Role of gastrin and cholecystokinin in the ontogenic development of the gastrointestinal tract.

The role of gastrin and cholecystokinin (CCK) in postnatal development of the small intestine was examined in infant rabbits. Experimental animals received daily intraperitoneal injections of pentagastrin, 500 micrograms/kg, or CCK-octapeptide, 40 micrograms/kg, starting on day 3 of life. The animals were sacrificed at age 17-18 days. Weight and histologic sections of pancreas, stomach, duodenum, proximal jejunum, and ileum were obtained and mucosal lactase and sucrase activities determined in the intestinal segments. No differences were seen in any of the parameters assessed in pentagastrin-treated animals compared to saline-injected littermate controls. Body weight, weight and morphology of pancreas, stomach and intestinal segments, and enzyme activities did not differ significantly. Na+ transport in proximal jejunum under short-circuited conditions was not altered by pentagastrin. CCK-octapeptide also had no effect on weight or morphology of pancreas, stomach, and duodenum, but did lead to a significant increase in weight of proximal jejunum and ileum. Mucosal enzyme activities and morphometric measurements of villus height and mucosal thickness, however, did not differ significantly between CCK-octapeptide-treated animals and saline-injected littermate controls. The increase in weight of jejunal and ileal segments was reflected by an increase in thickness of the muscle layer. The findings indicate that neither gastrin nor CCK plays a role in the ontogenic development of the small intestine.