Chronic oral administration of protease inhibitor decreases CCK-A receptor mRNA expression but increases pancreatic growth in rats

It is well-known that chronic oral administration of trypsin inhibitors induces pancreatic hypertrophy and hyperplasia via stimulation of endogenous cholecystokinin (CCK) release. Because the growth-promoting effect of CCK on the pancreas is specifically mediated by the CCK-A receptor. we examined the plasma CCK concentrations, the expression of CCK mRNA in the intestine and CCK-A receptor mRNA in the pancreas, and pancreatic growth in rats after chronic oral administration of synthetic protease inhibitor (PI). PI at a dose of 100 mg/kg body weight was administered via an orogastric tube once daily For 20 days. Plasma CCK concentrations at 24 hours after the first PI administration were significantly higher than those in randomly fed rats (6.57 +/- 0.67 pmol/L vs 4.31 +/-: 0.51 pmol/L; p < 0.001), and further increased to 14.24 +/- 1.63 pmol/L after PI for 10 days and decreased to 10.05 +/- 0.72 pmol/L after 15 days of PI administration. Treatment with PT for 20 days significantly increased the pancreatic weight, and the total pancreatic protein and DNA content by 190%, 290%, and 170%, respectively, when compared to the control rats. Chronic oral administration of PI, however, reduced CCK-A receptor mRNA expression in the pancreas by 60%. These findings suggest that chronic oral administration of PI induces an elevation of endogenous CCK release and stimulates pancreatic growth, but down-regulates the biosynthesis of CCK-A receptor at the transcriptional level in the pancreas.