Valsartan reduced the vulnerability to atrial fibrillation by preventing action potential prolongation and conduction slowing in castrated male mice

Deficiency of testosterone was associated with the susceptibility of atrial fibrillation (AF). Angiotensin‐II (AngII) receptor antagonists were shown to reduce AF by improving atrial electrical remodeling. This study investigated the effects and mechanism of valsartan, an AngII receptor antagonist, on the susceptibility to AF with testosterone deficiency. Methods and Results: Five‐week‐old male ICR mice were castrated and valsartan was administered orally (50 mg/kg/d). High‐frequency electrical stimulation method was used to induce atrial arrhythmia. Patch‐clamp technique was used for recording action potential duration (APD), transient outward potassium current ( I to ), sustained outward potassium current ( I ksus ), and late sodium current ( I Na‐L ). Optical mapping technique was used to examine atrial conduction velocity (CV). The expression of connexin40 (Cx40) and Cx43 were detected by Western blot analysis. The occurrence rate of AF was significantly increased in castrated mice and APDs measured at 50% and 90% repolarization were markedly prolonged in castrated mice than controls, which were alleviated by the administration of valsartan. Valsartan suppressed the increase of I Na‐L and rescued the reduction of I to and I ksus in castrated mice. The left atrial CV in castrated mice was decreased and the expression of Cx43 reduced than controls, which were restored after valsartan treatment. Conclusions: Valsartan reduced the susceptibility of AF in castrated mice, which may be related to the inhibition of action potential prolongation and improvement of atrial conduction impairment. This study indicates that valsartan may represent a useful agent for the prevention of AF pathogenesis in elderly male patients.