Reduced cholesterol levels in renal membranes of undernourished rats may account for urinary Na⁺ loss.
OBJECTIVE
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.


CONCLUSIONS
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.
Departamento de Fisiologia e Farmacologia, Centro de Ciências Biológicas, Universidade Federal de Pernambuco, Av. Prof. Moraes Rego, s/n, Cidade Universitária, Recife, PE, 50670-901, Brazil.
Fabiana S T
FS
Oliveira
Leucio D
LD
Vieira-Filho
Edjair V
EV
Cabral
Luzia S
LS
Sampaio
Paulo A
PA
Silva
Vera C O
VC
Carvalho
Adalberto
A
Vieyra
Marcelo
M
Einicker-Lamas
Vera L M
VL
Lima
Ana D O
AD
Paixão
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D027682:Cation Transport Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D015536:Down-Regulation; D005260:Female; D007668:Kidney / Q000166:cytology / Q000201:enzymology / Q000378:metabolism / Q000503:physiopathology; D007671:Kidney Concentrating Ability; D007687:Kidney Tubules, Proximal / Q000201:enzymology / Q000378:metabolism / Q000503:physiopathology; D007774:Lactation; D008297:Male; D044342:Malnutrition / Q000151:congenital / Q000378:metabolism* / Q000503:physiopathology / Q000652:urine; D039382:Maternal Nutritional Physiological Phenomena; D010743:Phospholipids / Q000378:metabolism; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D051437:Renal Insufficiency / Q000209:etiology*; D012964:Sodium / Q000652:urine; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D027682:Cation Transport Proteins; D010743:Phospholipids; D002784:Cholesterol; D012964:Sodium; D000251:Adenosine Triphosphatases; C021838:sodium-translocating ATPase; D000254:Sodium-Potassium-Exchanging ATPase