PARADOXES OF BODY-FLUID VOLUME REGULATION IN HEALTH AND DISEASE - A UNIFYING HYPOTHESIS

The body's normal homeostasis is maintained by the integrity of the ex cretory capacity of the kidneys. In advanced cardiac failure, however, the avidity of the renal sodium and water retention contributes to th e occurrence of pulmonary congestion and peripheral edema. In patients with advanced cirrhosis, the kidneys again fail to excrete the amount s of sodium and water ingested, thus leading to ascites and peripheral edema. The signals for this renal retention of sodium and water in a patient with cirrhosis must be extrarenal because when the same kidney s are transplanted into persons with normal liver function, renal sodi um and water retention no longer occurs; rather, the kidneys maintain normal fluid and electrolyte balance. Excessive sodium and water reten tion by the kidneys also occurs during pregnancy despite a 30% to 50% increase in plasma volume, cardiac output, and glomerular filtration r ate. What are the afferent and efferent signals whereby normal kidneys retain sodium and water so that total extracellular, interstitial, an d intravascular volumes expand far beyond those limits observed in nor mal subjects? These dilemmas are the subject of this review, in which a ''unifying hypothesis of body fluid volume regulation'' is presented .