Impaired hypothalamus-pituitary-adrenal axis in men with spinal cord injuries

Twenty-five men with spinal cord injuries were studied for evaluation of the hypothalamus-pituitary-adrenal axis, using corticotropin-releasing hormone and insulin-induced hypoglycemia. Twenty-five age-matched healthy male volunteers served as controls. Three spinal cord-injured subjects had hyperprolactinemia, three had elevated basal follicle-stimulating hormone levels, one had an elevated basal luteinizing hormone level, and four had hypotestosteronemia. The mean plasma adrenocorticotropin response to corticotropin-releasing hormone of spinal cord-injured subjects was smaller than that of the healthy controls but did not reach a statistical significance. The cortisol response to corticotropin-releasing hormone of the spinal cord-injured subjects was significantly lower than that of healthy controls. However, the difference disappeared if a correction was made for baseline values. Six spinal cord-injured subjects did not have a cortisol response to insulin-induced hypoglycemia, and they had either a minimal or no adrenocorticotropin response. Another 11 spinal cord-injured subjects had a maximal cortisol response to insulin-induced hypoglycemia below the lowest limit of normal, i.e., 0.5 micromol/l. Among these spinal cord-injured subjects, three had a less than 50% increase of plasma adrenocorticotropin after insulin-induced hypoglycemia. These findings are consistent with the notion that spinal cord-injured subjects have an altered central neurotransmitter tone and substantiate the hypothesis that an afferent neural pathway exists between the adrenal and hypothalamus and may modulate stress-induced secretion of adrenocorticotropin. Long-term abnormal adrenocorticotropin secretion may cause mild adrenocortical atrophy and, thereby, a reduced cortisol response.