A696 AGA ABSTRACTS GASTROENTEROLOGY, Vol. 108, No. 4

• INVOLVEMENT OF ATP-SENSITIVE POTASSIUM CHANNEL OPENING IN NEURAL RELAXATION OF THE RABBIT SPHINCTER OF ODDI. Z~ Szilvassy, I Jakab, J. Lonovics. 1st Dept Medicine, Albert Szent-Gyorgyi Medical University Szeged, Hungary

Study objective. The L-arginine nitric oxide (NO) pathway has been shown to play a major role in non-adrenergic non-cholinergic (NANC) relaxation of the rabbit sphincter of Oddi (SO). NO stimulates soluble guanylate cyclase increasing the formation of cyclic guanosine 3 ' ,5 ' monophosphate (cGMP) that results in activation of ATP-sensitive potassium channels (KATp) in various tissue preparations. We explored the possible involvement of KATp activation in NANC relaxation of isolated rabbit SO. Methods. Isolated SO muscle rings were cleaned of fat and adhering connective tissue, and the ampullary part of each muscl e ring was mounted horizontally on two small L-shaped hooks Of which one was connected to a force transducer for measurement of isometric tension. The experiments were carried out in thermostatically controlled (37 + 0.2°C) organ bath (5 ml) containing Krebs solution. The organ fluid was gassed with 95% O,. and 5% C Q to keep pH at 7,40+0.05. Neural effects on contractile activity of SO muscle rings were studied by means of electrical field stimulation (FS: 10 stimuli at 50 V, 0.1 ms and 20 Hz). Results. FS induced an initial twitchlike contraction followed by relaxation. The magnitude of the contractile component was considerably reduced by 1 /zM atropine, phentolamine and oxprenolol ('NANC' solution) with a marked increase in relaxation in response to field Stimulation. FS failed to induce either contractions or relaxations in the presence of 1 #M tetrodotoxin. Thirty/~M N°-nitro-L-arginine methyl ester (L-NAME) abolished the NANC relaxation with a moderate increase in NANC contractions in response FS. L-arginine but not D-arginine (both 3 mM) reversed the inhibitory effect of L-NAME on NANC relaxation. In the second set of experiments using seperate SO preparations, cumulative doses of glibenclamide (0.01-10 ~tM), a specific blocker of KArp was added to the NANC solution. These SO muscle rings were subjected to FS as well. Glibenclamide (GLIB) was found to attenuate NANC relaxation in a dose-dependent manner. In the presence of L-NAME, glibanclamide failed to influence NANC contractions. In the third set of experiments, 8-bromo cGMP (I/xM-I mM) induced relaxation in a concentration- dependent manner in SO preparations precontracted by cholecystokinin octapeptide (0.1 /~M). GLIB concentration-dependently attenuated 8-bromo cGMP-induced relaxation. Conclusion reached. The results indicate that K:,a. ~, Opening is involved NO/cGMP, mediated neural relaxation in the ampullary part of the rabbit SO.

This work was supported by grants from the National Scientific Research Ful'td (OTKA No. 1355) and the Ministry of Social Welfare (ETT No. T-86/1990).

• SUMATRIPTAN, A 5-HTI-RECEPTOR AGONIST, CAUSES A SIGNIFICANT RELAXATION OF THE GASTRIC FUNDUS IN MAN. LE~ ~af~, B. Coulie, A. Wiimer and J. Janssens. Center for Gastroentero|ogical Research, K.U.Leuven, Belgium.

Administration of sumatriptan (Sum), a selective 5-HTi-receptor agonist, delays gastric emptying of liquids in man (Houghton et al., 1992). We demonstrated that Sum acts as an agonist at 5-HTw-receptors on myenteric neurons in the stomach (Tack et al., 1993). Hypothesis: We hypothesized that Sum might cause a relaxation of the gastric fandus in man. Methods: In 6 healthy subjects (age 20-29 years), an electronic barostat was used to asses the effect of Sum on gastric tone and graded balloon distensions were used to asses the effect of Sum on perception of gastric distension and on gastric compliance. After introduction of a flaccid balloon (max. diameter = 17 cm) in the stomach and an accomodation period of 30 rain, graded distensions (increments of 2 mm Hg of 2 minutes duration at 4 minutes intervals) were performed until the subjects reported abdominal discomfort. Minimal distending pressure (MDP) was defined as the pressure level needed to overcome abdominal pressure. Volume and pressure changes were recorded and perception was scored by a questionnaire (score 0-4, 1--threshold sensation, 3=discomfort). Subsequently, the pressure level was set at MDP+2 mm Hg during 60 minutes, with administration of 6 mg of Sum s.c. after 30 minutes. Gastric tone was measured as the mean balloon volume over 5 minutes intervals. Afterwards, graded distensions were repeated. Result s (mean±SD) were compared by paired t-tast (ct<0.05). Results: MDP was 6.2±0.4 mm Hg. Administration of Sum caused an immediate relaxation of the gastric fundus, reflected by an increase in the balloon volume. The maximum increase in balloon volume was 207:t:l 15 ml (P=0.007) and this occurred 10-15 minutes after the admir~istration of Sum. The mean balloon volume over a 30 minute period increased from 245±105 to 382±!08ml after Sum (P=0.01). The volume and pressure thresholds for perception of gastric distension before and a0er Sum were 469~219ml; ' 12.2±3.5mmHg and 565±264ml; 13.4±6.4mmHg respectively (NS). Similarly, the volume and pressures at which abdominal discomfort was reported were not significantly altered by Sum (742±269ml; 19.0±4.3mmHg and 748±195ml; 18:6±3.7mmHg respectively, NS). Gastric

compliance was not significantly altered by Sum (38.3±15.g versus 36.1±12.2 ml/mm Hg, NS). Conclusion: Administration of 6 mg of Sum s.c. causes a significant relaxation of the gastric fundus. This may account fdr the delay in gastric emptying of liquids caused by Sum, Our previous observations suggest an action on the intrinsic innervation of the stomach, but other modes of action in man cannot be excluded. (Supported by NFWO Belgium)

• SUMATRIPTAN, A 5-HT1-RECEPTOR AGONIST, MIMICKS THE EFFECT OF SOMATOSTATIN ON INTERDIGESTIVE GASTROINTESTINAL MOTILITY IN MAN.. IF , Tack, A. Wilmer, B. Coulie and J. Janssens. Center for Gastroenterological Research, K.U.Leuven, Belgium.

We demonstrated that sumatriptan (Sum), a selective 5-HTt-receptor agonist, acts as an agonist at 5-HTip-receptors on myenteric neurons in the stomach and the small intestine (Tack et aL, t993). Hypothesis; We hypothesized that Sum might influence interdigestive gastrointestinal motility in man. Methods: In 10 healthy subjects (age 20-25 years), antroduodenojejunal motor activity was studied by stationary, perfused catheter manometry with 4 recording orifices in the antrum, 1 in the duodenum and 2 in the jejunum. Basal interdigestive motor activity was recorded until the passage of two activity f(onts. Five minutes after the second activity front, 6 mg of Sum were adminstered s.c. Recording continued until the passage of two more activity fronts. The origin of the activity fronts (gastric vs small intestinal) was determined by visual inspection of the tracings. Computer analysis was used to determine the MMC-cyele length, the duration of the different phases of the MMC, and the number of contractions per min during phase 2 in the antrum or in the jejunum. Results (mean+SD) ' were compared by Wilcoxon Signed Rank test (cc<0.05). Results: Sum significantly shortened MMC cycle length from 77~:23 min to 48±23 min (p=0.02). Before Sum, 14 out of 20 activity fronts (70%) had a gastric origin. After Sum, only 1 of 19 activity fronts (5%) had a gastric origin (p<0.05). The duration oPph~tse 1 of the MMC-cyele was not affected by Sum (26±17 rain vs 304-18 min, NS). In contrast, the duration of phase 2 of the MMC-cycle was significantly shortened after Sum (56:t:32 min vs 21a:15 min, p=0.018). While the number of contractions per min during phase 2 at the antral level was not affected by Sum (0.6:~0.3 con/min vs 0.5:~0.2 con/rain, NS), jejunaIcontractile activity after Sum was significantly reduced (2.4±0.6 eon/min vs 1.7±0.9 con/min, p=0.02). The velocity of propagation of the activity front was nog significantly altered by Sum (6.04-2.8 cm/min vs 5.6±3.1 cm/min, NS). Conclusion: In man, administration of 6 mg of Sum s.c. inhibits gastric activity fronts and stimulates the occurrence of small intestinal activity fronts. Moreover, intestinal phase 2 is suppressed. Similar effects have also been observed with somatostatin (Peeters et al., 1983). Our previous observations suggest an action of Sum on the enteric nervous system, but other modes of action in man, such as the release of somatostatin, cannot be excluded. (Supported by NFWO Belgium)

• FUNCTIONAL AND M O R P H O L O G I C EVIDENCE THAT GASTRIC NITRIC OXIDE (NO) N E U R A L P A T H W A Y IS DEFECTIVE IN DIABETIC BB/W RATS. T Takahashi, AAF Sima, C Owyang . Department of Internal Medicine, University of Michigan, Ann Arbor, MI.

The e t io logy o f diabet ic gas t ropares i s is u n k n o w n . W e have demonstrated that nitric oxide (NO) neurons in the gastric myenteric plexus play important roles in mediating the gastric accommodation reflex, which allows the stomach to hold large volumes with a minimal increase in pressure. We hypothesized that N O neural pa thways in the gastric myentedc plexus are impaired in diabetes, resulting in impairment of accommodation. We studied non-adrenergic, non-cholinergic relaxation (NANC), N O synthesis, and NADPH-diaphorase staining o f the gastric myenteric plexus in spontaneously diabetic BB/W rats. Age-matched, non- diabetic Wistar rats were controls. Rats were sacrificed 6 months after the onset o f diabetes. Gastric neuromuscular preparations from control rats demonstrated frequency-dependent NANC relaxations with t ransmurai stimulation (1-20 Hz), which were markedly antagonized by the NO biosynthesis inhibitor , L -NAME, and complete ly abol ished by the pretreatment with tetrodotoxin, indicating mediat ion by the neuronal release of N O . Amplitudes o f NANC relaxations in preparations f rom diabetic rats were only 35% of those in control rats. Sodium nitroprusside, a direct activator of soluble guanylate cyclase, induced similar degrees of relaxation in preparations f rom control and diabetic rats, indicating that responses to NO remain intact in diabetic rats. NO synthesis measured as 3H-citruUine formation in gastric tissue with transmurai stimulation was significantly impaired in diabetic rats. In contrast, contraction and 3H- acetylcholine release with transmural stimulation (1-20 Hz) remained intact in diabetic rats.

% increase over basal of 3H-Citrulline formation 1 Hz 2.5 Hz ~ Hz

Control 82.5_+7.8 134.05:13.8 176.5_+12.1 BBAV 30.3_+3.3* 53.7+_.3.4* 64.3+_5.6*

*P<0.05

Morphologically, control rats had 4.8_-t-0.5 NADPH diaphorase positive cells/ganglion versus 1.8-+0.7/ganglion in diabetic rats (P<0.05). These results indicate that, in contrast to cholinergic transmission which remains intact, gastric relaxation is impaired in diabetic rats due to defective NO release, which results from reduced numbers of NO synthesizing neurons in the gastric myenteric plexus. This may contribute to gastric motor abnormalities in diabetic gastroparesis.