Cardiac chronotropic hypo-responsiveness and atrial fibrosis in rats chronically treated with lithium.

Lithium is a widely used mood-stabilizing agent; however, it causes a variety of cardiovascular side effects including sinus node dysfunction. In this study we explored the potential adverse effects of lithium on cardiac chronotropic responsiveness, atrial tissue histology and gene expression in rats that were chronically treated with therapeutic doses of lithium. Male Wistar albino rats were given lithium chloride (2.5 g/kg) orally for 2 or 3 months. Following treatment, the atria were isolated and spontaneously beating rate and chronotropic responsiveness to ß-adrenergic stimulation was evaluated in an organ bath. Development of cardiac fibrosis was examined by histological methods. The expression of atrial Col1a1 (collagen I, alpha 1) and ß-arrestin2 was also assessed using quantitative RT-PCR. Treatment with lithium induced a significant hypo-responsiveness to adrenergic stimulation (P < 0.001) and caused fibrosis in the atrial tissue of treated rats. In addition, the expression of atrial Col1a1 mRNA was significantly increased in atrial tissues of lithium-treated animals, while ß-arrestin2 mRNA expression did not show a significant difference compared with control animals. Altogether, these findings indicate that cardiac chronotropic hypo responsiveness and associated cardiac fibrosis are side effects of chronic lithium treatment. Moreover, it seems that lithium treatment does not influence ß-arrestin2 mRNA expression.

Evaluation of Chronic Losartan Treatment Effect on Cardiac Chronotropic Dysfunction in Biliary Cirrhotic Rats.

Cirrhosis is associated with cardiac chronotropic and inotropic dysfunction which is known as cirrhotic cardiomyopathy. Cardiac responsiveness to adrenergic stimulation is impaired in cirrhosis. Moreover, there is vagal nerve dysfunction which is related to neuromodulatory dysfunction of the angiotensin II in the cirrhosis. This study was aimed to explore the hypothesis that administration of Losartan-angiotensin II receptor antagonist increases cardiac chronotropic response to isoproterenol in cirrhotic rats; and if so, whether this is associated with altered cardiac TGF-ß receptor expression. Cirrhosis was induced by surgical ligation of the bile duct (BDL) in male Wister rats. Half of the BDL-group and control group were treated with losartan for four weeks. Four weeks after bile duct ligation or sham surgery the atria were isolated and spontaneously beating rate and chronotropic responsiveness to ß-adrenergic stimulation was assessed using standard organ bath. The pathological assessment was done on the atria. Moreover, the expression of TGF-ß has assessed the atria using quantitative RT-PCR. Bile duct ligation could induce a significant hypo-responsiveness to adrenergic stimulation. In cirrhotic rats, the chronotropic responses increased after chronic treatment with losartan, but it was not significant. The pathological study showed that losartan could not decrease fibrosis in atria in losartan treated cirrhotic group. TGF-ß expression is markedly increased in cirrhotic rats which are significantly decreased in atria following administration of losartan. These results might be considered as angiotensin II role in cirrhotic cardiomyopathy, but further studies are required to elaborate the mechanism as well as the possible advantage of losartan. We conclude that cirrhosis in rats is associated with altered expression of TGF-ß in the atrium which losartan can ameliorate it.