Pressure-independent effects of AT1-receptor antagonism on cardiovascular remodeling in aortic-banded rats

To determine the role of angiotensin II-receptor blockade on cardiovascular remodeling in a pressure-overload model of cardiac hypertrophy, a subdiaphragmatic aortic band was placed in adult male Sprague-Dawley rats. Aortic-banded (AB) rats were left untreated or were losartan (Los; 250 mg/l) treated (AB-Los). Sham-operated (S) controls were either left untreated or treated with Los (S-Los). After 4 wk, rats were catheterized for measurement of mean arterial pressures carotid (CMAP) and femoral (FMAP), in mmHg. Hearts were perfused on a modified Langendorff system, and minimal coronary resistance (MCR) was determined. Hearts were then perfusion fixed, total and regional heart weights were recorded, and sections were processed for morphology. Changes in coronary artery medial thickness and perivascular fibrosis were assessed by quantitative image analysis. CMAP was significantly higher in AB and AB-Los than in S or S-Los (P < 0.05). There was no difference in FMAP in AB vs. S, but AB-Los and S-Los had lower FMAPs than S. Total heart weight and left ventricular weight-to-body weight ratios were increased in AB and AB-Los compared with S and S-Los (P < 0.05). MCR of AB was greater than S and S-Los. MCR of AB-Los was significantly lower than AB and was not significantly different from S and S-Los. In coronary vessels, medial thickness was greatest in AB, whereas there was no difference among AB-Los, S, and S-Los. Similarly, the increase in perivascular fibrosis was greatest in AB, and there was no difference among AB-Los, S, and S-Los. These data suggest that angiotensin II, independent of increased arterial pressure, is critical for the development of the vascular and fibrotic changes that occur in this model of pressure-overload hypertrophy.