Source of circulating levels of inhibin A, pro alpha C-containing inhibins and activin A in early pregnancy.

It is now established that the glycoprotein hormone inhibin is produced by primate granulosa cells, corpus luteum and trophoblast of human placenta. This study was designed to investigate the major source of inhibins and activin A in early pregnancy using a novel panel of assays with high specificity and sensitivity. A total of 12 women (aged 20-35 years) with singleton pregnancy undergoing first trimester (group 1: 6-8; group 2: 8-10; group 3: 10-12 weeks of gestation) termination of pregnancy (TOP) was recruited for the study. Blood samples were taken before TOP, every 15 min for the first hour and hourly for the next 3 h after TOP (total of 4 h of measurements). Circulating concentrations of inhibin A, pro alpha C, activin A, human chorionic gonadotrophin (HCG), oestradiol and progesterone were higher in early pregnancy than at any stage of the menstrual cycle. Peripheral concentrations of inhibin A and activin A were significantly decreased within the first hour in all three groups and gradually decreased to even lower concentrations within the study period. Pro alpha C concentrations decreased within the first hour and then remained unaltered during the next 3 h. Similarly, HCG, oestradiol and progesterone concentrations in circulation decreased substantially within 4 h of TOP. Correlation analyses showed a significant positive correlation (P < 0.001) between inhibin A, activin A, HCG, and oestradiol concentrations throughout the study period. In summary, this study shows that the feto-placental unit is the major source of increased circulating concentrations of inhibin A in early pregnancy. Activin A is produced by the feto-placental unit and the corpus luteum. Pro alpha C-containing inhibins are mainly secreted by the corpus luteum in early pregnancy.