ALTERATIONS IN THE VASOREACTIVITY OF HYPERTENSIVE RAT AORTIC RINGS - ROLE OF NITRIC-OXIDE AND SUPEROXIDE RADICALS

Objectives: Present study was undertaken to investigate involvement or nitric oxide (NO) and superoxide radicals in the modulation of vasore activity in a model of renal hypertension. Method: Hypertension was in duced 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 (-5) M) Or phenylephrine (PE, 1 x 10(-8) to 1 x 10(-5) mol/l) was studied in the aortic rings obtai ned from sham operated normotensive, hypertensive and captopril pretre ated 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). Sp ontaneous release of NO from the aortic rings was evaluated by studyin g the inhibition of adenosine diphosphate stimulated platelet aggregat ion, while superoxide radicals were estimated by cytochrome c reductio n method Results. Ach induced vasorelaxation in PE precontracted rings was impaired following 8 wk after aortic banding, while spontaneous r elease of NO remained unaffected. Captopril pretreatment restored the aortic ring responsiveness to Ach. An increase in the superoxide radic al generation and PE induced contraction following L-NAME treatment in the hypertensive rat aortic rings was observed. Conclusion: Attenuati on in the Ach induced NO release and augmentation in the superoxide ra dical generation seems to play an important role in the modulation of vasoreactivity following renal hypertension in rats.