Published in:
01-04-2013 | Original Contribution
Reduced cholesterol levels in renal membranes of undernourished rats may account for urinary Na+ loss
Published in: European Journal of Nutrition | Issue 3/2013
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Purpose
It has been demonstrated that reabsorption of Na+ in the thick ascending limb is reduced and the ability to concentrate urine can be compromised in undernourished individuals. Alterations in phospholipid and cholesterol content in renal membranes, leading to Na+ loss and the inability to concentrate urine, were investigated in undernourished rats.
Methods
Sixty-day-old male Wistar rats were utilized to evaluate (1) phospholipid and cholesterol content in the membrane fraction of whole kidneys, (2) cholesterol content and the levels of active Na+ transporters, (Na+ + K+)ATPase and Na+-ATPase, in basolateral membranes of kidney proximal tubules, and (3) functional indicators of medullary urine concentration.
Results
Body weight in the undernourished group was 73 % lower than in control. Undernourishment did not affect the levels of cholesterol in serum or in renal homogenates. However, membranes of whole kidneys revealed 56 and 66 % reduction in the levels of total phospholipids and cholesterol, respectively. Furthermore, cholesterol and (Na+ + K+)ATPase activity in proximal tubule membranes were reduced by 55 and 68 %, respectively. Oxidative stress remained unaltered in the kidneys of undernourished rats. In contrast, Na+-ATPase activity, an enzyme with all regulatory components in membrane, was increased in the proximal tubules of undernourished rats. Free water clearance and fractional Na+ excretion were increased by 86 and 24 %, respectively, and urinary osmolal concentration was 21 % lower in undernourished rats than controls.
Conclusion
Life-long undernutrition reduces the levels of total phospholipids and cholesterol in membranes of renal tubular cells. This alteration in membrane integrity could diminish (Na+ + K+)ATPase activity resulting in reduced Na+ reabsorption and urinary concentrating ability.