Adrenal medullary control of muscular and hepatic glycogenolysis and of pancreatic hormonal secretion in exercising rats

Abstract

We have previously shown that in exercising adrenodemedullated rats chemically sympathectomized with 6‐hydroxydopamine, the muscular and hepatic glycogen breakdown were diminished and the plasma glucagon and insulin concentrations were lower and higher, respectively, than in controls. To elucidate whether these effects could be ascribed selectively to the lack of the adrenal medulla or to the lack of the sympathetic nerve endings, rats were either surgically adrenodemedullated, chemically sympathectomized with 6‐hydroxydopamine, both adrenodemedullated and chemically sympathectomized, or sham‐treated. 3 weeks after adrenodemedullation a liver biopsy and cardiac blood was obtained. Subsequently the rats either rested or swam with a tail weight for 100 min. Immediately afterwards, cardiac blood was drawn and liver and muscle tissue were collected. The effects of combined adrenodemedullation and chemical sympathectomy were found to be due to the lack of the adrenal medulla. Furthermore, in adrenodemedullated rats, compared to controls, the concentration of norepinephrine in plasma was markedly reduced during exercise. The total activity (a+b) of glycogen phosphorylase in muscle was reduced 20% by adrenodemedullation. The findings indicate that during prolonged exercise adrenomedullary hormones enhance muscular and hepatic glycogenolysis as well as glucagon secretion, but inhibit insulin secretion in the rat. Furthermore, in contrast to the findings in man, in the rat a major part of the circulating norepinephrine is of adrenomedullary origin during exercise.