Production of androgen and estradiol-17 beta by Xenopus ovaries treated with gonadotropins in vitro.

Abstract

Radioimmunoassays were developed for measuring estradiol-17β and testosterone in ovaries of Xenopus laevis and the effects of gonadotropins on ovarian production of these two steroids and of progesterone were assessed. In an initial series of experiments, ovarian pieces were incubated in medium alone or medium containing a frog pituitary homogenate (FPH; 0.02 pituitary/ml). After 10 hr the pieces were scored for maturation and ovulation and the tissue and medium were frozen separately. Steroids were extracted from tissue and medium samples with ether and the extracts were reextracted with 70% methanol to decrease lipid content. Some aliquots of the methanol extract were measured for estradiol and testosterone by radioimmunoassay (RIA) and other aliquots were chromatographed and measured for progesterone by an RIA that was developed previously. FPH significantly increased the concentration of all three steroids in both tissue and medium and stimulated oocyte maturation and ovulation in full-grown follicles. The concentration of all three steroids was greater in tissue than in medium in both control and FPH-treated incubation samples. Testosterone accumulation in both control and FPH-treated samples was much greater than progesterone or estradiol accumulation. In a second series of experiments, the temporal pattern of estradiol and testosterone accumulation was determined over 10 hr of incubation. In FPH-treated samples the increase in testosterone concentration was greatest during the first 5 hr of incubation, while in control samples testosterone concentrations changed only very slightly with time. In contrast, estradiol concentrations increased slowly, but steadily, in both control and FPH-treated samples. Since the testosterone antiserum used is not specific for testosterone but cross-reacts with 17β-hydroxy-5α-androstan-3-one (DHT), testosterone and DHT were separated chromatographically in some samples and assayed separately. Testosterone constituted the bulk of the androgen measured by the antiserum, but detectable levels of DHT were also present. It is concluded that Xenopus ovaries contain and secrete the three major classes of sex steroids. A gonadotropin preparation that stimulated oocyte maturation and ovulation also increased ovarian content of estradiol, testosterone, and progesterone. The high concentrations of testosterone in Xenopus ovaries suggest that, although testosterone probably serves as a precursor for estradiol synthesis, it may also play some other role in Xenopus.