REGULATION OF MOTILIN RELEASE FROM ISOLATED-PERFUSED PIG DUODENUM

The release of motilin from an isolated preparation of pig duodenum ha s been studied. Three different types of stimuli were applied: electri cal nerve stimulation, intraarterially administered peptides, and inst illation of test solutions into the lumen of the duodenum. Furthermore , extracts of 20 different regions of the pig digestive system have be en analyzed for motilin content. Analysis of the extracts only detecte d significant presence of motilin in the pig duodenum and jejunum (79 +/- 15 and 60 +/- 19 pmol/g). The stimulation experiments showed: (1) a significant noncholinergic depression of motilin release during elec trical stimulation of the vagus nerve (nadir at 74 +/- 5% of baseline level; (2) a significant elevation of motilin release in response to i ntraarterially administered vasoactive intestinal peptide (VIP) (peak at 330 +/- 35% of baseline level), and (3) a significantly elevated mo tilin release in response to instillation of autologuous bile (peak at 170 +/- 16% of baseline level) and hydrochloric acid (peak at 196 +/- 42% of baseline level) into the duodenal lumen. In conclusion, lumina l acidification and bile are important factors in stimulation of motil in release, whereas the vagally stimulated VIP release was insufficien t to overcome the general inhibitory effect of vagus stimulation.