MECHANISMS OF THE RENAL RESPONSE TO PLASMA VOLUME EXPANSION

Abstract

Expansion of the plasma volume by infusions either of plasma or iso-oncotic albumin solution resulted almost uniformly in diuresis and natriuresis in anaesthetized dogs. Although the clearance of para-aminohippurate (RPF) usually increased, changes in clearance of creatinine (GFR) were neither large nor consistent in direction, indicating that the renal response depended on altered tubular reabsorption. The usual temporal dissociation between the peak values for water and sodium output during the response was interpreted as evidence of operation of two effector mechanisms. Reasons are given for believing that the renal response was not due to a direct action of the infusate, but rather to activation of a reflex mechanism by expansion of vascular volume. Bilateral cervical vagotomy did not prevent either the diuresis or the natriuresis, again implying that receptors additional to those in the cardiac atria must contribute to the sensory limb of the reflex. The average magnitude of diuretic and natriuretic responses after cervical vagotomy was, however, less than a quarter of that before the denervation, supporting the contention that the vagi do contribute to the renal response to expansion of the plasma volume when plasma is infused. The diuresis and the natriuresis still occurred during infusion in adrenalectomized animals, indicating that inhibition of aldosterone secretion is not the only effector mechanism leading to a natriuretic response to expansion of vascular volume.