Role of gluconeogenesis in epinephrine-stimulated hepatic glucose production in humans

To evaluate the contribution of gluconeogenesis to epinephrine-stimulated glucose production, we infused epinephrine (0.06 micrograms X kg-1 X min-1) for 90 min into normal humans during combined hepatic vein catheterization and [U-14C]alanine infusion. Epinephrine infusion produced a rise in blood glucose (50-60%) and plasma insulin (30-40%), whereas glucagon levels increased only at 30 min (19%, P less than 0.05). Net splanchnic glucose output transiently increased by 150% and then returned to base line by 60 min. In contrast, the conversion of labeled alanine and lactate into glucose increased fourfold and remained elevated throughout the epinephrine infusion. Similarly, epinephrine produced a sustained increase in the net splanchnic uptake of cold lactate (four- to fivefold) and alanine (50-80%) although the fractional extraction of both substrates by splanchnic tissues was unchanged. We conclude that a) epinephrine is a potent stimulator of gluconeogenesis in humans, and b) this effect is primarily mediated by mobilization of lactate and alanine from extrasplanchnic tissues. Our data suggest that the initial epinephrine-induced rise in glucose production is largely due to activation of glycogenolysis. Thereafter, the effect of epinephrine on glycogenolysis (but not gluconeogenesis) wanes, and epinephrine-stimulated gluconeogenesis becomes the major factor maintaining hepatic glucose production.