Autoregulation and vascular reserve in the coronary circulation of the spontaneously hypertensive rat

Hypertension causes structural and functioning changes in blood vessels. Experiments were performed in isolated hearts of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats perfused by the Langendorff technique. Spontaneously hypertensive rats had significantly higher left heart to body weight ratios than WKY rats, indicating left ventricular hypertrophy. Coronary flow per unit cardiac mass was lower and vascular resistance was higher at 75 cm H2O perfusion pressure in SHR. This difference was maintained during maximal vasodilatation. In WKY rats, but not in SHR, autoregulation of flow was observed in the pressure range 75-150 cm H2O due to an increase in coronary vascular resistance. After maximal vasodilatation the pressure-flow relationship was linear in SHR and WKY rats, but less steep and shifted to the right in SHR. We conclude that structural adaptations of the coronary circulation in SHR lead to decreased coronary vascular reserve and a loss of autoregulation in the normal blood pressure range.