EFFECT OF RENAL ARTERIAL INFUSION OF ALBUMIN ON SALINE DIURESIS IN THE DOG.

Abstract

It has been suggested that the protein concentration of peritubular plasma may be an important determinant of sodium and water reabsorption by the renal tubule (1,2 −3). The effect of protein on excretion of water and electrolyte has been the subject of several investigations (4,5,6,7). Infusions of hyperoncotic albumin reduce excretion of sodium in normal man(4,5,7). In the dog, infusion of hyperoncotic albumin may not result in increased excretion of sodium(6)) whereas the infusion of iso-oncotic “plasma-like” solutions is associated with a natriuresis similar to that resulting from the infusion of equal volumes of saline(8). Since the excretion of sodium must be the difference between total filtered load and net tubular reabsorption, changes in filtration rate could mask changes in tubular reabsorption when plasma volume is expanded during the infusion of solutions containing protein. Thus, an increase in filtration rate associated with infusions of protein solutions may result in a natriuresis which could be independent of any effect that plasma protein concentration may have on tubular reabsorption. Despite the demonstration by micropuncture that active reabsorption by the proximal tubule of Necturus is not grossly influenced by the transtubular gradient of oncotic pressure (9), the possibility cannot be excluded that overall net tubular reabsorption by the mammalian kidney is in some way affected by the protein concentration of peritubular plasma. Even though the osmotic gradient for water produced by the protein concentration gradient between tubular lumen and capillary is too small to account for a major fraction of tubular reabsorption(9), changes in protein concentration could conceivably influence net reabsorption indirectly through such mechanisms as a change in interstitial volume or a redistribution of blood within the kidney. The present studies were designed to determine whether increasing the protein concentration of renal arterial blood during the natriuresis of saline loading results in any major change in sodium excretion.