THE NEPHROPATHY OF EXPERIMENTAL MAGNESIUM DEFICIENCY: AN ELECTRON MICROSCOPIC STUDY

Thirty rats were divided into three equal groups; the control group C and the two experimental groups were fed on diets identical in all respects other than the magnesium content. Group A were kept on a magnesium deficient diet for 13 days, and group B for 3 days. At the end of the experimental period, muscle, kidney and plasma were analyzed for their Mg and Ca contents and the kidneys were examined by the light and electron microscopes. No significant change was noted in the magnesium content of the kidneys of the deficient rats. In skeletal muscles, there was progressive depletion of magnesium, and the plasma magnesium also fell. The only highly significant result in the calcium content was a marked increase in the kidneys of the deficient groups. After as early as 3 days on the deficient diet, foci of dilated proximal tubules were seen in the cortico‐medullary zone even by the light microscope, but after 13 days they were observed all over the cortex and outer zone of the medulla. The lining cells of the slightly dilated tubules were swollen and vacuolated. As the dilatation increased, the tubular lining cells appeared to lose their brush border and to become flattened. The cells contained structureless cytoplasmic granules. Important negative findings are the normal appearance of the mitochondria, the normal thickness of the basement membrane, and the absence of any demonstrable obstruction in the dilated tubules or in more distal sites. It seems possible that in magnesium deficiency the proximal tubule cells, which normally reabsorb Ca ++ and Mg ++ by a common transport mechanism, reabsorb an excess of Ca ++ from the glomerular filtrate which is deficient in Mg ++ . The excess of absorbed calcium ions is largely deposited locally in these cells, appearing as the dense granules. This would explain the high calcium content in the kidneys and the nephrocalcinosis in late stages.