Androgen metabolism, androgen and oestrogen receptors in the male rat anterior pituitary

Abstract

In the male rat pituitary, testosterone is mainly metabolized to 5α-reduced steroids: 5α-dihydrotestosterone (5α-DHT), 5α-androstane-3α,17β-diol (3α-Diol) and 5α-androstane-3β,17β-diol (3β-Diol). Thus, 5α-reductase could be considered as the key-enzyme of pituitary testosterone metabolism. 3α-Diol was largely converted into 5α-DHT. It seemed likely that 3α-Diol per se is devoid of physiological action and represents only a cellular store of 5α-DHT. 3β-Diol was intensively metabolized into 5α-androstane-3β,6α,17β-triol and into 5β-androstane-3β,7α,17β-triol; the 6α-isomer was prevalent. The physiological role of triols is as yet unknown, but they could be considered as a regulating mechanism of the 3β-Diol pituitary level. In pituitary cytosol, specific receptors for testosterone, 5α-DHT, 3β-Diol and also for 17β-oestradiol were found. On the contrary, there was no receptor for 3α-Diol; this is in good agreement with the fact that 3α-Diol is intensively re-converted into 5α-DHT. The pituitary 3β-Diol receptor exhibited some peculiar properties and it could play an important part in the onset of puberty. In purified nuclei two forms of 5α-DHT binding were found: a 5.6 S complex was soluble in the nuclear sap, and a 4.6 S complex was bound to chromatin. Concerning 17β-oestradiol only a 5 S complex bound to chromatin was found. The presence of both androgen and oestrogen receptors raises the problem of their respective localization in the different types of pituitary cells and also the problem of their respective role on the regulation of gonadotrophin secretion.