Circulating concentrations of immunoreactive inhibin and FSH during the estrous cycle of mares

Abstract

Summary A heterologous radioimmunoassay developed to measure inhibin in rat plasma was validated and used to characterize changes in peripheral concentrations of immunoreactive inhibin (ir-inhibin) in relation to follicle stimulating hormone (FSH) concentrations during the estrous cycle of mares. The primary antiserum used in the assay was developed against a synthetic porcine inhibin α-subunit [(1-26)-Gly-Tyr] fragment. The same synthetic peptide was used for preparation of standards and tracer. Slopes of the dose-response curves for pooled estrus and diestrus mare plasma and equine follicular fluid were similar to the slopes for the porcine inhibin α-subunit standard curve and porcine follicular fluid dose-response curve. Twelve mares were bled once daily beginning when diameter of the largest follicle reached ≤25 mm and continuing until 3 days after the end of an interovulatory interval (ovulation=Day 0). Each of the 12 interovulatory intervals were normalized to the mean length of the interovulatory interval (22.2 days; range, 19 to 26). There was an effect of day for concentrations of ir-inhibin (P