Effects of Catecholamines and Glucagon on Amino Acid Transport in the Liver

Abstract

The effects of epinephrine and glucagon on amino acid uptake (and glucose release) by the isolated perfused rat liver were studied using a nonmetabolizable amino acid. Pretreatment of liver donor rats with epinephrine 1 or 2 hr prior to sacrifice resulted in increased blood glucose in the intact animal and enhanced amino acid uptake by livers isolated from these animals. Epinephrine added directly to the isolated system, either as a single pulse or by constant infusion, increased the glucose in the perfusate but did not significantly alter the uptake of amino acid by the isolated liver. Glucagon, on the other hand, increased amino acid uptake by the isolated liver when the hormone was administered in vivo prior to sacrifice, or when it was added directly to the isolated system. The adrenergic blocking agent, dihydroergotamine, when administered in vivo, inhibited the effect of epinephrine on transport of amino acid into the liver. The blocking agent also reduced the effect of glucagon on amino acid transport in vitro. The similarities in the effects of the hormones and the inhibition of both glucagon and epinephrine by the same blocking agent suggest similar mechanisms of action. The fact that only glucagon was effective in vitro may indicate that the action of epinephrine in vivo is mediated by glucagon, released from the pancreas by epinephrine. (Endocrinology83: 1185, 1968)