CHANGES IN BIOACTIVE AND IMMUNOACTIVE INHIBIN LEVELS AROUND HUMAN LABOR

The changes in bioinhibin (B-inhibin) and immunoinhibin (I-inhibin) levels were studied in the serum of healthy term pregnant women by ovine pituitary cell culture and immunoenzymatic assay systems before and 24 h after delivery. In the maternal serum, a sharp decline in both B-inhibin and I-inhibin levels was observed within first 6 h after delivery. B-inhibin and I-inhibin in maternal serum were 3.45 +/- 0.25 and 3.77 +/- 0.43 U/mL, respectively, before labor and decreased by 35.82% and 38.89% 30 min after labor. One hour after delivery, B-inhibin and I-inhibin were reduced by 56.74% and 61.48%, respectively. After 6 h, B-inhibin and I-inhibin levels were lowered by 93.86% and 78.90%, respectively. Twenty-four hours later, both inhibins were nearly undetectable. In the retroplacental serum, B-inhibin and I-inhibin were 4.92 +/- 0.34 and 10.13 +/- 1.16 U/mL, respectively, i.e. 42.48% and 168.60% higher than the levels of B-inhibin (P < 0.05) and I-inhibin (P < 0.001) in maternal serum before delivery. In the umbilical cord serum, the B-inhibin concentration was 0.75 +/- 0.16 U/mL, whereas the I-inhibin concentration was 9.58 +/- 0.75 U/mL, which was much higher than that of B-inhibin (P < 0.001). No difference was found in B-inhibin or 1-inhibin levels in the serum samples collected separately from umbilical arteries and veins (P > 0.05). In addition, inhibin levels were measured in amniotic fluid and placental extract. In amniotic fluid, B-inhibin and I-inhibin concentrations were 2.37 +/- 0.35 and 8.01 +/- 0.55 U/mL, respectively. In the comparison, B-inhibin in amniotic fluid was 31.3% lower than that in maternal serum before delivery (P < 0.05), but I-inhibin was 112.5% higher than that in the maternal serum (P < 0.001). In the placental extract, the B-inhibin concentration was 12.80 +/- 0.35 U/g tissue, while the I-inhibin concentration was 33.86 +/- 2.93 U/g tissue, which was more than twice as high as the B-inhibin level (P < 0.001). Our data provide further evidence that inhibin may be mainly produced in the placenta during pregnancy.