EFFECT OF TESTOSTERONE DEPRIVATION ON EXPRESSION OF THE ANDROGEN RECEPTOR IN RAT PROSTATE, EPIDIDYMIS AND TESTIS

Adult rats were treated with ethane dimethane sulphonate (EDS) to eliminate the Leydig cells. This treatment resulted in very low levels of testosterone in the blood and in the testis. Furthermore, histological evaluation of spermatogenesis showed no marked differences between control and EDS-treated animals. In the ventral prostate, 5 days after EDS-treatment, a 4.0 +/- 0.3-fold up-regulation of androgen receptor (AR) mRNA was observed, together with a 2.2 +/- 0.2-fold increase in actin mRNA. In the epididymis, a 2.0 +/- 0.5-fold increase in AR mRNA level was observed, without a change in actin mRNA level. In the testes of EDS-treated rats, the AR mRNA level was not changed (1.02 +/- 0.17-fold of controls), and there was also no change in actin mRNA level at 5 days after EDS-treatment. These results indicate that AR mRNA expression in the ventral prostate and epididymis is regulated differentially by testosterone when compared to regulation in the testis. Testicular androgen binding sites were assayed by Scatchard analysis of the binding of H-3-R1881 to a nuclear fraction, that was isolated by a method which involved the use of liquid nitrogen and high sucrose buffer. The number of specific binding sites per testis in EDS-treated rats with testosterone-implants, remained unaltered compared to control rats (9.1 +/- 1.4 pmol/testis). In these rats, 20% of the normal testicular testosterone level was sufficient to maintain the androgen receptor in a tight nuclear binding (transformed) form. In testes from EDS-treated rats without testosterone-implants, the AR did not fractionate into the nuclear fraction; however, the total testicular AR content in these animals was close to control levels, as measured by nuclear H-3-R1881 binding after receptor transformation through injection of a high dose of testosterone (10 mg) 2 h before killing the rats (testosterone pulse). In the different experimental groups, FSH was not required to maintain the total testicular AR content (ligand binding). Immunoprecipitation and Western blotting of the testicular AR using specific monoclonal and polyclonal antibodies indicated that the total testicular amount of immunodetectable AR protein in long-term testosterone deprived rats was very low when compared to that in control rats or rats with testosterone-implants. This is in disagreement with results obtained in the ligand binding assay, and may point to a structural modification of the AR in the testis that possibly occurs in the prolonged absence of androgens.