Steroid hormones during embryonic development in Japanese quail: Plasma, gonadal, and adrenal levels

The purpose of this experiment was to measure plasma, gonad, and adrenal st eroid hormones during embryonic and early posthatch development in Japanese quail. Blood plasma samples were collected from male and female Japanese q uail embryos at 2-d intervals between Day 10 of incubation and Day 5 postha tch. Gonads and adrenal glands were collected from a separate set of embryo s at the same ages. Concentrations of androgen (testosterone and 5 alpha -d ihydrotestosterone) and 17 beta -estradiol (E-2) were determined by RIA. Pl asma androgen changed significantly (P < 0.001) with age in males and femal es, and there were significant differences (P < 0.001) between sexes in the hormonal patterns. Males had higher plasma androgen than females; converse ly, females consistently had overall higher levels of estradiol than males. Adrenal gland steroid content remained relatively high and did not change significantly with age. In contrast, steroid content of gonads followed pat terns similar to those observed for plasma levels. These results provide ev idence for steroid hormone production by the gonads of both sexes, as well as for distinct differences in the patterns observed in the adrenal gland a nd gonads. These results provide evidence for gonadal regulation of changes in circulating hormone levels. Further, these hormonal patterns were assoc iated with the timing of steroid-induced sexual differentiation in the Japa nese quail, suggesting that plasma gonadal steroids are critical in sexual differentiation.