Role of Adrenergic Mechanisms in the Development of Cardiac Hypertrophy

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Abstract
This experiment was designed to study the role of cardiac .beta.-adrenergic mechanisms in the development of hypertrophy in rats. The suprarenal abdominal aorta was banded, resulting in an increase in cardiac wt-body wt ratio. A group of rats received a sham operation. Half of the banded rats were treated with practolol, 2.0 mg/kg intraperitoneally every 12 h for the 6 days after banding. The effectiveness of cardiac beta-adrenergic blockade was confirmed by absence of an increase in heart rate following i.v. isoproterenol at various times between practolol injections. Practolol did not affect the gradient in the banded groups. Animals (6) in each banded group were sacrificed daily for 6 days. The right (RV) and left (LV) ventricles were dissected separately and weighed. RV-body weight ratios increased similarly in both banded groups. LV-body weight ratio (g/kg) was 2.17 .+-. 0.043 in sham rats, and it attained maximal levels of 3.03 .+-. 0.10 within 6 days in banded untreated rats and 2.96 .+-. 0.14 in banded rats receiving practolol. Therefore, .beta.-adrenergic mechanisms were not involved in the development of hypertrophy due to increased afterload. These findings are not consistent with the Meerson hypothesis, since hypertrophy occurred despite the reduction in myocardial 02 consumption due to practolol.

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