Pituitary and brain 5alpha-reductase messenger RNA levels in control, castrated, and dihydrotestosterone-treated rats.
In (28- to 40-day-old) male rats, the influence of castration or hormone-replacement treatment with dihydrotestosterone (5alpha-DHT) upon pituitary or hypothalamic 5alpha-reductase was assessed. The efficacy of the treatments was demonstrated by measuring serum LH and ventral prostate weight. Pituitary 5alpha-reductase enzyme activity was estimated by isolating [5alpha-(3)H]DHT by thin-layer chromatography after incubations with [(3)H]testosterone, and the identity of the [5alpha-(3)H]DHT formed was confirmed by recrystallization experiments. Pituitary and hypothalamic 5alpha-reductase mRNA content was determined by RNA blot analysis utilizing a rat 5alpha-reductase (type 1 or type 2) cDNA as probe. Pituitary 5alpha-reductase activity was significantly increased as a function of days after castration, whereas castration plus DHT treatment (at Day 12 post-castration) significantly decreased the activity to less than one-third of control levels. In controls, pituitary 5alpha-reductase mRNA content was barely detectable using the rat 5alpha-reductase (type 1) cDNA as probe. However, castration resulted in a clear increase in mRNA abundance, while in DHT-injected castrated animals pituitary mRNA content was undetectable. Hypothalamic mRNA content was clearly detectable in all treatment groups with the rat 5alpha-reductase type 1 probe. However, there were no apparent changes in hypothalamic mRNA abundance as affected by the treatments. On the other hand, pituitary or hypothalamic 5alpha-reductase mRNA was undetectable using the rat 5alphareductase (type 2) cDNA as probe. These results indicate that in the rat pituitary the content of mRNA encoding 5alpha-reductase is negatively regulated by DHT. The increase in pituitary 5alpha-reductase enzymatic activity in castrates is due, in part, to higher mRNA levels detected by the 5alpha-reductase type 1 probe. Hypothalamic 5alpha-reductase mRNA levels (type 1) encoding this protein are not regulated by DHT, but presumably are, to some extent, under transcriptional control.
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Cecil H. and Ida Green Center for Reproductive Biology Sciences, Departments of Biochemistry and Obstetrics and Gynecology, The University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75235.