The effects of serum oestrogen-binding components on the unbound oestradiol-17 beta fraction in the serum of developing female rats and on inhibition of [3H]oestradiol uptake by uterine tissue in vitro.
Total oestradiol concentrations in the serum of young female rats were high and decreased after about 21 days of age. High affinity serum oestradiol-binding components (EBP), however, fell steadily from 5 to 23 days of age while the unbound oestradiol-17 beta fraction, which was low early in development, increased between 21 and 28 days of age. Injection (i.v.) of immature (EBP-rich) oestradiol-free serum into 21-day-old female rats led to a decrease in the unbound oestradiol fraction and an increase in serum FSH concentrations. Incubation of uterine tissue with [3H]oestradiol, with or without the addition of diethylstilboestrol (DES), showed the rate and degree of total and DES-suppressible uptake of [3H]oestradiol to be greatest from buffer, less from adult (EBP-poor) serum and negligible from immature (EBP-rich) serum; moreover, there was a positive correlation between the degree of uptake of [3H]oestradiol and the unbound fraction of [3H]oestradiol in the incubate. It is concluded that, at least in young rats, oestradiol activity depends more on the availability of free oestradiol than on its total plasma concentrations.
D000367:Age Factors; D000818:Animals; D004958:Estradiol / Q000097:blood / Q000378:metabolism*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D066298:In Vitro Techniques; D051381:Rats; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism / Q000494:pharmacology*; D014599:Uterus / Q000187:drug effects / Q000378:metabolism*
D012738:Sex Hormone-Binding Globulin; D004958:Estradiol; D005640:Follicle Stimulating Hormone