TONIC SUPPRESSION OF GASTRIC-ACID SECRETION BY ENDOGENOUS PEPTIDES INNEONATAL RATS

Stimulation of gastric acid secretion by secretagogues was measured in developing rats by in vivo and in vitro techniques. Basal acid output s in vivo were very low in 8- and 14-day-old rats compared with those in 20- and 30-day-old rats. In 20-day-old rats, all secretagogues incr eased acid output in vivo, whereas only carbachol, pentagastrin, and s ulfated cholecystokinin octapeptide (CCK-8S) were active in 14-day-old rats. In contrast, basal acid output in vitro and stimulation by secr etagogues did not differ significantly with age. CCK-8S-stimulated aci d output in vitro in 14-day-old rats was blocked by L-365,260, L-364,7 18, tetrodotoxin, and atropine, but not by hexamethonium, whereas gast rin-stimulated acid output was blocked only by L-365,260. Furthermore, acid output in vivo was elevated three- to fourfold by subcutaneous n aloxone-methiodide or L-364,718, but not by L-365,260, in 14-day-old r ats; none of these antagonists produced an effect in 20-day-old rats. These studies show that low basal gastric acid output in neonatal rats is caused by tonic inhibitory regulation by endogenous regulatory pep tides.