Objectives Dietary salt plays a major role in the regulation of blood pressure. However, the mechanisms underlying endothelial cell dysfunction induced by sodium have not yet been completely elucidated.
Methods SD rats were randomly divided into high salt group (n = 10, 1.5% NaCl in drinking water) and control group (n = 10, no NaCl in drinking water). Systemic blood pressure (SBP) was measured weekly by the tail-cuff method. Blood samples were collected at 8 and 12 weeks for later analysis. Human coronary artery endothelial cells were firstly cultured in medium containing aldosterone at physiological concentration (0.45 nmol/L) for 3 days. Secondly sodium at different concentrations, i.e. 125, 135, 145, 155, 165 mmol/L, were applied to these cells for 3 hours. For mechanical study, SB203580 and tempol were used for 1 hour prior to NaCl stimulation. Cells and supernatant were collected after NaCl stimulation for later analysis. F-actin of endothelial cells was observed by immunofluorescence. The plasma and cell supernatant Nitric Oxide (NO) were determined by Nitrate reductase method. The plasma and cell supernatant ONOO- were assessed by ELISA. The endothelial nitric oxide synthetase (eNOS), gp91, p-P38 and p-HSP27 in endothelial cells were detected by Western Blot.
Results Compared to control group, administration of 1.5% NaCl water to rats for 8 or 12 weeks significantly increased blood pressure (P < 0.05), decreased plasma NO generation (P < 0.05) and improved plasma ONOO¯ generation (P < 0.05). F-actin of endothelial cells was unaffected by acute changes under sodium concentration ≤135 mmol/L but rose steeply under sodium concentration ≥145 mmol/L. NO generation and expression of eNOS were found down-regulated, but ONOO¯ generation, the expression of gp91, p-P38 and p-HSP27 were found up-regulated in endothelial cells cultured in sodium concentration ≥145 mmol/L. Tempol and SB203580 markedly inhibited NaCl-induced alterations in endothelial actin reorganisation and activation of p38 MAPK. Tempol markedly inhibited NaCl-induced alterations in the generation of NO, ONOO¯, the expression of eNOS and gp91, but SB203580 did not prevent these responses.
Conclusions The results suggest that salt may induce endothelial cell dysfunction and thus control vascular tone by activating oxidative stress and p38 MAPK.