Concentrations of immunoreactive inhibin in ovarian and peripheral venous plasma and follicular fluid of Booroola ewes that are homozygous carriers or non-carriers of the Fec(B) gene

Abstract

No gene-specific differences were found during either the luteal or follicular phases of the oestrous cycle in the venous secretion rates of ovaries or in concentrations of immunoreactive inhibin in peripheral plasma between Booroola ewes that were homozygous carriers (BB) or non-carriers (++) of the Fec(B) gene. In three experiments in which concentrations of plasma inhibin and follicle-stimulating hormone (FSH) were compared, gene-specific differences were noted for FSH (P < 0.05), but no significant correlations were noted between FSH and inhibin for either genotype. Granulosa cells and follicular fluid, but not theca interna, stroma or corpora lutea, were the major intra-ovarian sites of inhibin; no gene-specific differences were noted for inhibin concentrations in follicular fluid or in any of the intra-ovarian tissues. The mean concentrations of inhibin in follicular fluid remained constant irrespective of follicular diameter whereas the mean total contents of inhibin increased significantly with increasing diameter (P < 0.05). Inhibin secretion rates were four times higher in ovaries with oestrogen-enriched follicles (i.e. ≥ 50 ng oestradiol ml-1) than in ovaries with no such follicles (P < 0.01). Moreover, inhibin concentrations were higher in follicular fluid of oestrogen-enriched follicles than in those with low oestrogen (i.e. < 50 ng ml-1; p < 0.05). Ovariectomy resulted in a significant reduction in concentrations of immunoreactive inhibin from plasma (P < 0.01). The residual plasma inhibin in some Booroola ewes was not associated with genotype. It is concluded that, although antral follicles are a major source of inhibin in Booroola ewes, immunoreactive inhibin is not associated with the Fec(B) gene and is not responsible for the gene-specific differences in concentrations of FSH in plasma.