Possible feedback mechanisms involved in exocrine pancreatic secretion in pigs and rats

This paper presents the results of a series of experiments undertaken to te st the hypothesis of the existence of unrecognised elements of regulatory f eedback for the exocrine pancreas of pigs and rats. In pigs, the preprandial pancreatic juice secretion was not affected by jui ce diversion or intraduodenal juice loading. The prandial secretion was red uced by intraduodenal and intraileal administration of non-activated juice and bile. Intravenous administration of trypsin significantly reduced the p randial protein and trypsin outputs in pigs and the effectiveness of exogen ous CCK-33 in rats. One group of rats was infused with a constant dose of C CK-33 and the second group with a constant dose of secretin, 150 pmol in bo th cases, during 2 h. At the same time, the first group was infused with se cretin(150 pmol) and the second group with CCK-33 (150 pmol) in increasing doses in the proportion 0:1:10:100, every 30 min. Total protein and trypsin activity outputs were higher in the second group. There is a proved existence of feedback regulation of prandial pancreatic s ecretion in conscious pigs at the duodenal and ileal levels. The inhibition of pancreatic secretion in pigs and desensitisation of pancreatic secretio n to exogenous CCK-33 in rats by exogenous elevation of plasma trypsin conc entrations indicate the presence of a trypsin-related feedback mechanism in the plasma, regulating the exocrine pancreas. The results obtained from experiments on both rats and pigs encouraged us t o speculate that the concerted action of the volume secreted and protein co ncentration of the pancreatic juice are factors governing the pancreatic pr otein outflow. However, it seems the volume of pancreatic juice secreted is the driving force in this process.