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KMID : 0438219720090020251
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Korea University Medical Journal
1972 Volume.9 No. 2 p.251 ~ p.258
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Effect of isotonic saline Ioading on distribution of electrolytes and urea in the rabbit kidney
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Abstract
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Rapid intravenous infusion of saline is known to suppress reabsorption of sodium and water in the proximal tubule. It is now well established that the increase in urinary excretion of sodium which occurs during acute saline loading is due to a decrease in sodium reabsorption by the tubules rather than to a increase in the amount of sodium filtered by the glomeruli. The mechanism responsible for this decrease in tubular reabsorption is not entirely clear.
It is well known that expansion of the extracellular fliud volume with isotonic saline solution inhibits both fractional and over all salt and water reabsorption in the proximal tubule. Depression of the fraction of filtrate reabsorbed by the proximal tubule during saline loading greatly exceeds the simultaneous fractional increase in sodium excretion, making it unnecessary to propose that decreases in distal tubular reabsortion are involved in the natriuretic response to saline infusion.
However, other evidence indicates that large depression of reabsorption by the proximal tubule alone may not effect large changes in, sodium excretion, and may be necessary to postulate that the effect of saline infusion to increase sodium excretion results from limited reabsorption both the proximal tubule and some more distal segment of the nephron. At the moment the role of changes in distal tubular reabsorption in the natriuretic response to volume expansion is not clear.
This study was made to clear the still unsolved problem of which osmotic gradient is made in the inner medulla or not during saline loading.
On experiments 31 rabbits weighing between 1.5-2.5kg, 11 in unloaded control group, 11 in saline loaded group, and 9 in saline loaded with aortic constriction, were studied.
Inuline clearance for GFR, PAH clearance for RPF, sodium, potassium, urea, and osmolarity in serum and urine were measured.
The kidney slices were made for analysis of sodium, potassium and urea.
The results were as follows:
1) Natriuresis was observed without any relation to glomerular filtration rate and renal plasma flow by saline loading, and filtrered sodium was not paralleled to excreted sodium.
2) Free water reabsorption was increased in saline loaded rabbits.
3) Sodium did not make any significant gradient in inner medulla by saline loading.
4) The distributed rate of urea did not make any significant gradient in inner medulla by saline loading.
5) The distributed rate of potassium in the kidney was similar to normal control rabbit.
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