Development of the fetal pituitary‐testicular system based on observation of leydig cells in encephalectomized, hypophysectomized and control fetal rats

The time of onset of brain regulation of the pituitary-Leydig cell system in fetal rats was assessed by fetal encephalectomy, which allowed the pituitary to persist in situ. The effects of encephalectomy were compared with those of fetal hypophysectomy (surgical decapitation). The parameter for interpretation of these effects was the collective volume of Leydig cells, measured by the method of Chalkley ('43). The normal increase in the collective volume of Leydig cells in fetuses encephalectomized on day 17 of gestation and autopsied on day 18 was not retarded, whereas that in decapitated fetuses of the same age was retarded. In all other one-day experimental periods (day 18-19, 19-20, 20-21, and 21-22), the increase in volume was retarded to approximately the same extent in encephalectomized as in decapitated fetuses. The collective volume of Leydig cells continued to increase to some extent without the brain until day 20, after which it ceased to increase. The results suggest that in fetal rats, the brain control of the pituitary-Leydig cell system begins to operate from day 18 of gestation, when the day following overnight mating was designated as day 1 of gestation.