Renal Hemodynamic and Urinary Response to Baroreflex-Mediated Sympathetic Modulation: Insights from High-Resolution Arterial Impedance Analysis in Rats

This study investigated the short-term regulatory mechanisms of systemic and renal hemodynamics at the whole-organism level by independently controlling sympathetic nerve activity (SNA) and arterial pressure. In anesthetized male rats (N = 8), SNA was altered via carotid sinus pressure ( P cs ) control, while mean arterial pressure was regulated at 100 mmHg using an arterial pressure control system (APC-On) or allowed to vary with SNA (APC-Off). Renal blood flow remained stable across P cs levels or APC status. In contrast, urine flow decreased with increasing P cs under APC-Off but increased under APC-On (32.2 ± 6.7 vs. 71.3 ± 3.7 µL·min −1 ·kg −1 at a P cs of 140 mmHg, P = 0.012). A three-element Windkessel model was applied to describe systemic ( Z sys ) and renal arterial impedance ( Z renal ). Characteristic impedance ( R c ) showed opposite trends in Z sys and Z renal with increasing P cs under APC-Off, whereas such differential responses were not observed under APC-On. Distal resistance ( R d ) decreased with increasing P cs in both Z sys and Z renal under APC-Off, reflecting a vasodilatory effect of SNA suppression. Under APC-On, R d in Z sys showed a decreasing trend with increasing P cs , whereas R d in Z renal increased, indicating that maintaining arterial pressure elicited a renal vasoconstrictive effect counteracting SNA suppression. Compliance ( C) in Z sys remained relatively stable across P cs under both APC conditions. In contrast, C in Z renal markedly increased with Pcs reaching 230.0 ± 45.5%, under APC-Off, whereas it remained stable under APC-On. In conclusion, systemic vascular tone is primarily governed by SNA, whereas renal hemodynamics is stabilized by local autoregulatory adjustments.