Changes in water and ion metabolism and in kidney functions during the development of oedema in rats fed on protein-deficient diets

Abstract

When a protein-deficient isocalorific diet was substituted for a standard diet in rats, there was a sudden decrease of the amt. of water excreted by the kidneys. This decrease of the urinary volume could not be explained by a change in the total water load. The urinary concn. of Cl- and Na+ remained unaffected. The urinary excretion of Cl- and Na+/ 24 hrs. was, however, markedly decreased. After several weeks on a protein-deficient diet, the urinary concn. of Cl- and Na+ decreased, while the urine vol. increased. In spite of this increase of the urine vol. there was a further decrease of the urinary excretion of Cl- and Na+. Correlating these changes in the urinary excretion with those occurring in blood plasma and skeletal muscle in rats fed on a protein-deficient diet it could be shown that: (a) the initial decrease of the urine vol., without changes in the ionic concn., corresponded to a slight but significant water retention accompanied by a small increase of the extracellular fluid space: (b) the decrease of the urinary concn. of Cl- and Na+ coincided with a marked increase of the extracellular fluid phase. Clearance estimations of inulin, diodone, Cl- and Na+ showed that: (a) Soon after the rats were put on a protein-deficient diet, the mean glomerular filtration rate decreased, but remained independent of the urine flow; this decrease in the glomerular filtration rate was accompanied by an increase in the tubular rate of water reabsorption. Diodone, Cl- and Na+ clearances were normal. (b) After several weeks on a protein-deficient diet, glomerular filtration rate was closely correlated with that of urine flow. The clearances of diodone, Cl- and Na+ were significantly depressed. The admn. of a standard amt. of water by stomach tube to rats fed on a protein-deficient diet resulted in a diuresis which was delayed in its onset and decreased in its amt., when compared with that in normal rats. The first decrease in the renal response to water admn. occurred in rats after 1-2 weeks on a protein-deficient diet; the min. response was observed after about 7 weeks. The urine of rats fed on a protein-deficient diet contained an anti-diuretic substance. The antidiuretic activity of the urine increased the longer the animals were fed on one of the exptl. diets. The first appearance of antidiuretic activity in the urine coincided with the decreased glomerular filtration rate, the increased tubular water reabsorption and the decreased renal response to water admn. Max. antidiuretic activity of the urine was found in rats fed for 7-9 weeks on a protein-deficient diet. It is concluded that a renal factor is involved in the onset and maintenance of the edema of protein deficiency.