First-trimester villous placenta has high prorenin and active renin concentrations.

Objective: Term villous placental concentrations of prorenin are known to be very low, whereas those of decidua and fetal membranes are high. It has been demonstrated that prorenin synthesis is modulated by hormones in other reproductive tissues, thus suggesting a means for paracrine regulation in the placenta. This study was performed to test the hypothesis that placental tissue prorenin concentrations may be influenced by gestational age and are temporally related to alterations in the hormonal milieu.

Study Design: Decidua and villous placental tissue were obtained from term and first-trimester human pregnancies, and concentrations of prorenin, active renin, prolactin, and human chorionic gonadotropin were measured. Values were compared between gestational periods, and relationships between renin and hormone values were analyzed.

Results: Prorenin concentrations in first-trimester placenta were nearly 200-fold higher than at term. The proportion of active renin was higher with early gestation. Decidual prorenin and active renin concentrations were similar in both groups. Placental prorenin correlated with chorionic gonadotropin but not prolactin in both groups.

Conclusions: This study demonstrates large differences in placenta prorenin and active renin in villous placental tissue between first-trimester and term gestation tissues, yet these differences were not observed in decidual tissues. The contrast in placental prorenin values observed at the extremes of pregnancy parallel those of placental human chorionic gonadotropin.