Cytosol and nuclear receptors for 5α-dihydrotestosterone and testosterone in the hypothalamus and hypophysis, and testosterone receptors isolated from neonatal female rat hypothalamus

Abstract

Characterization of cytosol receptor macromolecules for 5α-dihydrotestosterone, (DHT) and testoster one (T) was compared in the hypothalamus of 27-day-old male rats. The binding of [ 3H]DHT increased rapidly after starting incubation, and approached a maximum at 1 h. In contrast, the [ 3H]T binding increased slowly with a maximum at 4h. On analysis of the saturation kinetics of the binding of androgens by the Lineweaver-Burk plot the dissociation constant (K D) and the number of binding sites (NBS) for DHT binding were determined to be 0.3 nM and 3.8 ( n = 2) fmol/mg protein, respectively, and the values for T binding 1.5 ± 0.28 (S.E.) nM and 2.2 ± 0.23 ( n = 3) fmol/mg protein, respectively; indicating higher affinity of the hypothalamic cytosol for DHT than for T. Maximal binding capacities for DHT and T were 3.9 ± 0.36 [4] and 2.1 ± 0.15 [4], respectively. Relative affinity of competition of the [ 3H]T binding by DHT was 2.8 times than by T. Hypothalamic and hypophyseal [ 3H]DHT binding was inhibited in a competitive way by the addition of 17β-estradiol, but not by estrone, estriol, diethylstilbestrol or clomiphene citrate. The injections of estradiol even in large amount did not affect the binding of [ 3H]DHT. From these results it seems that the hypothalamic cytosol can bind DHT and T in a different way, indicating different characterization of cytosol receptors for DHT and T in the hypothalamus of 27-day-old male rats, and further suggesting the possibility of individual receptors for DHT and T Receptors macromolecules of 5–6 S for DHT were isolated from purified nuclei of the hypothalamus and the anterior hypophysis. From these results, together with nuclear T receptors, it is tempting to speculate that androgens can directly act on the brain through the interaction with the receptors for DHT and T in the hypothalamus and hypophysis. The presence or absence of receptors for T was investigated in the hypothalamus of neonatal female rats at 3 and 7 days of age. On sucrose density gradients there was a small but definite peak of radioactive androgen in the 8 S region. The 8 S binding components were found to be saturable and steroid-specific. These suggest the presence of ‘receptors’ for T in the hypothalamus on neonatal female rats. The function of neonatal hypothalamic T ‘receptor’ was discussed in relation with the mechanism of induction of androgenization.