Inhibitory neural pathway regulating gastric emptying in rats

The relaxation of the pylorus is one of the most important factors for prom oting gastric emptying. However, the role of inhibitory neurotransmitters i n the regulation of pyloric relaxation and gastric emptying remains unclear . In this study, we investigated the effects of NO biosynthesis inhibitor, N-G-nitro-L-arginine methyl ester (L-NAME), and calcium dependent potassium channel blocker, apamin, on vagal stimulation-induced pyloric relaxation a nd gastric emptying in rats. Sodium nitroprusside (SNP), adenosine 5'-triph osphate (ATP), vasoactive intestinal polypeptide (VIP) and pituitary adenyl ate cyclase-activating peptide (PACAP) caused pyloric relaxations in a dose dependent manner in vivo. Apamin (120 mu g/kg) significantly reduced ATP a nd PACAP-induced pyloric relaxations without affecting SNP- or VIP-induced relaxations. Vagal stimulation (10 V, 1 ms, 1-20 Hz)-induced pyloric relaxa tion was significantly inhibited by L-NAME (10 mg/kg). The combined adminis tration of L-NAME and apamin almost completely abolished vagal stimulation- induced pyloric relaxation. L-NAME and apamin significantly increased spont aneous contractions in the antrum, pylorus and duodenum. Increased motility index by L-NAME and apamin was significantly higher in the pylorus and duo denum, compared to that of antrum. L-NAME and apamin significantly delayed liquid gastric emptying. These results suggest that besides NO, probably AT P and PACAP, act as inhibitory neurotransmitters in the rat pylorus and reg ulate gastric emptying. (C) 2000 Elsevier Science B.V. All rights reserved.