Myocardial effects of beta-agonist stimulation in rats with chronic left ventricular dysfunction treated with an angiotensin-converting enzyme inhibitor.

Background: This study measured morphological and hemodynamic changes and renin-angiotensin responsiveness of the left ventricle (LV) to beta-agonist stimulation in a Sprague-Dawley rat model of myocardial dysfunction produced by coronary artery ligation.

Methods: The LV function and papillary muscle mechanics were measured after 12 weeks of captopril treatment (2 g/l in drinking water) following left coronary artery ligation or a sham operation. Fifty-two rats were divided into three groups: those with sham operations, those with small infarcts (infarct size [IS] < 30% LV) and those with large infarcts (IS > or = 30% LV).

Results: The results showed that LV end-diastolic pressures were elevated in the large-infarct group regardless of treatment with the angiotensin-converting enzyme inhibitor (ACEI), and the LV weight was reduced in the ACEI-treated rats. In addition, the uninfarcted LV posterior papillary muscle of the large-infarct rats showed an impaired response to isoproterenol stimulation, including the developed tension, positive and negative rate of tension development, time to peak tension, and time to half relaxation.

Conclusion: Chronic captopril treatment improved isoproterenol-stimulated muscle isometric function in rats following myocardial infarction, possibly through the beta-receptor pathway.