Description:
Previous studies indicate that increased dietary salt intake enhances sympathetic nerve activity (SNA) and arterial blood pressure (ABP) responses evoked from sympathetic neurons of the rostral ventrolateral medulla. The present study sought to extend these findings and determine whether dietary salt intake enhances SNA and ABP responses various sympathetic reflexes that depend on RVLM neurotransmission. Male Sprague-Dawley rats were fed 0.1% (n=6-8) or 4.0% (n=6-8) NaCl diets for 14-21 days. Then, animals were anesthetized with Inactin. Electrical stimulation (1-20 Hz, 1 ms pulse, 500 uA) of sciatic afferents produced frequency-dependent changes in SNA and ABP in both groups. However, rats ingesting 4% versus 0.1% NaCl displayed significantly larger increases in lumbar SNA (5Hz: 213±25 vs 146±25%, P<0.05), renal SNA (5Hz: 187±24 vs 120±11%), splanchnic SNA (5Hz: 203±21 vs 136±9%), and mean ABP (5Hz: 28±2 vs 12±2 mmHg). Rats ingesting 4% vs 0.1% NaCl also displayed greater increases in lumbar SNA (24±6 vs 13±2%, P<0.05) and mean ABP (12.1±0.9 vs 8.2±1.3mmHg, P<0.05) during increases in cerebrospinal fluid sodium concentration produced by intracerebroventricular infusion of 1M NaCl (5ul/10min). Lastly, hypercapnia (7% CO2, 33% O2, 63% N2, 60s) produced greater increases in lumbar SNA in rats ingesting 4% versus 0.1% NaCl (24±2% versus 9±3%, respectively; P<0.01). These findings suggest increased dietary salt intake enhances several sympathetic and cardiovascular reflexes.