title: 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.
abstract: 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.
mesh_terms: 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*
chemical_list: D012738:Sex Hormone-Binding Globulin; D004958:Estradiol; D005640:Follicle Stimulating Hormone