Simultaneous Changes in Tissue and Serum Levels of Luteinizing Hormone, Follicle-Stimulating Hormone, and Luteinizing Hormone/Follicle-Stimulating Hormone Releasing Factor after Castration in the Male Rat

The changes in hypothalamic and peripheral serum levels of LH/FSH releasing factor (RF) and pituitary and serum levels of LH and FSH were examined at systematic intervals from 1–60 days after gonadectomy in the adult male rat. On the basis of our results, it appears that the post-castrational changes in RF and LH can be divided empirically into two phases. Phase I is characterized by an immediate 15-fold rise in serum LH levels of castrates, relative to shams, which is detectable within 24 h after castration. During this phase, which lasted until the seventh post-castrational day, there were no significant differences in pituitary LH content or in serum or hypothalamic RF levels. At about the seventh day, Phase II seemed to begin and was characterized by an abrupt, marked rise in serum LH levels which reached a level 3 times that seen during Phase I by the 14th post-castrational day. Coincident with these increases in LH levels, pituitary LH increased by 3-fold and hypothalamic RF dropped to less than 50% of the shams. In vitro studies indicated that the response of the pituitary to synthetic LHRH could also be divided into two phases after castration. Before day 7, there were no differences between pituitaries from castrates or shams in terms of their release of LH in response to LHRH. After day 7 and during what we have termed Phase II of castration, the LHRH-induced release of LH from the pituitaries of castrates was markedly greater than that observed in the shams. Serum concentrations of FSH were significantly greater in castrates than shams by 24 h post-castration and continued to rise steadily until plateauing 30 days after castration. The pituitary FSH content of castrated rats did not change after 60 days of castration. It does not appear that the post-castrational changes in serum and pituitary levels of FSH occurred in two phases as observed for LH.