Decreased trabecular smooth muscle and caveolin-1 expression in the peniletissue of aged rats

Purpose: Because decreased trabecular smooth muscle content is reportedly a ssociated with vasculogenic impotence in men, we performed a rodent study t o investigate the effect of aging on trabecular smooth muscle content and c aveolin-1 protein expression in penile smooth muscle cells. Materials and Methods: In 6 young (age 3 months) and 6 old (age 24 months) rats erectile function was evaluated by cavernous nerve stimulation. At sac rifice penile tissue samples were collected for Western blot analysis, Mass on's trichrome staining, caveolin-1 immunostaining and electron microscopy. The percent of smooth muscle in the trabecular tissue was assessed by comp uter assisted image analysis. Results: In the aged rats mean intracavernous pressure plus or minus standa rd deviation was decreased (70 +/- 8.8 versus 107 +/- 12.3 cm, water) and t he latency period was increased (7.8 +/- 1.2 versus 4.5 +/- 0.5 seconds) si gnificantly compared to values in the young rats (p <0.001). The mean ratio of trabecular smooth muscle-to-connective tissue was also significantly al tered in old versus young rats (27% +/- 2.9% versus 42.1% +/- 5.1%, p <0.00 1). Immunostaining for caveolin-1 was noted in each group in the sarcolemma of smooth muscle cells and endothelium of trabecular sinusoids but the sta ining pattern was less intense and the percent of smooth muscle positive fo r caveolin-1 was decreased in aged versus young rats (17.9% +/- 2.5% versus 27.5% +/- 3.6%, p <0.001). Moreover, young trabecular smooth muscle cells had more caveolae in the sarcolemma on electron microscopy and a higher exp ression of caveolin-1 protein on Western blot analysis. In contrast, higher endothelial nitric oxide synthase protein expression was noted in the peni le tissue of old rats. Conclusions: In these aged rats the decreased ratio of trabecular smooth mu scle-to-collagen and the reduced expression of caveolin-1 may contribute to erectile dysfunction.