Effect of passive immunization to gonadotropin-releasing hormone (GnRH) using GnRH antiserum on the mitotic activity of gonadotrophs in castrated male rats.

In order to reveal the mechanism of elevation in the mitotic activity of gonadotrophs in the pituitary gland of castrated rats, passive immunization to GnRH designed to block the activity of GnRH in castrates was performed, and changes in the mitotic activity of pituitary gonadotrophs and mammotrophs were studied. The increased serum levels of gonadotropins and their subunits in castrates were dramatically suppressed by the administration of rabbit anti-GnRH serum (RAGnRH). However, this treatment had no effect on the serum levels of PRL, suggesting that the passive immunization to GnRH used in this study was only effective in blocking the hormonal activity of GnRH to the gonadotropin secretion. Mitosis of the gonadotrophs in normal rat anterior pituitary was rarely observed, but it was dramatically increased by castration. This elevated mitotic activity of gonadotrophs in the castrated rats was significantly suppressed by the administration of RAGnRH. On the other hand, mitotic activity of mammotrophs was decreased by castration. This diminution in the mitotic activity of mammotrophs was not changed by administration of RAGnRH. These results showed that GnRH is an important factor for stimulation of gonadotroph cell proliferation in castrated rats.