Reassessment of gastric acid inhibition by cholecystokinin and gastric inhibitory polypeptide in dogs.

The inhibition of gastrin 17-stimulated acid secretion by a partially purified cholecystokinin preparation (PcB) containing 1.2% cholecystokinin and 0.7% gastric inhibitory polypeptide immunoreactivity was compared with the inhibition produced by immunopurified cholecystokinin, cholecystokinin-depleted PcB, and gastric inhibitory polypeptide in 6 dogs with gastric fistulas. The dose-response curves for PcB and "pure" cholecystokinin were parallel and relative inhibitory potency of the pure peptide was 1.2. Dose-response curves of gastric inhibitory polypeptide and cholecystokinin-depleted PcB were similar, nonparallel to cholecystokinin dose response, and demonstrated potency significantly lower than that of PcB. When prepared without human albumin there were significantly higher losses of cholecystokinin-immunoreactivity by nonspecific adsorption from pure cholecystokinin solutions compared with PcB solutions. We conclude that inhibition of gastrin-stimulated acid secretion by partially pure cholecystokinin preparations can be explained by their cholecystokinin content and that previously reported differences in inhibitory potencies may be explained by nonspecific adsorption to glass from protein-free solutions.