Steroid 5α-Reductase Activity in the Harderian Glands of Male and Female Syrian Hamster (Mesocricetus auratus)

Abstract

The activity of the enzyme steroid 5α-reductase in Harderian glands of adult syrian hamsters was assessed by measuring the conversion of testosterone (T) to 5αdibydrotestosterone (DHT). The optimal conditions for this reaction were determined in vitro using whole gland homogenates and [3H]testosterone as substrate. Enzyme activity was maximal at pH 5.5. The Michaelis-Menten constant of the Harderian enzyme for T was 4.6 ± 1.2 × 10-6M in females and 4.2 ± 0.39 × 10-6M in males, estimated by Eadie-Hofstee plots. On the basis of relative maximum velocity values, there was 9 or 10 times more 5α-reductase in females (2.8 ± 0.67 nmol/mg protein/hr) than in males (0.289 ± 0.029 nmol/mg protein/hr). Consistently, glands of intact male hamsters had lower 5α-reductase activities than those of females. Castration of males significantly increased the enzymatic activity, which within 4 weeks reached female-like values. The levels of 5α-reductase mRNA also increased with castration. There was a direct correlation between activity and mRNA levels of the enzyme in castrated male glands. Further, the administration of T or DHT to ovariectomized hamsters led to intact male values in the enzymatic activity of the gland. The sex differences in 5α-reductase activity may be of relevance to the differential regulation exerted by androgen upon the physiology of male and female glands. The results are consistent with the view that 5α-dihydrotestosterone is the active androgen in the Harderian gland.