Both Dietary Salt Restriction and Excess Dietary Salt Intake Exaggerate Cardiovascular Reflex Responses to Activation of the Sciatic Afferents, Aortic Depressor Nerve, and Vagal Afferents

Abstract

Excess dietary salt intake exaggerates sympathetic nerve activity (SNA) and arterial blood pressure (ABP) responses to several cardiovascular reflexes in salt‐resistant animals. Recently, observational cohort studies suggest that salt restriction increases cardiovascular morbidity/mortality in several cardiovascular diseases, and the relationship between cardiovascular morbidity and dietary salt intake resembles a J‐shaped curve. However, little evidence exists to document the impact of salt restriction on cardiovascular reflex responses and whether this relationship resembles a J‐shaped curve. Thus, the aim of the present study was to determine whether salt restriction affects SNA and ABP responses to activation of sciatic afferents, the aortic depressor nerve, and cervical vagal afferents. To address this hypothesis, male Sprague‐Dawley rats were fed low (0.01% NaCl, D17010, Research diets), normal (0.1% NaCl, D17020, Research Diets), and high (4.0% NaCl, D17013, Research Diets) salt diet for 14–21 days. Then, reflex responses were measured in Inactin‐anesthetized animals. Baseline mean ABP was not different across groups (low: 112±4, normal: 101±5, high: 109±3mmHg; P>0.1 overall ANOVA). Electrical stimulation of sciatic afferents (1ms pulse, 500uA, 5s duration, 2–20Hz) produced frequency‐dependent increases in ABP. Interestingly, the pressor response to sciatic nerve stimulation was significantly greater in rats fed low and high versus normal NaCl (5Hz; low: 22±4, normal: 12±2, high: 27±2 mmHg, n=5–10, P<0.05). Activation of the aortic depressor nerve (2ms pulse, 500uA, 15s duration, 2–20Hz) produced frequency‐dependent decreases in ABP. The depressor response to aortic nerve stimulation was significantly greater in rats fed low and high versus normal NaCl (5Hz; low: −29±6, normal: −11±3, high: −29±4 mmHg; n=3–7, P<0.05). Finally, electrical stimulation of the cervical vagal afferents (1ms pulse, 500uA, 5s duration, 2–20Hz) produced frequency‐dependent decreases in ABP. Again, the depressor response to vagal nerve stimulation was significantly greater in rats fed low and high versus normal NaCl (5Hz; low: −25±3, normal: −15±2, high: −29±2 mmHg; n=5–10, P<0.05). Simultaneous recordings of lumbar, renal, and splanchnic SNA followed the changes in ABP across low, normal, and high NaCl diets. The present findings showed that both dietary salt restriction and excess dietary salt intake exaggerates sympathetic and cardiovascular responses. These cardiovascular responses to activation of sciatic afferents, the aortic depressor nerve, and vagal afferents as a function of dietary salt resemble a J‐shaped curve.Support or Funding InformationNIH R01 HL128388 (WBF, SDS)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.