Hormonal studies of pituitary-testicular function in insulin-dependent diabetes mellitus were examined at rest and during moderate exercise to assess whether diabetes per se caused abnormalities of nocturnal penile tumescence and androgen function in men with normal sexual function. The present study compared 10 healthy men and eight men with Type I diabetes mellitus in whom normal sexual function was determined by clinical history. Urinary gonadotropin excretion, semen analysis and diurnal variation of serum glucose, prolactin, testosterone and free testosterone were determined in both groups. In addition, the serum levels of testosterone, free testosterone, prolactin, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were measured at rest, during 45 minutes of exercise on a bicycle ergometer at 50% of the subjects previously determined maximal oxygen uptake (VO2 max) and during a 30-minute recovery period. Nocturnal penile tumescence and parameters of semen analysis were similar in both groups. Urinary FSH excretion and serum FSH were higher (P less than or equal to 0.01) in the diabetic subjects while urinary LH excretion was similar. Diurnal variation of serum prolactin, testosterone and free testosterone were similar in both groups. Exercise produced a significant (P less than or equal to 0.01) increase in maximal free and total testosterone in both groups without changes in serum FSH or LH. Prolactin increased significantly (P less than or equal to 0.01) during exercise in the diabetic group only. We conclude that, for the most part, the pituitary-testicular axis and nocturnal penile tumescence under basal conditions and the pituitary-testicular axis during moderate exercise are similar in healthy males and insulin-dependent diabetic males with normal sexual function.
