Effect of fasting and refeeding on pancreatic enzymes and secretagogue responsiveness in rats.

Fasting reduced amylase and increased lipase concentrations but did not affect trypsinogen concentrations in the adult rat pancreas. Fasting also decreased the pancreatic contents of trypsinogen and amylase. A decrease in the responsiveness of dispersed pancreatic acini to carbachol was evident after 3 days of fasting but only at high concentrations of secretagogues. Acini regained their responsiveness, and enzyme concentrations returned to normal after refeeding. Serum insulin levels of fasted rats decreased to one-fourth of control levels but rose to normal 24 h after refeeding. Insulin or glucose given alone prevented the increase in lipase after fasting. Both insulin and glucose were needed to maintain the acinar response to secretagogues in fasted rats. Although cholecystokinin restored the protein and trypsinogen content in fasted rats, it did not correct the relative changes in the exocrine enzymes. There are therefore reversible changes in the exocrine pancreas after fasting. Insulin, glucose, and cholecystokinin seem to regulate these changes.