Age decreases nitric oxide synthase-containing nerve fibers in the rat penis

Purpose: To study the effect of aging on erectile function in a rat model. Materials and Methods: We investigated: 1) the number and distribution of nerve fibers within the corpus cavernosum and dorsal nerve containing vasoactive intestinal polypeptide (VIP) and nitric oxide synthase (NOS); and 2) the erectile response to apomorphine (a central dopamine receptor agonist), electrostimulation of the cavernous nerve, and intracorporeal papaverine injection. Results: The number of NOS-containing nerve fibers was significantly less in the old rats (24 months) than in the young (2.5 months) and intermediate (8.5 months)-aged (63.3 +/- 3.35 vs. 135.1 +/- 10.88 [p less than or equal to 0.0002] and 127.8 +/- 11.65 [p less than or equal to 0.0002]). The number of erections induced by apomorphine was significantly less in the old rats than in the young (1.0 +/- 3.1 vs. 3.6 +/- 0.26; p < 0.002). With electrostimulation, the latency period before the onset of the intracavernous pressure rise was noted to increase with age (2.3 +/- 0.24 sec. for the young vs. 6.77 +/- 0.98 sec. for the old, p less than or equal to 0.0001). The maximal intracavernous pressure after intracavernous papaverine injection decreased with age. Conclusion: The erectile mechanism appears to remain intact as rats age, but the response to central and peripheral stimulation decreases. The reduction in NOS-containing nerve fibers might account for these observations.