Effects of duration and severity of arterial hypertension and cardiac hypertrophy on coronary vasodilator reserve.

Cardiac hypertrophy is associated with a decrease in coronary reserve. However, factors which may modulate the interaction between myocardial growth and vascular proliferation, such as duration and severity of hypertrophy, have not been evaluated. We measured myocardial perfusion with microspheres in conscious, chronically instrumented. Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats at 3, 7, and 15 months of age; and in SHR stroke-prone (SHR-SP) rats at 13-14 months of age. Myocardial perfusion was measured with microspheres in awake rats at rest and during maximal coronary dilation produced by dipyridamole infusion (2.0 mg/kg per min, iv). Arterial pressure was significantly elevated (P less than or equal to 0.05) in all hypertensive groups (vs. age-matched WKY), both at rest and during dipyridamole infusion. Left ventricular mass in the SHR rats was increased significantly (P less than or equal to 0.05) by 14%, 28%, and 29% at 3, 7, and 15 months, respectively. Left ventricular mass in the SHR-SP group was increased by 50% (P less than or equal to 0.05) compared to the 15-month-old WKY. Left ventricular minimal coronary vascular resistance (per gram) was significantly greater (P less than or equal to 0.05) in SHR at 7 months, and in the SHR-SP group (66% and 60%, respectively). Right ventricular minimal coronary vascular resistance was significantly greater (P less than or equal to 0.05) in SHR at 7 and 15 months (50%), and in the SHR-SP group (122%), compared to 15-month-old WKY. The results indicate the following: (1) the increase in minimal coronary vascular resistance between SHR and WKY rats was greatest when left ventricular hypertrophy peaked (7 months) and was no longer present after left ventricular hypertrophy had stabilized. (2) In 14-month-old SHR-SP rats, with more severe left ventricular hypertrophy and hypertension, minimal coronary vascular resistance was considerably higher than in SHR of approximately the same age. (3) Long-term arterial hypertension was associated with a higher right ventricular minimal coronary vascular resistance. Resistance appeared to change in proportion to the severity of hypertension, and the changes were independent of the presence of right ventricular hypertrophy.