Rapid Reciprocal Changes in Rat Tissue Enzyme Activities following Epinephrine Injection

Abstract

Epinephrine infusion into the portal vein produced rapid changes in the activities of certain hepatic, epididymal fat, and skeletal muscle glycolytic enzymes and fructose diphosphatase in the rat. Epinephrine produced a rapid increase in hepatic, epididymal fat, and skeletal muscle fructose diphosphatase activity. In contrast, epinephrine produced a rapid decrease in hepatic phosphofructokinase, pyruvate kinase, and glucokinase activities. Epinephrine also lowered skeletal muscle phosphofructokinase and pyruvate kinase activities. However, epinephrine had no significant effect upon epididymal fat pyruvate kinase and phosphofructokinase activities. Fructose diphosphate aldolase activities were unchanged in the liver, epididymal fat, and skeletal muscle. The epinephrine effect on the hepatic enzymes was maximal within 2 to 5 min following injection of 2 µg and then gradually returned to control levels over the remaining 35 to 38 min of testing. The magnitude of the epinephrine effect was dose-dependent. No effect was detected when 0.25 µg per min was injected. Phosphofructokinase, pyruvate kinase, and fructose diphosphatase activities were significantly altered at a dose level of 1.0 µg per min, with maximal changes occurring at the 2.0- to 4.0-µg per min dose level. The epinephrine effect was associated with a significant increase in hepatic cyclic adenosine 3′:5′-monophosphate concentrations. Actinomycin D and puromycin treatment did not alter the response of the enzymes to epinephrine. Insulin given 5 min following epinephrine partially reversed the epinephrine effect. Similarly, epinephrine given 5 min following insulin partially reversed the insulin effect. We suggest that the epinephrine effect is mediated through cyclic adenosine 3′:5′-monophosphate and may be due to phosphorylating mechanisms analogous to that responsible for the regulation of glycogen metabolism.