Photoperiodic control of androgen metabolism and binding in androgen target organs of hamsters ( Phodopus sungorus)

Abstract

Male Dshungarian dwarf hamsters ( Phodopus sungorus, Pallas 1776) aged 90 ± 7 days were used throughout the study. They were kept either under long photophase days of 16L:8D (group L) or under short photophase days of 8L:16D (group S). Testes and prostate weight and total radioactivity uptake into various organs 30 min. after intracardial injection of [ 3H]-testosterone ([ 3H]−T) were determined. Photoperiodical changes in the action of steroids were investigated by the determination of the [ 3H]−T metabolite pattern in vivo, and by in vitro studies on the available androgen receptor of prostate cytosol. The S-group reduced the weight of the testes to 3% and that of the prostate and seminal vesicles to 10% of the L-group values. The decrease in the weight of the accessory sex organs was accompanied by a dramatic increase in the radioactivity uptake relative to plasma. The plasma of S-hamsters retained less radioactivity than that of L-hamsters. The metabolite pattern of [ 3H]-T in prostate and seminal vesicles in vivo changed towards increased inactivation with less 5α-dihydrotestosterone and more steroids of high polarity formed. An increase in the concentration of available binding sites of the prostate cytosol androgen receptor was observed in S-hamsters when compared to the L-group. Short term castration (16h) increased the receptor in both, L- and S-hamsters, while long term castration (7 days) lowered the receptor by 60% compared toshort term castrated hamsters. The data indicate, that a photoperiodic control of androgen action exists on the level of the target organs, which is assisted by peripheral changes of androgen metabolism, as reflected in plasma, which are not directly controlled by the hypophyseal-gonadal feed back system. The peripheral changes lead to a higher elimination and inactivation of plasma T under short photoperiods. Furthermore, in the target organs also a higher inactivation and a lower formation of biologically active metabolites suppress the biological action of the remaining active androgen. The decreasing androgen levels are also accompanied by increasing available cytosolic androgen receptor concentrations. The decrease of receptor after long term castration suggests that the regressed testes are involved in the maintainance of the androgen receptor and of androgen responsiveness.