Abstract
The metabolic conditions required for noradrenaline (NA) release from ischaemic and anoxic perfused hearts of the rat were studied. Forty minutes of flow reduction to approximately 0.25 ml g-1 min-1 did not elicit enhanced noradrenaline overflow from the isolated heart perfused with normoxic perfusate even in the absence of added substrate. Enhanced overflow did occur when substrate-free ischaemia was induced after a 60 min period of substrate-free perfusion. Noradrenaline overflow was enhanced by perfusion at normal flow rates with an anoxic (Po2 less than or equal to 1 mmHg) perfusate containing no substrate. Such enhanced overflow occurred in the absence of calcium in the perfusate and was almost completely abolished by the addition of 11 mM glucose. Enhanced noradrenaline overflow occurring either during low flow ischaemia after substrate deprivation or during anoxic substrate-free perfusion at normal flow rates was markedly suppressed by desipramine. Exocytotic noradrenaline overflow induced by electrical stimulation of the left cervico-thoracic ganglion continued unchanged during 60 min of anoxia if the perfusate contained 11 mM glucose. In the absence of added substrate there was a decline in the overflow induced by such stimulation which was more rapid with anoxic than normoxic perfusate. Re-introduction of calcium, oxygen and substrate after 10, 20 or 30 min of calcium-free, substrate-free, anoxic perfusion was associated with a massive overflow of the intracellular enzyme lactate dehydrogenase.(ABSTRACT TRUNCATED AT 250 WORDS)
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