Role of Angiotensin in Pressure Overload-Induced Hypertrophy in Rats

The renin-angiotensin system (RAS) has been proposed to play a major role in causing the heart to hypertrophy during pressure overload. We examined whether blockade of this system by the angiotensin-converting enzyme (ACE) inhibitors enalapril (0.5 to 20 mg/kg p.o.) or ramipril (1.0 mg/kg p.o.) or the angiotensin receptor (AT1) antagonist losartan (3.0 mg/kg p.o.) could prevent pressure overload-induced hypertrophy. Pressure overload was produced by abdominal aortic constriction in rats. Cardiac hypertrophy was assessed by an increase in the ratio of left ventricular (LV) weight to body weight and total protein content of the left ventricle. Treatment with enalapril or ramipril, initiated 3 weeks after aortic banding and continued for 3 more weeks, failed to prevent the progression or cause regression of cardiac hypertrophy. Treatment for 6 weeks with ramipril initiated immediately after aortic banding also failed to prevent cardiac hypertrophy. Losartan treatment initiated 3 weeks after aortic banding and continued for 3 more weeks resulted in a slight but significant reduction in the extent of cardiac hypertrophy (45.6% hypertrophy in controls and 35.6% hypertrophy in losartan-treated animals, p < 0.05, n = 11 and 10, respectively). Surgical removal of bands 3 weeks after placement reduced cardiac hypertrophy to a greater extent than that observed in losartan-treated animals. These results suggest that angiotensin may not play a major role in causing pressure overload-induced hypertrophy or in maintaining such hypertrophy.