Total renal nerve activity is enhanced during renal venous congestion to maintain renal medullary tissue oxygenation

Renal venous congestion is one of the most important hemodynamic factors driving renal dysfunction in patients with heart failure. However, the mechanisms whereby increases in renal venous pressure (RVP) impair renal function are not well understood. An anesthetized ovine model was used to test the hypothesis that elevations in RVP increase renal nerve activity and mediate impairments in renal hemodynamics and renal tissue oxygenation. The protocol was carried out in two groups: renal nerve intact (n = 8) and right unilateral renal denervated (n = 7) animals. During experimentally induced renal venous congestion, there was a significant increase in directly recorded renal nerve activity. RVP increases led to elevation-dependent increases in plasma renin activity, decreases in renal blood flow (RBF), renal vascular conductance (RVC), urine output, glomerular filtration rate (GFR), and renal medullary perfusion in both the intact and unilateral denervated groups. RVP increase had no significant effect on renal cortical perfusion in the intact group but markedly reduced cortical perfusion in the unilateral denervated group. Interestingly, there were no changes in renal medullary and cortical oxygenation during RVP elevation in the intact group, and reductions in these variables in the right unilateral renal denervated group. Our study provides direct evidence that renal venous congestion increases renal nerve activity and the renin-angiotensin system (RAS), impairs renal hemodynamics, and decreases GFR. The data during unilateral renal denervation suggest that the renal nerves do not regulate renal venous congestion-induced renal hemodynamic impairments. The nerves do play an important role in maintaining renal medullary tissue oxygenation.NEW & NOTEWORTHY Our study shows that renal venous congestion is not associated with an alteration in renal medullary oxygenation, although renal function is altered. Direct recordings of renal nerve activity indicate an elevation during renal venous congestion. The renal nerves do not regulate renal venous congestion-induced renal dysfunction since this is not different in a unilateral renal denervated group. The renal nerves exert a protective effect in maintaining renal medullary tissue oxygenation.