Erectile dysfunction (ED), defined as the consistent or recurrent inability of a man to attain and/or maintain a penile erection sufficient for sexual activity. It is well recognized that the causes of ED are frequently multiple, with psychological, neurological, endocrinological, vascular, traumatic and iatrogenic components. In the present study we investigated on physiological and physiopathological mechanisms involved in erectile function. The Peyronie’s disease (PD, is characterized by an inflammatory response beneath the tunica albuginea with fibroblast proliferation forming a thickened fibrous plaque that may cause pain, penile curvature and ED. To date the PD is poorly understood mainly by the lack of an appropriate animal model. In the present study, we proposed a new animal model of spontaneous PD by using tight skin (Tsk) mice that present a mutation of fibrillin-1 gene associated with hypodermal fibrosis. The Tsk mice were followed up to 24 months of age and sacrificed at different ages in order to verify the time course of the development and progression of the disease. Gross anatomy of the Tsk mouse penis clearly showed fibrosis and bending of the penis that become more evident with age, reaching the maximum at 12 months. In addition, we demonstrated by molecular studies that Tsk mice displayed i) a gradual increase in synthesis and deposition of collagen of type I ii) an high level of TGFβ especially in the earlier stage of the disease iii) an increase of iNOS mRNA level during the development of the pathology. PD represents a particular condition associated with ED. However, ED is characterized by a lack of balance between vasorelaxant and vasoconstrictor factors. Thus, we investigated on urotensin II pathway (UII), an endogenous peptide previously described as an important vasoactive peptide, in erectile function by using human corpus cavernosum. Interestingly, we reported that i) UII receptor is expressed in rat and human corpus cavernosum (HCC) as protein and as well as mRNA and that it is localized on endothelial cells ii) HCC strips relaxed to UII in endothelium and nitric oxide (NO) dependent manner. Next, we evaluated the involvement of eNOS in UII-induced relaxation by using pharmacological inhibitors. Geldanamicin or wortmannin, Hsp 90 and Akt inhibitors respectively, abrogated UII induced relaxation. This latter result was also confirmed by western blot. Finally, the UII intracavernous administration in anaesthetized rats caused an increase of intracavernous pressure, thus penile erection. To date, the International Index of Erectile Function (IIEF) represents the primary endpoint in clinical studies on erectile dysfunction (ED). The IIEF demonstrates the sensitivity and specificity for detecting treatment-related changes in patients with ED. However, following the launch on the market of all three PDE5 inhibitors, clinical and practical studies have evidenced some limitations and/or variables related to the IIEF. Thus, the present study has been set to validate the measurement of platelet cGMP as possible effect measure of PDE5 inhibitors efficacy. 46 patients with ED were enrolled and were scheduled either on placebo or on vardenafil (5 mg/die bed time) for 6 weeks. All patients were asked to complete IIEF and SEP and were underwent to the rigiscan analysis as well as to donate blood samples, before starting the protocol and after 6 week of treatment. Washed platelet challenged with a nitric oxide donor were prepared, in order to measure cGMP in both groups of patients. Our data showed that platelet cGMP production was significantly increased in patients receiving vardenafil versus placebo. Vardenafil treatment caused an amelioration in IIEF-EF and SEP scores that was not significant compared with placebo group. Conversely, the rigiscan analysis revealed a marked amelioration only in Vardenafil group. The changes in platelet cGMP well correlated with rigiscan but not with IEEF-EF and SEP. The study clearly demonstrated that platelet cGMP can be a reliable measure of PDE5 inhibitors efficacy since it is not influenced by the placebo and it well correlates with the rigiscan clinical data. Thus, the measurement of platelet cGMP may represents an easy, not invasive, and objective biomarker of PDE5 inhibitors activity in ED management as well as in preference studies. In conclusion we proposed a naturally occurring model of PD contributing either to a better knowledge of the mechanisms involved or to asses new treatments. Then, we evidenced a novel pathway involved in human erectile function. Our results may help to unravel the complex mechanisms underlying the pathophysiology of human penile erection and may lead to the development of innovative therapeutic approaches in the treatment of ED. Finally, we suggested a relatively simple, reliable, and objective method to evaluate the PDE5 inhibitors efficacy in the ED management.
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