Testosterone replacement therapy and sleep-related erections in hypogonadal men

Hypogonadal men usually have diminished libido and erectile dysfunction, and testosterone replacement therapy in these men increases sexual activity, erotic thoughts, and self-reported nocturnal erections. The polygraphic assessment of nocturnal penile tumescence (NPT) provides an objective index of erectile capability and is useful for differentiating psychogenic from organic erectile dysfunction. In this study we evaluated NPT in six hypogonadal adult men during and after termination of androgen therapy. Multinight sleep studies were conducted within 1 week and 7-8 weeks after each man received 20 mg testosterone cypionate, im. The mean serum testosterone level 4-7 days after testosterone injection was 35.9 +/- 3.4 (+/- SE) nmol/L, and it fell to 2.3 +/- 0.9 nmol/L after 7-8 weeks. Significant declines (P less than 0.05) in the number of NPT episodes (3.7 to 2.0), maximum penile circumference increase (24 to 13 mm), and total tumescence time (107 to 55 min) accompanied the fall in the serum testosterone level. No androgen-related changes in the amount or integrity of rapid eye movement sleep were found. Finally, the mean penile rigidity (buckling pressure) decreased from 770 +/- 98 to 590 +/- 81 g (P less than 0.05). Comparison of these results to those in normal men revealed that none of these men met all diagnostic criteria for organic impotence, even 7-8 weeks after discontinuation of testosterone administration. While men with androgen deficiency may have normal NPT, sleep-related erections increase in response to testosterone administration.