Abstract
Influence of insulin on liver glycogen metabolism and on lipolysis appears to be mediated by a decreased intracellular 3′,5′-AMP concentration. Reduced formation of 3′,5′-AMP had been shown in adipose tissue incubated with insulin. The influence of insulin on 3′,5′-AMP degradation has been investigated. — 3′,5′-AMP phosphodiesterase (PDE) activity was reduced in liver, adipose tissue and, insignificantly, in skeletal muscle of insulin deficient, i.e. alloxan diabetic or starved rats. I.V. injection of a low dose of insulin (0.5 U/kg) or stimulation of endogenous insulin secretion by injection of glucose led to a rapid increase of PDE activity in these tissues. 15 min after insulin injection liver PDE activity was increased. The maximal effect occurred after 30–45 min. Renal PDE activity was not decreased in alloxan diabetes, insulin injection has been found ineffective. —In vitro, there was an activating effect of crystalline insulin on PDE purified from beef heart. Insulin concentration required for duplication of enzyme activity was of the order of 2 · 10−5 M. Treatment with actinomycin D nearly prevented stimulation of liver PDE by insulin. This may indicate that the action of insulin on PDE activity is essentially based on an increased enzyme synthesis. — Owing to the influence of insulin secretion on liver and adipose tissue 3′,5′-AMP concentration, glycogen metabolism and lipolysis can be quickly adapted to food intake.
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