Vardenafil enhances clitoral and vaginal blood flow responses to pelvic nerve stimulation in female dogs.

The relaxation of the smooth muscle in the vagina and clitoris and the increase of blood flow into these organs is thought to be essential in the female sexual response. Vardenafil is a type 5 phosphodiesterase (PDE5) inhibitor that potentiates the nitric oxide (NO)/cGMP pathway facilitating penile smooth muscle relaxation and improving penile erection in men. Although the potentiation of the NO/cGMP pathway through PDE5 inhibitors can clearly enhance blood flow into the penis and is used in the therapy of male sexual dysfunction, there is controversy about the efficacy of these agents in improving female sexual function. The aim of this work was to evaluate the effects of vardenafil on the increase of blood flow into the vagina and clitoris induced by pelvic nerve electrical stimulation (PNES) in a female dog model. Application of PNES produced consistent and frequency-related increased blood flow into the vagina and clitoris of anesthetized female dogs. The magnitude and duration of the blood flow responses to PNES were variable among the different animals but remained stable over time within the same animal. The intravenous administration of vardenafil (1 mg/kg) significantly potentiated the increases in blood flow produced by PNES into the vagina (381.4 and 206.2% of control response at 5 and 10 Hz, respectively, P<0.01, n=6) and clitoris (379.4 and 238.5% of control response at 5 and 10 Hz, respectively, P<0.01, n=6) 20 min after administration. The significant enhancement of PNES-induced responses was maintained 50 min (224.5 and 181.0%, P<0.01 in vagina; 294.8 and 258.9%, P<0.05 in clitoris) and 80 min after vardenafil administration (209.5 and 156.9%, P<0.05 in vagina; 268.9 and 194.9%, P<0.05 in clitoris). Here we present a feasible model for research into female sexual function. Our results show that vardenafil effectively potentiates the blood flow responses to PNES in the genitalia of female dogs. These results emphasize the role of the NO/cGMP pathway in the local vasodilatory response in female sexual organs and provide a rationale for testing PDE5 inhibitors, such as vardenafil, as a treatment for certain forms of female sexual dysfunction.