Administration of increasing doses of gonadotropin-releasing hormone in men with spinal cord injury to investigate dysfunction of the hypothalamic-pituitary-gonadal axis.

STUDY DESIGN: Prospective. OBJECTIVES: To determine the optimum gonadotropin-releasing hormone (GnRH) dose to identify dysfunction of the hypothalamic-pituitary-gonadal axis in men with spinal cord injury (SCI). SETTING: Metropolitan Area Hospitals, New York and New Jersey, USA. METHODS: SCI men (16 hypogonadal (HG = serum testosterone <12.1 nmol/l) and 14 eugonadal (EG)) and able-bodied (AB) men (27 HG and 11 EG) were studied. GnRH (10, 50, and 100 µg) was randomly administered intravenously on three separate visits. Blood samples were collected post-GnRH for serum-luteinizing hormone (LH) and follicular-stimulating hormone (FSH). RESULTS: HG and EG men had a similar proportion of clinically acceptable gonadotropin responses to all three GnRH doses. The incremental gonadotropin responses to GnRH were not significantly different across the groups. However, in the SCI-HG group, GnRH of 100 µg resulted in the greatest integrated FSH response, and in the SCI-EG group, GnRH of 50 µg resulted in the greatest integrated LH response compared with the AB groups. A consistent, but not significant, absolute increase in gonadotropin release was observed in the SCI groups at all GnRH doses. CONCLUSIONS: Lower doses of GnRH did not improve the ability to identify the clinical dysfunction of the hypothalamic-pituitary-gonadal axis. However, the absolutely higher SCI-HG FSH response to GnRH of 100 µg and a higher SCI-EG LH response to GnRH of 50 µg, along with a higher gonadotropin release at all GnRH doses, albeit not significant, suggests a hypothalamic-pituitary dysfunction in persons with SCI.