Endogenous catecholamines are not necessary for ischaemic preconditioning in the isolated perfused rat heart.

ABSTRACT

OBJECTIVE: The mechanism of the protective effect of ischaemic preconditioning in the myocardium is not yet known. The aim of this study was to test the hypothesis that endogenous myocardial catecholamines may be mediators of preconditioning. METHODS: To test whether endogenous catecholamines are involved in preconditioning, experiments were performed in hearts from rats which had been catecholamine depleted with either reserpine or 6-hydroxydopamine. Experiments were also done to determine if noradrenaline can mimic preconditioning. RESULTS: Catecholamine depletion with either reserpine or 6-hydroxydopamine had no effect on preischaemic coronary flow or cardiac function. Ischaemic preconditioning (four episodes of 5 min global ischaemia and 5 min reperfusion) resulted in a significant increase in postischaemic cardiac function and a 50% decrease in lactate dehydrogenase (LDH) release following 30 min ischaemia and 30 min reperfusion compared with non-preconditioned hearts. Reserpine pretreatment did not affect the response to ischaemia or to preconditioning, although LDH release tended to be greater than in normal hearts, especially in the non-preconditioned group. Although 6-hydroxydopamine significantly increased postischaemic cardiac function in the preconditioned group, no other index of ischaemic damage (for example, LDH release, left ventricular end diastolic pressure) was affected. Further studies showed that 10 nmol.min-1 noradrenaline did not affect the severity of ischaemia, indicating that it does not mimic preconditioning. CONCLUSIONS: Endogenous catecholamines are not necessary for ischaemic preconditioning in isolated rat hearts and play little or no role in the functional responses to ischaemia.