Effect of locally released catecholamines on lipolysis and injury of the hypoxic isolated rabbit heart.

The ability of endogenous myocardial catecholamines to stimulate lipolysis of endogenous triglycerides and the role of this process in the development of myocardial injury were studied in isolated, Langendorff-perfused rabbit heart preparations exposed to 3 h of hypoxic perfusion followed by 30 min of aerobic perfusion. Untreated hearts responded not only to hypoxia but also to reoxygenation with surges of noradrenaline outflow lasting 10 and 5 min, respectively. During hypoxia but not during reoxygenation a parallel surge of glycerol outflow was observed. Nicotinic acid (10(-5) M) prevented glycerol outflow during hypoxia but did not influence the outflow of noradrenaline during either hypoxia or reoxygenation. Neither noradrenaline nor glycerol were detected in the effluent from the hearts depleted of endogenous catecholamines by reserpine pretreatment. Those hearts also showed a smaller lactate dehydrogenase release during hypoxia (49% reduction) and no increase in lactate dehydrogenase release during reoxygenation. Similar reduction of lactate dehydrogenase release during hypoxia (52% reduction) was observed in the hearts treated with nicotinic acid. This drug, however, did not prevent the reoxygenation-induced lactate dehydrogenase release. The effects of reserpinization and nicotinic acid treatment on lactate dehydrogenase release were not additive. It is concluded that hypoxia is a stimulus for lipolysis in the isolated rabbit heart and most probably this process is catecholamine dependent. At least part of the deleterious effect of endogenous catecholamines on hypoxic myocardium might be attributed to catecholamine-stimulated lipolysis of endogenous triglycerides. The latter, however, does not seem to contribute to deleterious effects of endogenous catecholamines during reoxygenation.