Tissue levels of active and total renin, angiotensinogen, human chorionic gonadotropin, estradiol, and progesterone in human placentas from different methods of delivery.

The components of the renin system are present in placental tissue, but their function in this tissue is not known. We investigated the relative distribution of the various components throughout the placenta to determine whether the distribution is consistent with a role for them in parturition or in stimulation or inhibition of placental hormone biosynthesis. Thus, active and total renin were measured in fetal membranes (chorion laeve and amnion) and in discoid placenta (chorion frondosum and chorion plate) of women who were delivered vaginally (n = 12) or by cesarean section with (n = 6) or without labor (n = 9). The interrelationships between active and total renin and angiotensinogen, progesterone, hCG, and estradiol concentrations were investigated. Labor had no significant effect on the concentration of active or total renin, angiotensinogen, hCG, or estradiol in any part of the placenta. Tissue progesterone concentrations were higher in placentas from women who underwent vaginal deliveries than in those who had cesarean sections with or without labor (P less than 0.02). The chorion laeve had 20 times more total renin per g than the discoid placenta and 3 times more than the amnion. In contrast the discoid placenta had 5 times more hCG per g and 3 times more progesterone per g than the fetal membranes. The concentration of estradiol was lower in amnion, while that of angiotensinogen was lower in the chorion frondosum than in all other regions. The tissue concentrations of active renin, prorenin, or total renin were not related to those of any of the other hormones. Altogether these data do not provide evidence of a role for the placental renin system in parturition or placental hormone biosynthesis.