Serum testosterone and growth hormone/insulin-like growth factor-I in adults with spinal cord injury

Aging is associated with relative growth hormone and/or testosterone (T) hormone deficiency, and those with SCI may have a premature deficiency of these two hormones. The effects of SCI, duration of injury (DOI), and advancing age with that of human growth hormone (hGH) and insulin-like growth factor I (IGF-I), as well as potential associations between them, were studied. Data were obtained from 20 male subjects with SCI and 16 gender- and age-matched controls. Serum total and free T were lower in subjects with SCI compared with controls (mean ± SEM, 3.12 ± 0.29 versus 4.68 ± 0.28 ng/ml, p < 0.001 and 1.89 ± 0.18 versus 2.46 ± 0.22 ng/ml, p < 0.05, respectively). Nine of the 20 subjects with SCI, but none of the controls, had abnormally low serum total T. Arginine-stimulated values for hGH were lower in the group with SCI compared with controls (198 ± 18 versus 267 ± 27 ng/ml, p < 0.05). Serum luteinizing hormone and follicular stimulating hormone, as well as body mass index, were not significantly different between the groups. Serum total and free T were correlated with advancing age in controls (r = 0.62, p < 0.01 and r = 0.51, < 0.05, respectively) but not in SCI (r = 0.19, p > 0.43 and r = 0.39, p = 0.09). However, serum total and free T declined with increasing DOI in SCI (r = 0.56, p < 0.01 and r = 0.44, p = 0.05, respectively). Serum IGF-I appeared to decline with advancing age in SCI (r = 0.51, p 0.02), but the decrease in serum IGF-I with age was stronger in controls (r = 0.77, p = 0.0005). In the total group, age had no significant effect on hGH, but age did have a significant effect on serum total T (r = 0.40, p = 0.02). The multiple regression of peak hGH response given age on serum total T was significant (R = 0.51, p < 0.01); peak hGH had an independent effect over and above age on serum total T (partial r = 0.38, p < 0.05). A nonlinear relationship was found between serum free T and IGF-I (r = 0.61, p = 0.02), where serum free T appears to plateau when serum IGF-I is equal to or greater than 250 ng/ml. In controls, a nonsignificant relationship could be demonstrated between serum total T and IGF-I (r = 0.48, p = 0.06). Our findings suggest that SCI is associated with impaired secretion of both T and hGH, which is not the result of advancing age per se. DOI appears to have an adverse effect on serum T, a finding compatible with the hypothesis that those with SCI have a condition which predisposes to age-related changes.