Potential effects of yohimbine and sildenafil on erectile dysfunction in rats

In this study the effects of yohimbine and sildenafil on cold stress-induced erectile dysfunction in rats were investigated. Yohimbine hydrochloride (0.2 mg/kg, i.p.) and sildenafil citrate (20 mg/kg, i.p) were administered to rats 1 h before the stress session daily for 14 consecutive days and their effect was assessed. Results of this section revealed that, immersion of rats in cold water significantly decreased sexual arousal and motivation as indicated by increased latencies and intervals. Furthermore decreased copulatory performance and potency as indicated by decreased ejaculation frequency was observed. Decreased copulatory activity was confirmed by decreased testosterone, luteinizing hormone (LH) and follicle-stimulating-hormone (FSH) levels as well as decreased cholesterol content in rat testes. Treatment with yohimbine or sildenafil significantly increased the sexual arousal and potency and corrected the effects induced by stress on the mating behavior of male rats. On the contrary they did not significantly alter testosterone, FSH and LH levels which is reflected by failure of both drugs to alter cholesterol content in rat testes. Regarding the effect of yohimbine and sildenafil on isolated rat corpus cavernosum, their cumulative dose response curves (3×10−7, 3×10−6 and 3×10−5 M) were determined in corpus cavernosum strips isolated from normal rats and pre-contracted with phenylephrine (3×10−6 M) were also assessed. Results of this part showed that both yohimbine and sildenafil have a relaxant effect on rat corpus cavernosum strips in a dose dependant manner, which is confirmed by the increase in nitric oxide content in rats' penis shown by sildenafil.