The physiological role of gastrin in H+ secretion is well established. We decided to study the effects of physiological doses of gastrin (as evidenced by H+ secretion and postprandial serum gastrin levels) on antroduodenal motility in order to delineate its role in antral motility regulation. Nine healthy male subjects, mean age 31 years, had two studies on different days. On day 1, gastroduodenal motility was monitored with a continuously perfused catheter system while gastric secretions were aspirated. After a basal period of 45 min, human synthetic gastrin (hG-17) was infused intravenously in consecutive doses of 6.25, 25, 100, and 400 pmol/kg/hr during 45 min each. On day 2, all subjects had a standard protein meal. Blood was withdrawn on both days for gastrin measurement by RIA. Increasing amounts of hG-17 caused a stepwise increase in serum gastrin and acid output. The D50 for H+ secretion was 25 pmol/kg/hr hG-17. The mean postprandial gastrin level was 31 +/- 5 pM, a level which was comparable to that seen during infusion of hG-17 6.25 pmol/kg/hr. At these serum gastrin levels, antral motility was either reduced or unchanged. Duodenal motility was unchanged. A reduction in the antroduodenal motility ratio was seen at these levels, but there was no interruption of the interdigestive motility complex. These results suggest that at physiological levels, gastrin by itself does not seem to have a major role in human antroduodenal motility regulation.