The effects of clomiphene on the distribution of radioactivity 1 hr after intravenous injection of 3H-estradiol were determined in adult female rats 48 hr after ovariectomy. Because clomiphene competitively blocks uptake of estradiol by specific receptors, this procedure identified tissues and brain areas with high concentrations of estradiol receptors. Having determined those tissues containing receptors, the effect of neonatal testosterone treatment on 3H-estradiol distribution was investigated in a second study, in order to determine which receptor areas, if any, are affected by androgenization. Clomiphene treatment significantly reduced tissue:plasma ratios of radioactivity in uterus, anterior pituitary and anterior hypothalamus to 10, 8 and 35 %, respectively, of ratios in rats not injected with clomiphene, thus showing that these tissues contain high concentrations of estradiol receptors. Tissue’.plasma ratios of radioactivity also showed that posterior hypothalamus, prehypothalamic area, septum and amygdala-periamygdaloid cortex also contain estradiol receptors, but in relatively lower concentrations. In the second study, adult female androgenized rats and their litter mate controls were ovariectomized. Two days later the distribution of radioactivity was determined 2 hr after injection of 3H-estradiol. Levels of radioactivity were less in uterus and anterior and posterior hypothalamus of animals treated neonatally with 100 μg testosterone propionate than in control rats, whereas levels were not altered in pituitary, 5 brain areas, and the peripheral nontarget tissues analyzed. Treatment with 30 μg testosterone significantly reduced uptake of radioactivity in the anterior and posterior hypothalamus only. Thus, comparison of the pattern of uptake of radioactivity in the 2 studies reveals that neonatal androgen treatment does not cause a general impairment of receptor binding capabilities, but rather appears to affect the receptors in some target tissues only.
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