Reduced platelet MAO activity during pregnancy.

The kinetics and thermolability of platelet MAO were studied in twenty-three women during and after pregnancy. The maximal velocity of the enzyme (Vmax) was significantly reduced during pregnancy, whereas the apparent, Michaelis constant (Km) was unaltered. The initial velocity of the enzyme (vo) was significantly lowered during the pregnant period compared to after delivery. However, when the enzyme activity was determined in the presence of autologous plasma, no significant difference in deaminating activity between the two occasions could be detected. This was caused by a significantly increased activating capacity of the plasma collected during the pregnant period, expressed as the ratio of MAO activity determined in the presence and absence of plasma. Moreover, pregnant women showed an increased thermal stability of the platelet MAO compared to non-pregnant women.