COMPOSITION OF THE RENAL CORTEX AND MEDULLA OF RATS DURING WATER DIURESIS AND ANTIDIURESIS.

Abstract

The composition of the renal papilla, medulla and cortex was studied in rats during hydropenia and water diuresis, and a few observations were made on hamsters.In confirmation of earlier findings, osmolality increased progressively from the outer medulla towards the tip of the papilla in hydropenia; this osmolal gradient was due largely to increasing concentration and content of sodium and urea. The osmolality at the tip was close to that of simultaneously collected urine. In water diuresis, this osmolal gradient was smaller but still present.Ammonium content and concentration increased progressively from the outer medulla towards the papilla.In water diuresis, the concentration and content of urea fell, but the gradient was still present. Sodium was little altered, and the fall in ammonium content, though considerable, contributed little to the total osmolal change.Potassium concentration and content were high in the terminal segment in diuresis and antidiuresis, and in water diuresis exceeded the hydropenic value.The water content increased progressively from the outer towards the inner medulla, but at the tip it was lower than in the adjacent segment. This distribution was qualitatively similar in both conditions, but the absolute level was higher in all medullary segments in water diuresis.The results are discussed in relation to the mechanism of production and maintenance of medullary hypertonicity.