THE NEPHROPATHY OF EXPERIMENTAL POTASSIUM DEFICIENCY. AN ELECTRON MICROSCOPIC STUDY

¹ Departments of Pathology and Therapeutics, Edinburgh University

The most prominent abnormality in renal function in potassium depletion in man and in experimental animals is a defect in concentrating power. Although it has been suggested that in rats this may be due to lesions in the collecting tubules, the virtual absence of these histological abnormalities in human material and in dogs is paradoxical. In the experiments reported here, mild potassium depletion has been induced in rats by dietary restriction and the kidneys of these animals examined by the electron microscope. The most obvious early and constant abnormality was found in the basement membrane of the thin segment of the loop of Henle. The width of this membrane is increased to 3-5 times normal and it becomes fibrillar in appearance. This thickening and fibrillation involves also the pars recta of the proximal tubule, but does not extend into the thick ascending segment of the loop of Henle, the convoluted tubules or the collecting tubules. In the later stages of potassium depletion electron microscopy confirmed the abnormalities already reported in light microscopic studies— i.e. granulation, hyperplasia and degeneration of the cells of the collecting tubules. The relationship between the basement membrane abnormality and the known effect of potassium depletion on renal concentrating power is discussed in the light of the counter-current hypothesis. It is suggested that the physical state of the ground substance of the basement membrane may have an important influence on the movement of water and electrolytes within the medullary region of the kidney and may be responsible for the renal defect in water conservation which occurs in potassium depletion.