Emergency colonoscopy for distal intestinal obstruction syndrome in cystic fibrosis patients

Abstract

Background and aims: Impaired accommodation and hypersensitivity to distension of the proximal stomach are considered to be important factors in the pathogenesis of dyspeptic complaints. As fundus relaxing agents may be effective in the treatment of these symptoms, insight into the mediators involved in fundic accommodation and associated perceptual responses is important. Therefore, we studied the effect of nitric oxide (NO) synthase inhibition by N G-monomethyl-L-arginine (L-NMMA) on fundic tone, postprandial sensations, and gastric perception in healthy volunteers. Subjects and methods: Eighteen healthy volunteers participated in a double blind, placebo controlled , randomised study. They underwent a gastric barostat study to evaluate the effect of L-NMMA on meal and distension induced sensations and on fundic relaxation in response to oral meal intake, intraduodenal lipid, and glucagon administration. Results: Compared with placebo, L-NMMA decreased fundic volume after oral meal intake (438 (55) v 304 (67) ml; n=8; p<0.05) and during intraduodenal lipid infusion (384 (37) v 257 (43) ml; n=10; p<0.05) but not after glucagon injection (570 (62) v 540 (52) ml; n=4; p=0.4). In addition, basal fun-dic volume was significantly reduced by L-NMMA. Scores for nausea and satiation were decreased by L-NMMA after oral meal intake but not during intraduodenal lipid infusion. Perception scores to gastric distension were not altered by L-NMMA. Conclusions: NO is involved in maintaining basal fundic tone and in meal induced fundic relaxation in humans, but not in visceral perception.

Full text

MOTILITY AND VISCERAL SENSATION
Role of nitric oxide in gastric motor and sensory functions
in healthy subjects
S D Kuiken, M Vergeer, S H Heisterkamp,GNJTytgat,GEEBoeckxstaens
.............................................................................................................................
Gut
2002;51:212–218
Background and aims: Impaired accommodation and hypersensitivity to distension of the proximal
stomach are considered to be important factors in the pathogenesis of dyspeptic complaints. As fundus
relaxing agents may be effective in the treatment of these symptoms, insight into the mediators involved
in fundic accommodation and associated perceptual responses is important. Therefore, we studied the
effect of nitric oxide (NO) synthase inhibition by N
G
-monomethyl-L-arginine (L-NMMA) on fundic tone,
postprandial sensations, and gastric perception in healthy volunteers.
Subjects and methods: Eighteen healthy volunteers participated in a double blind, placebo control-
led, randomised study. They underwent a gastric barostat study to evaluate the effect of
L-NMMA on
meal and distension induced sensations and on fundic relaxation in response to oral meal intake,
intraduodenal lipid, and glucagon administration.
Results: Compared with placebo,
L-NMMA decreased fundic volume after oral meal intake (438 (55)
v
304 (67) ml; n=8; p<0.05) and during intraduodenal lipid infusion (384 (37)
v
257 (43) ml; n=10;
p<0.05) but not after glucagon injection (570 (62)
v
540 (52) ml; n=4; p=0.4). In addition, basal fun-
dic volume was significantly reduced by
L-NMMA. Scores for nausea and satiation were decreased by
L-NMMA after oral meal intake but not during intraduodenal lipid infusion. Perception scores to gastric
distension were not altered by
L-NMMA.
Conclusions: NO is involved in maintaining basal fundic tone and in meal induced fundic relaxation
in humans, but not in visceral perception.
N
ormal digestion and perception of sensations associ-
ated with meal intake are dependent on a reflex
relaxation of the proximal stomach initiated by food
ingestion. This so-called gastric accommodation reflex allows
storage of the meal without a concomitant increase in
intragastric pressure. Impaired relaxation of the proximal
stomach may contribute to the development of meal induced
symptoms in conditions such as functional dyspepsia,
diabetes mellitus, postfundoplication syndrome, rumination,
postsurgical gastroparesis, and diabetic gastroparesis.
1–5
Phar-
macological interventions aimed at relaxing the proximal
stomach may be effective in conditions characterised not only
by impaired gastric accommodation but also by increased sen-
sitivity to gastric distension, as seen for example in patients
with functional dyspepsia.
6
This has been suggested previ-
ously in studies using the 5-HT
1
agonist sumatriptan, which
was shown to increase meal induced gastric relaxation, to
increase the threshold for discomfort during gastric disten-
sion in healthy volunteers, and to increase caloric intake in
dyspeptic patients.
17
Therefore, to develop fundus relaxing
drugs, insight into the mediators involved in the regulation of
proximal gastric tone and associated perceptual responses is
important.
Nitric oxide (NO) is recognised as an important neurotrans-
mitter in the human gut, mediating a variety of motility
patterns.
8–10
Animal studies have provided abundant evidence
that both basal fundic tone and relaxation of the proximal
stomach induced by vagal stimulation, meal ingestion, or
intraduodenal lipid are mediated by NO.
11–17
In addition,
evidence is available that NO is involved in the modulation of
visceral perception, for example from rat experiments,
showing that intraperitoneal injection of acetic acid results in
an increase in nitrergic neurones in specific regions of the
brain.
18
Also, NO synthase immune reactivity has been
demonstrated in lumbosacral afferents and preganglionic
neurones innervating the pelvic viscera.
19
Data illustrating a role for NO in human proximal gastric
motility and perception are limited to in vitro studies
10
or to in
vivo studies investigating the effect of NO donors such as
nitrates.
20–22
However, to gain more insight into the role of
endogenous NO, studies evaluating the effect of an NO
synthase inhibitor are required. We previously demonstrated
that the selective NO synthase inhibitor N
G
-monomethyl-L-
arginine (
L-NMMA) dose dependently affects small intestinal
and oesophageal motility, illustrating that this chemical is a
useful tool to investigate the role of endogenous NO in
humans.
8923
Therefore, in the present study, we investigated
the effect of
L-NMMA in healthy volunteers on basal fundic
volume and fundic relaxation. In addition, perception of fun-
dic distension and meal induced sensations were assessed.
SUBJECTS AND METHODS
Subjects
Eighteen healthy male volunteers (mean age 24 years, range
19–30) were studied. All subjects were free of gastrointestinal
symptoms, with no previous gastrointestinal surgery, and
were not taking any medications. Subjects were studied after
an overnight fast and were not allowed to smoke or drink
alcohol for at least 24 hours before the study. All volunteers
gave written informed consent to participate in the study
which was approved by the medical ethics committee of the
Academic Medical Centre, Amsterdam.
Methods
Gastric barostat
The barostat allows continuous recording of proximal gastric
volume using an intragastric bag set at a fixed pressure level.
.............................................................
Abbreviations: NO, nitric oxide; L-NMMA, N
G
-monomethyl-L-arginine;
MDP, minimal distending pressure; VAS, visual analogue scale.
See end of article for
authors’ affiliations
.......................
Correspondence to:
Dr G Boeckxstaens,
Department of
Gastroenterology and
Hepatology, Academic
Medical Centre,
Meibergdreef 9, 1105 AZ
Amsterdam, the
Netherlands;
g.e.boeckxstaens@amc.uva.nl
Accepted for publication
29 January 2002
.......................
212
www.gutjnl.com

In addition, gastric sensitivity can be assessed by distending
the intragastric bag. Following anaesthesia of the throat (10%
xylocaine spray), subjects swallowed a 1200 ml polyethylene
bag, tightly wrapped on the distal end of a double lumen poly-
vinyl tube (Salem Sump tube, Sherwood Medical St Louis,
USA; outer diameter 4 mm). The bag was unfolded by inflat-
ing it with 500 ml of air and was positioned in the proximal
stomach by gently pulling the catheter back. The catheter was
connected to an electronic barostat that automatically
corrected for the compressibility of air (Medtronic Functional
Diagnostics, Stockholm, Sweden). Recorded data were stored
on a personal computer using commercially available software
(Polygram for Windows, Medtronic Functional Diagnostics,
Stockholm, Sweden).
Intraduodenal infusion
Study II. A polyurethane nasoduodenal feeding tube was
placed for lipid infusion (Flocare, Châtel Medical Devices SA,
Switzerland; length 125 cm, outer diameter 3.3 mm). The
catheter, containing a guidewire in the central lumen, was
positioned 30 cm beyond the pyloric region, under fluoro-
scopic control. The guidewire was then removed and the cath-
eter was connected to a perfusion pump. Based on previous
studies,
24
a 10% lipid solution (Intralipid, Pharmacia and
Upjohn, the Netherlands; energy load 1.1 kcal/ml) was infused
atarateof1ml/min.
Sensation scores
Sensations of bloating, nausea, pain, and satiation were
assessed individually, using a 10 cm continuous visual
analogue scale (VAS: 0 cm=no sensation, 10 cm=worst ever).
Perception of sensations induced by feeding was scored just
before and at five minute intervals after meal intake or
following the start of intraduodenal infusion of lipid (study I
and II, respectively). Sensations perceived during gastric
distension (study II) were scored halfway through each
distension step, both during fasting and during intraduodenal
infusion of lipid.
Drugs
L-NMMA (N
G
-monomethyl-L-arginine monoacetate) was sup-
plied by Alexis Corporation (Switzerland) and donated by a
generous grant from the Janssen Research Foundation
(Belgium).
L-NMMA was dissolved in a sterile 0.9% NaCl
solution to a concentration of 15 mg/ml. Equal volumes of the
vehicle were used in the control studies. Glucagon (GlucaGen;
glucagon hydrochloride) was supplied by Novo Nordisk
Pharma (the Netherlands).
Experimental protocols
Three study protocols were used (see fig 1). Of the 18
volunteers, three participated in studies I and II and three
participated in studies II and III. Therefore, the total number
of subjects studied was 10 for study I, 10 for study II, and four
for study III. All studies were designed in a double blind pla-
cebo controlled manner, performed on two separate days at
least three days apart. Study I was designed to investigate the
effect of
L-NMMA on fundic relaxation after oral intake of a
liquid caloric meal. In addition, sensations evoked by the test
meal were studied. In study II, subjects received lipids
intraduodenally via a nasoduodenal feeding tube. We chose
this approach (1) to bypass the possible effects of NO synthase
inhibition on gastric emptying and (2) to create a situation of
increased sensitivity to gastric distension, as described
previously.
24
The effects of L-NMMA on sensations induced by
duodenal lipid and by gastric distension were studied before
and during intraduodenal administration of lipids. In addi-
tion, we studied fasting fundic volume and fundic relaxation
induced by intraduodenal lipid. Study III was designed to
evaluate a possible postjunctional effect of
L-NMMA. There-
fore, in study III, we evaluated the effect of
L-NMMA on basal
volume and fundic relaxation after glucagon administration,
known to relax the proximal stomach, probably via a direct NO
independent mechanism.
25
Study I: fundic accommodation and sensations after oral
meal intake
In this study, both proximal stomach and antropyloro-
duodenal motility were recorded by combining a gastric baro-
stat test with antropyloroduodenal manometry. However, for
clarity, the manometry data are presented in a separate
paper.
26
Subjects reported to the laboratory at 7:45 am. The barostat
bag was positioned in the proximal stomach as described
above. An intravenous line was placed in the left arm for infu-
sion of either placebo or
L-NMMA. Heart rate, and systolic and
diastolic blood pressures were measured every 10 minutes
during the protocol using an automatic sphygmomanometer
(Boso, Jungingen, Germany). After an equilibration period of
30 minutes, minimal distending pressure (MDP) was deter-
mined as the minimum pressure at which balloon volume was
>30 ml. Baseline operating pressure was set at MDP+2 mm
Hg. Intragastric bag volume was recorded under basal condi-
tions over 15 minutes.
L-NMMA was infused intravenously at
a rate of 12 mg/kg over five minutes (bolus) followed by main-
tenance infusion of 6.7 mg/kg/h (fig 1). In the control studies,
an equal volume of saline was infused at equal rates. Twenty
minutes after the start of the infusion, 200 ml of a liquid test
meal (Nutridrink, Nutricia Zoetermeer, the Netherlands;
energy load 300 kcal) was consumed with the aid of a straw.
Fundic volume was recorded over the following 60 minutes.
Postprandial sensations were scored every five minutes.
Study II: fundic tone and sensations before and after
intraduodenal lipid
Subjects reported to the laboratory at 7:45 am. After
placement and positioning of the nasoduodenal catheter and
the barostat bag, an intravenous line was placed and an equi-
libration period of 30 minutes was allowed. Thereafter, MDP
was determined as described above. Operating pressure was
Figure 1 Schematic representation of the study protocols (see text
for detailed descriptions of the different studies).
NO and human stomach function 213
www.gutjnl.com

set at MDP+2 mm Hg and baseline intragastric bag volume
was recorded for 15 minutes. Intravenous administration of
either
L-NMMA (bolus of 12 mg/kg over five minutes, followed
by maintenance infusion of 6.7 mg/kg/h) or placebo was then
started (fig 1). Basal volume during the first 15 minutes of
infusion was recorded, followed by a series of four isobaric
distensions at 3, 6, 9, and 12 mm Hg above MDP, in random
order. Each pressure step lasted 60 seconds, with 120 second
intervals at the level of MDP. Perception scores were assessed
at each pressure step. Again, operating pressure was set at
MDP+2 mm Hg and continuous intraduodenal lipid infusion
was started 30 minutes after the first distension series.
Perceived meal related sensations were scored every five min-
utes during lipid infusion. A second series of four random iso-
baric distensions at MDP+ 3, 6, 9, and 12 mm Hg was
performed 30 minutes later while continuously infusing
lipids, and perception scores were assessed at each distension
level. Heart rate and blood pressure were measured every 10
minutes.
Study III: glugacon induced fundic relaxation
Subjects reported to the laboratory at 8:00 am. Placement of
the barostat bag, equilibration, determination of MDP, and
baseline volume recording (15 minutes) were performed as
described above. The same dose of
L-NMMA was used as in the
previous two studies. Similar to study II, fasting fundic
volume was recorded for 55 minutes (fig 1). At t=55 minutes,
subjects received 1 mg of glucagon intravenously, flushed with
5 ml of saline, in the right forearm. Heart rate and blood pres-
sure were measured every 10 minutes.
Data analysis
Fundic volume
Study I
Basal volume 15 minutes before and 20 minutes after the start
of infusion (
L-NMMA or placebo) was determined as mean
volume over the given period. Meal induced relaxation was
expressed as mean volume over the 60 minutes after the meal.
Volume change (or ∆V) was determined as the difference
between mean basal volume (before infusion) and mean
postprandial volume. Based on previous studies, a volume
change of >64 ml was considered normal.
1
Study II
Basal volume was measured 15 minutes before and 15
minutes after the start of infusion of
L-NMMA or placebo. In
addition, basal volume was measured between 40 and 55
minutes after the start of infusion (that is, 15 minutes after
the first distension series). Lipid induced relaxation was
expressed as mean volume over 30 minutes after the start of
intraduodenal infusion of lipid. ∆V was determined as the dif-
ference between mean basal volume (before infusion) and
mean postprandial volume.
Study III
Similar to study II, basal volume was measured 15 minutes
before and 15 minutes after the start of infusion of
L-NMMA
or placebo and between 40 and 55 minutes after the start of
infusion. Fundic relaxation in response to glucagon adminis-
tration was determined as mean volume over five minutes fol-
lowing injection. ∆V was determined as the difference
between mean basal volume (before infusion) and mean vol-
ume after glucagon.
Fundic compliance
Study II. Gastric distension was performed at fixed pressure
levels (3, 6, 9, and 12 mm Hg) above MDP. The mean of the
corresponding volumes over the last 30 seconds of each
distension step was measured and plotted against the
corresponding distending pressure. Fundic compliance was
calculated as the slope of the pressure-volume curve, as
described previously.
1
Meal induced sensations
Following meal ingestion and the start of intraduodenal lipid
administration (studies I and II, respectively), perceived
sensations were scored every five minutes. Scores for bloating,
nausea, pain, and satiation were analysed individually as
repeated measures in time using a customised mixed effects
model.
Sensation induced by gastric distension
Study II. We performed two series of four distensions at fixed
pressure levels applied in random order: one during fasting
and one during intraduodenal lipid administration (disten-
sion series 1 and 2, respectively). For each distension series,
scores for bloating, nausea, pain, and satiation were plotted
against the corresponding distending pressure.
Statistical analysis
For analysis of meal induced sensation scores, a mixed effects
model was fitted using a standard software package (S-PLUS
2000). As each sensation score is dependent on the previous
score, it is not possible to use standard techniques for statisti-
cal analysis such as t tests. Mixed effects models are similar to
linear regression but account for the structure of the repeated
measures using random effects.
27
Random effects allow the
intercept and the value of some other coefficients to vary from
person to person. In our analysis of the data on meal induced
sensations, we used a model that accounted for the time post-
prandial and the square of the time. The random effects were
a constant and the gradient associated with time.
The model used to describe meal induced sensations
perceived at time t by person i under treatment j, y
ijt
was:
y
ijt
= á
i
+ â
j
+ ã
i
t
+ ä
t
2
+ å
ijt
where e
ijt
∼ N(0, σ
2
).
Distension induced sensations were compared using a
repeated measures ANOVA with the Greenhouse-Geisser cor-
rection, using a standard software package (SPSS 9.0). All
other data were compared using a Student’s t test (SPSS 9.0)
and are presented as mean (SEM); p values <0.05 were con-
sidered statistically significant.
RESULTS
Effect of L-NMMA on blood pressure and heart rate
All subjects tolerated the studies well. In study I, mean diasto-
lic blood pressure was significantly increased from 73 (2) mm
Hg after placebo to 84 (2) mm Hg after
L-NMMA infusion
(p<0.01) whereas mean heart rate was significantly decreased
from 69 (5) bpm (placebo) to 58 (3) bpm (
L-NMMA)
(p<0.01). In study II, diastolic blood pressure increased from
75 (1) mm Hg (placebo) to 82 (2) mm Hg (
L-NMMA)
(p<0.01) and heart rate decreased from 60 (2) bpm (placebo)
to 54 (2) bpm (
L-NMMA) (p<0.01). In study III, L-NMMA
increased diastolic blood pressure from 69 (3) mm Hg
(placebo) to 79 (4) mm Hg (p<0.05) and heart rate decreased
from 58 (4) bpm (placebo) to 52 (3) bpm (p<0.05). Systolic
blood pressure was not significantly altered by
L-NMMA.
Cardiovascular effects were sustained during the course of the
studies. No side effects were reported.
Effect of
L-NMMA on basal fundic volume and fundic
relaxation
Basal fundic volume and fundic relaxation induced by
oral meal intake (study I)
Mean fundic volume was similar before the start of placebo and
L-NMMA (fig 2A). L-NMMA did not significantly alter basal
volume 20 minutes after the start of infusion (fig 2A). In eight
214 Kuiken, Vergeer, Heisterkamp, et al
www.gutjnl.com

of 10 subjects, ingestion of the meal resulted in fundic
relaxation that was considered normal (∆V >64 ml) during
placebo. Mean observed relaxation (or ∆V) in these individuals
(n=8) decreased from 274 (35) ml (placebo) to 143 (55) ml
(
L-NMMA) but this did not reach statistical significance
(p=0.08). In contrast, as shown in fig 2A, mean postprandial
volume was significantly decreased by
L-NMMA compared with
placebo.
Basal fundic volume and fundic relaxation induced by
intraduodenal lipid (study II)
Baseline fasting fundic volume was similar before the start of
placebo and
L-NMMA (fig 2B). L-NMMA did not significantly
alter fasting volume during the first 15 minutes. However,
L-NMMA gradually decreased fasting fundic volume during
the course of the study which was statistically significant over
the last 15 minutes before the start of intraduodenal lipid
administration (40–55 minutes following the start of drug
infusion) (fig 2B). All (n=10) subjects showed marked fundic
relaxation following the start of intraduodenal lipid which
was significantly decreased by
L-NMMA compared with
placebo (∆V: from 204 (32) ml to 129 (32) ml; p<0.05). In
addition, mean postprandial volume was significantly de-
creased by
L-NMMA compared with placebo (fig 2B).
Basal fundic volume and fundic relaxation induced by
glugacon (study III)
Baseline fasting fundic volume before the start of placebo or
L-NMMA was comparable for both groups (fig 2C). Similar to
study II,
L-NMMA did not significantly alter fasting volume
during the first 15 minutes but significantly decreased mean
fasting fundic volume over the last 15 minutes of the record-
ing time, 40–55 minutes following the start of drug infusion
(fig 2C). Glucagon administration induced an instant and
marked relaxation of the fundus in all (n=4) subjects which
was not altered by
L-NMMA (∆V: 397 (71) ml and 356 (66) ml
for placebo and
L-NMMA, respectively; p=0.2). In addition,
mean volume after glucagon was not significantly altered by
L-NMMA compared with placebo (fig 2C).
Effect of
L-NMMA on visceral perception
Sensations after oral meal intake (study I)
At baseline, subjects reported comparable sensation scores
(see fig 3, t=0). Following the meal, subjects reported
increased sensations of bloating, satiation, pain, and nausea.
Scores for bloating and pain were not altered by
L-NMMA
whereas subjects reported significantly decreased scores for
nausea and satiation during
L-NMMA infusion compared with
placebo (fig 3).
Sensations after duodenal lipid infusion (study II)
Sensation scores were comparable before the start of
intraduodenal lipid administration. No significant scores for
nausea and pain were reported during intraduodenal admin-
istration of lipid, during both placebo and
L-NMMA adminis-
tration (maximum score for nausea: 0.6 (0.4) and 0.4 (0.3) cm,
respectively; maximum score for pain: 0.3 (0.2) and 0.3 (0.1)
cm, respectively). Although sensation scores for bloating and
satiation tended to increase slightly during intraduodenal
lipid, subjects perceived only very low scores, during both pla-
cebo and
L-NMMA (maximum score for bloating: 1.4 (0.5) and
1.6 (0.7) cm, respectively; maximum score for satiation: 1.4
(0.6) and 1.4 (0.6) cm, respectively).
L-NMMA did not signifi-
cantly alter any of the sensation scores compared with
placebo.
Sensation induced by gastric distension (study II)
Subjects reported only mild sensations of pain and nausea
during fundic distension while fasting. As shown in fig 4,
intraduodenal lipid tended to increase the perception of pain
and nausea, although this did not reach statistical difference.
Scores for bloating and satiation were more pronounced in
both distension series and significantly increased during
intraduodenal lipid compared with placebo (fig 4). No signifi-
cant effect on sensation scores during distension was seen
between
L-NMMA and control studies during both fasting and
intraduodenal lipid infusion (fig 4).
Effect of
L-NMMA on fundic compliance
Fundic compliance during fasting was not significantly
altered (placebo 50 (4) v
L-NMMA 46 (6) ml/mm Hg).
Likewise, during infusion of lipid, mean fundic compliance
was not significantly affected by
L-NMMA (placebo 46 (3) v
L-NMMA 50 (5) ml/mm Hg). Pressure-volume curves are
shown in fig 5.
DISCUSSION
In this study, we evaluated the effect of NO synthase
inhibition by
L-NMMA on proximal gastric volume and
perception in healthy human subjects. We showed that
L-NMMA decreased basal fundic volume and reduced fundic
relaxation both after ingestion of a liquid meal and during
intraduodenal lipid infusion, indicating that NO is involved in
modulating fundic tone. Finally, no effect of
L-NMMA on per-
ception was seen, indicating that, at least in healthy
volunteers, NO has no major role in visceral perception.
Figure 2 Effect of N
G
-monomethyl-L-arginine (L-NMMA) and
placebo on basal and postprandial fundic volume (A) after oral
ingestion of a liquid meal, (B) after intraduodenal infusion of lipid,
and (C) after injection of glucagon. Data are mean (SEM). *p<0.05,
paired
t
test versus placebo; †p<0.05 paired
t
test versus basal
(before infusion).
NO and human stomach function 215
www.gutjnl.com

Animal studies have provided abundant evidence that both
basal tone and relaxation of the proximal stomach, induced by
vagal stimulation, meal ingestion, or intraduodenal lipid, are
mediated by NO.
11–17
Similarly, we showed that NO synthesis
inhibition by
L-NMMA contracted the gastric fundus, result-
ing in a reduction in basal fundic volume. The effect was only
observed after prolonged infusion of
L-NMMA, most likely due
to the time dependent inhibitory effect of
L-NMMA on NO
synthase activity.
28
In addition, L-NMMA reduced fundic
volume following ingestion of a nutrient liquid meal and dur-
ing intraduodenal lipid. It should be emphasised that the
reduction in postprandial volume observed during
L-NMMA
may simply reflect functional antagonism, resulting from the
contractile effect of
L-NMMA on basal tone. However, fundic
relaxation induced by glucagon, known to act by a direct and
NO independent mechanism,
25
was not affected by L-NMMA.
Therefore, we concluded that the reduction in postprandial
volume by
L-NMMA resulted from an effect on NO release,
illustrating that NO is involved in meal induced relaxation of
the human proximal stomach. These findings are in line with
the recent in vitro study by Tonini et al demonstrating that
relaxation of muscle strips of the human proximal stomach
induced by nerve stimulation is inhibited by NO synthase
inhibition.
10
With respect to the site of action, L-NMMA may act at all
possible levels as NO is found to act throughout the central
nervous system and the enteric nervous system. The fact that
fundic relaxation induced by glucagon was not inhibited by
L-NMMA excludes a possible postjunctional effect on the fun-
dic smooth muscle. In addition, we did not observe an effect of
NO synthase inhibition on plasma pancreatic polypeptide
concentrations,
29
indicating that vagal efferent output was not
altered by
L-NMMA. Finally, no significant effect on reaction
time was noted (data not shown), suggesting no sedative
effect of
L-NMMA. Thus although a central action of L-NMMA
cannot be excluded under the current experimental condi-
tions, these findings suggest that
L-NMMA increases fundic
tone by reducing nitrergic neuronal input at a peripheral level.
Figure 3 Effect of N
G
-monomethyl-L-arginine (L-NMMA) and placebo on sensation scores for bloating, satiation, pain, and nausea after oral
ingestion of a nutrient liquid meal (study I). Visual analogue scale (VAS) scores for satiation and nausea after oral meal intake were
significantly decreased by
L-NMMA compared with placebo (*p<0.05, customised mixed model). Data are expressed as the observed rough
mean (SEM).
Figure 4 Effect of N
G
-monomethyl-L-arginine (L-NMMA) (filled
symbols) and placebo (open symbols) on sensation scores for
bloating, satiation, pain, and nausea in response to fundic distension
during fasting and intraduodenal lipid infusion. Data are mean
(SEM). MDP, minimal distending pressure.
Figure 5 Effect of
N
G
-monomethyl-L-arginine
(
L-NMMA) (filled symbols) and
placebo (open symbols) on
pressure-volume curves in
response to isobaric fundic
distension during fasting and
intraduodenal lipid infusion.
MDP, minimal distending
pressure.
216 Kuiken, Vergeer, Heisterkamp, et al
www.gutjnl.com

Impaired accommodation to a meal, as encountered in a
number of clinical conditions, is considered an important
pathophysiological mechanism responsible for dyspeptic
complaints.
1–5
For example, in functional dyspepsia, impaired
accommodation is associated with early satiety and weight
loss.
1
Therefore, we anticipated that reduction in gastric
relaxation by
L-NMMA should increase postprandial sensation
scores. In contrast, scores for nausea and satiation were
significantly decreased. As NO is also involved in the modula-
tion of visceral sensation,
18 30
this effect could result from
interaction of
L-NMMA with perception. However, no changes
in perception of gastric distension were reported during fast-
ing. Furthermore, when the stomach was distended during
intraduodenal infusion of lipid, which is known to cause
increased sensitivity in healthy subjects,
24
no effect of
L-NMMA was observed, excluding interference with visceral
perception. The observation that during
L-NMMA infusion
subjects only reported decreased sensation scores after oral
meal intake may therefore result from an effect of
L-NMMA on
gastric emptying. Alternatively, as gastric wall tension seems
to be the major determinant of gastric perception,
31
reduced
perception of meal induced sensations may also be explained
by the reduction in volume and the associated reduction in
wall tension. The fact that healthy volunteers also experienced
mild degrees of nausea and pain during the experiment prob-
ably reflects the artefact that is introduced by measuring meal
induced sensations while having a barostat balloon inflated in
the stomach. Our finding that reduction of meal induced
relaxation is not accompanied by an increase in perceived
sensations questions the direct relationship between impaired
accommodation and symptoms, as found in functional
dyspepsia. Similar conclusions were drawn from a recent
study showing that in patients with functional dyspepsia,
abolishing gastric relaxation by the cholecystokinin A antago-
nist dexloxiglumide was associated with reduced rather than
increased dyspeptic symptoms.
32
In contrast with several animal studies, we did not observe
an effect of
L-NMMA on visceral perception. This may be
explained by the knowledge that NO has been shown to be
mainly involved in the perception of visceral pain.
18 19 30 33
The
healthy volunteers in our study predominantly reported
bloating and satiation on gastric distension, rather than pain.
One might however anticipate that NO synthase inhibition
may have an effect on perception in dyspeptic patients with
visceral hypersensitivity.
6
Animal models of visceral hyperal-
gesia indeed show upregulation of NO synthase producing
neurones in the spinal cord. More importantly, NO synthase
blockade normalised the hyperalgesic response but had no
effect on perception in control animals.
33 34
Therefore,
L-NMMA may only affect visceral perception in the presence of
hypersensitivity. Further studies investigating the effect of NO
synthase inhibition in patients with functional dyspepsia are
therefore warranted.
The use of NO donors in conditions characterised by
impaired accommodation and/or hypersensitivity to gastric
distension is controversial. Nitrates are known to induce gas-
tric relaxation and earlier studies showed some relief of
symptoms in functional dyspepsia but not in diabetes.
20 21
Moreover, significant side effects, in particular headaches, are
associated with the use of nitrates. Therefore, development of
fundus relaxing drugs may need to be aimed at selectively
activating NO producing neurones at the level of the
myenteric plexus. For example, the 5-HT
1
agonist su-
matriptan has been shown to relax the proximal stomach by
activating NO producing neurones.
11 35
Reduction of gastric
tone by sumatriptan allowed higher gastric distension
volumes in healthy volunteers before the threshold of
discomfort was reached, and increased the amount of calories
inducing maximum satiety in functional dyspeptics.
17
Al-
though these studies are promising, confirmation in larger
clinical studies is awaited.
In summary, we showed that NO is involved in basal fundic
tone and fundic relaxation in healthy volunteers but not in
gastric perception. Reduction of meal induced relaxation did
not result in increased perception of postprandial sensations.
As NO inhibition did not affect gastric perception to
distension and had no effect on sensations scored during
intraduodenal lipid, the reduced scores for nausea and
satiation by
L-NMMA after oral meal intake are most likely
caused by delayed gastric emptying.
ACKNOWLEDGEMENTS
SDK is supported by a grant from the Netherlands Digestive Diseases
Foundation (MLDS), grant number WS 99-38. Parts of the study have
been published previously in abstract form.
.....................
Authors’ affiliations
S D Kuiken, M Vergeer, G N J Tytgat, G E E Boeckxstaens,
Department of Gastroenterology and Hepatology, Academic Medical
Centre Amsterdam, the Netherlands
S H Heisterkamp, Department of Clinical Epidemiology and
Biostatistics, Academic Medical Centre Amsterdam, the Netherlands
REFERENCES
1 Tack J, Piessevaux H, Coulie B,
et al
. Role of impaired gastric
accommodation to a meal in functional dyspepsia.
Gastroenterology
1998;115:1346–52.
2 Vu MK, Straathof JW, Schaar PJ,
et al
. Motor and sensory function of the
proximal stomach in reflux disease and after laparoscopic Nissen
fundoplication.
Am J Gastroenterol
1999;94:1481–9.
3 Thumshirn M, Camilleri M, Hanson RB,
et al
. Gastric mechanosensory
and lower esophageal sphincter function in rumination syndrome.
Am J
Physiol
1998;275:G314–21.
4 Azpiroz F,.Malagelada J-R. Gastric tone measured by an electronic
barostat in health and postsurgical gastroparesis.
Gastroenterology
1987;92:934–43.
5 Samsom M, Salet GA, Roelofs JM,
et al
. Compliance of the proximal
stomach and dyspeptic symptoms in patients with type I diabetes mellitus.
Dig Dis Sci
1995;40:2037–42.
6 Mearin F, Cucala M, Azpiroz F,
et al
. The origin of symptoms on the
brain-gut axis in functional dyspepsia.
Gastroenterology
1991;101:999–1006.
7 Tack J, Coulie B, Wilmer A,
et al
. Influence of sumatriptan on gastric
fundus tone and on the perception of gastric distension in man.
Gut
2000;46:468–73.
8 Russo A, Fraser R, Adachi K,
et al
. Evidence that nitric oxide
mechanisms regulate small intestinal motility in humans.
Gut
1999;44:72–6.
9 Hirsch DP, Holloway RH, Tytgat GNJ,
et al
. Involvement of nitric oxide
in human transient lower esophageal sphincter relaxations and
esophageal primary peristalsis.
Gastroenterology
1998;115:1374–80.
10 Tonini M, De Giorgio R, De Ponti F,
et al
. Role of nitric oxide- and
vasoactive intestinal polypeptide-containing neurons in human gastric
fundus strip relaxations.
Br J Pharmacol
2000;129:12–20.
11 Coulie B, Tack J, Sifrim D,
et al
. Role of nitric oxide in fasting gastric
fundus tone and in 5-HT1 receptor-mediated relaxation of gastric fundus.
Am J Physiol
1999;276:G373–7.
12 Boeckxstaens GE, Pelckmans PA, Bogers JJ,
et al
. Release of nitric oxide
upon stimulation of nonadrenergic noncholinergic nerves in the rat gastric
fundus.
J Pharmacol Exp Ther
1991;256:441–7.
13 Iversen HH, Celsing F, Leone AM,
et al
. Nerve-induced release of nitric
oxide in the rabbit gastrointestinal tract as measured by in vivo
microdialysis.
Br J Pharmacol
1997;120:702–6.
14 Boeckxstaens GE, Pelckmans PA, De Man JG,
et al
. Evidence for a
differential release of nitric oxide and vasoactive intestinal polypeptide
by nonadrenergic noncholinergic nerves in the rat gastric fundus.
Arch Int
Pharmacodyn Ther
1992;318:107–15.
15 Lefebvre RA. Non-adrenergic non-cholinergic neurotransmission in the
proximal stomach.
Gen Pharmacol
1993;24:257–66.
16 Meulemans AL, Eelen JG, Schuurkes JA. NO mediates gastric
relaxation after brief vagal stimulation in anesthetized dogs.
Am J Physiol
1995;269:G255–61.
17 Meulemans A, Schuurkes J. Intralipid-induced gastric relaxation is
mediated via NO.
Neurogastroenterol Mot
1995;7:151–5.
18 Rodella L, Rezzani R, Agostini C,
et al
. Induction of NADPH-diaphorase
activity in the rat periaqueductal gray matter after nociceptive visceral
stimulation.
Brain Res
1998;793:333–6.
19 Vizzard MA, Erdman SL, de Groat WC. Increased expression of
neuronal nitric oxide synthase (NOS) in visceral neurons after nerve
injury.
J Neurosci
1995;15:4033–45.
20 Undeland KA, Hausken T, Gilja OH,
et al
. Gastric meal
accommodation and symptoms in diabetes. A placebo-controlled study of
glyceryl trinitrate.
Eur J Gastroenterol Hepatol
1998;10:677–81.
NO and human stomach function 217
www.gutjnl.com

21 Gilja OH, Hausken T, Bang CJ,
et al
. Effect of glyceryl trinitrate on
gastric accommodation and symptoms in functional dyspepsia.
Dig Dis
Sci
1997;42:2124–31.
22 Thumshirn M, Camilleri M, Choi MG,
et al
. Modulation of gastric
sensory and motor functions by nitrergic and alpha2-adrenergic agents in
humans.
Gastroenterology
1999;116:573–85.
23 Hirsch DP, Tiel-Van Buul MM, Tytgat GNJ,
et al
. Effect of L-NMMA on
post-prandial transient lower esophageal sphincter relaxations in healthy
volunteers.
Dig Dis Sci
2000;45:2069–75.
24 Feinle C, Grundy D, Read NW. Effects of duodenal nutrients on sensory
and motor responses of the human stomach to distension.
Am J Physiol
1997;273:G721–6.
25 Shibata C, Naito H, Jin XL,
et al
. Effect of glucagon, glicentin,
glucagon-like peptide-1 and -2 on interdigestive gastroduodenal motility
in dogs with a vagally denervated gastric pouch.
Scand J Gastroenterol
2001;36:1049–55.
26 Kuiken SD, Tytgat GNJ, Boeckxstaens G. Role of endogenous nitric
oxide in regulating antropyloroduodenal motility in humans.
Am J
Gastroenteral
2002 (in press).
27 Crowder MJ, Hand DJ.
Analysis of repeated measures
. London:
Chapman and Hall, 1993.
28 Olken NM, Rusche KM, Richards MK,
et al
. Inactivation of macrophage
nitric oxide synthase activity by NG-methyl- L-arginine.
Biochem Biophys
Res Commun
1991;177:828–33.
29 Kuiken SD, Tytgat GNJ, Masclee AAM,
et al
. Effect of L-NMMA on
human proximal stomach function and gastrointestinal hormone release.
Neurogastroenterol Mot
2001;13:A407.
30 Rouzade ML, Anton P, Fioramonti J,
et al
. Reduction of the nociceptive
response to gastric distension by nitrate ingestion in rats.
Aliment
Pharmacol Ther
1999;13:1235–41.
31 Distrutti E, Azpiroz F, Soldevilla A,
et al
. Gastric wall tension determines
perception of gastric distention.
Gastroenterology
1999;116:1035–42.
32 Feinle C, Meier O, Otto B,
et al
. Role of duodenal lipid and
cholecystokinin A receptors in the pathophysiology of functional
dyspepsia.
Gut
2001;48:347–55.
33 Coutinho SV, Gebhart GF. A role for spinal nitric oxide in mediating
visceral hyperalgesia in the rat.
Gastroenterology
1999;116:1399–408.
34 Meller ST, Gebhart GF. Nitric oxide (NO) and nociceptive processing in
the spinal cord.
Pain
1993; 52:127–36.
35 Tack J, Demedts I, Vos R,
et al
. Role of nitric oxide in the
accommodation reflex, in meal-induced satiety and in the treatment of
impaired accommodation in man.
Gastroenterlogy
2001;118:A388.
218 Kuiken, Vergeer, Heisterkamp, et al
www.gutjnl.com