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Chronic propranolol treatment promotes left ventricular dilation without altering systolic function after large
1Department of Internal Medicine, Veterans Administration Medical Center, Portland, Oregon 97201.
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)
Insights
Propranolol did not improve cardiac function in rats with myocardial infarction (MI). However, it did reduce heart rate and increase left ventricular (LV) weight in MI rats, suggesting potential adverse remodeling despite beta-blockade.
Area of Science:
- Cardiology
- Pharmacology
- Physiology
Background:
- Myocardial infarction (MI) leads to impaired left ventricular (LV) function.
- Beta-adrenergic blockade is a common treatment for cardiovascular conditions.
- The long-term effects of propranolol on chronic MI require further investigation.
Purpose of the Study:
- To investigate the effects of prolonged beta-adrenergic blockade with propranolol on LV performance, weight, and volumes in rats with chronic MI.
- To determine if propranolol alters cardiac function or remodeling post-MI.
Main Methods:
- Rats with chronic MI were treated with propranolol in drinking water for 5-6 weeks.
- Measurements included LV pressures, aortic blood flow, and LV pressure-volume relations ex vivo.
- Control groups included sham-operated and MI rats without propranolol treatment.
Main Results:
- Rats with chronic MI showed decreased LV systolic performance and increased pressures.
- Propranolol did not improve LV systolic pressure, cardiac index, or ejection fraction in MI rats.
- Propranolol decreased heart rate and increased LV weight/body weight in MI rats, but not in sham-operated rats.
Conclusions:
- Prolonged beta-adrenergic blockade with propranolol did not improve cardiac function in chronic MI rats.
- Propranolol treatment in MI rats led to increased LV weight, suggesting adverse cardiac remodeling.
- These findings indicate that propranolol may not be beneficial and could potentially be detrimental in chronic MI settings.