The in-vivo regulatory effect of androgens on steroidogenesis was investigated. Adult (2 to 3 months old) hypophysectomized rats were treated intratesticularly with increasing doses of 5α-dihydrotestosterone (DHT; 10–200 μg/100 g body weight) or vehicle (50 μl dimethyl sulphoxide; DMSO) in the contralateral testis. Intratesticular testosterone concentrations were extremely low in hypophysectomized rats 15–20 days after surgery. Treatment with DHT caused a dose-dependent inhibition of testicular 3β-hydroxysteroid dehydrogenase/Δ5–4 isomerase (3β-HSD) 2 h later, and this effect was apparent at the dose of 20 μg/100 g body weight (P < 0·01). The inhibitory effect of 3β-HSD was not due to a possible interference of DHT in the enzyme assay, since various concentrations of the androgen (0·1–100 μmol/l) were ineffective as inhibitors of 3β-HSD. The highest dose of DHT used in this study (200 μg/100 g body weight) resulted in a rapid (1–2 h) and transient (4–6 h) inhibition (approximately 80%) of 3β-HSD activity. Pretreatment of rats with the antiandrogen cyproterone acetate (5 mg/rat) or the protein synthesis inhibitor cycloheximide (10 mg/rat) did not affect the enzyme activity of testes injected with DMSO, but counteracted the inhibitory effect of DHT on 3β-HSD activity in the contralateral testis. The results presented suggest that the inhibitory effect of the non-aromatizable androgen DHT is receptor-mediated and involves the synthesis of a factor(s) that modulates 3β-HSD activity.
Journal of Endocrinology (1992) 133, 237–243
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