STEROID 5-ALPHA-REDUCTASE ACTIVITY IN THE HARDERIAN GLANDS OF MALE AND FEMALE SYRIAN-HAMSTER (MESOCRICETUS-AURATUS)

The activity of the enzyme steroid 5 alpha-reductase in Harderian glan ds of adult syrian hamsters was assessed by measuring the conversion o f testosterone (T) to 5 alpha-dihydrotestosterone (DHT). The optimal c onditions for this reaction were determined in vitro using whole gland homogenates and [H-3]testosterone as substrate. Enzyme activity was m aximal at pH 5.5. The Michaelis-Menten constant of the Harderian enzym e for T was 4.6 +/- 1.2 x 10(-6) M in females and 4.2 +/- 0.39 x 10(-6 ) M in males, estimated by Eadie-Hofstee plots. On the basis of relati ve maximum velocity values, there was 9 or 10 times more 5 alpha-reduc tase 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 ha msters had lower 5 alpha-reductase activities than those of females. C astration of males significantly increased the enzymatic activity, whi ch within 4 weeks reached female-like values. The levels of 5 alpha-re ductase mRNA also increased with castration. There was a direct correl ation between activity and mRNA levels of the enzyme in castrated male glands. Further, the administration of T or DHT to ovariectomized ham sters led to intact male values in the enzymatic activity of the gland . The sex differences in 5 alpha-reductase activity may be of relevanc e to the differential regulation exerted by androgen upon the physiolo gy of male and female glands. The results are consistent with the view that 5 alpha-dihydrotestosterone is the active androgen in the Harder ian gland. (C) 1994 Academic Press, Inc.