Abstract

The Role of Nitric Oxide Pathway in Cardiac Functional Inotropic Disorders and Portal hypertension in Cirrhotic Rats: An Approach to Minocycline

Introduction:
“Cirrhotic cardiomyopathy” is associated with abnormalities of heart structure and its function. The main clinical outcome of cirrhotic cardiomyopathy includes decrement of systolic contractility, altered diastolic relaxation in response to physiologic and pharmacological agents, and hyper dynamic state in cirrhotic patients. An increase in nitric oxide production has been reported in cirrhotic cardiomyopathy and, portal hypertension. Since minocycline has been shown to inhibit NO overproduction, we aimed to examine its role in a rat model of CCl4-induced cirrhotic cardiovascular complications. Portal pressure and inotropic responsiveness of isolated papillary muscles to isoproterenol were measured in cirrhotic rats, following minocycline (50 mg/kg/day for 8 weeks) treatment. Moreover, isolated papillary muscles were incubated with selective and nonselective NOS inhibitors, N (ω)-nitro-L-arginine methyl ester (L-NAME) and amino guanidine (AG) respectively, in an organ bath. Ventricular expression and localization of inducible NOS (iNOS), tumor necrosis factor-alpha (TNF-α) and serum nitrite concentration were evaluated. We found a decreased portal hypertension in minocycline-treated cirrhotic rats. Cirrhosis decreased contractility in response to isoproterenol stimulation, which was significantly attenuated by minocycline. Incubation with either L-NAME or AG reversed the impaired contractility in cirrhotic rats. Furthermore, minocycline decreased iNOS expression and localization in cardiomyocytes. A drop in serum nitrite and cardiac TNF-α level were also observed in cirrhotic rat that were treated by minocycline. The Results suggest that minocycline may improve impaired cardiac contractility and hyper dynamic state in cirrhotic rats, and this effect could be mediated by NO-dependent mechanism. Nitric oxide (NO) participates in the control of contractility and heart rate, limits cardiac remodeling after an infarction and contributes to the protective effect of ischemic pre- and postconditioning. Low concentrations of NO, with production of small amounts of cGMP, inhibit phosphodiesterase III, thus preventing the hydrolysis of cAMP. The subsequent activation of a protein-kinase A causes the opening of sarcolemmal voltage-operated and sarcoplasmic ryanodin receptor Ca(2+) channels, thus increasing myocardial contractility. A reduction of heart rate is an evident effect of NO-synthase (NOS) inhibition. It is noteworthy that the direct effect of NOS inhibition can be altered if baroreceptors are stimulated by increases in blood pressure. Finally, NO can limit the deleterious effects of cardiac remodeling after myocardial infarction possibly via the cGMP pathway. The protective effect of NO is mainly mediated by the guanylyl cyclase-cGMP pathway resulting in activation of PKG with opening of mitochondrial ATP-sensitive potassium channels and inhibition of the mitochondrial permeability transition pores. NO acting on heart is produced by vascular and endocardial endothelial NOS, as well as neuronal and inducible synthases. In particular, while in the basal control of contractility, endothelial synthase has a predominant role, the inducible isoform is mainly responsible for the cardiodepression in septic shock.


Author(s): Seyedeh Elaheh Mousavi*

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