ROLE OF ATRIAL-NATRIURETIC-PEPTIDE IN LONG-TERM VOLUME HOMEOSTASIS

1. Long-term volume homeostasis is linked very closely to long-term ar terial pressure control through the renal-body fluid feedback mechanis m, A key feature of this control system is the ability of the kidneys to respond to changes in arterial pressure by altering renal excretion of salt and wager, often referred to as renal-pressure natriuresis. 2 . Quantitative studies indicate that ANP secretion is relatively sensi tive to changes in atrial pressure and that the rate of hormonal secre tion does not adapt to continuous long-term stimulation. 3. Under norm al conditions, the renal-body fluid feedback mechanism for arterial pr essure control is very efficient in minimizing changes in body fluid v olumes during alterations in sodium intake. Therefore, only small chan ges in atrial pressure and ANP secretion occur. Alterations in plasma ANP concentration within physiological levels have little effect on re nal-pressure natriuresis and, therefore, have little impact on volume homeostasis. 4. When the renal-body fluid feedback mechanism for arter ial pressure control is impaired and body fluid volumes are elevated, such as in heart failure, large increases in atrial pressure and ANP s ecretion occur, The resultant pathophysiological plasma levels of ANP exert sustained natriuretic effects and chronically shift renal-pressu re natriuresis to lower arterial pressures, In the absence of this chr onic effect of ANP on renal-pressure natriuresis, reduced arterial pre ssure in compensated heart failure would result in protracted retentio n of salt and water and additional increments in body fluid volumes.