Studies on rat cardiovascular monoamine oxidase activity

Studies were performed to determine the characteristics of rat cardiac monoamine oxidase (MAO) activity. Rat major blood vessels were also examined, since the coronary vasculature constitutes a significant portion of cardiac tissue. MAO is known to exist in two types, A and B, as determined by the inhibitor clorgyline. However, rat heart MAO is claimed to differ radically from that found in other tissues and a multiplicity of MAO activities within the A and B types has been postulated. Thus, a comparison was made between rat heart MAO with that of the rat vas deferens and human cardiovascular tissues. Rat cardiac and vas deferens MAO activity revealed no major differences regarding apparent Km values, inhibitor sensitivity (with the exception of pargyline), or mixed substrate interactions using kynuramine as the substrate. However, rat major blood vessels contained MAO activities which varied in substrate and inhibitor selectivity. While the rat heart had predominantly type A activity, the blood vessels contained type A and a cl orgy 1 ine-resistant species. In contrast, the rat vas deferens had approximately equal amounts of A and B activity. The large A:B ratio in the rat heart explains why many MAO substrates are metabolized only by type A in that organ. [...]