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 < or = 0.0002] and 127.8 +/- 11.65 [p < or = 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 < or = 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.