Further characterization of the influence of supine posture on renal function in late pregnancy. Effect of rapid saline infusions on renal sodium, water and uric acid metabolism.

Abstract

Renal function was measured in hydrated, mineralcorticoid treated third-trimester women positioned in lateral recumbency. One group of the women remained in lateral recumbency and the remainder assumed a supine position for two additional hours during which hypotonic saline was infused. Infusions of the lateral recumbent group were followed by increments in both filtered and excreted sodium. In the supine-subjects a similar increase in filtered sodium, but decrease in sodium excretion took place. When extracellular volume was expanded decrements in percent proximal tubular reabsorption of filtrate occurred in the lateral recumbent women but not in those positioned on their backs. Hypotonic saline infusions did not alter fractional uric acid clearances in the lateral recumbent group. Despite infusion these clearances decreased in the supine group. The physiologic alterations observed in the supine pregnant women therefore simulated three renal metabolic abnormalities associated with toxemia: persistently decreased sodium excretion in spite of interstitial fluid volume expansion, impaired ability to handle a water load, and decreased fractional uric acid clearance.