Experiments were then performed to examine the effect of pituitary transplants (2/rat, implantation on Day 21 of life) on sexual maturation. Balano-preputial skinfold cleavage occurred one week earlier in rats bearing pituitary grafts compared with sham operated rats. The advanced cleavage was associated with the advancement of the increase in testicular testosterone production at puberty.

To find out whether prolactin, secreted by pituitary transplants, would possibly be responsible for advancement of sexual maturation, experiments were performed to study the release of pituitary hormones during the initial period after transplantation; also studied was the effect on sexual maturation of pituitary transplants that were present only between the ages of 21-23 days and of the presence from Day 21 onward of pituitary transplants that had been in hosts prior to transplantation to deplete the glands of hormones. In both of these latter groups of rats, the skinfold cleavage occurred at a significantly earlier age than in sham operated animals, but the advancement was significantly less than when freshly obtained pituitary transplants had been present continuously from Day 21 onwards.

The results are consistent with a possible effect of prolactin to advance sexual maturation in male rats. However, the role of other pituitary hormones cannot be excluded. If the other hormones, secreted during the initial period after transplantation, establish premature sexual maturation, the time course of changes caused by these hormones on testicular maturation is greatly different from their effect on ovarian maturation in female rats: in the latter, exogenous hormones precipitate sexual maturation generally within a few days.