Anatomical Assessment of Sympathetic Peri-Arterial Renal Nerves in Man
What is the anatomic distribution of peri-arterial sympathetic nerves around human renal arteries?
Bilateral renal arteries were collected from human autopsy subjects, and peri-arterial renal nerve anatomy was examined using morphometric software. The ratio of afferent to efferent nerve fibers was investigated by dual immunofluorescence staining using antibodies targeted for anti-tyrosine hydroxylase (TH) and anti-calcitonin gene-related peptide (CGRP). Comparisons between hypertensive and nonhypertensive subjects were performed by independent t-test or Wilcoxon rank-sum test. Categorical data were analyzed by χ2 test or Fisher's exact test.
A total of 10,329 nerves were identified from 20 (12 hypertensive and 8 nonhypertensive) patients. The mean individual number of nerves in the proximal and middle segments was similar (39.6 ± 16.7 and 39.9 ± 13.9/section), while the distal segment showed fewer nerves (33.6 ± 13.1/section) (p = 0.01). Mean subject-specific nerve distance to arterial lumen was greatest in proximal (3.40 ± 0.7 mm), followed by middle (3.10 ± 0.69 mm), and least in distal segments (2.60 ± 0.77 mm) (p < 0.001). The mean number of nerves in the ventral region (11.0 ± 3.5/section) was greater compared to the dorsal region (6.2 ± 3.0/section) (p < 0.001). Efferent nerve fibers were predominant (p < 0.0001, TH/CGRP ratio: 25.1 ± 33.4). Nerve anatomy in hypertensive patients was not considerably different compared to nonhypertensive patients.
The authors concluded that there is a clear predominance of efferent nerve fibers around renal arteries, with decreasing prevalence of afferent nerves from proximal to distal peri-arterial and renal parenchyma.
This study reports that compared to proximal and middle renal segments, the mean number of peri-arterial renal nerves in distal segments was significantly less. The total number of nerves in the dorsal arterial region was less than in the ventral region. Peri-arterial renal nerves were dominantly composed of efferent rather than afferent fibers, and the relative proportion of afferent fibers was not different between the proximal, middle, and distal segments. Furthermore, peri-arterial renal nerve anatomy among hypertensive and nonhypertensive patients was not different. Understanding these anatomical characteristics will be important for the development and refinement of renal denervation devices.
Keywords: Nerve Fibers, Staining and Labeling, Renal Artery, Denervation, Autopsy, Fluorescent Antibody Technique
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