Activation of the Cori cycle by epinephrine

The effect of epinephrine on Cori cycle activity has been studied by a tracer kinetic technique. The subcutaneous injection of epinephrine into fasted adrenodemedullated rats activated gluconeogenesis and increased glucose utilization. Most of the glucose utilized in epinephrine-treated rats was converted to lactate, and the conversion to the metabolites other than lactate was markedly suppressed by epinephrine. As a result, not only hyperglycemia and hyperlactacidemia developed, but also the contribution of the Cori cycle to glucose metabolism increased after epinephrine. The glucose-alanine cycle, which is roughly one-third as active as the Cori cycle, was only slightly activated by epinephrine. No evidence was obtained, in vivo and in vitro, for the increased formation of lactate from muscle glycogen which decomposed in response to epinephrine. It is suggested that, in epinephrine-treated rats, blood glucose was converted to blood lactate predominantly while muscle glycogen selectively yielded the metabolites other than blood lactate. This suggests compartmentalization of glycolytic pathway in the peripheral tissues of epinephrine-treated rats.