The Influence of Coarctation Hypertension on the Pharmacodynamic Behaviour of Rat Isolated Conduit Vessels

Abstract

We have studied the effects of coarctation hypertension on the reactivity of the aorta with respect to α₁ adrenoceptor mediated vasoconstriction and methacholine-induced endothelium-dependent vasodilation. The experiments were performed in aortic rings taken from rats that had been subjected to banding of the abdominal aorta, aortic stenosis rats (ASR), and from SHAM operated control rats. As expected, the thoracic aorta was subjected to elevated blood pressure, whereas the pressure in the abdominal aorta region was much lower. Concomitantly, the thoracic and abdominal aorta regions were studied separately as isolated vessels. Both the thoracic and abdominal aortic rings taken from ASR were more sensitive to phenylephrine than those obtained from control rats. The increase in sensitivity cannot be explained by elevated pressure alone and neurohormonal factors are likely to play a role. The maximal relaxation induced by methacholine in thoracic aortic rings obtained from ASR was significantly less when compared with that in preparations taken from SHAM rats. No changes in maximal relaxation were observed in the abdominal aortic rings. It is concluded that i) the enhanced responsiveness of the rat aorta to α₁-adrenoceptor stimulation cannot be explained by elevated blood pressure alone and ii) coarctation hypertension impairs the endothelium-dependent relaxation of the aortic region exposed to high blood pressure.

Key Words:

• aortic banding
• hypertension
• α₁-adrenoceptor agonist
• endothelium-dependent vasodilation