High NaCl Intake Decreases both Flow‐Induced Dilation and Pressure‐Induced Myogenic Tone in Resistance Arteries from Normotensive Rats: Involvement of Cyclooxygenase‐2

Abstract

The effect of high NaCl diet on resistance arteries is not yet fully documented. In order to assess the effect of NaCl on myogenic tone and flow-induced dilation independent of arterial blood pressure change, we used normotensive rats which did not develop hypertension upon high NaCl intake. Normotensive Wistar Kyoto Rats received a high (8%) or a normal NaCl diet (0.4%). Mesenteric resistance arteries (150 mm, internal diameter) were cannulated in an arteriograph to allow perfusion of arteries under controlled pressure and flow. Pressure-induced myogenic tone was lower in the high NaCl group than in the control group. Cyclooxygenase inhibition with indomethacin and (N-(2-cyclohexyloxy)-4-nitro-phenyl)-methanesulphonamide, 1 mmol/l) NS 398 (specific cyclooxygenase-2 inhibitor) similarly decreased myogenic tone in rats fed high NaCl but had no effect in those fed a normal NaCl diet. Flow-induced dilation was decreased in the high NaCl group. Inhibition of nitric oxide synthesis with N G -nitro-L-arginine methyl ester decreased flow-induced dilation in both groups. Indomethacin and NS 398 did not change flow-induced dilation. As shown by immunofluorescence COX-2 was present in the endothelium of arteries from rats with a high NaCl diet but not in those fed a normal NaCl diet. Thus, chronic high NaCl intake decreased both flow-induced dilation and myogenic tone in resistance arteries. The chronic high NaCl did not affect the participation of nitric oxide on flow-induced dilation, but induced the expression of cyclooxygenase-2, which participates in myogenic tone. These results suggest that high NaCl changes flow and pressure mechanosensing processes and strengthen the hypothesis that sodium ions have an important role in both pressure and flow-mechanotransduction in vascular cells.

Reduced Arteriolar Responses to Skeletal Muscle Contraction after Ingestion of a High Salt Diet

“…Finally, shear stress-dependent NO release can also contribute to the dilation of proximal arterioles during larger increases in metabolic demand [22], and we have found that consumption of a 7% salt diet decreases arteriolar responsiveness to shear stress due to a selective loss of NO activity [7]. This salt-induced attenuation of arteriolar responsiveness to pressure and shear stress has been documented in other vascular beds as well [39,40,41]. Based on the above findings, we postulated in the current study that active hyperemia would be compromised in the contracting spinotrapezius muscle of HS rats.…”

Characteristics of myogenic tone in the rat ophthalmic artery

“…COX products were shown to augment arterial tone in mesenteric arteries by inhibiting nitric oxide synthesis that is decreased in L-NAME-mediated hypertension in rats (4). Furthermore, endothelial COX-2 was shown to be upregulated in mesenteric arteries from rats with high NaCl intake, mediating myogenic tone suggesting a compensatory or protective role of COX-2 in pressure-mechanotransduction (38).…”

Vascular TRP Channels: Performing Under Pressure and Going with the Flow

“…Shear stress is nearly universally associated with vasodilation in the peripheral vasculature, where research has consistently demonstrated a predominant vasodilatory response to blood flow in conduit arteries, such as femoral (205) and carotid (6,15,16,116,156) arteries, as well as resistance arteries and arterioles, including mesenteric arteries (16,23,98,116,123,188,234), coronary arteries (22,54,78,79,90,91,99,101,105,112,113,133,134,178,203,204,236,237), skeletal muscle feed arteries/arterioles (5-7, 55, 77, 86 -89, 96, 97, 166, 171, 180, 186, 187, 189, 190, 196, 202, 208, 228 -230), and adipose arterioles (153). Interestingly, shear stress is clearly capable of causing vasoconstriction in the cerebral circulation (20, 145,201).…”