The actions of bombesin on gastric secretion of the dog and the rat.

1. Bombesin stimulated acid secretion from the denervated fundic pouch of the dog. Whereas the concentration of hydrochloric acid in bombesin-produced juice was always higher than in control juice this did not occur for pepsin, the concentration of which remained below the basal values. The threshold dose of bombesin was 5-30 ng/kg by the subcutaneous route and 0.05-0.2 (mug/kg)/h by intravenous infusion. At low doses bombesin was more active than caerulein, even on a molar basis, and at high dose levels was as active as caerulein. In contrast to gastrin and caerulein, bombesin elicited a moderate secretory response also following rapid intravenous injection.2. The acid secretion provoked by bombesin was almost completely inhibited by atropine and reduced by approximately 50% by hexamethonium.3. Bombesin did not stimulate acid secretion in the lumen-perfused preparation of the rat stomach when administered by subcutaneous injection (up to 10 mug/kg) or by intravenous infusion (up to 10 (mug/kg)/hour). An irregular increase in acid output was observed only following rapid intravenous injection and this was of doubtful significance.4. The mechanism of the secretagogue action of bombesin on the dog stomach is discussed.