Development of the Pancreas and Small Intestine in Rat

We have investigated the relationship between the growth of the pancreas and small intestine in rats, especially in relation to cholecystokinin (CCK) concentrations in the latter. Because negative feedback regulation controls exocrine pancreatic secretion, we administered a trypsin inhibitor (TI), camostat mesilate (200 mg/kg body weight (BW), p.o.) for 10 days, and examined its effect on plasma CCK concentrations. We also investigated the effect of TI on pancreatic growth in young (17 and 24 days old) and in mature (76 days old) rats. In untreated rats the wet weight of the pancreas and small intestine increased almost in parallel with overall growth. The CCK concentration in the small intestine remained almost constant, and increased in parallel with the wet weight of the small intestine. Administration of TI increased the plasma CCK concentration in accordance with the overall growth of the rat. TI increased the pancreatic wet weight at all days of age. The pancreas was hypertrophic at all ages and pancreatic cells started to proliferate at day 24 and day 76. Among the pancreatic enzymes, the trypsinogen concentration increased at all ages whereas amylase increased only in mature rats. These results indicated that the growth of the pancreas and small intestine proceeded in concert with the effect of CCK. In addition, the oral administration of TI caused pancreatic hypertrophy, although the effect differed according to the developmental stage of the pancreas.