Early steps in prostaglandin metabolism in the human placenta

Abstract

The activities of the enzymes catalyzing the early steps in prostaglandin metabolism (the nicotinamide adenine dinucleotide [NAD]-linked 15-hydroxyprostaglandin dehydrogenase, the nicotinamide adenine dinucleotide phosphate [NADP]-linked 15-hydroxyprostaglandin dehydrogenase, and the 15-ketoprostaglandin Δ 13 reductase) were measured in homogenates of term placenta. The NAD-linked enzyme possesses the highest activity of the three. The NADP-linked enzyme has much lower activity and probably acts physiologically as a 9-ketoprostaglandin reductase rather than as a 15-hydroxyprostaglandin dehydrogenase. Placental homogenates contain a low-molecular-weight, heat-stable inhibitor of the NADP-linked enzyme. The reaction catalyzed by the 15-ketoprostaglandin Δ 13 reductase is the rate-limiting step. Analysis of the activity of these enzymes has shown that there is no significant relationship between them; furthermore, whether the placentas are from spontaneous single or twin deliveries, induced deliveries, or cesarean sections (in labor or not in labor) does not have a significant effect on the activity of the NAD- or NADP-linked dehydrogenases.