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NEUROHUMORAL CONTROL OF CARDIOVASCULAR FUNCTION
1Tulane Hypertension and Renal Center of Excellence, and Department of Physiology, Tulane University Health Sciences Center, New Orleans, Louisiana; and 2Michael E. DeBakey Veterans Affairs Medical Center, and Departments of Medicine and Pharmacology, Baylor College of Medicine, Houston, Texas
Submitted 8 November 2004 ; accepted in final form 3 December 2004
Vascular tissues express arginase that metabolizes L-arginine to L-ornithine and urea and thus reduces substrate availability for nitric oxide formation. Dahl salt-sensitive (Dahl-S) rats with salt-induced hypertension show endothelial dysfunction, including decreased vascular nitric oxide formation. This study tests the hypothesis that increased vascular arginase activity contributes to endothelial dysfunction in hypertensive Dahl-S rats. Male Dahl-S rats (56 wk) were placed on high (8%) or low (0.3%) NaCl diets for 4 wk. With respect to the low-salt group, mean arterial blood pressure was increased in the high-salt animals. Immunohistochemical stainings for arginase I and II were enhanced in arterioles isolated from high-salt Dahl-S rats. Experiments used isolated Krebs buffer-superfused first-order gracilis muscle arterioles with constant pressure (80 mmHg) and no luminal flow or constant midpoint but altered endpoint pressures to establish graded levels of luminal flow (050 µl/min). In high-salt arterioles, responses to an endothelium-dependent vasodilator acetylcholine (1 nmol/l to 3 µmol/l) and flow-induced dilation were decreased. Acute in vitro treatment with an inhibitor of arginase, 100 µmol/l (S)-(2-boronoethyl)-L-cystine, or the nitric oxide precursor, 1 mmol/l L-arginine, similarly enhanced acetylcholine and flow-induced maximal dilations and abolished the differences between high- and low-salt arterioles. These data show that arteriolar arginase expression is increased and that endothelium-dependent vasodilation is decreased in high-salt Dahl-S rats. Acute pretreatment with an arginase inhibitor or with L-arginine restores endothelium-dependent vasodilation and abolishes the differences between high- and low-salt groups. These results suggest that enhanced vascular arginase activity contributes to endothelial dysfunction in Dahl-S rats with salt-induced hypertension and identifies arginase as a potential therapeutic target to prevent endothelial dysfunction.
salt-sensitive hypertension; vascular tone; arterioles
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