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

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.

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).

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.

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