ARTICLES

Effects of selective insulin or glucagon deficiency on glucose turnover

To study the importance of glucagon and insulin in diabetes, somatostatin (ST) was infused, alone or with insulin or glucagon, in 11 conscious dogs. Plasma immunoreactive insulin (IRI) and glucagon (IRG) levels fell 65 +/- 4% and 33 +/- 3%, respectively, with somatostatin infusion. Glucose production (Ra) assessed by [3-3H]glucose, [2-3H]glucose, or [1-14C]glucose decreased transiently. This is in contrast to the rise in Ra seen after insulin withdrawal in depancreatized dogs, which have normal levels of IRG. Thus, suppression of IRG with somatostatin prevented an increase in Ra in spite of suppression of IRI. When near basal IRG levels were provided during ST infusion in normal dogs, Ra increased, indicating that glucagon contributes to the acute development of diabetes. When basal IRI levels were provided with ST, suppression of Ra was maintained, suggesting that the transience of the metabolic effects of ST-induced glucagon suppression requires concomitant insulin suppression. A comparison of glucose turnover measured using different tracers showed that ST-related hormonal changes did not alter the rate of futile cycling in the liver. ST induced a rise in plasma free fatty acid (FFA) levels, attributed solely to insulin deficiency, as glucagon suppression did not significantly alter FFA concentrations when normal insulin levels were maintained.