DIMERIC INHIBINS IN AMNIOTIC-FLUID, MATERNAL SERUM, AND FETAL SERUM, AND FETAL SERUM HUMAN-PREGNANCY

Using new specific and sensitive enzyme-linked immunosorbent assays fo r inhibin A and inhibin B, we measured these proteins in amniotic flui d (AF), maternal serum (MS), and umbilical cord serum in normal pregna ncies. Inhibin A levels in AF rose from a median (10-90th percentile) level of 615 (158.2-1124.6) pg/mL at 14 weeks to 1336.0 (489.4-2084.1) pg/mL at 20 weeks, and inhibin B rose from 216.6 (67.4-554.6) to 1078 .2 (439.5-2482.2) pg/mL over the same period. In MS, inhibin A levels fell from a median (10-90th percentile) level of 177.5 (101.4-290.7) p g/mL at 10 weeks to a nadir of 111.9 (59.5-200.3) pg/mL at 17 weeks, r ising again to 180.3 (74.1-327.2) pg/mL at 20 weeks. No inhibin B was detectable in MS. In 47 pairs of matched samples (14-16 weeks gestatio n) there was no correlation of inhibin A levels in AF with those in MS (r = 0.19; P > 0.05). In 45 term umbilical cord Serum samples, no dim eric inhibin was detectable in serum from female babies, but inhibin B was detectable in male sera; the median (10-90th percentile) concentr ation was 167.4 (111.2-224.8) pg/mL. These data suggest that for the g estation periods studied, although the placenta secretes inhibin A, an other source, probably the fetal membranes, secretes both inhibin A an d inhibin B. Further, the presence of inhibin B in male fetuses is con sistent with a testicular origin, suggesting that inhibin B may be imp ortant in the development of the fetal hypothalamo-pituitary-testicula r axis.