Inhibin secretion in the adult female duck was investigated. The bovine inhibin radioimmunoassay (RIA) system and human enzyme-linked immunosorbent assay (ELISA) of inhibin A and inhibin B were first validated for use in the duck. In both RIA and ELISA, the dilution curves of plasma and homogenate of the first largest follicle (F1) were parallel to each standard curve, indicating that plasma and the F1 follicle contained immunoreactive (ir) and dimeric inhibins. Short-term food deprivation caused follicular atresia in the ovary and significantly depressed the plasma concentration of ir-inhibin. Positive immunostaining for inhibin alpha-, betaA-, and betaB-subunits was clearly detected in the granulosa cells of the four largest preovulatory follicles. Immunolocalization of these three inhibin subunits was also weakly seen in the interna theca cells of these follicles. These results demonstrate that inhibin alpha-, betaA-, and betaB-subunit proteins are colocalized in the granulosa cell and theca cell of the four largest preovulatory follicles in the duck ovary. The present results, therefore, indicate that the four largest follicles in the ovary are the main source of circulating inhibin in the female duck.
Copyright 2001 Academic Press.