Influence of castration and androgen treatment on the synthesis of prostatic binding protein and the concentration of its mRNA in the rat ventral prostate.

The regulation by androgens of the synthesis of prostatic binding protein (PBP), an abundant secretory protein of the rat ventral prostate, was studied by measuring the rate of incorporation of [3H]leucine into total protein and into PBP by prostatic tissue in vitro. PBP-specific synthesis dropped to 30% of the intact level after 3 days and to 5.5% after 7 days. Administration of androgens to 7 day-castrated rats reversed these changes: 36% of the control value was reached after 3 days of treatment and 70% after 5 days. The mRNAs of PBP were measured under similar conditions by means of dot hybridization, using C1-, C2- and C3-specific cDNA-clones. The 3 mRNAs followed a parallel course. They decreased to about 18% on the third day after castration and to about 2% after 7 days. Androgen treatment of 7-day castrated rats produced a small increase of these levels after 1 day. After 3 days 15% of the intact level was reached. The general similarity of the time course of PBP synthesis and PBP mRNA levels in castrated and androgen treated rats supports a transcriptional regulation mechanism, although there also is some evidence for an influence on protein synthesis in general.