Systemic arterial compliance in normotensive and hypertensive rats

A decreased compliance of the large arteries is generally associated with hypertension. However, it has not been determined if the increased stiffness of the arterial wall is related to etiology or if it represents the response of the arterial wall to elevated arterial pressure. We attempted to measure the arterial compliance (SAC) and the aortic diameter in 10 normotensive (WKY) rats and 10 spontaneously hypertensive rats (SHR) before and after injection of an alpha-blocker (Nicergoline 2 mg/kg). SAC was calculated from the diastolic decay of the aortic pressure, using a simple Resistance Capacitance model of the arterial system. The end diastolic diameter of the aorta was measured with a macrophotographic method. In basal conditions, SAC was significantly lower in the hypertensive rats (2.25 +/- 0.81 X 10(-3) ml/mm Hg) than in normotensive rats (5.09 +/- 1.29 X 10(-3) ml/mm Hg). The external diameter of the aorta was larger in SHR: 1.61 +/- 0.04 vs. 1.32 +/- 0.13 mm in WKY. After infusion of Nicergoline, there was no significant difference in blood pressure in either strain. SAC increased significantly in SHR and WKY rats (+60 and +43%, respectively), whereas the aortic diameter did not change significantly in either group. These data suggest that (a) the arterial wall has stiffer intrinsic mechanical properties in SHR as compared with WKY rats, and (b) the alpha-blocking agent used produces a more marked smooth muscle relaxation in the arterial wall of SHR as compared with control animals.