Quick release of FSH stimulated by repeated applications of synthetic luteinizing hormone-releasing hormone (LH-RH) in immature male rats.

Serum FSH and LH levels were estimated by radioimmunoassay following single subcutaneous administration, and repeated subcutaneous administration at various intervals in immature male rats. Single injection of LH-RH induced slight increase in FSH levels in comparison with considerable increase in LH. By two successive injections, the release of FSH was markedly stimulated when the time intervals were 15, 30, and 60 minutes,and rapidly elicited to release after the second injection. The greatest response was observed by two injections at 60 minutes interval. Moreover, the elevation of serum FSH level after the third injection was particularly remarkable, and the response was much stronger than that to the second injection. On the other hand, serum LH levels following the repeated injections were quite similar to that of FSH. And both FSH and LHwere linearly responded to doses of LH-RH repeatedly administered. These results indicated that the repeated quick administrations of LH-RH under appropriate intervals caused the acute high release of FSH, which was quite similar to LH release, and that these acute release of FSH and LH showed the dose-response relationship.