In vivo Nuclear 3H-Estradiol Binding in Brain Areas of the Rat: Reduction by Endogenous and Exogenous Androgens

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Abstract
In vivo specific nuclear binding of [2, 4, 6, 7 (n)-3H] estradiol (3H-E2), as indicated by diethylstilbestrol(DES)-blockable radioactivity, was measured 1 h after injection in adult intact male, untreated and testosterone propionate (TP)-pretreated or 5α-dihydrotestosterone (DHT)-pretreated gonadectomized (GDX) male and female rats. There was no sex difference in specific 3H-E2 binding in brain areas and anterior pituitary (PIT) of untreated GDX animals. DHT pretreatment had no effect on binding in any tissue. Specific nuclear binding in the preoptic area-anterior hypothalamus (POA-AH), median eminence-basal hypothalamus (ME-BH), amygdala (AMYG), septum (SEP), and dorsal hypothalamus (DH) was lower in intact males and TP-pretreated GDX males and females than in untreated GDX animals. Uptake in the PIT was not affected by TP pretreatment or by the presence of the testes, suggesting that the reduction in nuclear 3H-E2 binding observed in other tissues was caused by competition by estradiol formed in situ from TP or endogenous androgens for nuclear binding sites. Thus, the reduction in 3H-E2 uptake caused by the presence of TP or the testes could be used to estimate the degree of aromatization that occurred in these brain areas. In males, specific nuclear binding of