Absolute or relative testosterone deficiency is associated with loss of lean body tissue and gain of fat, with associated adverse carbohydrate, lipid, and energy expenditure changes that increase the risk of cardiovascular disease. Impotence and infertility are common in patients with SCI. Of the many possible explanations of poor semen quality, one possible etiology is dysfunction of the hypothalamic-pituitary-testicular axis. Early reports have been inconclusive with regard to testicular function. These apparent discrepancies could, at least in part, be attributed to varying factors in population selection, including health and nutrition parameters, medication effects, and level and duration of injury, or to differences in methodology. Recently, two large population studies found a sizeable proportion of persons with SCI having testosterone deficiency. Huang et al. (1993) found significantly elevated luteinizing hormone (LH) responses to LH releasing hormone (LHRH) in subjects with SCI compared to controls. Of those studied with LHRH stimulation, 16/30 subjects with SCI had exaggerated LH responses and 6/30 had elevated follicular stimulation hormone (FSH) responses. Bulat et al., (1995) have shown that persons with tetraplegia tend to have increased gonadotropin release to standard provocative stimulation compared with able-bodied controls or those with paraplegia. In a preliminary report, testicular stimulation with standard doses of hCG for 2 days was similar in 10 subjects with SCI and 8 able-bodied controls.

Inclusion Criteria:

1. SCI with serum total testosterone 3.0 ng/ml (SCI eugonadal, n=25),
2. SCI with serum total testosterone <3.0 ng/ml (SCI hypogonadal, n=25),
3. able-bodied controls with serum total testosterone 3.0 ng/ml (control eugonadal, n=25), and
4. able-bodied controls with serum total testosterone <3.0 ng/ml (control hypogonadal, n=25). All SCI and control subjects will be screened for serum gonadotropin levels within the normal range as an inclusion criterion.

Exclusion Criteria:

1. acute illness,
2. active thyroid disease,
3. pyschotropic medications,
4. anti-hypertensive medications (centrally acting, i.e., guanethidine, reserpine, methyldopa, b-adrenergic blockers, clonidine, etc.),
5. H2-blockers,
6. digoxin,
7. alcoholism,
8. anti-convulsant medications (dilantin or barbiturates)
9. diuretics (thiazides or spironolactone),
10. chemotherapeutic agents,
11. antibiotics,
12. opiates,
13. hormones (other than replacement doses),
14. history of pituitary or testicular surgery. Abstinence from alcoholic beverages will be required for 48 hours prior to study.