Studies on the monoamine oxidase and catechol-O-methyltransferase of the rat cerebral microvessels

The rat cerebral microvessels were isolated and assayed both for monoamine oxidase (MAO) and catechol-o-methyltransferase (COMT) activities. Cerebral microvessels and brain filtrate were found to contain both forms (A & B) of MAO. On a per mg protein basis, the cerebral microvessels contained the greatest activity of MAO and COMT than that of brain filtrate and mesenteric artery. Chemical sympathectomy using 6-hydroxydopamine neither decreased total MAO activity, nor the A form of the enzyme, nor did it have any effect on COMT activity in the brain microvessels. These results suggest that COMT and both forms of MAO in the rat brain microvessels are extraneuronal in origin.