Abstract
In rats with chronic myocardial infarction (MI), we have examined the effects of prolonged beta-adrenergic blockade with propranolol on left ventricular (LV) performance, weight, and volumes. Sham-operated rats and rats with large MI (greater than 30%) were evaluated. Four groups of rats were studied: control, sham-operated (n = 12); control, MI (n = 12); propranolol (500 mg/L of drinking water)-treated, sham-operated (n = 10); and propranolol treated, MI (n = 10). Treatment was started 3 weeks after coronary ligation. After 5-6 weeks, LV, systemic arterial, and right atrial pressures in addition to aortic blood flow before and during volume loading were measured. LV pressure-volume relations were measured ex vivo. The rats with chronic MI demonstrated expected decreases in LV systolic performance and increased LV end-diastolic and right atrial pressures. Propranolol had no independent effect on LV systolic pressure, LV end-diastolic pressure, resting cardiac index, stressed cardiac index during volume loading, peak developed aortic pressure during aortic occlusion, or ejection fraction index in either sham-operated or infarcted rats; however, heart rate was decreased. LV weight/body weight was 2.17 +/- 0.04 mg/g in control sham-operated rats, which was not different from the propranolol-treated sham-operated rats (2.09 +/- 0.04 mg/g). The LV weight/body weight was increased (p less than 0.01) to 2.21 +/- 0.08 mg/g in the propranolol-treated MI group from 1.94 +/- 0.06 mg/g in the control MI group. The LV pressure-volume relation was not altered by propranolol in the sham-operated rats but was shifted to the right by MI.(ABSTRACT TRUNCATED AT 250 WORDS)
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