Renal sensory and sympathetic nerves reinnervate the kidney in a similar time-dependent fashion after renal denervation in rats

Abstract

Efferent renal sympathetic nerves reinnervate the kidney after renal denervation in animals and humans. Therefore, the long-term reduction in arterial pressure following renal denervation in drug-resistant hypertensive patients has been attributed to lack of afferent renal sensory reinnervation. However, afferent sensory reinnervation of any organ, including the kidney, is an understudied question. Therefore, we analyzed the time course of sympathetic and sensory reinnervation at multiple time points (1, 4, and 5 days and 1, 2, 3, 4, 6, 9, and 12 wk) after renal denervation in normal Sprague-Dawley rats. Sympathetic and sensory innervation in the innervated and contralateral denervated kidney was determined as optical density (ImageJ) of the sympathetic and sensory nerves identified by immunohistochemistry using antibodies against markers for sympathetic nerves [neuropeptide Y (NPY) and tyrosine hydroxylase (TH)] and sensory nerves [substance P and calcitonin gene-related peptide (CGRP)]. In denervated kidneys, the optical density of NPY-immunoreactive (ir) fibers in the renal cortex and substance P-ir fibers in the pelvic wall was 6, 39, and 100% and 8, 47, and 100%, respectively, of that in the contralateral innervated kidney at 4 days, 4 wk, and 12 wk after denervation. Linear regression analysis of the optical density of the ratio of the denervated/innervated kidney versus time yielded similar intercept and slope values for NPY-ir, TH-ir, substance P-ir, and CGRP-ir fibers (all R(2) > 0.76). In conclusion, in normotensive rats, reinnervation of the renal sensory nerves occurs over the same time course as reinnervation of the renal sympathetic nerves, both being complete at 9 to 12 wk following renal denervation.

Fig. 1.

For analyses of the optical intensity of the renal sensory nerves, the renal pelvic wall was outlined (arrow) and for analyses of the intensity of the sympathetic nerves four areas of the renal cortex were outlined, C1 through C4. C1 and C4 represent the peripelvic area, and C2 and C3 represent the renal cortical areas more distal from the renal hilus. C2 and C3 also included the outer part of the outer medulla. *Vessels; **fat tissue.

Fig. 2.

Immunohistochemical labeling of renal tissue for neuropeptide Y (NPY) showed NPY-immunoreactive (ir) fibers close to vessels and tubular structures in the peripelvic cortical area in innervated kidneys at all time points (left). In the contralateral denervated kidneys (right), there were no NPY-ir fibers in the peripelvic cortical area 4 days (b) and 2 wk (d) after denervation and markedly reduced numbers 4 wk (f) after denervation. At 9 wk after denervation, the distribution of NPY-ir fibers in the peripelvic cortical are was similar in the innervated and denervated kidneys (g and h). Arrows; nerves, A; arteriole, G; glomerulus.

Fig. 3.

The ratio between the denervated and innervated kidney in each rat of the optical density of NPY/tyrosine hydroxylase (TH)-ir fibers in the renal pelvic wall at various time points following unilateral renal denervation. Closed and open symbols, denervated-to-innervated ratio of the optical density of NPY-ir and TH-ir fibers, respectively; solid and dashed lines, linear regression of the denervated-to-innervated ratio of the optical density of NPY-ir and TH-ir fibers, respectively, vs. time; n = 17.

Fig. 4.

Immunohistochemical labeling of renal tissue for substance P (SP) showed dense distribution of SP-ir fibers in the renal pelvic wall in innervated kidneys at all time points (left). In the contralateral denervated kidneys (right), there were no SP-ir fibers in the pelvic wall 4 days after denervation (b) and markedly reduced numbers at 2 and 4 wks after denervation (d, f). At 9 wks after denervation, the distribution of SP-ir fibers in the pelvic wall was similar in the innervated and denervated kidneys (g, h).

Fig. 5.

The ratio between the denervated and innervated kidney in each rat of the optical density of SP/calcitonin gene-related peptide (CGRP)-ir fibers in the renal pelvic wall at various time points following unilateral renal denervation. Closed and open symbols, denervated-to-innervated ratio of the optical density of SP-ir and CGRP-ir fibers, respectively; solid and dashed lines, linear regression of the denervated-to-innervated ratio of the optical density of SP-ir and CGRP-ir fibers, respectively, vs. time; n = 16.