Testosterone effects on luteinizing hormone and follicle-stimulating hormone responses to gonadotropin-releasing hormone in the mouse

Studies in the mouse have demonstrated for the first time in vivo regulatio n of gonadotropin-releasing hormone (GnRH) on the minute-to-minute dynamics of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release and the effects of testosterone on this regulation. Intact and castrated m ice with different testosterone revels (3-9 ng/mL) were challenged with exo genous GnRH while under general anesthesia to block endogenous GnRH release . Plasma concentrations of LH and FSH were determined by radioimmunoassay f rom sequential blood samples collected from anesthetized mice with in-dwell ing catheters. The release of LH was correlated with the infusion of differ ent doses of GnRH (0.35, 3.5, and 35 ng) in both intact and castrated mice (r = 0.942, similar to0.999). GnRH-stimulated LH release was significantly lower in intact mice and in castrated mice with high testosterone levels th an in castrated mice with low testosterone levels (P < .05). However, GnRH did not induce FSH release except in castrated males with low testosterone levels and at the highest dose of GnRH. The profiles of FSH release in inta ct mice and castrated mice with the highest testosterone levels were signif icant lower than the other groups (P < .05). In conclusion, release of LH, but not FSH, was correlated with increasing dosages of GnRH (r = 0.970), an d testosterone significantly suppressed GnRH-stimulated LH release in the m ouse (P < .05).