After crossing into smooth muscle cells, NO reacts with guanylate cyclase to catalyze the conversion of guanosine triphosphate (GTP) to guanosine monophosphate (GMP). The lack of free oxygen, transported to the penis by oxygenated hemoglobin, is theoretically detrimental to the synthesis of NO and cyclic guanosine monophosphate (cGMP) formation. Poor oxygenation Inhibitors,research,lifescience,medical prevents

the synthesis of cGMP and predisposes to cavernous fibrosis due to increased synthesis of collagen via transforming growth factor beta (TGF-β), with resulting ED. The induction of collagen is related to decreased corporal oxygenation or hypoxia. Cavernous neurotomy was demonstrated to produce hypoxia and fibrosis in rat corpus cavernosum.8 In this study, ablation of cavernous nerves bilaterally was associated with increased TGF-β1 Inhibitors,research,lifescience,medical mRNA expression and hypoxiainducible factor 1 α, TGF-β1, and collagen I and III protein expression. It was theorized that agents that decrease corporal hypoxia might improve erectile function after RP. Treatment of human corpus cavernosum

smooth muscle cells with TGF-β1 increased collagen synthesis9; this increase in collagen was attenuated by simultaneous administration of prostaglandin E1 (PGE1). In addition, PGE1 suppressed TGF-β1 induction of TGF-β1 mRNA. Kim and colleagues10,11 showed that isolated human and rabbit corpus cavernosum tissue strips exposed to arterial-like PO2 relaxed with acetylcholine Inhibitors,research,lifescience,medical and with electrical stimulation of the autonomic dilator nerves. Decreasing PO2 to levels measured in Inhibitors,research,lifescience,medical the flaccid penis resulted in loss of the relaxation response. Normoxic conditions readily restored endothelium-dependent and neurogenic relaxation. In the rabbit corpus cavernosum, low PO2 reduced basal levels of cGMP and prevented cGMP accumulation induced by stimulation of dilator nerves. Furthermore, low PO2 inhibited nitric oxide synthase activity in corpus cavernosum cytosol. The investigators concluded that physiological concentrations of oxygen modulate penile erection by regulating

Inhibitors,research,lifescience,medical NO synthesis in corpus cavernosum tissue. Limited invasive blood gas studies in human models have shown decreased oxygen tension in vasculogenic impotence and a hypoxic cavernosal state in the flaccid penis. Corporal and penile flaccid oximetry was examined in a comparative study of 101 men (22 potent, 26 non-RP ED, and 53 RP ED).12 Although there was Dichloromethane dehalogenase no significant difference in StO2 among ED patients, RP ED patients had significantly lower corporal StO2 than potent patients. Histomorphological studies in men suggest there are changes in cavernous smooth muscle and collagen content after RP.13 As soon as 2 months after surgery, trabecular elastic fibers and smooth muscle fibers were decreased, and collagen content was increased, in the corpora Nutlin-3a in vivo cavernosa compared with presurgical levels; these changes were exacerbated after 1 year. This fibrosis appears to be due to denervation and/or ischemia.