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High Loading and Low Maintenance Doses of a Gonadotropin-Releasing Hormone Antagonist Effectively Suppress Serum Luteinizing Hormone, Follicle-Stimulating Hormone, and Testosterone in Normal Men¹

Institute of Reproductive Medicine of the University (WHO Collaborating Center for Research in Human Reproduction) (H.M.B., S.K., G.P., E.N.), Münster; and Asta Medica (T.R.), Frankfurt am Main, Germany

Address all correspondence and requests for reprints to: Prof. Dr. E. Nieschlag, FRCP, Institute of Reproductive Medicine of the University, Domagkstrasse 11, D-48129 Münster, Germany.

The GnRH antagonist cetrorelix effectively suppresses serum LH, FSH, and testosterone (T) in normal men without major side-effects. However, as with other available GnRH antagonists, relatively high doses of 10 mg/day were required for sustained reduction of T levels during 1-week administration in normal men. Therefore, we investigated whether a suppression of LH, FSH, and T achieved by initial high dose cetrorelix can be maintained by continued low dose injections. Sixteen young male volunteers were randomly assigned to four study groups (n = 4/group). Twelve men were injected sc with 10 mg cetrorelix at 0800 h for 5 days, followed by injections of 2 mg/day (group I), 2 x 1 mg/day (group II), and 1 mg/day (group III) up to the end of the 3-week injection period. For the control, group IV was given daily placebo injections for 3 weeks. Morning and evening blood samples were obtained daily for 4 weeks and then at increasing time intervals up to week 13. Initial injections of 10 mg/day cetrorelix suppressed LH, FSH, and T effectively. This initial reduction of serum levels was maintained during the following low dose maintenance injections in all groups. In comparison to the initial suppression, significantly lower levels of LH, FSH, and T near the assay detection limits were measured during study weeks 2 and 3. The results show that compared to previous long term studies, much lower daily doses of the GnRH antagonist are sufficient for effective suppression of LH, FSH, and T after initial high loading dose injections. In addition to competitive receptor blockage, other mechanisms of GnRH antagonist action, such as receptor down-regulation, appear to be involved during long term administration in men.

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