Effects of sex steroids on regulation of the levels of Cl peptide of rat prostatic steroid-binding protein mRNA evaluated by in-situ hybridization

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Abstract
Prostatic steroid-binding protein (PBP) is the most abundant protein synthesized in the rat ventral prostate. The protein is under strict androgenic control and is made of two subunits containing the polypeptides Cl, C2 and C3. Using an 35S-labelled cDNA probe, we have used quantitative in-situ hybridization to assess the regulation of polypeptide Cl mRNA levels by sex steroids in the adult male rat. Densitometric quantification of autoradiographic hybridization signals revealed that a significant decrease in Cl mRNA levels could be detected 5 h after castration. Levels of Cl mRNA decreased by 50% 2·5 days after castration, while undetectable levels were reached within 7 days. Administration of the potent androgen 5α-dihydrotestosterone to castrated rats caused a progressive increase in Cl mRNA levels which became significant 5 h after the first injection, while prolonged treatment, for 3 and 7 days, caused 50 and 100% reversals respectively of the effect of castration on Cl mRNA levels. Similar results were obtained by dot-blot hybridization using the same 32P-labelled cDNA probe, thus confirming the specificity and quantification achieved by in-situ hybridization. Administration of oestradiol-17β to orchiectomized adult rats for 14 days had no effect on steady-state Cl mRNA levels. Progesterone, on the other hand, at the dose used (2 mg twice daily) caused a marked increase in Cl mRNA levels, measured by in-situ hybridization, which was completely reversed by concomitant administration of the pure antiandrogen flutamide.

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