Regulation of A- and B-cell function by insulin and glucagon.

In monolayer cultures of pancreases from neonatal rats, glucagon added to the medium (5 or 50 ng/ml) stimulated insulin secretion. In contrast, exogenously added insulin (1.0 mU/ml) inhibited glucagon secretion when glucose was 1.7 or 5.5 mM, but not when glucose was 16.5 mM. This suggests that insulin may reduce glucagon release by enhancing glucose uptake by A-cells. Suppression of glucagon secretion by high glucose (16.5 mM) may be mediated by endogenously released insulin. These observations support the in vivo findings favoring a modulatory interaction between A- and B-cells.