Abstract
An epinephrine infusion of 6 mug/min decreased the rapid insulin response to a 5 g glucose pulse by 96% (P < 0.001) compared with the preinfusion control. In contrast when an identical epinephrine infusion was superimposed on a prolonged glucose infusion, elevated steady-state insulin levels did not decrease, but increased from 26.9 +/-6 (mean +/-SD, muU/ml) to 56.8 +/-15 muU/ml (P < 0.05) in parallel with the epinephrine-induced hyperglycemia. Thus epinephrine inhibition of insulin secretion was observed during acute but not chronic glucose stimulation. To evaluate further the insulin responses during a prolonged glucose infusion, a 5 g glucose pulse was given before and 60 min later during a concomitant epinephrine infusion. Although the acute insulin response to the first glucose pulse was observed during the elevated steady-state glucose and insulin levels associated with the glucose infusion, epinephrine again inhibited the acute insulin response to the subsequent 5 g glucose pulse by 91% (P < 0.01). Thus epinephrine appears to inhibit selectively the rapid insulin response to glucose but not to influence insulin output stimulated by prolonged hyperglycemia. These observations provide further evidence for a model of insulin secretion which includes a small storage pool available for immediate release to a glucose challenge and a more slowly responding pool regulating insulin secretion in the basal and steady state.