Enzymes for epinephrine synthesis and metabolism in the myometrium, endometrium, red blood cells, and plasma of pregnant human subjects.

The enzyme phenylethanolamine-N-methyl transferase (PNMT) converts norepinephrine (NE) to epinephrine (E), and cathechol-O-methyl transferase (COMT) and monoamine oxidase (MAO) both metabolize NE and E. We were able to measure the activity of these enzymes in myometrial and endometrial samples obtained from 27 pregnant women between 32 and 40 weeks' gestation at the time of cesarean section. In addition, these enzymes were measured in red blood cells and plasma obtained from 45 normal pregnancies between 10 and 40 weeks' gestation. PNMT activity was significantly higher in myometrium than in endometrium. During labor myometrial and red blood cell PNMT activity is significantly lower than in specimens from patients at term not in labor, while myometrial PNMT activity is significantly elevated in patients with dystocia. Under these conditions no significant alterations in myometrial, red blood cell, or plasma COMT or myometrial MAO activities were observed. This study identifies for the first time the presence of PNMT in myometrium, endometrium, and red blood cells and provides the necessary step for the conversion of NE to E, a concept previously limited to the adrenal bland, brain, and heart. This could provide an important physiologic mechanism for the control of uterine activity during pregnancy and parturition.