Effect of labor and prostaglandins on phenylethanolamine N-methyltransferase in human fetal membranes.

Abstract

Biochemical investigations have shown the presence of the enzyme phenylethanolamine N-methyltransferase (PNMT), which converts norepinephrine (NE) to epinephrine (E) in human pregnant tissues, e.g. myometrium and fetal membranes. The enzymatic activity of PNMT in myometrium is known to decrease during labor. In the present study, PNMT activity in chorio-decidua was measured and the effect of labor and prostaglandins (PG) on PNMT activity was determined. A cytosol fraction of chorio-decidua was incubated with [14C]-S-adenosyl-L-methionine and normetanephrine for 60 min to measure PNMT activity. Fetal membranes were obtained at elective Cesarean section and normal vaginal delivery from full term pregnant women, and the activity of PNMT in chorio-decidua was compared. Significantly lower activity in chorio-decidua obtained from normal vaginal delivery than that from elective Cesarean section was observed. The concentration of 13, 14-dihydro-15-keto-prostaglandin F2 alpha (DHK-PGF2 alpha) in amniotic fluid obtained at normal vaginal delivery were measured by RIA, and the relationship of the DHK-PGF2 alpha level to PNMT activity was studied. There was a significantly negative correlation between the concentration of DHK-PGF2 alpha in amniotic fluid and PNMT activity in chorio-decidua. When various concentrations of PGF2 alpha were pre-incubated with mined chorio-decidua for 2 h, PNMT activity was decreased in a dose dependent manner. These results indicated that PGF2 alpha might affect the bioconversion of NE to E in fetal membranes. The presence of this enzyme in fetal membranes may play an important role in regulating the concentration of catecholamines during pregnancy and parturition.