Actions of Androgen and Estrogen on Guinea Pig Seminal Vesicle Epithelium and Muscle*

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Abstract
Using the guinea pig seminal vesicle, experiments were designed to gain insight into the relative contributions of androgen and estrogen to the growth of accessory sex organ epithelium and muscle. Treatment of castrated animals with daily injections of either testosterone or dihydrotestosterone completely prevented the castration-induced reduction in the size and number of epithelial cells. Estrogen treatment of castrated animals alone or in combination with dihydrotestosterone revealed no detectable anabolic effect on the epithelium. Therefore, estrogens would not normally appear to exert significant influences on the normal growth of this accessory sex organ epithelium. In the muscle, castration-induced regression was due only to a reduction in cell size, which was prevented by maintenance of castrated animals with either testosterone or dihydrotestosterone. Although treatment with estradiol prevented loss of wet weight, maintained cell size, and, in addition, increased cell numbers, there was no detectable interaction of estradiol and dihydrotestosterone in the muscle. Using cyproterone acetate (6-chloro-1β,2β-dihydro-17-hydroxy-[3H]cyclopropa-[l,2]-pregna-l,4,6-triene-3,20-dione acetate), a specific antagonist for the androgen receptor, it was determined that dihydrotestosterone and estradiol stimulate muscle growth through separate receptor mechanisms. These findings indicate that androgen and estrogen can each stimulate muscle growth, and that the action of testosterone in the muscle does not involve its aromatization to estradiol. Resolution of the relative importance of androgen and estrogen on muscle growth was obtained from two observations. First, treatment of normal animals with cyproterone acetate did not decrease plasma testosterone or estradiol, yet reduced muscle weight to castrate levels. This suggests that although castration lowered both plasma testosterone and estradiol, the castrationinduced decrease in muscle weight was secondary only to reduced plasma androgen. Secondly, the findings that androgen maintained normal muscle growth in the castrate animal while estrogen induced a qualitatively different growth from that of animals normally maintained indicates that androgen is the dominant or normal physiological stimulus to the muscle.