It is known that the effectiveness of a physiologic increment in glucagon to stimulate glucose production wanes with time even when counterregulatory insulin secretion is prevented. The aim of the present study was to establish whether the converse is true: does glucagon become a more effective stimulus of glucose production following a period of acute hypoglu-cagonemia?

To determine this, somatostatin was infused along with basal replacement amounts of glucagon (0.65 ng/kg - min) and insulin (228 μU/kg · min) into five postabsorptive conscious dogs. After 1.5 h of basal hormone replacement, the glucagon infusion was terminated and a selective fall in the plasma glucagon level (75 ± 6 to 30 ± 4 pg/ml) occurred. This resulted in a drop in tracer (3H-glucose)-determined glucose production from 3.0 ± 0.4 to 1.5 ± 0.3 mg/kg min. The plasma insulin level remained unchanged at 10 ± 1 μU/ml throughout the experiment. Euglycemia (110 ± 4 mg/dl) was maintained by exogenous glucose infusion. After 3 h of glucagon lack, restoration of the glucagon infusion returned the IRG level to control values (78 ± 6 pg/ml) but restored glucose output only partially (42 ± 9%), necessitating continued glucose infusion to preserve euglycemia. Repetition of the experiment in dogs whose pancreatic glucoregulatory feedback loops were broken surgically (two-stage pancreatectomy) rather than pharmacologically resulted in similar findings. It is concluded that glucagon deficiency of 3-h duration leads to a decrease, rather than an increase, in hepatic sensitivity to glucagon.

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