Purpose: Erectile dysfunction is a common problem in aging men. The molecular mechanisms associated with aging erectile dysfunction are not completely understood. We hypothesized that apoptosis is a downstream event in erectile dysfunction, and pro-apoptotic (Bak and Bax) and anti-apoptotic (Bcl-2 and Bcl-x) factors are involved in the etiology of aging erectile dysfunction. To test this hypothesis intracavernous pressure in aging rats was measured to assess erectile function. Gene and protein expression of pro-apoptotic and anti-apoptotic factors was then analyzed in aging rat crura to assess its role in aging erectile dysfunction.
Materials and methods: A total of 25 male Sprague-Dawley rats divided into 5 groups of 5 each based on age (6, 12, 18, 24 and 28 months old, respectively) were used in functional and apoptotic studies. In addition, 5, 3-month-old male Sprague-Dawley rats were used in the apoptotic study. The rats were anesthetized with pentobarbital. Erectile function was assessed by measuring intracavernous pressure after electrostimulation of the cavernous nerves. After completion of the functional study the penile crura were immediately harvested for histochemical and molecular studies. Gene expression of pro-apoptotic (Bak and Bax) and anti-apoptotic (Bcl-2 and Bcl-x) factors were then analyzed by reverse transcription-polymerase chain reaction. Protein expressions of these apoptotic factors were also analyzed by immunohistochemistry using specific antibodies.
Results: Mean intracavernous pressure plus or minus SD in 18, 24 and 28-month-old rats was significantly lower than in 6-month-old rats (101.6 +/- 24.8, 77.7 +/- 24.5 and 45.7 +/- 7.3 versus 136.7 +/- 11.4 cm. water, respectively; p <0.05). The reduction in intracavernous pressure was an age dependent phenomenon. Gene and protein expression of the pro-apoptotic genes Bak and Bax was detected in the crura of all age groups but there was no significant difference in young and old rat crura. The anti-apoptotic Bcl-2 and Bcl-x genes were expressed in 3, 6 and 12-month-old crura, whereas this expression was lost at 18, 24 and 28 months. Anti-apoptotic Bcl-2 and Bcl-x proteins were also expressed in young rat crura, whereas this expression was lost in old rat crura.
Conclusions: The decline in intracavernous pressure correlated significantly with a loss of anti-apoptotic genes in aging rat crura. To our knowledge this is the first report to show the loss of anti-apoptotic factors in aging rat crura and suggest their role in the pathogenesis of aging erectile dysfunction.