Inhibin and related peptides in human pregnancy

The studies described in this thesis were designed to investigate inhibin and inhibin-related peptides throughout human pregnancy. The first approach was to characterize antibodies raised against the intact inhibin molecule or different peptide fragments of inhibin subunits in order to obtain suitable antibodies for radioimmunoassay and Western blot analysis. The results showed that two sheep antibodies, Y29 and Y33, which were raised against synthetic human inhibin α-(1-23)-NH_2, were specific to inhibin-like molecules in placental extracts and amniotic fluids. An antibody (Monash antibody) raised in a rabbit against 32 kDa inhibin was the most sensitive antibody for measuring inhibin in plasma and placental extracts. The development of the Western blot analysis for inhibin was successful with Y29 and R187 antibodies and another monoclonal antibody raised against human βA-(87-114)-NH_2. These three antibodies showed specificity to purified 32 kDa bovine inhibin and the antibodies to βA-subunit fragments also showed specificity to recombinant human activin A. Inhibin levels were measured during pregnancy. The pattern of secretion showed an increase in inhibin levels after the luteinizing hormone (LH) surge and reached a peak during the first two weeks of pregnancy. The levels of inhibin declined after this first peak and then rose again, reaching a second peak during 7-8 weeks of pregnancy. A second fall was observed until 30 weeks of gestation followed by a dramatic increase at approximately 36 weeks which was sustained until delivery. These results suggest that before the formation of the placenta, the corpus luteum is a potential source of inhibin. Human chorionic gonadotrophin (hCG), oestradiol (E_2) and progesterone (P_4) were also measured in order to investigate any interactions between inhibin and these hormones in vivo. The results showed that oestradiol and progesterone increased throughout pregnancy as did inhibin. hCG increased during early pregnancy and declined after 12 weeks and remained at this level until delivery.