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) & 14 eugonadal (EG)] and able-bodied (AB) men (27 HG & 11 EG) were studied. GnRH (10, 50, 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 100 μg resulted in the greatest integrated FSH response, and in the SCI-EG group, GnRH 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. CONCLUSION: Lower doses of GnRH did not improve the ability to identify clinical dysfunction of the hypothalamic-pituitary-gonadal axis. However, the absolutely higher SCI-HG FSH response to GnRH 100 μg and higher SCI-EG LH response to GnRH 50 μg, along with higher gonadotropin release at all GnRH doses, albeit not significant, suggests a hypothalamic-pituitary dysfunction in persons with SCI.