THE EFFECTS OF AN INCREASE IN PLASMA VOLUME ON THE METABOLISM AND EXCRETION OF WATER AND ELECTROLYTES BY NORMAL SUBJECTS 12

Abstract

This investigation was an attempt to study the alterations in the metabolism and excretion of electrolytes and water promoted by expansion of the plasma volume with hyper- and iso-oncotic solns. of purified salt-poor human albumin in normal human subjects. Infusions of hyperoncotic solns. (25-10%) of albumin were associated with decreases in the rates of excretion of Na and chloride and, sometimes, water as well. This appeared to be the case even if the extracellular space was initially expanded by the prior infusion of several liters of normal saline. Moreover, the decreased rate of excretion of salt was not mediated via the adrenal cortex, since this same response was observed in a patient with well-validated Addison''s disease. These changes were unassociated with significant changes in the clearance of endogenous creatinine. In contrast, infusions of iso- or hypo-oncotic solns. of albumin were followed by sharp increases in the rate of excretion of water, without a clear alteration in the rate of excretion of Na or chloride. This diuresis could be inhibited by the incorporation of posterior pituitary material in the infusate. It is suggested that an increase in plasma volume promotes the suppression of secretion of antidiuretic hormone by the posterior pituitary gland; and, that an increase in the colloid osmotic pressure of the plasma promotes an increased reabsorption of Na by the renal tubules, perhaps, following a stimulus to an onco-receptor organ located within the vascular tree. The increased reabsorption of Na leads to a secondary retention of water and, hence, inhibits the diuresis of water when the expansion of the plasma volume is associated with an increase in colloid osmotic pressure. This latter situation obtains when the plasma volume is expanded by an infusion of 10% or 25% albumin.