Loss of endothelium and receptor-mediated dilation in pial arterioles of rats fed a short-term high salt diet

A high salt diet often is regarded as an accessory risk factor in hypertension, coincidental to the deleterious effect of high blood pressure on vasodilator function. The aim of this study was to determine whether short-term ingestion of a high salt diet per se impairs vasodilator function in the cerebral circulation independent of blood pressure changes. Adult Sprague-Dawley rats were fed a normal salt (0.8%) or high salt (4%) diet for 3 days. Mean arterial pressures were similar in the normal and high salt groups (123 +/- 2 and 125 +/- 2 mm Hg, respectively). Subsequently, the responses of the in situ pial arterioles to acetylcholine. iloprost, and sodium nitroprusside were determined in cranial windows using intravital videomicroscopy. Pial arterioles of rats fed normal and high salt diets showed similar resting diameters of 69 +/- 2 and 72 +/- 3 mu m, respectively, but their reactivity patterns to vasodilator stimuli were markedly different. Arterioles of rats fed a normal salt diet dilated progressively up to 17 +/- 3% in response to the endothelium-dependent agent acetylcholine (10(-9) to 10(-6) mol/L) and dilated by 22 +/- 2% in response to the prostaglandin I-2 receptor agonist iloprost (3 X 10(-11) mol/L), In contrast, pial arterioles of rats fed a high salt diet constricted by 4 +/- 3% and 8 +/- 2% in response to acetylcholine and iloprost, respectively. Sodium nitroprusside (10(-6) mol/L), a nitric oxide donor, dilated pial arterioles of rats fed low and high salt diets by a similar amount (19 +/- 3% and 16 +/- 2%, respectively), suggesting that signaling mechanisms for dilation distal to the vascular smooth muscle membrane were intact after high salt intake. These results provide the first evidence that the short-term ingestion of a high salt diet may severely impair the vasodilator function of the in situ cerebral microcirculation independent of blood pressure elevation.