Abstract 473: Evidence for Afferent Re-innervation After Renal Denervation in Rats

Abstract

Interventional renal ablation is a promising treatment procedure for therapy-resistant arterial hypertension. However, the underlying mechanisms are not completely understood: The efferent sympathetic renal nerves are known to play a key role in salt retention and renin release, but the role of the afferent nerves is not yet clearly defined, although strong evidence exists for a sympathoinhibitory function. It is widely accepted that there is some re-innervation of efferent sympathetic nerves after the denervation procedure, but re-innervation of afferent nerves is still doubted. Hence, we wanted to test the hypothesis that besides a sympathetic re-innervation a considerable afferent re-innervation occurs after renal denervation in rats. 50μm kidney slices from 12 male SD rats were stained for thyrosin hydroxylase (TH), calctonine gene related peptide (CGRP) and smooth muscle actin (SMA). Kidneys were examined 1, 4 and 12 weeks after left sided surgical renal denervation. The right innervated kidney served as control. Image stacks were generated using a confocal laser scanning microscope (0.5μm z-axis steps). Analysis of nerve density was done by 4 blinded investigators in 183 image stacks. Staining for TH (i.e. efferent) and CGRP (i.e. afferent) was visually scored (0-3). Stacks were visualized by Fiji Image J software. At week 1 both efferent [TH+] and afferent [CGRP+] fiber density was clearly reduced but was still detectable ([TH+]: right 2.43±0.10 vs. left 1.47±0.11; [CGRP+]: right 1.96±0.17 vs. left 0.86±0.12; P<0.001, each). After 4 weeks a clear-cut increase in nerve densities could be detected in the denervated kidneys, which further increased until week 12 ([TH+]: right 2.67±0.07 vs. left 2.35±0.12, P<0.03; [CGRP+]: right 2.06±0.16 vs. left 1.82±0.17, P=ns). Our study clearly indicates for the first time that there is not only a relevant sympathetic re-innervation but also a re-innervation of afferent nerves in the kidney. The afferent re-innervation process even seems to be more complete compared to sympathetic nerve fiber re-growth. Further studies have to be done to prove the functional relevance of our findings.