A novel method of selective ablation of afferent renal nerves by periaxonal application of capsaicin

Abstract

Renal denervation has been shown to lower arterial pressure in some hypertensive patients, yet it remains unclear whether this is due to ablation of afferent or efferent renal nerves. To investigate the role of afferent renal nerves in arterial pressure regulation, previous studies have used methods that disrupt both renal and nonrenal afferent signaling. The present study was conducted to develop and validate a technique for selective ablation of afferent renal nerves that does not disrupt other afferent pathways. To do this, we adapted a technique for sensory denervation of the adrenal gland by topical application of capsaicin and tested the hypothesis that exposure of the renal nerves to capsaicin (renal-CAP) causes ablation of afferent but not efferent renal nerves. Renal-CAP had no effect on renal content of the efferent nerve markers tyrosine hydroxylase and norepinephrine; however, the afferent nerve marker, calcitonin gene-related peptide was largely depleted from the kidney 10 days after intervention, but returned to roughly half of control levels by 7 wk postintervention. Moreover, renal-CAP abolished the cardiovascular responses to acute pharmacological stimulation of afferent renal nerves. Renal-CAP rats showed normal weight gain, as well as cardiovascular and fluid balance regulation during dietary sodium loading. To some extent, renal-CAP did blunt the bradycardic response and increase the dipsogenic response to increased salt intake. Lastly, renal-CAP significantly attenuated the development of deoxycorticosterone acetate-salt hypertension. These results demonstrate that renal-CAP effectively causes selective ablation of afferent renal nerves in rats.

Keywords: afferent renal denervation; hypertension; salt-sensitivity.

Fig. 1.

Representative immunohistochemistry (IHC) images stained for CGRP and tyrosine hydroxylase (TH) from a sham-operated kidney and renal-CAP kidney 10 days after intervention. The image on left shows the entire slice of the kidney. The boxed in portion of the left image is magnified in the image on the right. CGRP is shown in brown, while TH is shown in pink.

Fig. 2.

Tissue content of neurochemical markers 10 days, 4 wk, and 7 wk following sham operation or renal-CAP. A: IHC labeling of TH. B: IHC labeling of CGRP. C: NE content of the renal parenchyma by HPLC. D: CGRP content of the pelvic wall by ELISA. ND, not detectable. *P < 0.05 compared with the 10-day Sham. †P < 0.05 compared with the 4-wk Sham. #P < 0.05 compared with the 7-wk Sham group. §P < 0.05 compared with the 10-day renal-CAP.

Fig. 3.

Time course of afferent reinnervation following renal-CAP. Renal pelvic CGRP content of renal-CAP (left) kidneys is expressed as % of within-animal control (right) kidneys. A linear regression was performed (R² = 0.65, P < 0.0001) and group averages ± SE are overlaid.

Fig. 4.

Physiological responses to pharmacological stimulation of afferent renal nerves in Sham and renal-CAP rats. Changes in MAP (ΔMAP; top) and HR (ΔHR; bottom) following intrarenal (left) and intravenous (right) infusions of bradykinin. *P < 0.05 for Sham vs. renal-CAP. Error bars not shown for SE <1.1 mmHg for ΔMAP and <3.6 beats per minute for ΔHR.

Fig. 5.

Mean arterial pressure (MAP) and heart rate (HR) in sham and renal-CAP rats subjected to the salt-sensitivity protocol. *P < 0.05 for Sham vs. renal-CAP.

Fig. 6.

Sodium intake, excretion, and balance in sham and renal-CAP rats subjected to the salt sensitivity protocol. There were no significant differences between groups.

Fig. 7.

Water intake, urine output, and water balance in Sham and renal-CAP rats subjected to the salt-sensitivity protocol. *P < 0.05 for renal-CAP vs. Sham.

Fig. 8.

MAP and HR responses in sham, RDNX, and renal-CAP rats that underwent the DOCA-salt protocol. A: baseline MAP and HR. B: change in MAP from baseline (ΔMAP) and change in HR from baseline (ΔHR) upon DOCA implantation. *P < 0.05 for RDNX vs. Sham. #P = 0.05 for renal-CAP vs. Sham.

Fig. 9.

Tissue content of neurochemical markers in the kidneys of rats that underwent the DOCA-salt protocol A: NE content in the renal parenchyma. B: CGRP content in the renal pelvic wall. *P < 0.05 compared with Sham.