Circulating monoamine oxidase B and phenolsulfotransferase activities in essential hypertensive patients

Circulating monoamine oxidase (MAO) and phenolsulfotransferase M and P (PST M, PST P) activities were determined in 24 untreated essential hypertensive patients and in 35 age-matched normotensive healthy controls. These enzymes are involved in the inactivation of monoamines and their metabolites. After lysis of blood, enzymatic activities were determined by radioenzymatic techniques using as substrates [14C]-beta-phenylethylamine for MAO, 3-methoxy-4-hydroxyphenylglycol for PST M and phenol for PST P. MAO activity measured by this method is fully accounted for by platelet MAO B activity. Women presented higher MAO activity than men. Significantly lower MAO-B activities were observed in hypertensive patients, both in men and in women, when compared to normotensive controls. Circulating PST activities, of which more than 80% is platelet-derived, were similar in hypertensive and normotensive subjects. These data suggest that the intracellular serotonin inactivation processes, through MAO and PST, cannot account for the reduction of platelet 5-HT content observed in essential hypertension.