International Journal of Impotence Research (2012) 24, 221 -- 227 & 2012 Macmillan Publishers Limited All rights reserved 0955-9930/12 www.nature.com/ijir ORIGINAL ARTICLE The effects of the combined use of a PDE5 inhibitor and medications for hypertension, lower urinary tract symptoms and dyslipidemia on corporal tissue tone JH Lee1,2, MR Chae1,2, JK Park1,3, JH Jeon1,4 and SW Lee1,2 ED is closely associated with its comorbidities (hypertension, dyslipidemia and lower urinary tract symptoms (LUTS)). Therefore, several drugs have been prescribed simultaneously with PDE5 inhibitors. If a specific medication for ED comorbidities has enhancing effects on PDE5 inhibitors, it offers alternative combination therapy in nonresponders to monotherapy with PDE5 inhibitors and allows clinicians to treat ED and its comorbidities simultaneously. To establish theoretical basis of choosing an appropriate medication for ED and concomitant disease, we examined the effects combining a PDE5 inhibitor with representative drugs for hypertension, dyslipidemia and LUTS on relaxing the corpus cavernosum of rabbits using the organ- bath technique. The effect of mirodenafil on relaxing phenylephrine-induced cavernosal contractions was significantly enhanced À4 À6 À6 À7 À9 by the presence of 10 M losartan, 10 M nifedipine, 10 M amlodipine, 10 M doxazosin and 10 M tamsulosin (Po0.05). The maximum relaxation effects were 47.2±3.8%, 57.6±2.6%, 64.0±3.7%, 76.1±5.7% and 71.7±5.4%, respectively. Enalapril and simvastatin had no enhancing effects. The relaxation induced by sodium nitroprusside alone (39.0±4.0%) was significantly À4 enhanced in the presence of the 10 M losartan (66.0±6.0%, Po0.05). Tetraethylammonium (1 mM) significantly inhibited the enhancement effects of tamsulosin and doxazosin on mirodenafil-induced relaxation (doxazosin: 76.1±5.7% vs 45.3±2.3%; tamsulosin: 71.7±5.4% vs 48.1±3.5%). On the basis of these findings, losartan seemed to induce synergistic effects through an interaction with nitric oxide. In addition, K þ channel activation could be one of the mechanisms for the synergistic effect of combining mirodenafil with doxazosin or tamsulosin. We believe that the combination of a PDE5 inhibitor with losartan, nifedipine, amlodipine, doxazosin or tamsulosin could be a pharmacologic strategy for simultaneously treating ED and its comorbidities and increasing response rates to PDE5 inhibitors. International Journal of Impotence Research (2012) 24, 221--227; doi:10.1038/ijir.2012.19; published online 5 July 2012 Keywords: comorbidity; ED; PDE5 inhibitor INTRODUCTION Considering the aforementioned investigational and clinical ED is a common condition, with a reported prevalence of 52% in reports, we hypothesized that combining a PDE5 inhibitor with men aged 40--70 years in the United States1 and 49% in men aged antihypertensive drugs, alpha-adrenergic blockers or hypolipi- 50--80 years in Europe.2 It can affect patients’ lives in different demic agents might relax the corpus cavernosum synergistically. ways, including disrupting interpersonal relationships, interfering There is little information available in the literature concerning with sexual life, causing problems with partners and increasing these issues. Therefore, we examined the effects of combining stress, all of which make ED a major quality of life issue.3 a PDE5 inhibitor with antihypertensive drugs, alpha-adrenergic ED has multifactorial causes and is associated with several blockers and hypolipidemic agents on the in vitro relaxation of the chronic diseases, such as hypertension4--7 dyslipidemia,8 and lower rabbit corpus cavernosum. urinary tract symptoms (LUTS).2,9--13 Therefore, several drugs have been prescribed simultaneously with PDE5 inhibitors in ED patients. Several investigational and clinical reports have sug- MATERIALS AND METHODS gested that some types of medication, including antihypertensive Corporal tissue strip preparation drugs, alpha-adrenergic blockers and hypolipidemic agents, can All animal experiments were conducted with the approval of the Institute help treat ED. In vitro studies examining alpha-adrenergic for Animal Care and Use Committee of the Samsung Medical Center (Seoul, blockers,14,15 calcium channel blockers16,17 and angiotensin-con- South Korea). Sexually mature male New Zealand white rabbits (2.2± verting enzyme inhibitors18 have shown direct relaxation or induced 0.3 kg) were killed with an air embolism in the ear vein. Each entire penis increased relaxation in response to electrical field stimulation was then surgically excised and cleaned by removing the corpus (EFS). Angiotensin receptor blockers have also been shown to spongiosum and urethra. The corporal tissue was subsequently carefully improve sexual function19--21 in clinical trials and have improved dissected from the surrounding tunica. Three to four corporal strips of endothelial function in hypercholesterolemic rats.22 approximately equal size (2 Â 2 Â 10 mm) were obtained from each penis 1Genitourinary Disease Oriented Translational Research, Seoul, Korea; 2Department of Urology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea; 3Department of Urology, Jeonbuk National University of Medicine, Jeonju, Korea and 4Department of Physiology, Seoul National University School of Medicine, Seoul, Korea. Correspondence: SW Lee, Department of Urology, Samsung Medical Center, Sungkyunkwan University School of Medicine #50 Ilwon-dong, Kangnam-ku, Seoul 135-710, Korea. E-mail: [email protected] Received 19 August 2011; revised 21 February 2012; accepted 20 April 2012; published online 5 July 2012 Use of PDE5 inhibitor on corporal tissue tone JH Lee et al 222 À5 À6 À7 À7 À6 and were separately prepared for organ-bath studies. Each corporal strip 10 M), amlodipine (10 or 10 M), nifedipine (10 or 10 M), doxazosin À7 À6 À10 À9 À6 was tied with silk in one organ chamber, with one end fixed to a tissue (10 or 10 M), tamsulosin (10 or 10 M) or simvastatin (10 or À5 À9 À5 holder and the other secured to a force transducer. The latter was 10 M). The relaxation effects of mirodenafil (10 to 10 M) were then connected to an appropriately calibrated four-channel polygraph (Power- studied on PE-induced precontracted cavernosal strips. Lab; ADInstruments, Sydney, NSW, Australia) in which the transducer In the second series of experiments, to ascertain whether the synergetic output was recorded. The corporal strips were kept in the organ baths with relaxation effects of alpha-adrenergic blockers and mirodenafil were Krebs solution maintained at 37 1C by a thermoregulated water circuit and mediated through K þ channel activation, we investigated the response of À5 by continuously bubbling with a mixture of 95% O2 and 5% CO2. Each mirodenafil (10 M) on PE-induced tone after incubating the tissue with À9 À6 corporal strip was stretched to an optimal isometric tension of 1.0 g and tamsulosin (10 M) or doxazosin (10 M) for 20 min. After three washes at À5 was equilibrated for 90 min. During the equilibration period, the tissues 10 min intervals, the relaxation effects of mirodenafil (10 M) were studied were washed with fresh Krebs solution every 30 min, and the tension was on PE-induced precontracted cavernosal strips of the corpus tissue þ adjusted if necessary. exposed in the organ bath to 1 mM tetraethylammonium (TEA), a K channel inhibitor, for 40 min. We then incubated the tissue with tamsulosin À9 À6 Organ-bath studies in vitro (10 M) or doxazosin (10 M) for 20 min. Finally, we compared the relaxa- For antihypertensive drugs, we used losartan, an angiotensin II receptor tion magnitude of pre- and post-TEA incubation. Lastly, the following experiment was conducted to confirm the direct antagonist that blocks the activation of angiotensin II AT1 receptors, and enalapril, which inhibits the angiotensin-converting enzyme, a component effect of losartan on the corpus cavernosum. Control tissue strips were precontracted with PE, and cumulative response curves were constructed of the blood pressure-regulating renin--angiotensin system. We also used À9 À5 for sodium nitroprusside (SNP) (10 to 10 M). The tissues were then nifedipine and amlodipine, which block the calcium channels in cardiac À5 muscle and blood vessels. For LUTS, we used doxazosin and tamsulosin. washed three times, followed by the addition of losartan (10 M) to the Tamsulosin is a selective a receptor antagonist that has preferential organ bath for 20 min. The tissues were recontracted with PE, and cumu- 1 lative response curves were again constructed for SNP. We then compared selectivity for the a1A and a1D receptors. Doxazosin is a non-selective a1 receptor antagonist. Simvastatin was used as a class of drugs to lower the the relaxation magnitude of pre- and post-losartan incubation. cholesterol levels by inhibiting the enzyme HMG-CoA reductase, which has a central role in the production of cholesterol in the liver. Lastly, mirodenafil was used for PDE5 inhibitor and the receptor selectivity of Solution and drugs 23 --1 mirodenafil is summarized in Table 1. The Krebs solution had the following composition: NaCl, 118 mM l ; --1 --1 --1 --1 In the first series of experiments, the following experiment was con- NaHCO3,25mM l ; glucose, 5.6 mM l ; KCl, 4.7 mM l ;KH2PO4, 1.2 mM l ; --1 --1 ducted to ascertain whether amlodipine, nifedipine, enalapril, doxazosin, MgSO47H2O, 1.17 mM l ; and CaCl2 2H2O, 2.5 mM l . Mirodenafil and tamsulosin or simvastatin enhanced mirodenafil-induced relaxation in the enalapril were provided by SK (Seoul,