Provocative stimulation of the hypothalamic–pituitary–testicular axis in men with spinal cord injury

Abstract

The pituitary response to stimulation in healthy men with SCI revealed an augmented FSH response; LH response only trended higher. The testicular response to provocative stimulation was similar in hypogonadal and eugondal subjects and in GnRH responders and non-responders. These findings suggest a lack of hypothalamic drive of pituitary gonadotropin release in healthy people with chronic SCI.

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

“…In a prior study, about 75% of the participants in the SCI group, and a similar percent in the AB group, had a clinically acceptable gonadotropin response to standard provocative GnRH pituitary stimulation (“responders”). 18 Of note, the SCI responder group had a significantly increased FSH release at several time points compared to the AB responder group; the average and integrated LH release in the SCI responder group approached significance compared with that of the AB-responder group. 18 Because serum T responses to standard hCG stimulation testing was not significantly different for able-bodied or SCI men, regardless of gonadal status, it was suggested that the preponderance of hypogonadism identified in men with SCI is probably associated with hypothalamic-pituitary dysfunction, and not end-organ failure.…”

“…Our group reported that the hypothalamic-pituitary-gonadal axis is generally intact when evaluated by standard challenge testing in persons with spinal cord injury (SCI); albeit, the absolute gonadotropin response to GnRH 100 μg was higher in persons with SCI who were classified as “responders” (i.e., adequate response by conventional clinical criteria) to provocative pituitary stimulation compared to healthy able-bodied controls who were classified as “responders”. 18 The testicular response to a conventional dose of human chorionic gonadotropin (hCG; 4000 IU) or with lower doses of hCG (400 and 1000) in those with SCI was generally appropriate, regardless of whether the participants had low or normal serum testosterone levels. 18 , 19 Of note, whether an individual with SCI was hypogonadal or eugonadal was not predictive of whether the person would respond with an appropriate clinical response to the standard stimulation dose of hCG.…”

“… 18 The testicular response to a conventional dose of human chorionic gonadotropin (hCG; 4000 IU) or with lower doses of hCG (400 and 1000) in those with SCI was generally appropriate, regardless of whether the participants had low or normal serum testosterone levels. 18 , 19 Of note, whether an individual with SCI was hypogonadal or eugonadal was not predictive of whether the person would respond with an appropriate clinical response to the standard stimulation dose of hCG. The authors speculated that because peripheral stimulation to hCG was essentially normal in those with SCI that a more subtle central problem due to insufficient hypothalamic drive to gonadotropin release should be considered.…”

Dynamic GnRH and hCG testing: establishment of new diagnostic reference levels

“…As mentioned in the results, the FSH levels correlated with the LH levels, and the decrease was not associated with their testis size, semen quality or genotypes. However, it is well known that the FSH response is much smaller than the LH response after GnRH stimulation (3,8,24).…”

“…Dynamic testing of the HPG axis may facilitate the diagnostic process of testosterone deficiency. The capacity of the pituitary gland for gonadotropin secretion can be assessed by the GnRH test, whereas the capacity of the Leydig cells in the testicles to produce T can be assessed by the human chorionic gonadotropin (hCG) test (1,2,3,4,5,6,7,8).…”