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 regulation 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 mice with different testosterone levels (3-9 ng/mL) were challenged with exogenous GnRH while under general anesthesia to block endogenous GnRH release. Plasma concentrations of LH and FSH were determined by radioimmunoassay from sequential blood samples collected from anesthetized mice with in-dwelling catheters. The release of LH was correlated with the infusion of different doses of GnRH (0.35, 3.5, and 35 ng) in both intact and castrated mice (r = 0.942, approximately 0.999). GnRH-stimulated LH release was significantly lower in intact mice and in castrated mice with high testosterone levels than 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 intact mice and castrated mice with the highest testosterone levels were significant 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), and testosterone significantly suppressed GnRH-stimulated LH release in the mouse (P < .05).