The effect of glucagon on pancreatic secretion and plasma secretin in dogs.

The inhibitory effect of glucagon on pancreatic exocrine secretion induced by endogenously released secretin was studied in 4 dogs with chronic pancreatic fistulas and open gastric fistulas. After a constant level of pancreatic secretion was established by intraduodenal hydrochloric acid perfusion (9 mEq/hr), glucagon (30 microng/kg-hr) was administered intravenously for 1 hr. Compared to a separate control study in which dogs received intraduodenal HC1 alone, glucagon caused a significant decrease in both pancreatic volume flow and bicarbonate output. Glucagon had no effect on pancreatic protein secretion, and circulating levels of endogenously released secretin remained unchanged. It is concluded that the inhibitory effect of glucagon on pancreatic secretion is not mediated through inhibition of secretin release. The chemical homology between glucagon and secretin suggests that glucagon may mediate its inhibitory action by competing with secretin at the level of the pancreatic receptor site.