Activités des enzymes du métabolisme du glycogène cardiaque: Etude dans un protocole d'hypoxie in situ chez le rat

Abstract

Myocardial hypoxia, induced by arrest of the artificial ventilation of anaesthetized open-chest rats, was utilized in order to study some aspects of the regulation of myocardial glycogen metabolism.

Atenolol, a cardioselective beta-adrenergic receptor antagonist, and verapamil, an inhibitor of sarcolemmal calcium transfer, were used to determine the respective role of adenosine 3′, 5′- cyclic monophosphate (cAMP) and calcium in the activation of the enzymes of glycogen phosphorolysis and synthesis.

Glycogen degradation is reduced by atenolol treatment, as a consequence of a reduced activation of glycogen phosphorylase. Verapamil treatment has no significant effect, neither on the enzyme activation nor on the glycogen utilization.

The activation of glycogen synthase, expressed by the conversion of the enzyme from the D to the I form, which results from the decrease in glycogen stores during hypoxia, is lowered under the effect of both drugs. However, in the beta-blocker treatment case, this effect results from a lower glycogen depletion while this effect is more specific in hearts from rats treated with verapamil. Under the effect of verapamil, the reduction of synthase activation, for a similar depletion of glycogen stores, was confirmed by experiments using isolated rat hearts submitted to ischaemia.