THE CHANGING RATIO OF SERUM BIOACTIVE TO IMMUNOREACTIVE FOLLICLE-STIMULATING HORMONE IN NORMAL MEN FOLLOWING TREATMENT WITH A POTENT GONADOTROPIN RELEASING HORMONE ANTAGONIST

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Abstract
Using a recently developed granulosa cell aromatase bioassy (GAB), we measured serum bioactive follicle-stimulating hormone (bio-FSH) levels in 5 normal men after administration of a potent GnRH antagonist. Although only minimal suppression of immunoreactive FSH (immuno-FSH) was detected during administration of 20 mg of the antagonist, ([N-Ac-D-Nal(2)1D-pCl-Phe2 D-Trp3D-h(Arg(Et2)6 D-Ala10]GnRH, pronounced inhibition (79 to89÷) of bio-FSH levels occurred. Concomitantly, the ratio of bio- to immuno-FSH levels dramatically decreased within 6 h after antagonist administration. These data reinforce earlier expectations that GnRH antagonists might be potential male contraceptives and provide the first report of changes in circulating bio- to immuno-FSH levels. The GAB assay will facilitate future studies on the biochemical mechanisms by which GnRH antagonists induce changes in the bioactivity of circulating FSH.