Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

No abstract

High calcium diet down-regulated kidney ACE, reduced albuminuria and blood pressure, and favorably influenced kidney morphology in experimental renal failure. These findings suggest a link between calcium metabolism and kidney ACE expression, which may play a role in the progression of renal damage.

Abstract-It is not known whether angiotensin II type 1 receptor antagonists can influence the function and morphology of small arteries in renal failure. We investigated the effect of 8-week losartan therapy (20 mg/kg per day) on isolated mesenteric resistance arteries by wire and pressure myographs in 5/6 nephrectomized rats. Plasma urea nitrogen was elevated 1.6-fold after nephrectomy, and ventricular synthesis of atrial and B-type natriuretic peptides was increased 2.2-fold and 1.7-fold, respectively, whereas blood pressure was not affected. Losartan did not influence these variables. The endothelium-mediated relaxation to acetylcholine was impaired in nephrectomized rats in the absence and presence of nitric oxide synthase and cyclooxygenase inhibition. Blockade of calcium-activated potassium channels by charybdotoxin and apamin reduced the remaining acetylcholine response, and this effect was less marked in nephrectomized than in sham-operated rats. Relaxation to levcromakalim, a vasodilator acting through adenosine triphosphate-sensitive potassium channels, was also impaired after nephrectomy. The arteries of nephrectomized rats showed eutrophic inward remodeling: Wall-to-lumen ratio was increased without change in wall cross-sectional area. All changes in arterial relaxation and morphology were normalized by losartan therapy. Aortic ACE content, measured by autoradiography, directly correlated to the plasma level of urea nitrogen, suggesting that renal failure has an enhancing influence on the vascular renin-angiotensin system. Losartan normalized relaxation and morphology of resistance arteries in experimental renal failure, independent of its influence on blood pressure, impaired kidney function, or volume overload. The mechanism of improved vasodilation by losartan may include enhanced relaxation through potassium channels. Key Words: arteries Ⅲ receptors, angiotensin II Ⅲ endothelium-derived factors Ⅲ angiotensin II Ⅲ potassium channels Ⅲ kidney failure C hronic renal failure is associated with a high prevalence of cardiovascular disease. 1 Large arteries in renal failure are characterized by reduced compliance, 2 the possible explanations of which are increased extracellular matrix content, hyperplasia of smooth muscle, and calcification in media. 3,4 However, increased vascular stiffness has also been observed in the absence of vascular hypertrophy, 5 and decreased endothelial vasodilator function may contribute to vascular pathophysiology in renal failure. 6 Indeed, endothelium-dependent vasodilation is impaired in the forearm circulation of hemodialysis patients. 7 We found that in experimental renal failure, endotheliumdependent vasorelaxation is impaired by a mechanism involving K ϩ channels in arterial smooth muscle. 8 In hypertension, the impaired endothelium-mediated relaxation is ameliorated by treatment with angiotensin II type 1 (AT 1 ) receptor blockers. 9,10 Angiotensin II receptor antagonists have the potential to modulate K ϩ channel-mediated vasorelaxation, since stimulation of AT 1 r...