Dietary salt increases arterial stiffness independent of blood pressure and lifestyle factors

Background: Human studies show an association between high salt consumption and increased large artery stiffness, but are confounded by concomitant differences in blood pressure and altered lifestyle factors. Aims: To examine the effects of a high-salt diet on aortic function independent of all other factors. Methods: Sprague-Dawley rats were fed normal chow (control, 0.26% sodium chloride, n=8) or high-salt diet (HS, 8% sodium chloride, n=6) from weaning. A third group received a high-salt diet and an antihypertensive (HS+Tx, s.c. amlodipine 5 mg/kg/day, n=6). At 14–17 weeks, thoracic and abdominal aortic pressure (invasive solid-state catheters) was recorded under anesthesia over a mean arterial pressure (MAP) range of 60–150 mmHg (i.v. phenylephrine and sodium nitroprusside, 30 μg/kg/min). Aortic stiffness was assessed by pulse wave velocity (PWV) and thoracic to abdominal aortic pulse pressure amplification (PPA). Results: Conscious systolic blood pressure (tail-cuff) was greater in HS rats (control 117±13 mmHg, HS 125±12 mmHg; P=0.004) and normalized by antihypertensive treatment (HS+Tx 112±13 mmHg, P=0.12). Higher blood pressure was associated with increased kidney mass (normalized to body weight, control 0.8±0.1%, HS 1.0±0.2%; P=0.002; HS+Tx 0.9±0.1%; P=0.17) without left ventricular hypertrophy (P=0.58). Food intake was similar amongst all groups but HS and HS+Tx rats drank more with correspondingly higher urine output. HS had higher PWV (across MAP range 60–150 mmHg: control 3.6±0.1 to 4.0±0.3 m/s; HS, 4.2±0.2 to 4.6±0.3 m/s; P<0.001 at each 5 mmHg MAP interval). Increased PWV was maintained with antihypertensive treatment (HS+Tx 3.9±0.1 to 4.8±0.1 m/s; P<0.001). PPA was greater in HS (across MAP range 60 to 150 mmHg: control 0.64±0.08 to 1.24±0.11; HS 0.89±0.02 to 1.54±0.04; P<0.001 at each 5 mmHg MAP interval) and with antihypertensive therapy (HS+Tx 0.79±0.05 to 1.39±0.03; P<0.001). Conclusion: Under controlled blood pressure, a high-salt diet induced greater aortic stiffness and higher PPA, indicating salt effects on arterial stiffness are independent of blood pressure and other lifestyle factors.