Steroid hormone synthesis and secretion by testes, ovary, and adrenals of embryonic and postembryonic ducks.
To elucidate the relationship between steroidogenesis and sex differentiation or sexual development in the birds, plasma LH, testosterone, 17 beta-estradiol, progesterone, corticosterone and cortisol, testicular and ovarian testosterone, 17 beta-estradiol and progesterone, and adrenal corticosterone, cortisol, progesterone, and testosterone concentrations from 15- to 26-day-old embryonic and 1- to 14-day-old postembryonic male and female ducks were determined by radioimmunoassays. Plasma LH level was high in embryos and decreased after hatching in both sexes. Both plasma testosterone and 17 beta-estradiol concentrations were statistically higher in female embryos than in male embryos, while sex differences were not observed in plasma progesterone, corticosterone, or cortisol concentrations. Both plasma corticosterone and cortisol reached a peak at hatching, and decreased thereafter. Testicular and ovarian testosterone, 17 beta-estradiol, or progesterone was much higher in female embryos than in male embryos. Adrenal corticosterone, cortisol, progesterone, and testosterone concentrations reached a peak 1 day after hatching, and decreased thereafter in both sexes. These results indicate that duck embryonic ovary is much more active in production and secretion of sex steroid hormones than the embryonic testes. It is suggested that the sex of the avian species is basically male having homozygoty of sex chromosomes (ZZ), and that estrogens secreted by the embryonic ovary have important roles in female sex differentiation. Very high levels of corticosterone and cortisol either in plasma or adrenals observed shortly after hatch suggest that corticosteroids have an important role in hatching of ducks to adapt themselves to a new environment.