Progestin Receptors in Female Rat Brain and Hypophysis in the Development from Fetal to Postnatal Stages*

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Abstract
The fetal and postnatal development of the progestin receptors in the intact female rat brain was investigated by means of the in vitro cytosol binding and the nuclear exchange assay using 3H-R5020 ([17.alpha.-methyl-3H]17.alpha.,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione). A large 7S peak of progestin binding in the cerebral corticol cytosols was observed at days 7-14 with less evident binding to the hypothalamus-preoptic area (HPOA). The cortical cytosol receptors, first detectable at day 0, rapidly increased at days 1-7, reaching a maximum at day 10, then gradually declined thereafter. The receptors in the HPOA and other brain areas appeared at day 1, increased during the 1st wk, then remained constant at days 10-28. Hypophyseal cytosol receptors, first detectable at day 10, increased at day 28. Nuclear progestin binding was low in the HPOA and cortex of the neonates at days 1-3. Interestingly, despite the low level of serum progesterone, the cortical nuclear binding suddenly increased at days 7-10, then remained high at days 14-21. A similar, though less pronounced, pattern was seen in the HPOA. Diethylstilbestrol injection caused an increase in the cytosol binding capacities in the HPOA, but did not in the cortex. The appearance of the brain progestin receptor system immediately after birth and differential patterns of their postnatal development in the intact female rat was suggested. The onset of increased nuclear translocation of endogenous progestin-receptor complex may occur in the cortex, and possibly HPOA, around days 7-10. Progestin receptors in the postnatal rat HPOA are estrogen inducible, but not in the cortex.

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