BLUNTED GROWTH-HORMONE RESPONSE TO INTRAVENOUS ARGININE IN SUBJECTS WITH A SPINAL-CORD INJURY

The influence of the activities of daily living on human growth hormon e (hGH) release and plasma insulin-like growth factor (IGF-1) levels i s not known. Individuals with spinal cord injury (SCI) and paralysis g enerally have reduced levels of activity compared with ambulatory subj ects. We studied sixteen subjects with SCI and sixteen nonSCI subjects matched for age, gender and body mass index (BMI) as controls. After an intravenous infusion of arginine hydrochloride (30 g/subject over 3 0 minutes), mean plasma hGH values at 30 and 60 minutes were significa ntly lower in the group with SCI compared with the control group (3.4 +/- 0.7 versus 10.7 +/- 2.5 ng/ml, p<0.01; and 5.2 +/- 1.5 versus 12.5 +/- 2.7 ng/ml, p<0.05). Also, peak and sum hGH responses were signifi cantly lower in the group with SCI than in the control group (5.8 +/- 1.5 versus 14.1 +/- 2.8 ng/ml, p<0.01; and 15.2 +/- 3.1 versus 34.8 +/ - 7.2 ng/ml, p < 0.02). Controlling for age and BMI, the results remai ned significant. However, the mean plasma IGF-I level was significantl y lower in SCI subjects younger than 45 years old than in the similar subgroup of age-restricted controls (202 +/- 19 versus 324 +/- 27 ng/m l, p <0.05), whereas, a comparison of subgroups of subjects 45 years o r older did not reveal a significant difference. These findings suppor t the hypothesis that decreased daily physical activity results in dep ression of the hGH/IGF-I axis in younger individuals with SCI and may be considered to be a state of premature aging. The consequences of a relative hGH deficiency may contribute to the adverse body composition changes which accompany the paralysis and immobilization of SCI.