Effects of cholecystokinin and secretin on intestinal structure and function.

Cholecystokinin and secretin are believed to be trophic gastrointestinal hormones. Studies were designed to determine whether these hormones exert their effect through stimulation of endogenous secretion. First, four groups of parenterally nourished rats underwent bypass of the proximal two-thirds of the intestine. One group received secretin, another cholecystokinin octapeptide (CCK-OP), another CCK-OP plus secretin, while the fourth group served as control. After 1 wk, animals were killed; pancreas and segments of intestine were removed. First, mucosal weight, protein content, and fatty acid esterification activity were affected only in intestine in continuity with endogenous secretions after hormone administration. Second, the effects of these hormones were tested in chow-fed rats. The hormone-treated group, despite pancreatic hyperplasia, had similar indexes of intestinal mass compared with pair-fed controls. We conclude that CCK-OP and secretin mediate their trophic effects on the small intestine indirectly, probably through stimulation of pancreatic secretion. In addition, the effects of luminal nutrients have complex interactions with these hormones.