Hypothalamic control of the pituitary-testicular relation in fetal rats: measurement of collective volume of Leydig cells.

On the 20th day of gestation in pregnant rats, the male fetuses were subjected to surgical hypophysectomy by decapitation or to intracranial paraffin injection which compressed the fetal brain. Autopsy was done on the 22nd day of gestation. The collective volume of Leydig cells in the left fetal testis was estimated by Chalkley's method. Decapitation of a fetus caused a significant retardation in increase of the collective volume of Leydig cells 2 days later. In fetuses given an intracranial paraffin injection, the Leydig cell volume was increased significantly compared with normal fetuses on the 20th day of gestation but was far smaller than that in their intact littermates. This effect of paraffin compression was completely prevented by injections of LRH. The Leydig cell volume remained extremely small in decapitated fetuses given LRH. The observations suggest that in the male rat the hypothalamus begins to govern a pituitary gonadotropic function before birth.