Ontogeny of 5α-Androstan-3β,17β-diol and 17β-Estradiol Binding to Cytoplasm and Nuclei of the Male Rat Pituitary*

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Abstract
The concentrations of estradiol (E2) and 5α-androstane- 3β, 17β-diol (3β-Adiol) receptor were quantified in the pituitaries of male rats, aged 15–100 days. The available binding sites were measured directly in pituitary cytosol. E2 receptor levels reached a peak between days 22 and 30 and then declined slightly. 3β-Adiol-binding sites increased between days 15 and 37, reached a maximum level at the time of puberty (37–42 days of age), and then declined markedly to become undetectable on day 75. Occupation of cytosol binding sites by endogenous steroid was investigated by means of an exchange assay. No occupation was seen for E2 binding. On the other hand, 3β-Adiol-binding sites were partly occupied on day 43 and completely occupied on day 75. The E2 and 3β-Adiol association constants remained relatively constant throughout the entire period studied. Total E2- and 3β-Adiol-binding sites were measured by an exchange technique in nuclear extracts. The ontogenic patterns of E2- and 3β-Adiol-binding sites were similar at all ages. The number of E2-and 3β-Adiol-binding sites reached a maximum on days 28– 30 and remained constant up to day 75. These data demonstrate the developmental appearance of pituitary E2 and 3β-Adiol receptors in the male rat. They suggest two forms of estrogen receptor in pituitary cytosol; one could be involved in the onset of puberty. Moreover, the nuclear ontogenic pattern suggested a single class of binding sites for E2 and 3β-Adiol in the pituitary nuclei.