ± 38
Water intake (mL/day/kg body wt) 94 ± 3 90 ± 3 61 ± 8*
BT intake (mL/day/kg body wt) - - 68 ± 4
Data are means ± SEM for n=5 measurements in each group. Comparisons between groups were made using One Way ANOVA and
Student-Newman-Keuls Post-hoc test.*P<0.05 versus ND and HFD.
Figure 1: Body weight and epididymal adiposity.
Final body weight (A) and epididymal fat pad weight (B) of ND ( ), HFD ( ) and HFD+BT ( ) rats. Data are means ± SEM for
n=14-15 rats in each group. *p<0.05 versus ND; One way ANOVA and Student-Newman-Keuls Post-hoc test.

International Journal of Diabetology & Vascular Disease Research, 2013 © 32
Keske MA et al,. (2013) Blueberry Tea Enhances Insulin Sensitivity by Augmenting Insulin- Mediated Metabolic and Microvascular Responses in Skeletal Muscle of High Fat Fed Rats.
Int J Diabetol Vasc Dis Res. 1(5), 29-36
Figure 4 shows the time course of changes in plasma glucose
following the glucose tolerance test. ND, HFD and HFD+BT
groups had similar basal (non-fasting) plasma glucose levels. HFD
had signicantly higher plasma glucose at 15 and 30 min follow-
ing the glucose challenge. Interestingly, the HFD+BT group had
markedly (p<0.05) reduced plasma glucose levels at 15 and 30
min when compared to HFD. However, there were no statistical
differences in plasma glucose levels between groups at 0, 45, 60
or 90 min.
•
Protocol 2 - Euglycaemic Hyperinsulinaemic Clamp
Figure 5A shows the GIR required to maintain glycaemia during
insulin infusion for ND, HFD and HFD+BT groups. As expect-
ed, the HFD group had signicantly lower (p<0.05) GIR when
compared to the ND group conrming that the HFD rats were
insulin resistant. Importantly, the HFD+BT group had signi-
cantly (p<0.05) elevated GIR when compared to HFD, indicating
improved whole body insulin sensitivity. Insulin-mediated uptake
of radiolabeled glucose in skeletal muscle (R’g, Figure 5B) was
signicantly (p<0.05) impaired in HFD rats (18.6 ± 1.2 vs. 28.9 ±
2.9 μg/g/min, p<0.05). However, insulin-stimulated R’g in HFD
rats was markedly improved with BT treatment (24.4 ± 0.9 μg/g/
min, p<0.05).
Insulin increased FBF in all groups to a similar extent in ND,
Figure 2: Plasma glucose levels.
Non-fasting (A) and fasting (B) plasma glucose levels in ND ( ), HFD ( ) and HFD+BT ( ) rats. Data are means ± SEM for n=7-9
rats in each group. Data not signicant. One way ANOVA.
Figure 3: Fasting insulin and NEFA levels.
Fasting plasma insulin (A) and NEFA (B) levels of ND ( ), HFD ( ) and HFD+BT ( ) rats. Data are means ± SEM for n=7-9 rats
in each group. *p<0.05 versus ND; # p=0.07 versus HFD. One way ANOVA and Student-Newman-Keuls Post-hoc test.

International Journal of Diabetology & Vascular Disease Research, 2013 © 33
Keske MA et al,. (2013) Blueberry Tea Enhances Insulin Sensitivity by Augmenting Insulin- Mediated Metabolic and Microvascular Responses in Skeletal Muscle of High Fat Fed Rats.
Int J Diabetol Vasc Dis Res. 1(5), 29-36
HFD and HFD+BT groups (p= NS, Figure 6A). Femoral artery
vascular resistance (MAP divided by FBF) in response to insulin
was also similar between groups (107 ± 15 vs. 120 ± 21 vs. 109
± 15 mmHg.min/ml, ND, HFD and HFD+BT respectively, p=
NS). Hindlimb 1-MX metabolism, an indicator of microvascu-
lar perfusion, was signicantly (p<0.05) impaired in HFD when
compared to ND during insulin infusion (4.87± 0.63 vs. 8.43 ±
1.13 nmole/min; p<0.05, Figure 6B). BT treatment reversed the
impairment in insulin-mediated 1-MX metabolism induced by
HFD (7.87 ± 0.63 nmole/min).
Discussion
The main ndings from this study were that BT treatment ame-
liorated HFD-induced glucose intolerance and insulin resistance.
BT treatment improved insulin-stimulated glucose uptake and mi-
crovascular perfusion in skeletal muscle. These effects occurred
without any changes in body weight, epididymal pad weight, fast-
ing clinical chemistries or femoral artery blood ow. These data
indicate that BT is an insulin sensitiser in skeletal muscle and acts
by improving both the metabolic and microvascular actions of
insulin.
Figure 4: Glucose tolerance test.
Plasma glucose levels over time following the ip injection of 1g glucose/kg body weight in ND ( ), HFD ( ) and HFD+BT
( ) rats. Data are means ± SEM for n=8 rats in each group. *p<0.05 versus ND; # p<0.05 versus HFD. Two way repeated measures
ANOVA and Student-Newman-Keuls post-hoc test.
Figure 5: Glucose metabolism.
Glucose infusion rate (GIR) required to maintain euglycaemia of insulin clamp (A) and muscle glucose uptake (R’g) at end of clamp (B)
of ND ( ), HFD ( ) and HFD+BT ( ) rats during insulin clamp (10mU/min/kg). Data are means ± SEM for n=7-9 rats in each
group. *p<0.05 versus ND; # p<0.05 versus HFD. Two way repeated measures ANOVA, or One way ANOVA where appropriate, and
Student-Newman-Keuls post-hoc test.

International Journal of Diabetology & Vascular Disease Research, 2013 © 34
Keske MA et al,. (2013) Blueberry Tea Enhances Insulin Sensitivity by Augmenting Insulin- Mediated Metabolic and Microvascular Responses in Skeletal Muscle of High Fat Fed Rats.
Int J Diabetol Vasc Dis Res. 1(5), 29-36
Blueberry Boost™ is a proprietary blend of dried blueber-
ries (37% wt/wt), blueberry leaves, raspberry leaves, spearmint
leaves and cinnamon. Blueberries [19-21], blueberry leaves [20]
and cinnamon [30-32] have each been reported to improve insu-
lin sensitivity or insulin action; however there are no reports of
raspberry leaves or spearmint on these measures. High fat fed
mice supplemented with freeze-dried blueberry powder (4% wt/
wt provided in the food x 8 weeks) prevented diet-induced obe-
sity and improved whole body insulin sensitivity in response to
an insulin tolerance test [19]. Blueberry fruit and blueberry leaf
extracts have been shown to stimulate insulin-dependent and –
independent glucose uptake in cultured C2C12 muscle cells but
not in 3T3-LI adipocytes [20], suggesting an insulin-mimetic and
insulin-sensitizing effect in muscle. More recently, freeze-dried
blueberry fruit supplementation (45g per day x 6 weeks) to obese
insulin resistant individuals improved whole body insulin sen-
sitivity (assessed by euglycaemic hyperinsulinaemic clamp tech-
nique) when compared to placebo [21]. Conversely high fat-fed
mice provided freeze-dried whole blueberry powder (10% wt/
wt in diet x 92 days) increased body weight and obesity, and did
not alter glucose tolerance (assessed by IPGTT) [33]. There are
a number of studies reporting on the effects of cinnamon on
insulin sensitivity and glucose homeostasis (see review [30] and
references therein). Cinnamon (20g/kg diet x 12 weeks) enhances
whole body insulin sensitivity in high fat/sucrose fed rats without
altering body weight or adiposity [31]. Similarly, cinnamon extract
(300mg/kg/day in drinking water x 3 weeks) prevents insulin re-
sistance in high fructose fed rats [32]. Numerous clinical studies
have reported that cinnamon or cinnamon extract can improve
glucose tolerance and/or whole body insulin sensitivity in healthy
lean [34,35] and insulin resistant [36] individuals. However the ef-
fect of these nutritional agents on insulin’s vascular and metabolic
actions in muscle has not been previously explored.
Insulin-mediated microvascular recruitment in skeletal muscle
plays an integral role in regulating muscle glucose uptake. We
have shown that acute defects in insulin-mediated microvascular
recruitment can contribute to the development of muscle insulin
resistance in vivo. Infusion of α-methyl serotonin [26], endothe-
lin-1 [27], L-NG-Nitroarginine methyl ester [7,29,37], TNFα [38],
Intralipid® plus heparin [39] and glucosamine [40] in healthy
animals attenuate insulin-mediated microvascular recruitment
and insulin-mediated muscle glucose uptake. In addition, chronic
models of insulin resistance including the high fat-fed rat (36%
fat wt/wt) [3], and obese Zucker rat [41] display marked attenu-
ation in insulin-mediated microvascular recruitment and muscle
glucose uptake. More recently we reported [14] that moderate in-
creases in dietary fat cause microvascular and not myocyte-derived
insulin resistance, which for the rst time positioned defects in
microvascular insulin action as an early event that contributes sig-
nicantly to fat-induced muscle insulin resistance. In the present
study, animals given BT for two weeks restored insulin-mediated
microvascular recruitment and this was associated with improved
insulin-stimulated muscle glucose uptake, potentially due to im-
proved delivery of insulin and glucose to myocytes.
This is the rst report of an agent that reverses microvascular
insulin resistance in muscle of the HFD rat model. Given that
the HFD model we used in this study displays both myocyte and
microvascular insulin resistance [14], the improvement in muscle
glucose uptake following BT treatment could be due to improve-
ments in both myocyte and microvascular insulin responsiveness.
However, given that BT treatment reversed the impairment in
microvascular insulin responsiveness and only ~40% of insulin-
stimulated glucose uptake in muscle, it can be speculated that BT
treatment has improved predominantly vascular and not myocyte
insulin action. The current study also demonstrates that BT treat-
ment markedly improved whole body, muscle and microvascular
insulin sensitivity without changing adiposity or fasting insulin
levels, two hallmarks of insulin resistance. This is suggestive of
BT treatment having an insulin-sensitising action in this animal
model, however whether these markers would be altered during
longer term supplementation is unknown.
As detailed previously, BT is a blend of ve plant based ingre-
dients. The present study does not indicate which ingredient(s)
Figure 6: Musclebloodow.
Femoral artery blood ow (A; FBF) and muscle microvascular recruitment (B) during insulin clamp in ND ( ), HFD ( ) and
HFD+BT ( ) rats. Data are means ± SEM for n=7-9 rats in each group. One way ANOVA and Student-Newman-Keuls post-hoc test.
*p<0.05 Versus ND; #p<0.05 Versus HFD

International Journal of Diabetology & Vascular Disease Research, 2013 © 35
Keske MA et al,. (2013) Blueberry Tea Enhances Insulin Sensitivity by Augmenting Insulin- Mediated Metabolic and Microvascular Responses in Skeletal Muscle of High Fat Fed Rats.
Int J Diabetol Vasc Dis Res. 1(5), 29-36
or bioactive components of BT are responsible for this insulin
sensitizing action, or whether in combination they have additive
or synergistic actions. Although dried blueberries are the main
constituent of this product, further studies using individual ingre-
dients would be required to fully resolve these issues.
Conclusions
This is the rst study to demonstrate that BT treatment markedly
improves microvascular and metabolic insulin sensitivity in skel-
etal muscle of HFD rats. These effects were apparent indepen-
dently of changes in adiposity, or clinical chemistries such as fast-
ing plasma glucose and insulin. Our study suggests that regular
consumption of BT may have important therapeutic implications
for insulin resistance and T2D, however its efcacy in humans
population remains to be determined.
Competing Interests
No conicts of interest, nancial or otherwise, are declared by
the authors.
Authors’ Contributions
D.P., K.M.R-T, M.A.K and were involved in design, conduct/
data collection, analysis and writing of the manuscript. E.A.B.,
H.L.H.N, S.M.R. and S. R. were involved in design, analysis and
writing of the manuscript. All authors read and approved the nal
manuscript.
Acknowledgements
This work was funded by the National Health & Medical Research
Council of Australia (grant number 1009962 to M.A.K. and S.R.).
Professor Stephen Rattigan is a Senior Research Fellow of the
National Health & Medical Research Council of Australia (grant
number 490034 to S.R). We thank Carl Sykes and Nadja Brearley
of Dromana Blueberries for donating Blueberry Boost™ for this
study.
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