Downloaded from http://journals.lww.com/cardiovascularpharm by BhDMf5ePHKbH4TTImqenVFqCQt94uE2AD8U7vwyaBvJJUYvtykJ2EIp2jotFaPIR on 12/08/2019 ORIGINAL ARTICLE Contrasting Effects of Inhibition of Phosphodiesterase 3 and 5 on Cardiac Function and Interstitial Fibrosis in Rats With Isoproterenol-Induced Cardiac Dysfunction Telma Mary Nakata, DVM, PhD, Kazuhiko Suzuki, DVM, PhD, Akiko Uemura, DVM, Kazumi Shimada, DVM, and Ryou Tanaka, DVM, PhD Abstract: Myocardial relaxation and stiffness are influenced by fibrillar collagen content. Cyclic nucleotide signaling regulators have been investigated targeting more effective modulation of collagen deposition during myocardial healing process. To assess the effects of phosphodiesterase type 3 and phosphodiesterase type 5 inhibitors on cardiac function and left ventricular myocardial fibrosis in catecholamine-induced myocardial injury, sildenafil and pimoben- dan were administered to male Wistar rats 24 hours after iso- proterenol injection. Echocardiography and electrocardiogram were performed to assess kinetic and rhythm changes during 45 days of drug administration. At the end of study, type I and type III collagen were measured through immunohistochemistry analysis, and left ventricular pressure was assessed through invasive method. Echo- cardiography assessment showed increased relative wall thickness at 45 days in pimobendan group with significant diastolic dysfunction and increased collagen I deposition compared with nontreated positive group (3.03 6 0.31 vs. 2.73 6 0.28%, P , 0.05). Diastolic pressure correlated positively with type I collagen (r = 0.54, P , 0.05). Type III collagen analysis did not demonstrate difference among the groups. Sildenafil administration attenuated type I colla- gen deposition (2.15 6 0.51 vs. positive group, P , 0.05) and suggested to be related to arrhythmic events. Arrhythmic events were not related to the quantity of fibrillar collagen deposition. Although negative modulation of collagen synthesis through cyclic nucleotides signaling have shown promising results, in this study, pimobendan postconditioning resulted in increased collagen type I formation and severe diastolic dysfunction while sildenafil postconditioning reduced collagen type I deposition and attenuated diastolic dysfunction. Key Words: myocardial stiffness, cardiac remodeling, fibrosis reg- ulation, arrhythmic substrate (J Cardiovasc Pharmacol Ô 2019;73:195–205) INTRODUCTION The myofibroblast formation and continued deposition of extracellular matrix (ECM) components within the border and remote segments of injured myocardium alter systolic and diastolic functions due to close relationship of ECM structural characteristics and myocardial function integrity. 1 Studies have suggested that the predominant collagen types in the ECM are type I providing myocardial tensile strength or stiff- ness, and type III, providing elasticity and structural integrity, even so the relative contribution of each component of ECM needs yet to be defined. 2 Although the response to a myocar- dial insult (eg, exogenous catecholamines and ischemia) is characterized histologically by increased collagen deposition, kinetically it may be represented by altered ventricular contraction–relaxation coupling. 2–4 The conventional therapeutic approach to improve postmyocardial ischemic cardiac dysfunction, although re- duces adverse remodeling, it does not regulate directly the myofibroblast activity. 5 Alternatively, modulators of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signals in cardiac hypertrophic and fibrotic diseases have been investigated. 3,6–9 Studies showed that sildenafil, a cGMP-specific phosphodiesterase type 5A inhibitor, blunted cardiac hypertrophy and remodeling in dif- ferent animal models. 8–10 However, conflicting results were observed in subsequent investigations of sildenafil effects on angiotensin II–induced fibrosis. 11,12 Previous studies dem- onstrated that increased intracellular levels of cAMP may inhibit fibroblast transformation and collagen synthesis. 6 Therefore, inhibition of cAMP hydrolysis by administration of a cAMP-specific phosphodiesterase inhibitor suggested a rationale for strategic pharmacological approach to reduce ECM collagen deposition. 13 Pimobendan, a calcium- sensitizing drug, which also has cAMP-specific phosphodi- esterase type 3 inhibitor (PDE3i) activity, has been used in patients with acute and end-stage heart failure (HF) refractory to conventional therapy for providing inotropic and lusitropic support without increase intracellular calcium concentration and myocardial oxygen consumption. 14–18 In a previous investigation, pimobendan administration provided blockage of myocardial fibrosis formation in mice with compensated Received for publication July 26, 2018; accepted December 18, 2018. From the Faculty of Veterinary Medicine, Tokyo University of Agricul- ture and Technology (TUAT), Tokyo, Japan. The authors report no conflicts of interest. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal’s Web site (www.jcvp.org). Experimental ethics: All institutional and national guidelines for the care and use of laboratory animals were followed. Institutional Animal Care and Use Committee of the Tokyo University of Agriculture and Technology approval 28–71. Reprints: Telma Mary Nakata, DVM, PhD, Department of Veterinary Surgery, Tokyo University of Agriculture and Technology (TUAT), 3-8-1 Harumi-cho, Fuchu, Tokyo, 183-8538 Japan (e-mail: nakatamary@ gmail.com). Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved. J Cardiovasc Pharmacol ä  Volume 73, Number 3, March 2019 www.jcvp.org | 195 Copyright © 2019 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.