Mast cells mediate gastric hypermotility induced by intracisternal TRH analog, RX 77368, in anesthetized rats

GASTROENTEROLOGY Vol. 118, No.4

A130 AGA ABSTRACTS

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HYPERSECRETED HYPOTHALAMIC NEUROPEPTIDE Y (NPY) IN HYPERGLYCEMIA IMPAIRS PYLORIC RELAXATION AND DELAYS GASTRIC EMPTYING IN RATS. Tadashi Ishiguchi, Arno K. Kumagai, Toku Takahashi, Univ of Michigan, Ann Arbor, MI. About one-half of patients with diabetes have delayed gastric emptying. Recent data suggest that hyperglycemia per se contributes to the pathogenesis of delayed gastric emptying. In the present study, we investigated the acute effects of hyperglycemia on gastric emptying and gastric distension-induced pyloric relaxation in rats. An extraluminal miniature force transducer was implanted on the serosal surface of the pylorus to monitor circular muscle contractions. Gastric distension-induced pyloric relaxation was compared between saline-infusion (euglycemia) and glucose infusion (hyperglycemia) in each rat. An intravenous (i.v.) infusion of glucose increased the blood glucose level from 5.4:!::0.5 mM to 13.0:!::1.3 mM. An i.v. infusion of glucose significantly delayed solid gastric emptying to 4:!::3%, compared to controls (64:!::5%). Gastric distension-induced pyloric relaxation was significantly reduced by L-NAME (10 mg/kg) and subdiaphragmatic vagotomy to 11.2:!::2.4% and 11.2:!::4.3% of controls, respectively. In contrast, gastric distension-induced pyloric relaxation was not affected by spinal cord transection or guanethidine (5 mg/kg). This suggests that gastric distension-induced pyloric relaxation is predominantly mediated via the vagal nerve and nitric oxide pathway. Gastric distentioninduced pyloric relaxation was significantly reduced by hyperglycemia to 28.7:!::6.2% of that in euglycemia. An intracerebroventricular (i.c.v.) injection of glucose (3 pomol), which had no significant effect on peripheral blood glucose levels, significantly reduced gastric distention-induced pyloric relaxation to 33.1:!::5.4% of controls. Hypothalamic neuropeptide Y (NPY) concentrations were significantly increased to 3323:!:: 164 pg/mg prot. in rats receiving glucose infusion, compared to those in rats receiving saline infusion (I 560:!:: 182 pg/mg prot). An i.c.v. injection of NPY (0.03-3 nmol) and the NPY receptor YI agonist, [leu31, pro34] NPY (0.03-3 nmol) significantly reduced gastric distension-induced pyloric relaxation in a dose dependent manner. The impaired pyloric relaxation in response to gastric distension observed in hyperglycemia was significantly improved by i.c.v. injections of polyclonal NPY antibody (3 pol) and the NPY receptor YI antagonist, BIBP 3226 (30 nmol). It is concluded that acute hyperglycemia stimulates hypothalamic NPY release, which, acting through the YI receptor, inhibits gastric distension-induced pyloric relaxation.

SOMATIC PAIN BLUNTS VISCERAL PERCEPTION AND AL· TERS THE CEREBRAL REPRESENTATION OF GASTRIC DISTENSION ON POSITRON EMISSION TOMOGRAPHY. Uri Ladabaum, Satoshi Minoshima, Donna Cross, Chung Owyang, William L. Hasler, Univ of Michigan, Ann Arbor, MI. The cerebral representations of gastric distension and somatic pain overlap substantially. Somatic stimulation has been shown to blunt perception of visceral distension. We hypothesized that somatic pain interferes with visceral perception and alters its cerebral representation by mechanisms beyond simple distraction. To test this hypothesis, we examined the effect of forearm thermal stimulation and mental distraction on symptoms and regional cerebral activities during distal gastric distension using positron emission tomography (PET). Methods: 14 healthy humans underwent ISO-water PET scanning during sham gastric distension and innocuous left arm heat (40:!:: j0C), noxious distension (30:!::8 mm Hg) and innocuous heat [V=visceraIJ, sham distension and painful heat (52:!::2°C) [S=somatic], distension and painful heat [V+ S = visceral+ somatic], and distension and innocuous heat with arithmetic task [V+M=visceral+mental]. With each condition, subjects rated nausea, bloating, pain and skin sensation (0-10; painful skin sensation e::5). Visceral symptoms were added in a Global Visceral Score (0-30). Image sets were coregistered, normalized and transformed to the standard stereotactic system and statistical subtraction analysis was performed. Results: Consistent with our previous results, V produced significant activation in several structures including the thalami, cerebellum, brainstem and left frontal cortex. The Global Visceral Score was lower with V+S (l0.5:!::1.0, P=0.02) but not with V +M (l2.7:!: 1.0, P=0.8) compared to V (l3.2:!::1.1). Along with the decrease in visceral symptoms, activity with V +S decreased in the left thalamus (Z=-4.l), right temporal cortex (Z=-4.3). and left frontal (Z=-3.7) and temporal (Z=-3.6) cortices compared to V. These structures did not show decreased activity with V + M compared to V. In contrast, skin sensation was unchanged with V+S compared to S (7.2:!::0.2 vs 6.9:!:0.4, P=0.25). Conclusion: Somatic pain decreases visceral perception, but noxious visceral stimulation does not diminish somatic pain perception. Corresponding to this one-directional interference, several structures including the left thalamus and left frontal cortex demonstrate decreased activity, suggesting that they may participate in coding visceral pain intensity. The lack of interference by mental distraction on visceral perception suggests that the interference of somatic pain on visceral perception cannot be attributed to attentional shift alone.

794 MAST CELLS MEDIATE GASTRIC HYPERMOTILITY INDUCED BY INTRACISTERNAL TRH ANALOG, RX 77368, IN ANESTHETIZED RATS. Keishi Kawakubo, David Adelsen, Yvette Tache, Kyushu Univ, Fukuoka, Japan; CUREIDDRC, VAMC, Dept of Med , UCLA, Los Angeles, CA. BACKGROUND: We showed that thyrotoropin-releasing hormone (TRH) and a stable TRH analog, RX 77368 (RX, 0-30 ng) injected intracisternally (IC) increased dose-dependently phasic gastric contractions, acid secretion and 5-hygroxytryptamine (5-HT) release through activation of vagal efferent pathways in urethane-anesthetized rats. IC RX at cytoprotective doses induced a vagal atropine sensitive gastric mucosal hyperemia which is prevented by ketotifen, a mast cell (Me) stabilizer. AIM: To investigate whether MC stabilizers also modulate the increase of intragastric luminal pressure induced by Ie RX at cytoprotective doses. METHODS: Fasted male SoD rats anesthetized with urethane (1.25 g/kg, ip) were used. Intragastric luminal pressure was monitored by pressure transducer via a fluid-filled catheter placed into the corpus through the forestomach. Consecutive IC injections of RX (2.5, 10 ng) were performed at 60 min intervals via a catheter placed into the cisterna magna. Ketotifen (3 rng/kg, bolus iv + 4 mg/kglh) and doxantrazole (5 mg/kg, bolus iv + 10 mg/kglh), which stabilize both mucosal MC and connective tissue MC (CTMe), cromolyn (0.5 mg/kglh), which stabilizes only CTMC, were administered 20 min before IC RX. The area of the response in gastric pressure (cmHzOxmin) was calculated. RESULTS: All the used MC stabilizers blocked the increase of the total intragastric luminal pressure and the peak intragastric luminal pressure induced by ic RX at both 2.5 ng and 10 ng. CONCLUSIONS: MC stabilizers blocked the increase of the total intragastric luminal pressure and the peak intragastric luminal pressure induced by central vagal stimulation using IC RX at 2.5 ng and 10 ng. Nerve-mast cell interactions may play an important role in mediating IC RX -induced gastric hypermotility.

796

Pretreatment RJ( (IC, ng) Saline Ketotifen Doxantrazole Cromolyn

t>. area ofresponse (cmH20xmin)

2.5 56.0±17.4 20.9±S.6' 0.6±4.9' 161+7.8'

10 122.2±30.S 39.8±11.7' 1.8±183' 23.4±18.1'

'p<0.05 vs. Saline (ANOVA followed by Fisher's PLSD)

t>. peak response (cmH20)

2.5 19.4±5.4 6.0±3.S' 1.3±0.6' 2.6+ 1.2'

10 29.4±81 9.3±2.6' 7.4±2.9' 16.0±8.6

INTRACEREBROVENTRICULAR BUT NOT INTRATHECAL BA· CLOFEN INHIBITS TRANSIENT LOWER ESOPHAGEAL SPHINCTER RELAXATIONS IN THE DOG. Anders Lehmann, Marianne Bremner-Danielsen, Lena Hansson-Branden, Lillevi Karrberg, Maria Wilsson, Gastrointestinal Pharmacology and Lab Animal Resources, AstraZeneca R&D Molndal, Molndal, Sweden. Transient lower esophageal sphincter relaxations (TLESRs) are responsible for most gastroesophageal reflux episodes and may therefore be targeted in reflux disease. Previous work has shown that systemic administration of the GABAB receptor agonist baclofen reduces the frequency of TLESR. It is unknown if this effect resides in the CNS or periphery. Further, if the site of action is central, the relative importance of cerebral vs. spinal mechanisms has to be established since GABA a receptors are abundant both in the brain and spinal cord. We therefore compared the effects on TLESR of intrathecal (i.t.) and intracerebroventricular (i.c.v.; one of the lateral ventricles) injection of baclofen. Two conscious beagles with an esophagostomy were intubated with a water perfused multilumen assembly fitted with a Dentsleeve to record TLESR and esophageal motility. An antimony pH electrode was used to detect acid reflux 3 cm proximal to the LES. An air-perfused tubing was inserted retrogradely to record swallows. TLESRs were stimulated by intragastric infusion of an acidified fluid meal followed by air insufflation. In control experiments, saline was given i.c.v. or i.t. (n=2-3 in each dog for each route of administration). The dose of baclofen (injected 10 min before infusion of nutrient) was chosen individually so that it would not produce any marked side-effects. Baclofen was given i.c.v. or i.t. in 4-5 separate experiments in each dog. TLESRs were rarely observed preprandially but were greatly stimulated by nutrient infusion/air insufflation. Almost all reflux episodes were secondary to TLESR. Baclofen (42 nmol in one dog and or 63 nmol in another) inhibited TLESRs after i.c.v. but not after i.t. administration (i.c.v.: 44:!::9% of control in the dog given 42 nmol and in 42:!:: 14% in the dog given 63 nmol; the corresponding figures for i.t. administration were 115:!::28% and l18:!:: 13%). The present results show that baclofen can inhibit TLESR through a central mode of action, and that the effect is due to stimulation of GABA B receptors in the brain but not in the spinal cord.