Alterations in the Vasoreactivity of Hypertensive Rat Aortic Rings: Role of Nitric Oxide and Superoxide Radicals

OBJECTIVES: Present study was undertaken to investigate involvement of nitric oxide (NO) and superoxide radicals in the modulation of vasoreactivity in a model of renal hypertension. METHOD: Hypertension was induced in the male Sprague Dawley rats by aortic banding just above the left kidney. Relaxation or contraction following cumulative addition of acetylcholine (Ach, 1 x 10(-8) to 1 x 10(-5) M) or phenylephrine (PE, 1 x 10(-8) to 1 x 10(-5) mol/l) was studied in the aortic rings obtained from sham operated normotensive, hypertensive and captopril pretreated rats. Ach and PE responses were taken in the presence or absence of NO synthase inhibitor (L-NAME; 1 x 10(-5) and 1 x 10(-4) mol/l). Spontaneous release of NO from the aortic rings was evaluated by studying the inhibition of adenosine diphosphate stimulated platelet aggregation, while superoxide radicals were estimated by cytochrome c reduction method. RESULTS: Ach induced vasorelaxation in PE precontracted rings was impaired following 8 wk after aortic banding, while spontaneous release of NO remained unaffected. Captopril pretreatment restored the aortic ring responsiveness to Ach. An increase in the superoxide radical generation and PE induced contraction following L-NAME treatment in the hypertensive rat aortic rings was observed. CONCLUSION: Attenuation in the Ach induced NO release and augmentation in the superoxide radical generation seems to play an important role in the modulation of vasoreactivity following renal hypertension in rats.