CHARACTERIZATION OF VAGAL PATHWAYS MEDIATING GASTRIC ACCOMMODATION REFLEX IN RATS

1. We investigated the vagal pathways mediating the gastric accommodat ion reflex in the rat stomach. 2. Gastric distension (6 mi) evoked an increase of 9.0 +/- 1.0 cmH(2)O of intragastric pressure in vivo. Pret reatment with tetrodotoxin (TTX) caused a significant pressure increas e by gastric distension, reaching 17.0 +/- 1.7 cmH(2)O, suggesting med iation by neural pathways. 3. The pressure increase evoked by gastric distension was significantly enhanced in vivo by acute truncal vagotom y (TV), hexamethonium (C6), and N-G-nitro-L-arginine methyl ester (L-N AME), but not by vasoactive intestinal polypeptide (VIP) antiserum, gu anethidine, or splanchnicotomy. 4. Gastric distension (6 mi) evoked a much larger intragastric pressure in the denervated, vascularly isolat ed, perfused rat stomach in vitro. Intra-arterial application of TTX a nd L-NAME did not cause further pressure increases evoked by gastric d istension. 5. The pressure increase evoked by gastric distension remai ned high 2 weeks after TV in vivo. However, the accommodation reflex w as fully restored 4 weeks after TV in vivo. This reflex was antagonize d by TTX, C6 and L-NAME, but not by VIP antiserum, guanethidine and sp lanchnicotomy. 6. Similar to in vivo studies, gastric distension cause d a smaller increase in intragastric pressure in response to gastric d istension in the denervated, vascularly isolated, perfused stomach obt ained from rats 4 weeks after vagotomies in vitro. The pressure increa se evoked by gastric distension was significantly enhanced by L-NAME, hexamethonium and TTX. 7. It is suggested that the vago-vagal reflex p lays an important role in mediating the accommodation reflex. This inv olves a vagal efferent pathway that uses nitric oxide as a final neuro transmitter mediating gastric relaxation in intact rats. It is also su ggested that the adaptive mechanism mediating the accommodation reflex following vagotomy occurs in the gastric myenteric plexus.