Effects of Aging and Hypertension on the Antithrombotic Function of Atrial Endocardium in Rats

We have previously reported that atrial endocardial remodeling is induced by atrial fibrillation (AF), and the endocardial dysfunction may be partly responsible for the thrombus formation in the left atrium associated with AF. However, the relationship between the endocardial dysfunction and the epidemiologically determined risk factors of AF-related strokes, including aging, hypertension, and diabetes mellitus, is yet to be elucidated.To test the hypothesis that aging, hypertension, and diabetes mellitus individually impair the atrial endocardial function in conjunction with AF, we have analyzed the expression of the tissue factor pathway inhibitor (TFPI) and thrombomodulin (TM) in the atrial endocardium in 30-week-old Wister-Kyoto (WKY), 60-week-old WKY, 30-week-old spontaneously hypertensive rats (SHR), and 30-week Goto-Kakizaki (GK) rats during normal sinus rhythm and after rapid atrial pacing at 1200 bpm for 8 hours, using Western blotting and immunohistochemical analysis. Even during sinus rhythm, the TFPI and TM expressions were noted to be remarkably downregulated in the atrial endocardium among 60-week-old WKY rats. In contrast, in SHR rats, only the TFPI expression has significantly decreased, while TM was preserved to the same level of control 30-week-old WKY rats. Rapid atrial pacing significantly reduced the TM and TFPI expression similarly in each model, thereby augmenting the endocardial dysfunction during normal sinus rhythm individually induced by the risk factors themselves prior to AF.Aging and hypertension, both of which are epidemiologically well-known risk factors for strokes in AF, have been associated with a specific atrial endocardial impairment prior to AF that could additionally disturb the antithrombotic function of the atrial endocardium.