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 glands of adult syrian hamsters was assessed by measuring the conversion of testosterone (T) to 5 alpha-dihydrotestosterone (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 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 relative maximum velocity values, there was 9 or 10 times more 5 alpha-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 5 alpha-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 5 alpha-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 5 alpha-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 5 alpha-dihydrotestosterone is the active androgen in the Harderian gland.
Vilchis
F
F
Department of Reproductive Biology, Instituto Nacional de la Nutrición Salvador Zubirán, México, D.F., Mexico.
Enriquez
J
J
Queipo
G
G
Pérez-Palacios
G
G
Chávez
B
B
D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000378:metabolism*; D000818:Animals; D002369:Castration; D006224:Cricetinae; D013196:Dihydrotestosterone / Q000378:metabolism / Q000493:pharmacokinetics; D005260:Female; D006243:Harderian Gland / Q000187:drug effects / Q000201:enzymology*; D066298:In Vitro Techniques; D008297:Male; D008647:Mesocricetus; D009249:NADP / Q000494:pharmacology; D010052:Ovariectomy; D013739:Testosterone / Q000378:metabolism / Q000493:pharmacokinetics; D014316:Tritium
D013196:Dihydrotestosterone; D014316:Tritium; D013739:Testosterone; D009249:NADP; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase