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Excretion Obstacle of Uric Acid in Kidneys

2012-09-13 14:45

Uric acid is the terminal product of purine metabolism. The increased production of uric acid due to purine metabolic disorders or decreased excretion of uric acid due to decline of renal functions can all cause uric acid in the blood to rise. When the concentration of urate is supersaturated in the blood, it will accumulate in the kidneys and cause damages to renal tissues and this is hyperuricemia nephropathy.

Kidney is crucial organ for regulating the concentration of uric acid in the blood. Uric acid has no physiological function in the body and under normal circumstances, 2/3 to 3/4 uric acid is excreted outsides through the kidneys and the rest is discharged through the intestinal tract. In case of renal dysfunction, there will be excretion obstacle of uric acid in the kidneys and nearly all the filtered uric acid by renal glomeruli is re-absorbed by the proximal renal tubules. The following are some factors affecting the excretion ability of the kidneys.

1. In the early stage of renal insufficiency there are still healthy nephrons and the increase of uric acid is not obvious and it is not inconsistent with the decrease of glomerular filtration rate (GFR). When GFR<10ml/min can there be obvious symptoms of hyperuricemia nephropathy. In case of primary hypertension, the renal tubular function of handling sodium is impaired and the early renal vascular lesions will cause excretion obstacle of uric acid of the renal tubules.

2. When the blood volume is reduced such as the limitation of sodium, usage of diuretic and diuresis can all cause reduced uric acid clearance. When the blood volume is reduced and urine flow velocity is less than 1ml/min, the uric acid will accumulate in the renal tubules and when its concentration exceeds that of the surrounding capillaries there will be back-diffusion.

3. Organic acid can affect the excretion of uric acid. The discharge of organic acid needs the aid of renal tubule anion pump and the accumulation of organic acid in proximal renal tubules will cause its metabolic disorder and affect the excretion of uric acid. The increase of organic acid is common in cases of alcohol poisoning, accumulation of lactic acid after strenuous exercises, diabetic ketoacidosis and other serious metabolic disorders.

4. Lead can inhibit the excretion of uric acid. Chronic lead poisoning can cause decrease of uric acid clearance which is more obvious than the decrease of creatinine clearance rate.


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