Early DOCA-Salt Hypertension Develops Without Increases in Renal or Lumbar Sympathetic Nerve Activity

BACKGROUND: Excessive salt intake is a major contributor to hypertension; however, the role of sympathetic nerve activity (SNA) remains controversial. Most existing evidence relies on indirect markers or single-time-point measurements. Therefore, we directly and continuously recorded SNA to test the hypothesis that SNA contributes to the initiation, progression, or both phases of salt-induced hypertension. METHODS: We continuously recorded renal and lumbar SNA, arterial pressure, and heart rate for 4 weeks in conscious sham-operated and uninephrectomized rats. After a control period on a normal-salt diet, rats received a subcutaneous deoxycorticosterone acetate (DOCA) pellet with a high-salt diet (4% NaCl) for 17 days, followed by pellet removal and a return to a normal-salt diet for 7 days. RESULTS: DOCA-salt treatment induced a biphasic increase in arterial pressure, with an immediate increase within 24 hours (initiation phase) and a progressive increase after day 6 (developmental phase), which was more pronounced in uninephrectomy rats. In contrast, heart rate and renal SNA decreased from day 1, and lumbar SNA progressively declined in all groups, providing no evidence of sympathetic overactivity during either phase. After DOCA withdrawal, AP declined, whereas renal SNA and lumbar SNA transiently increased. CONCLUSIONS: Continuous recordings demonstrated that neither renal SNA nor lumbar SNA mediated the initiation or development of DOCA-salt hypertension. In the absence of evidence for increased cardiac output, the biphasic rise in AP is attributed to increased peripheral vascular resistance of a nonsympathetic origin, likely driven by DOCA-sodium interactions in the perivascular region.