THE EFFECTS OF FUROSEMIDE ON THE OSMOLALITY OF THE URINE AND THE COMPOSITION OF RENAL TISSUE

¹ Department of Therapeutics, University of Edinburgh, Edinburgh, Scotland

In healthy human subjects furosemide is shown to reduce markedly the reabsorption of solute-free water (TcH₂O) during hydropenia and inhibit the normal rise in free-water excretion (CH₂O) during sustained maximal water diuresis. In order to determine the mechanism of the effect on TcH₂O, mannitol and furosemide were given to hydropenic rats to produce similar rates of solute excretion. In contrast to the effect of mannitol, furosemide produces a marked reduction in TcH₂O in the rat as in man. The concentrations of sodium and urea were measured in samples of papilla, inner medulla and cortex from rat kidneys during mannitol and furosemide diuresis. The renal medullary and papillary concentrations of sodium and urea were depressed by both diuretics to the same degree. The site of action of furosemide in the nephron is discussed in the light of these findings and it is suggested that part of its action is to reduce the permeability of the collecting ducts to water.