Altered contractions to endothelin-1, phenylephrine, potassium chloride and relaxations to acetylcholine at various stages of renal hypertension in the rat

Abstract

This study is aimed at investigating the contraction and relaxation responses in the thoracic and abdominal aortae at various stages of hypertension. Hypertension in the rats was produced by aortic banding and the responses in the abdominal and thoracic aortic rings were studied 2 and 8 weeks after aortic banding. Contractile responses to phenylephrine (10^-6M), KCl (80 mM) or to endothelin-1 (10^-12to 10^-6M) and the relaxation responses to acetylcholine (10^-7to 10^-5M) were similar in the thoracic and abdominal rings of normotensive rats. The intact thoracic rings from 2 week aortic-banded hypertensive rats (ABHR) showed attenuated responses to all the contractile agents used. However, the relaxation to acetylcholine was not altered. In the rings from 8 week ABHR, the responses to contractile agents were not significantly altered but the acetylcholine-induced relaxations were significantly attenuated. The endothelial-derived relaxing factors might act to antagonize the vasoconstrictive responses during the onset of hypertension but might be disabled, as the endothelial dysfunction becomes predominant after 8 weeks of hypertension. The results thus suggest that the contractile and relaxant responses are differentially altered during different stages of hypertension.