8-bromocyclic-gmp and Erectile-Dysfunction

INTRODUCTION.: Prevalence of erectile dysfunction (ED) increases progressively with aging, but the ED pathophysiology at its early stages is still poorly investigated. AIM.: This study aimed to evaluate the functional and molecular alterations of erectile function at middle age, focusing on the contribution of oxidative stress in erectile tissue for the ED. METHODS.: Young (3.5-month) and middle-aged (10-month) male Wistar rats were used. Rat corpus cavernosum (RCC) was dissected free and mounted in 10-mL organ baths containing Krebs solution. Intracavernosal pressure (ICP) in anesthetized rats was evaluated. MAIN OUTCOME MEASURES.: Concentration-response curves to endothelium-dependent and endothelium-independent agents, as well as to electrical field stimulation (EFS), were obtained in RCC strips. Measurement of cyclic guanosine monophosphate (cGMP) and expressions of neuronal nitric oxide synthase (nNOS) and endothelial NOS (eNOS), gp91(phox) and superoxide dismutase-1 (SOD-1) expressions in RCC were evaluated. RESULTS.: ICP was significantly reduced in middle-aged compared with young rats. RCC relaxations to acetylcholine (10(-8) to 10(-2)  M), sodium nitroprusside (10(-8) to 10(-2)  M), sildenafil (10(-9) to 10(-5)  M), BAY 41-2272 (10(-9) to 10(-5)  M), and EFS (4-32 Hz) were decreased in middle-aged group, which were nearly normalized by apocynin (NADPH oxidase inhibitor; 10(-4)  M) or SOD (75 U/mL). Prolonged treatment with apocynin (85 mg/rat/day, 4 weeks) also restored the impaired relaxations in middle-aged rats. Relaxations to 8-bromoguanosine 3',5'-cyclic monophosphate sodium salt (8-Br-cGMP; 10(-8) to 3 × 10(-4)  M) remained unchanged between groups. Basal and stimulated cGMP production were lower in middle-aged group, an effect fully restored by apocynin and SOD. Protein expression of nNOS and phosphorylated eNOS (p-eNOS) (Ser-1177) reduced, whereas gp(91phox) mRNA expression increased in RCC from middle-aged rats. CONCLUSIONS.: ED in middle-aged rats is associated with decreased NO bioavailability in erectile tissue due to upregulation of NADPH oxidase subunit gp91(phox) and downregulation of nNOS/p-eNOS. Antioxidant therapies may be a good pharmacological approach to prevent ED at its early stages.

Topics: Acetophenones; Acetylcholine; Aging; Animals; Blood Pressure; Cyclic GMP; Down-Regulation; Electric Stimulation; Endothelium, Vascular; Enzyme Inhibitors; Erectile Dysfunction; Free Radical Scavengers; Male; Membrane Glycoproteins; Muscle Relaxation; NADPH Oxidase 2; NADPH Oxidases; Nitric Oxide Synthase; Nitroprusside; Penile Erection; Phosphodiesterase 5 Inhibitors; Piperazines; Purines; Pyrazoles; Pyridines; Rats; RNA, Messenger; Sildenafil Citrate; Sulfones; Superoxide Dismutase; Superoxide Dismutase-1; Up-Regulation; Vasodilator Agents

A Rho-kinase inhibitor increases corpus cavernosum (CC) pressure in an in vivo rat model (Chitaley, K., Wingard, C. J., Webb, R. C., Branam, H., Stopper, V. S., Lewis, R. W., and Mills, T. M. (2001) Nat. Med. 7, 119-122) suggesting that Rho-mediated Ca(2+) sensitization of CC smooth muscle maintains the flaccid (contracted) state. We directly demonstrate Ca(2+) sensitization of permeabilized rabbit and human CC and identify a highly expressed molecular component of this pathway. Ca(2+) sensitization of force induced by endothelin or GTPgammaS was significantly greater in CC than in rabbit ileum smooth muscle and was accompanied by a 17-fold higher RhoA content. Pull-down assays with the RhoA binding domain of mDia showed the high RhoA content of CC to be available for activation by GTPgammaS. Ca(2+) sensitization induced by endothelin, phenylephrine, or GTPgammaS was completely relaxed by the Rho kinase inhibitor Y-27632. Human and rabbit CC both express the phosphatase inhibitor CPI-17, the myosin phosphatase regulatory (MYPT-1) and catalytic (PP1delta) subunits, and two isoforms of Rho kinase. We suggest that high expression of RhoA contributes, through RhoA-mediated Ca(2+) sensitization, to the flaccid state of CC that can be reversed by a water-soluble, orally active Rho kinase inhibitor suitable for therapy of erectile dysfunction.

Topics: Animals; Calcium; Cyclic GMP; Endothelins; Erectile Dysfunction; Guanosine 5'-O-(3-Thiotriphosphate); Humans; Male; Penile Erection; Rabbits; rhoA GTP-Binding Protein