Renal sympathetic nerve ablation for the management of resistant hypertension: an update

Increased Sympathetic Renal Innervation in Hemodialysis Patients Is the Anatomical Substrate of Sympathetic Hyperactivity in End-Stage Renal Disease

BACKGROUND

Renal denervation represents an emerging treatment for resistant hypertension in patients with end-stage renal disease, but data about the anatomic substrate of this treatment are lacking. Therefore, the aim of this study was to investigate the morphological basis of sympathetic hyperactivity in the setting of hemodialysis patients to identify an anatomical substrate that could warrant the use of this new therapeutic approach.

METHODS AND RESULTS

The distribution of sympathetic nerves was evaluated in the adventitia of 38 renal arteries that were collected at autopsy or during surgery from 25 patients: 9 with end-stage renal disease on dialysis (DIAL group) and 16 age-matched control nondialysis patients (CTRL group). Patients in the DIAL group showed a significant increase in nerve density in the internal area of the peri-adventitial tissue (within the first 0.5 mm of the beginning of the adventitia) compared with the CTRL group (4.01±0.30 versus 2.87±0.28×mm(2), P=0.01). Regardless of dialysis, hypertensive patients with signs of severe arteriolar damage had a greater number of nerve endings in the most internal adventitia, and this number was significantly higher than in patients without hypertensive arteriolar damage (3.90±0.36 versus 2.87±0.41×mm(2), P=0.04), showing a correlation with hypertensive arteriolar damage rather than with hypertensive clinical history.

CONCLUSIONS

The findings from this study provide a morphological basis underlying sympathetic hyperactivity in patients with end-stage renal disease and might offer useful information to improve the use of renal denervation in this group of patients.

Expression of adrenergic and cholinergic receptors in murine renal intercalated cells

Neurons influence renal function and help to regulate fluid homeostasis, blood pressure and ion excretion. Intercalated cells (ICCs) are distributed throughout the renal collecting ducts and help regulate acid/base equilibration. Because ICCs are located among principal cells, it has been difficult to determine the effects that efferent nerve fibers have on this cell population. In this study, we examined the expression of neurotransmitter receptors on the murine renal epithelial M-1 cell line. We found that M-1 cells express a2 and b2 adrenergic receptor mRNA and the b2 receptor protein. Further, b2 receptor-positive cells in the murine cortical collecting ducts also express AQP6, indicating that these cells are ICCs. M-1 cells were found to express m1, m4 and m5 muscarinic receptor mRNAs and the m1 receptor protein. Cells in the collecting ducts also express the m1 receptor protein, and some m1-positive cells express AQP6. Acetylcholinesterase was detected in cortical collecting duct cells. Interestingly, acetylcholinesterase-positive cells neighbored AQP6-positive cells, suggesting that principal cells may regulate the availability of acetylcholine. In conclusion, our data suggest that ICCs in murine renal collecting ducts may be regulated by the adrenergic and cholinergic systems.