Synergistic effects of estrogen with androgen on the prostate—effects of estrogen on the prostate of androgen‐administered rats and 5‐alpha‐reductase activity

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Abstract
To clarify the effects of estrogen on the prostate of androgen‐treated rats, we administered estradiol (E2; 0.01 mg/day) to testosterone (T; 1 mg/day)‐treated Wistar rats under various conditions. There were three variable factors: the age of the rat, the untreated period after castration, and the presence of testes. Under all conditions, E2 stimulated the growth of the prostate in T‐treated rats compared with growth in rats in treated with T only.To analyze the mechanism underlying this enhancement of prostate growth by estrogen, we measured 5‐alpha‐reductase activity and calculated its kinetic parameters, i.e., both Vmax and Km. The Vmax of the nuclear fraction was higher in E2‐administered T‐treated rats than in T only‐treated rats. In contrast, the Vmax of the microsomal fraction was lower in E2‐administered rats. Km values in the two groups showed no significant differences. Elevation of the nuclear fraction of 5‐alpha‐reductase activity could explain the synergistic effects of estrogen on the prostate growth of androgen‐treated rats.