Role of renal nerves in maintaining sodium balance in unrestrained conscious rats

Abstract

This study was designed to investigate the effects of bilateral renal denervation on sodium and water balance, the renin-angiotensin system, and systemic blood pressure in unrestrained conscious rats maintained on a normal- or low-sodium diet. Renal denervation was proven by chemical and functional tests. Both bilaterally denervated rats (n = 18) and sham-denervated rats (n = 15) maintained positive sodium balance while on a normal sodium intake. Both groups were in negative sodium balance for 1 day after dietary sodium restriction was instituted but were in positive sodium balance for the following 9 days. Systolic blood pressure was higher in sham-denervated (115 +/- 3 mmHg) than in denervated rats (102 +/- 3 mmHg) while on a normal diet (P less than 0.05) and remained so during sodium restriction. Plasma renin concentration (PRC) and plasma aldosterone concentration (PAC) were significantly diminished in the denervated rats during normal sodium intake (P less than 0.05). After dietary sodium restriction, PRC increased in both groups but remained significantly lower in the denervated rats (P less than 0.05). Following dietary sodium restriction, PAC also increased significantly to levels that were similar in both groups of rats. These results demonstrate that awake unrestrained growing rats can maintain positive sodium balance on a low sodium intake even in the absence of the renal nerves. However, efferent renal nerve activity influenced plasma renin activity in these animals.

Renal nerves and nNOS: roles in natriuresis of acute isovolumetric sodium loading in conscious rats

“…However, as the deviation in sodium balance was transient, this is unlikely to explain the chronic decrease in MABP. In the absence of lasting changes in sodium balance (compared to the steady positive balance of appropriate control animals), the present 20% decrease in PRC, confirming previous results of renal denervation (8,18), does not provide a convincing explanation of the relative hypotension. Only further studies, including measurements of sympathetic tone and vasoactive hormones, may disclose these mechanisms.…”

“…Other results have shown a modest decrease in systolic blood pressure (by tail cuff) after renal denervation (8). However, the time course of the development of hypotension after renal denervation has been unclear.…”

Renal denervation chronically lowers arterial pressure independent of dietary sodium intake in normal rats

“…This may be due, in part, to the methods used to measure arterial pressure and how these measurements influence basal sympathetic activity. Such studies have included anesthetized surgically stressed animals (3), tail cuff measurements in conscious restrained rats (17), and direct recordings of arterial pressure in conscious tethered rats (21) or dogs (35). The strongest demonstration of how measurement conditions alter the influence of renal nerves on renal function comes from studies in conscious rabbits, in which renal nerve activity and renal blood flow were measured simultaneously in one kidney and blood flow was measured in the contralateral denervated kidney.…”

“…A second possibility is that the reninangiotensin system is suppressed in RDNX rats, lowering arterial pressure. Several (7,17,20,35), but not all (19,21), investigators have reported that RDNX animals have low plasma renin activity compared with intact animals. In a recent study (11), we reported that Sham Fig.…”

“…Unfortunately, the results of these studies have also led to contradictory findings. Indeed, several investigators have observed that in dogs, rabbits, and rats, renal denervation impaired the ability of the kidneys to conserve sodium when animals were placed on a lowsodium diet (16, 18) but others did not (4,17,35). Such a discrepancy in renal sodium handling between studies is most likely due to variable degrees of sodium restriction with renal nerves becoming more important with more severe salt depletion (14).…”