Coordinate regulation of renal expression of nitric oxide synthase, renin, and angiotensinogen mRNA by dietary salt

Abstract

Experiments were performed to examine the effect of changes in dietary salt intake on the neuronal form of the constitutive nitric oxide synthase (ncNOS, type I NOS), renin, and angiotensinogen mRNA expression in the kidney. Three groups of Sprague-Dawley rats were studied as follows: rats maintained on a 3% Na diet plus 0.45% NaCl in the drinking fluid for 7 days (high salt), rats given a single injection of furosemide (2 mg/kg i.p.) and a 0.03% Na diet for 7 days (low salt), and rats on a diet containing 0.2% Na (control). mRNA expression was assessed with reverse transcription-polymerase chain reaction (RT-PCR) methods using cDNA prepared from samples of renal cortex and microdissected tubular segments. ncNOS PCR products were quantified by comparison with a dilution series of a mutant deletion template. Compared with their respective control, ncNOS mRNA levels in renal cortical tissue were elevated in rats on a low-salt diet and reduced in rats on a high-salt diet. Similar changes were seen in the expression of renin and angiotensinogen mRNA. Dietary salt intake did not alter the mRNA levels for ncNOS from the inner medulla or for endothelial constitutive NOS (ecNOS, type III NOS) and inducible NOS (iNOS, type II NOS) in the renal cortex. ncNOS mRNA was found in glomeruli dissected with the macula densa-containing segment (MDCS), but only at marginal levels in glomeruli without MDCS. Furthermore, a low-salt diet stimulated ncNOS mRNA in glomeruli with MDCS by 6.2-fold compared with a high-salt diet. There was no effect of salt diet on ncNOS mRNA in glomeruli without MDCS or in inner medullary collecting ducts. These results suggest that ncNOS expression in macula densa cells is inversely regulated by salt intake, thus following the known response of the renin-angiotensin system to changes in salt balance.

Enhancement of Intrarenal Angiotensinogen in Dahl Salt-Sensitive Rats on High Salt Diet

“…The HS diet suppressed PRA in both strains, and PRA was significantly lower in the DSϩLS group compared with the DRϩLS group, as previously shown. 4 The HS diet has been shown to suppress plasma and intrarenal expression of AGT in Sprague-Dawley 16,17 and Wistar-Kyoto 18 rats. Similarly, in the present study, plasma Ang II and AGT levels were also suppressed by HS diet in both DR and DS strains.…”

Changes of Cell Volume and Nitric Oxide Concentration in Macula Densa Cells Caused by Changes in Luminal NaCl Concentration

“…Results regarding the distal [NaCl] and the production of NO in MD in earlier studies are somewhat conflicting. In studies concerning the influence of sodium intake on NOS expression, it has been found that sodium deficiency stimulates nNOS expression, as do other conditions that are likely to result in reduced MD [NaCl] or transport, such as furosemide administration and unilateral stenosis of the renal artery (31,32). In contrast, high-salt diets and hyperfusion significantly inhibited nNOS mRNA expression (31,32).…”

“…In studies concerning the influence of sodium intake on NOS expression, it has been found that sodium deficiency stimulates nNOS expression, as do other conditions that are likely to result in reduced MD [NaCl] or transport, such as furosemide administration and unilateral stenosis of the renal artery (31,32). In contrast, high-salt diets and hyperfusion significantly inhibited nNOS mRNA expression (31,32). But in the other experiments in which the urinary excretions of nitrate and nitrite were measured, Shultz and Tolins (33) found that high salt intake generated more NO in MD cells.…”

Role of renal NO production in the regulation of medullary blood flow

“…Ni and Vaziri (76) observed a decrease in medullary protein expression of NOS I and II after 3 wk of an 8% sodium diet. Others found no change in medullary mRNA expression of any of the NOS isoforms (98,113).…”