Uptake, disposition and metabolism of histamine in isolated heart preparations

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Abstract
1 The uptake and metabolism of histamine by the guinea-pig heart and by the isolated electrically driven guinea-pig left atria was studied with both labelled and unlabelled histamine. 2 Histamine uptake took place against a concentration gradient and, at low concentrations, this was blocked by hypoxia plus glucose deprivation or by a toxic dose of ouabain. 3 The histamine taken up was retained by cardiac tissues and mainly metabolized into methyl-histamine and other metabolites. The uptake and metabolism of histamine was higher in atria than in ventricles thus reflecting the regional distribution of endogenous histamine and mast cell numbers. 4 The uptake and metabolism of histamine were greatly reduced in hearts which had been depleted of mast cells, by combining cardiac anaphylaxis and (+)-tubocurarine (1 mg/ml), but pretreatment of guinea-pigs with 6-hydroxydopamine failed to affect uptake of total radioactivity in the isolated left atria. 5 In the guinea-pig heart histamine appears to be taken up, stored and metabolized in at least two pools, one of which is linked to the mast cells.