Regulation of glycogen metabolism in liver by the autonomic nervous system. 3. Differential effects of sympathetic-nerve stimulation and of catecholamines on liver phosphorylase.

Abstract

Abstract Differences between the effects of splanchnic-nerve stimulation and of catecholamines on glycogenolytic enzymes in rabbit liver were investigated. 1. 1. Splanchnic-nerve stimulation caused a rapid increase in the activity of liver glucose-6-phosphatase ( d -glucose-6-phosphate phosphohydrolase, EC 3.1.3.9) while administration of catecholamines was without effect. 2. 2. Activation of liver phosphorylase (α-1,4-glucan: orthophosphate glucosyl-transferase, EC 2.4.1.1) by splanchnic-nerve stimulation was faster than that by catecholamines. The activation was maximal within 30 sec after the onset of the nerve stimulation, while the activation induced by epinephrine injection reached a maximum after about 60 sec. Furthermore, phosphorylase activation produced by endogenous catecholamines, released in response to sympathetic stimulation, required minutes rather than seconds. 3. 3. Activation of phosphorylase after splanchnic-nerve stimulation was not blocked by previous injection of reserpine which causes depletion of norepinephrine at the sympathetic-nerve terminals. 4. 4. The effect of catecholamines on liver phosphorylase was blocked by dichloroisoproterenol, whereas the effect of splanchnic-nerve stimulation was not. This suggests that sympathetic nerves and catecholamines activate liver phosphorylase by different mechanisms; their possible mechanisms are discussed. 5. 5. It seems likely that there are two separate mechanisms in the liver for controlling phosphorylase activation and glycogenolysis, and that neural control (by sympathetic nerves) is much faster than hormonal control (by catecholamines).