The Simultaneous Function of Catechol‐O‐Methyltransferase and Monoamine Oxidase in Human Placenta

Abstract.Norepinephrine (NE) metabolism in 18 fresh, healthy and full‐term placentas was studied. It was found that, in vitro, metabolism takes place in an oxygen atmosphere mainly through the action of monoamineoxidase (MAO). A reduction in the oxygen component pressure weakened the activity of MAO but not significantly that of catechol‐O‐methyltransferase (COMT). Increase in acidity also reduced MAO activity, but its fall to a level as low as pH 8.4 did not significantly affect the activity of either enzyme. After the addition of MgCl2and Sadenosyl methionine a significant increase in the NMN share during 10 min incubation was noted. However, these additions did not improve the decomposition of NE but reduced the proportion of DOMA. Pyrogallol failed to inhibit COMT but produced a significant reduction in the proportion of dihydroxymandelic acid (DOMA). Increase in acidity and CO2and the fall in O2content, all found in the placenta in connection with foetal asphyxia, individually reduced the decomposition of NE.