Cyclic AMP as mediator of catecholamine-induced enzyme release from isolated perfused working rat heart

Adrenaline causes a dose-related increase in enzyme (lactate dehydrogenase) release from the isolated perfused working rat heart and a rise in tissue cAMP. Rates of both enzyme release and tissue cAMP fell with beta blockade by propranolol (plus pacing to maintain heart rate). Theophylline also increased enzyme release and tissue cAMP. Dibutyryl cAMP, but not butyric acid or external cAMP, increased enzyme release. Hence the release of enzyme is mediated by cAMP according to the criteria of Sutherland et al (11) for mediating the action of catecholamines. However, factors other than cAMP are operative because the extent of enzyme release and the tissue cAMP can be dissociated by variations in external calcium or magnesium or glucose, which modulate the effects of a given level of cAMP.