The role of sex steroids in the formation of sex-differentiated concentrations of corticosteroid-binding globulin in rats

Abstract

ABSTRACT The role of sex steroids in the programming of the level of serum corticosteroid-binding globulin (CBG) in the rat has been studied at different stages of ontogenesis. The CBG content in the serum of mature female rats was 2·5 times higher than that in male rats. Sexual dimorphism of CBG content was absent in immature animals of 3–4 weeks of age. Castration of mature rats led to a 40–50% increase in CBG content. The CBG concentration in mature females or castrated adult males treated with testosterone propionate (TP; 3 mg/day for 4 days) was decreased by 40–50% compared with vehicle-treated rats. Oestradiol injection (1 μg/day for 4 days) had no influence on CBG levels in mature male and ovariectomized adult female rats. Immature rats were castrated on days 1, 7, 14, 21, 28 or 35 of age and the CBG level was determined at 10–12 weeks of age. The CBG content of rats castrated up to day 28 of age was 2·5 times higher than that in mature males and did not differ from that in mature females. The CBG content of male rats castrated on day 35 of age was the same as that of adult castrated males. The CBG level in castrated rats treated with TP (1·25 mg for days 1–3 or 300 μg/day for 5 days after castration at day 7 up to day 26) did not differ from that in controls (i.e. vehicle-treated rats). TP injection into castrated rats on days 29–33 of age (300 μg/day) led to a 40–50% decrease in CBG level when compared with controls. Ovariectomy of rats at different ages (on days 1 or 28 or 3 months) did not affect CBG concentration. TP injection (300 μg/day) into ovariectomized rats on days 29–33 had the same effect on CBG concentration as in males. Gonadectomized rats treated with diethylstilboestrol on days 29–33 (100 μg/day) had the same CBG concentrations as TP-treated rats. It was concluded that there is a short period during ontogenesis, from days 29 to 35 of age, which is critical for irreversible masculinization of the CBG concentration in male rats. Journal of Endocrinology (1992) 132, 235–240