The conditions under which dihydrotestosterone and 5α-androstane-3α, 17β-diol (3α-androstanediol) induce prostatic growth in the castrate dog have been investigated in animals in which the initial size of the prostate was either normal or large. When androgen replacement was commenced immediately after castration of dogs with preexisting prostatic hypertrophy, dihydrotestosterone was as effective as 3αandrostanediol in maintaining prostate weight. Under all other conditions examined (replacement commenced immediately after castration in dogs with small prostates or 2 weeks after castration in dogs with large prostates), 3α-androstanediol but not dihydrotestosterone induced significant prostatic growth. The maximal effect of 3α-androstanediol in inducing prostatic growth was observed in 12 weeks. The administration of 17β-estradiol enhanced the growth-promoting action of 3α-androstanediol, but did not affect the action of dihydrotestosterone or influence 3α-hydroxysteroid dehydrogenase activity in prostate. Thus, the synergistic effect of 17β-estradiol and 3αandrostanediol seems to be independent of any effect on the interconversion of the two androgens. The activity of the 3α-hydroxysteroid dehydrogenase in dog prostate was high under all conditions of accelerated prostatic growth and appeared to be under androgenic control.
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