Water retention and aquaporins in heart failure, liver disease and pregnancy

Water retention in excess of total body sodium frequently occurs in patients with cardiac failure or cirrhosis and in pregnancy. In fact, hyponatraemia signifies a poor prognosis in cardiac failure and cirrhosis1,2. The mechanism for this hyponatraemia, however, has not been well defined. In the era when the antidiuretic hormone (ADH) bioassay was performed in ethanol-anaesthetized rats, consistent alterations in ADH could not be demonstrated in hyponatraemic patients with cirrhosis or heart failure. Therefore it was suggested that intrarenal, non-ADH-dependent, mechanisms accounted for the water retention in these oedematous disorders. Another dilemma in understanding fluid balance in cardiac failure, cirrhosis and pregnancy relates to defining the afferent signals that could stimulate AVP release with resultant water retention. Expanded plasma volumes have been reported in all three conditions. This finding is typically associated with increased water excretion rather than water retention; thus, signals other than increased plasma volume must contribute to the water retention.