SOURCE OF INHIBIN IN-OVINE FETAL PLASMA AND AMNIOTIC-FLUID DURING LATE-GESTATION - HALF-LIFE OF FETAL INHIBIN

Immunoactive inhibin (ir-inhibin) concentrations were determined in ch ronically catheterized sheep between 120 and 145 days gestation. Mater nal plasma ir-inhibin concentrations remained basal (0.19 +/- 0.05 ng/ ml) throughout the period of study. Immunoactive inhibin concentration s in male and female fetal plasma were elevated above those observed i n maternal plasma, with the concentrations in plasma of male fetuses ( 7.38 +/- 0.04 ng/ml) being significantly greater (p < 0.001) than thos e in female fetuses (1.07 +/- 0.14 ng/ml). The concentrations of ir-in hibin in amniotic fluid of ewes bearing male fetuses (10.93 +/- 1.55 n g/ml) were significantly greater than in ewes bearing female fetuses ( 2.81 +/- 0.32 ng/ml; p < 0.05) but not significantly different from th e concentrations in male fetal plasma. Immunoactive inhibin concentrat ions decreased following surgery in gonadectomized fetuses, to 3.25 +/ - 0.99 ng/ml within 6 h, and remained at a mean value of 0.75 +/- 0.38 ng/ml from 24 h after gonadectomy. The half-life of circulating inhib in in fetal plasma, estimated from the decay curve during the first 6 h after surgery, was 3.94 +/- 0.88 h. There was a significant (p < 0.0 5) decrease in the concentration of ir-inhibin in amniotic fluid after gonadectomy; however, this decrease occurred gradually over 7 days, a nd ir-inhibin concentrations did not fall to those concentrations obse rved in fetal circulation at any time after gonadectomy. It is conclud ed that the major source of circulating ir-inhibin in male fetal plasm a, but not in amniotic fluid, is the gonads.