Oxidative stress-induced glomerular mineralocorticoid receptor activation limits the benefit of salt reduction in Dahl salt-sensitive rats.
BACKGROUND
Mineralocorticoid receptor (MR) antagonists attenuate renal injury in salt-sensitive hypertensive rats with low plasma aldosterone levels. We hypothesized that oxidative stress causes MR activation in high-salt-fed Dahl salt-sensitive rats. Furthermore, we determined if MR activation persisted and induced renal injury, even after switching from a high- to a normal-salt diet.


RESULTS
High-salt feeding for 4 weeks increased dihydroethidium fluorescence (DHE, an oxidant production marker), p22phox (a NADPH oxidase subunit) and serum and glucocorticoid-regulated kinase-1 (SGK1, an MR transcript) in glomeruli, compared with normal-salt feeding, and these changes persisted 4 weeks after salt withdrawal. Tempol treatment (0.5 mmol/L) during high-salt feeding abolished the changes in DHE fluorescence, p22phox and SGK1. Dietary salt reduction after a 4-week high-salt diet decreased both blood pressure and proteinuria, but was associated with significantly higher proteinuria than in normal control rats at 4 weeks after salt reduction. Administration of tempol during high-salt feeding, or eplerenone, an MR antagonist (100 mg/kg/day), started after salt reduction, recovered proteinuria to normal levels at 4 weeks after salt reduction. Paraquat, a reactive oxygen species generator, enhanced MR transcriptional activity in cultured rat mesangial cells and mouse podocytes.


CONCLUSIONS
These results suggest that oxidative stress plays an important role in glomerular MR activation in Dahl salt-sensitive rats. Persistent MR activation even after reducing salt intake could limit the beneficial effects of salt restriction.
Department of Pharmacology, Kagawa University, Kagawa, Japan.
Kento
K
Kitada
Daisuke
D
Nakano
Ya
Y
Liu
Yoshihide
Y
Fujisawa
Hirofumi
H
Hitomi
Yuki
Y
Shibayama
Hirotaka
H
Shibata
Yukiko
Y
Nagai
Hirohito
H
Mori
Tsutomu
T
Masaki
Hiroyuki
H
Kobori
Akira
A
Nishiyama
D000315:Adrenalectomy; D000450:Aldosterone / Q000097:blood; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects; D003497:Cyclic N-Oxides / Q000494:pharmacology; D004996:Ethidium / Q000031:analogs & derivatives / Q000378:metabolism; D005247:Feeding Behavior / Q000187:drug effects; D017930:Genes, Reporter; D017874:Immediate-Early Proteins / Q000378:metabolism; D007678:Kidney Glomerulus / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology* / Q000503:physiopathology; D008156:Luciferases / Q000378:metabolism; D008297:Male; D050527:Mesangial Cells / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D018384:Oxidative Stress / Q000187:drug effects*; D050199:Podocytes / Q000187:drug effects / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011507:Proteinuria / Q000097:blood / Q000473:pathology / Q000503:physiopathology; D051381:Rats; D020303:Rats, Inbred Dahl; D018161:Receptors, Mineralocorticoid / Q000378:metabolism*; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage / Q000494:pharmacology*; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D013113:Spin Labels; D013599:Systole / Q000187:drug effects; D013997:Time Factors; D000099184:Serum-Glucocorticoid Regulated Kinases
D000450:Aldosterone; D015415:Biomarkers; D003497:Cyclic N-Oxides; D004996:Ethidium; D017874:Immediate-Early Proteins; D008156:Luciferases; D017346:Protein Serine-Threonine Kinases; D018161:Receptors, Mineralocorticoid; D017673:Sodium Chloride, Dietary; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D013113:Spin Labels; D000099184:Serum-Glucocorticoid Regulated Kinases; C452850:Slc9a1 protein, rat; C067883:dihydroethidium; C001803:tempol