The rate of conversion of testosterone- l, 2-3H to dihydrotestosterone-3H has been measured in a variety of tissues in rabbit embryos from 17 days of development to 3 days following birth and in rat embryos from 15 days of gestation to 4 days after delivery. In the rabbit embryo dihydrotestosterone formation was rapid only in the urogenital sinus and urogenital tubercle of both sexes at the earliest stages studied and was not measurable in wolffian and mullerian ducts until after gender identification was easily demonstrable. A similar pattern of development was observed in the rat embryo. These findings suggest that the capacity to form dihydrotestosterone in urogenital sinus and tubercle is not the result of androgen action but rather an inherent or obligatory property of the tissue and may fulfill in part the function of an initial androgen receptor in these organs. In contrast, in the mullerian and wolffian ducts the ability to form dihydrotestosterone appears to be acquired after the initial stages of differentiation are complete and may actually be the result of hormonal action.
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