STEROID CONCENTRATIONS IN THE FOLLICULAR FLUID OF MARES AT VARIOUS STAGES OF THE REPRODUCTIVE CYCLE

Abstract

SUMMARY: The following steroids were estimated in each of twelve samples of follicular fluid collected from oestrous, luteal-stage and pregnant mares: progesterone, 17α-hydroxyprogesterone, androstenedione, epitestosterone, 19-norandrostenedione, oestrone, oestradiol-17β and 6 'α'-hydroxyoestradiol-17β. In ten of the samples oestradiol-17β was the major steroid present. In one sample taken from a pregnant animal oestradiol-17β could not be detected at all, and in its place large amounts of progesterone and 20α-hydroxypregn-4-en-3-one were found. The larger follicles tended to have the higher steroid concentrations. In this series, there was no significant difference in concentration between oestrous and luteal-phase animals with respect to any of the steroids measured (P > 0·05); the reasons for this are discussed. It is concluded that the gonadotrophic hormones do not act by influencing any rate-limiting reaction in the conversion of progesterone to oestrogens. Since the ratios of the various steroids seem to differ greatly between follicular fluid and luteal tissue, it is postulated that cell type may be the chief discriminant of the secretory activity of the ovary.