Effect of Selected Hexoses, of Epinephrine and of Glucagon on Insulin Secretion in Man

Immunochemical methods of measuring serum insulin have implemented studies in man confirming in vitro data which suggest that metabolizable sugars such as mannose and glucose cause insulin secretion, whereas galactose, a nonutilizable sugar, does not. Infusions of 2-deoxy-D-glucose are associated with greatly increased epinephrine secretion and sustained hyperglycemia, but no rise in serum insulin levels. Epinephrine infusions induce and prolong hyperglycemia without raising serum insulin levels and effectively inhibit insulin secretion during glucose administration. These findings agree with in vitro evidence that epinephrine directly inhibits pancreatic secretion of insulin. Glucagon, on the other hand, sharply stimulates insulin secretion, either alone or after glucose infusions. Data are presented which suggest that this may be a direct effect of glucagon on the release of insulin by the pancreatic beta cell.