Release of endogenous catecholamines in the ischemic myocardium of the rat. Part A: Locally mediated release.

Abstract

The accumulation of endogenous catecholamines within the extracellular space of the ischemic myocardium has been studied in the isolated perfused (Langendorff) heart of the rat subjected to various periods of complete ischemia, with subsequent collection of the reperfusate. Catecholamines and deaminated metabolites were measured by radioenzymatic methods, or high pressure liquid chromatography. Ischemic periods of less than 10 minutes are not associated with an increased overflow of catecholamines or metabolites. Longer periods of ischemia are accompanied by the overflow of noradrenaline and its deaminated metabolite 3,4-dihydroxyphenylglycol. This overflow increases with lengthening of the preceding ischemic period (10 minutes: 2.5 +/- 0.6, 20 minutes: 209.8 +/- 17.2, 60 minutes: 1270.5 +/- 148.1 pmol noradrenaline/g heart). Noradrenaline concentration is highest during the first minute of reperfusion, suggesting that the noradrenaline detected during reperfusion is released into the extracellular space of the myocardium during ischemia and is subsequently eluted. Experiments with variation of extracellular calcium concentration and with neuronal uptake (uptake1) blocking agents suggest that different mechanisms of catecholamine release are acting during the course of ischemia. A calcium-independent carrier-mediated efflux of noradrenaline from the nerve terminals is of major importance, using the same carrier as is normally responsible for transporting noradrenaline from the synaptic clefts into the neuronal varicosities. Thus, various uptake1-blocking agents diminish the noradrenaline overflow following ischemic periods of between 10 and 40 minutes. The noradrenaline overflow following longer periods of ischemia is unaffected by uptake1-blocking agents, and additional noradrenaline release at this time is probably consequent upon dissolution of cell membranes. Overflow of adrenaline and dopamine occurs to a minor degree (less than 5% of the corresponding noradrenaline overflow), and only after ischemic periods of more than 15 minutes.