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1Departments of Pharmacology and Toxicology, 2Physiology, and 3Internal Medicine, University of Tübingen, Tübingen; 4Department of Clinical Neurobiology, University Hospital of Neurology, Heidelberg; 5Department of Biology, Chemistry, and Pharmacy, Free University Berlin, Berlin, Germany; and 6Departments of Medicine and Pharmacology, University of California, and Veterans Affairs San Diego Healthcare System, San Diego, California
Submitted 22 July 2005 ; accepted in final form 2 May 2006
Mineralocorticoids enhance expression and insulin stimulates activity of the serum- and glucocorticoid-inducible kinase SGK1, which activates the renal epithelial Na+ channel (ENaC). Under a salt-deficient diet, SGK1 knockout mice (sgk1/) excrete significantly more NaCl than their wild-type littermates (sgk1+/+) and become hypotensive. The present experiments explored whether SGK1 participates in the hypertensive effects of a high-fat diet and high-salt intake. Renal SGK1 protein abundance of sgk1+/+ mice was significantly elevated after a high-fat diet. Under a control diet, fluid intake, blood pressure, urinary flow rate, and urinary Na+, K+, and Cl excretion were similar in sgk1/ and sgk1+/+ mice. Under a standard diet, high salt (1% NaCl in the drinking water for 25 days) increased fluid intake, urinary flow rate, and urinary Na+, K+, and Cl excretion similarly in sgk1/ and sgk1+/+ mice without significantly altering blood pressure. A high-fat diet alone (17 wk) did not significantly alter fluid intake, urinary flow rate, urinary Na+, K+, or Cl excretion, or plasma aldosterone levels but increased plasma insulin, total cholesterol, triglyceride concentrations, and systolic blood pressure to the same extent in both genotypes. Additional salt intake (1% NaCl in the drinking water for 25 days) on top of a high-fat diet did not affect hyperinsulinemia or hyperlipidemia but increased fluid intake, urinary flow rate, and urinary NaCl excretion significantly more in sgk1/ than in sgk1+/+mice. Furthermore, in animals receiving a high-fat diet, additional salt intake increased blood pressure only in sgk1+/+ mice (to 132 ± 3 mmHg) but not in sgk1/ mice (120 ± 4 mmHg). Thus lack of SGK1 protects against the hypertensive effects of a combined high-fat/high-salt diet.
insulin; blood pressure; aldosterone; mineralocorticoids; ENaC; kidney
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