A-Cell and gut glucagon in normal and depancreatized dogs. Inhibition by somatostatin and insulin.

The effect of somatostatin (SRIF) and of insulin on the plasma levels of immunoreactive glucagon (IRG) and glucose was examined in normal (N) and depancreatized (PX) dogs. The infusion of SRIF (3 microgram/min for 15 min) caused a rapid decrease of the total IRG measured by means of an antiglucanon serum (AGS 10) which cross reacts with extracts of intestinal mucosa. This decrease was due primarily to a fall in the IRG fraction measured by an antiserum (AGS 18) specific for the carboxyl terminus of pancreatic or A-cell IRG. When the dose of SRIF was increased to 10 microgram/min for 90 min, the difference between total and A-cell IRG in the systemic blood also decreased, indicating that other IRG fractions, such as gut IRG, had also been suppressed. The introduction of 50 ml of a 5% glucose solution into a loop of ileum was followed by an increase of gut IRG measured in the regional mesenteric blood. This response was suppressed by the infusion of SRIF (3 microgram/min). Insulin suppressed the basal level of total IRG, but did not alter the gut IRG response to glucose. The SRIF- and insulin-induced reduction in plasma IRG was not associated with a reduction in plasma glucose, suggesting that the high levels of total and A-cell IRG observed in depancreatized dogs were not essential for the maintenance of hyperglycemia.