Renal hemodynamic and urinary response to baroreflex-mediated sympathetic modulation: insights from high-resolution...

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, whereas 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 P_cs 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.NEW & NOTEWORTHY By integrating an open-loop baroreflex control system with high-resolution arterial impedance analysis, this study distinguished the neural and autoregulatory contributions to systemic and renal hemodynamics. Direct comparison of systemic and renal arterial impedance revealed stable renal circulation despite changes in sympathetic nerve activity, mediated by local autoregulation. This experimental evidence of robust autoregulation irrespective of sympathetic influence may facilitate physiologically relevant renal modeling and enhance understanding of disease and drug effects on renal hemodynamics.