Localization of monoamine oxidase of type A and B in blood vessels with different innervation patterns

Summary Homogenates of dog mesenteric artery, dog saphenous vein, denervated saphenous vein, rabbit ear artery, denervated ear artery and human umbilical artery were prepared in phosphate buffer. Monoamine oxidase activity was determined with ³H]-5-hydroxytryptamine (³H]-5-HT) as a preferential substrate for MAO type A and ¹⁴C]--phenylethylamine as a preferential substrate for MAO type B. The endogenous noradrenaline content was compared with the MAO activities in these blood vessels. The results show that there is a good relationship of MAO type A content with the density of adrenergic innervation, but it is evident that this type of MAO is present even in vessels devoid of adrenergic innervation. Thus, MAO type A in these vascular structures has both intraneuronal and extraneuronal locations whereas MAO type B is predominantly or exclusively extraneuronal.Some of the results were presented to the 11th Annual Meeting of the Portuguese Pharmacology Society (Lisboa, 1980) and to the 8th International Congress on Pharmacology (Tokyo, 1981)On leave from Faculdade de Farmácia, Universidade de Coimbra, with a grant from Instituto Nacional de Investigação Científica