Clinical findings indicate that Strogen forte (a standardized extract of the plant Sabalis serrulata) can be used successfully in the medical treatment of benign prostatic hyperplasia. The aim of the present study was to investigate the possible inhibitory effects of the Strogen forte extract on rat and human testicular Δ5-3β-hydroxysteroid dehydrogenase (Δ5-3β-HSD) and prostatic 5α-reductase (5α-R). Strogen forte proved to be a direct inhibitor of medium effectivity, with similar IC50 values for rat testicular Δ5-3β-HSD (400 ± 23 μg/ml) and human testicular Δ5-3β-HSD (212 ± 8.6 μg/ml). 5α-R activities were analysed by in vitro incubation of rat and human prostatic tissue homogenates with 14C-labelled testosterone as substrate in KRPG-DTT medium (pH = 7.4) with NADPH coenzyme, in air, at 37°C, in the presence of Strogen forte extract. The results clearly demonstrate that Strogen forte is a potent inhibitor of prostatic 5α-R, with IC50 values of 385 ± 35.6 μg/ml for rat and 245 ± 64.6 μg/ml for human prostatic 5α-R. The present study has revealed that this plant extract inhibits not only prostatic 5α-R, but also testicular Δ5-3β-HSD.
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