Erectile function in two-kidney, one-clip hypertensive rats is maintained by a potential increase in nitric oxide production

Animal models of erectile dysfunction

Erectile dysfunction (ED) is a prevalent male sexual dysfunction with profound adverse effects on the physical and the psychosocial health of men and, subsequently, on their partners. The expanded use of various types of rodent models has produced some advances in the study of ED, and neurophysiological studies using various animal models have provided important insights into human sexual dysfunction. At present, animal models play a key role in exploring and screening novel drugs designed to treat ED.

Limited effect of testosterone treatment for erectile dysfunction caused by high-estrogen levels in rats

Some studies suggest that high-estrogen levels lead to erectile dysfunction (ED); high-estrogen levels are known to decrease testosterone levels. However, no study has examined whether testosterone replacement can improve the ED induced by high-estrogen levels. We investigated the effects of testosterone on ED caused by high-estrogen levels in rats. Rats were distributed in the following groups: (1) control (vehicle for 2 weeks), (2) the estrogen-treated group (ES; estradiol (3 μg kg(-1) day(-1)) for 2 weeks), and (3) the estrogen- and testosterone-treated group (ES+TE; estradiol (3 μg kg(-1) day(-1)) and testosterone (3 mg kg(-1) day(-1)) for 2 weeks). We measured smooth muscle function via isometric tension and erectile function by measuring the intracavernosal pressure on cavernous nerve stimulation. In the ES group, the contraction of the corpus cavernosum smooth muscle increased in response to noradrenalin, and its relaxation decreased in response to the nitric oxide donor, sodium nitroprusside. Further, the erectile function was significantly decreased. In the ES+TE group, neither smooth muscle function nor erectile function was significantly improved. In conclusion, a high-estrogen milieu affected erectile function in rats, and testosterone treatment did not improve the ED caused by high-estrogen levels.

Long-term oral treatment with BAY 41-2272 ameliorates impaired corpus cavernosum relaxations in a nitric oxide-deficient rat model

OBJECTIVE

• To investigate the potential beneficial effects of 4-week oral treatment with 5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1Hpyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine (BAY 41-2272), a nitric oxide (NO)-independent soluble guanylate cyclase activator, on impaired rat corpus cavernosum relaxations in NO-deficient rats.

MATERIAL AND METHODS

• Male Wistar rats were divided into four groups: Control, N (G)-nitro-L- arginine methyl ester (L-NAME; 20 mg/rat/day), BAY 41-2272 (20 mg/kg/day) and L-NAME + BAY 41-2272. • Rats were treated with L-NAME concomitantly with BAY 41-2272 for 4 weeks. • Concentration-response curves to acetylcholine (ACh) and sodium nitroprusside (SNP), along with the nitrergic relaxations (1-32 Hz) were obtained in rat corpus cavernosum (RaCC). • The RaCC contractile responses to the α₁ -adrenoceptor agonist phenylephrine (PE) were obtained.

RESULTS

• Acetylcholine (0.01-1000 µmol/L) produced concentration-dependent relaxing responses in RaCC that were significantly enhanced (P < 0.05) in BAY 41-2272-treated rats. • The ACh-induced relaxations were largely reduced in L-NAME-treated rats, and co-treatment with BAY 41-2272 failed to significantly modify these impaired relaxations. • The SNP-induced relaxations were modified neither by L-NAME nor by co-treatment with BAY 41-2272. • The nitrergic relaxations were significantly amplified in BAY 41-2272-treated rats (at 16 and 32 Hz). A significant reduction in the nitrergic relaxations was observed in L-NAME-treated rats, an effect largely restored by co-treatment with BAY 41-2272. • The contractile RaCC responses produced by PE (0.001-100 µmol/L) were significantly higher (P < 0.05) in L-NAME-treated rats, and co-treatment of L-NAME with BAY 41-2272 nearly restored these enhanced contractile responses.

CONCLUSION

• Four-week therapy with BAY 41-2272 prevents the impaired corpus cavernosum relaxations of rats treated chronically with L-NAME, indicating that accumulation of cyclic guanosine monophosphate into erectile tissue counteracts the NO deficiency.