Korean Journal of Nephrology 1989;8(3):408-414.
정상 및 이뇨성 흰쥐 신장 조직에서 삼투성 유기물질의 농도
이권행 , 조규철
Abstract
It is well known that whereas the osmolalities of the cortex and plasma are identical, the osmolality of the medulla rise progressively from the corticomedullary junction to the papillary tip and the osmolality of the papillary tip is several times higher than that of the cortex. Because renal tubular cells cannot maintain any substantial pressure across their cell membranes, the intracellular osmolality is close to extracellular os- mola Jity. The intracellular levels of Na and K salts and urea in renal medulla are much too low to balance the high extracellular osmolality. Also, high levels of salts and urea within cells are toxic and inhibit celullar enzymes. Therefore, other nonperturbing osmotically active organic soultes (osmolytes) may substitute for salts and urea without deleterious effects. The osmolytes mostly fall into three groups; meth- ylamines, polyols, and certain amino acids. Two meth- ylamines have been identified in high concentration in the renal inner medulla, namely glycerophosphoryl- choline (GPC) and betaine. The high concentration of methylamines in the inner medulla is especially interest- ing since these compounds are known to offset the destabilizing effects of urea on metabolic enzymes. Two polyols, namely sorbitol and inositol, have been found in high concentrations in renal medulla. In an attempt to clarify the role of osmotically active organic solutes in kidney, we measured the levels of inorganic ions, urea, GPC, sorbitol and inositol in nor- mal and diuretic rat kidney tissues. 1) In normal rat, inorganic ion levels in medulla were slightly higher than that in cortex. Osmolality was highest in the inner medulla and decreased progressively to the cortex. During diuresis, the concentration of potassium ion and osmolality significantly decreased in whole renal tissues.2) In normal rat, urea level was highest in the inner medulla. Diuresis signifcantly decreased urea levels in the inner medulla from 233.1 to 122.3 mM/kg wet wt, but urea levels in the cortex and the outer medulla were unchanged. 3) In normal rat, GPC levels in the cortex and the medulla were 2.91 and 4.87 mM/kg wet wt respectively. Diuresis significantly decreased GPC levels in the cortex to 0.61 mM/kg wet wt and in the medulla to 1.49 mM/ kg wet wt. 4) In normal and diuretic rats, sorbitiol was not detected and inositol was below 2 mM/wet wt in the cortex. During diuresis, sorbitol in the medulla was decreased from 12.2 to 2.82 mM/kg wet wt and inositol in the medulla was also decreased from 16.3 to 6.31 mM/ kg wet wt. These data suggest that urea, polyols, and GPC may play a significant role as osmotically active organic solutes in the medulla of the rat kidney.
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