Characteristics of histamine disposition in vascular smooth muscle

This study has examined uptake, efflux and metabolism of 14C-histamine by vascular smooth muscle. 14C space in aortae reached 4.3 +/- 0.14 ml/g (mean +/- SE) after 1 h exposure to 14C-histamine (2 muM) in Tyrode's solution. Aminoguanidine (10(-5) M) and non-radioactive histamine (10(-4) and 10(-3) M) significantly reduced 14C space. Efflux experiments were performed on aortic strips exposed to 14C-histamine for 1 h. The rate of loss of radioactivity was not enhanced by nonradioactive histamine or compound 48/80. It appears that 14C-histamine was not accumulated and bound in mast cells in this tissue. After 1 h exposure to 14C-histamine, labeled material was extracted from tissues for identification of metabolites by paper chromatography. About 40% of the label was 14C-histamine, and the remainder was primarily imidazole acetic acid. After exposure to aminoguanidine, an inhibitor of diamine oxidase, about 80% of the label was 14C-histamine. These data suggest that oxidative deamination is the primary catabolic route for histamine in rabbit aorta.