Natriuresis and atrial natriuretic factor secretion during inappropriate antidiuresis

The mechanisms responsible for the natriuresis encountered in the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) are not fully understood. The present study explores the role of atrial natriuretic factor (ANF). Eight subjects unable to excrete ingested free water normally (three patients with SIADH and five healthy humans after intranasal administration of desmopressin) underwent a standard oral water loading test. Plasma ANF level and urinary sodium excretion increased during water retention, whereas plasma aldosterone value decreased later. The increment of urinary sodium excretion rate was significantly correlated with that of plasma ANF. In two patients with hyponatremia due to SIADH, plasma ANF levels were increased during the hyponatremic phase of their condition and decreased under water restriction. In one of them, marked natriuresis was observed when the plasma ANF level was high. It is concluded that secretion of ANF is acutely and chronically stimulated during water retention in SIADH and that ANF may be in part responsible for the natriuresis encountered in inappropriate antidiuresis.