Gastrin effects on growth and exocrine secretion in the neonatal rat pancreas

In adult rats, cholecystokinin (CCK) binds to pancreatic CCK-A receptors and stimulates exocrine secretion and pancreatic growth. In newborn rats there is very little mature intestinal CCK and few pancreatic CCK-A receptors. However, there is an abundant source of the related peptide gastrin, and in addition, there are pancreatic CCK-B/gastrin receptors. In this study, we have explored the hypothesis that gastrin may ''deputise'' for CCK in the neonate and cause pancreatic exocrine secretion, growth, and maturation. Newborn rats were injected intraperitoneally with the gastrin antagonist, CI-988, or placebo for 5 days and sacrificed on day 6. Body weight (CI 988, 8.25 +/- 0.48 g; placebo, 10.17 +/- 0.93 g) and pancreatic weight (19.41 +/- 1.5 vs. 21.58 +/- 1.72 mg) were the same. Protein (1,202 +/- 78 vs. 1,254 +/- 56 mu g), amylase (22.3 +/- 0.9 vs. 19.2 +/- 1.00 U), RNA (117 +/- 7 vs. 126 +/- 5 mu g), and DNA (95 +/- 8 vs. 100 +/- 7 mu g) contents of the pancreas were similar in the two groups. The weight of the stomach was reduced (p = 0.04) in the treated group (50.8 +/- 2.5 mg) compared to the placebo group (59.8 +/- 3.7 mg). In both neonates and adults, CCK-8 was similar to 1,000 times more potent than gastrin-17 in stimulating amylase release from isolated pancreatic acini. This suggests that enzyme release is probably mediated by the same receptors in both adults and neonates, and in adults previous work has shown this to be the CCK-A receptor. In conclusion, these data show that gastrin has very weak effects on neonatal pancreatic exocrine secretion, and furthermore, gastrin is not essential for growth and maturation of the neonatal pancreas. The role of gastrin and CCK-B/gastrin receptors in the neonatal pancreas remains speculative.