DIETARY-SODIUM MODULATES NEONATAL BUT NOT ADULT CARDIAC ATRIAL-NATRIURETIC-PEPTIDE IN RATS

After an initial postnatal diuresis, neonates are in positive sodium b alance. Because atrial natriuretic peptide (ANP) contributes to sodium homeostasis, this study was designed to evaluate the maturational eff ects of increased dietary sodium intake on cardiac ANP production. Pre weaned Sprague-Dawley rat pups were artificially reared by feeding the m either a normal-sodium or high-sodium diet for 7 d and were compared with maternally reared rat pups. Adult rats were divided into three g roups: the first group was given ad libitum rat food and 1% sodium chl oride to drink, the second group was pair-fed with this group but give n tap water to drink, and the third group was fed ad libitum rat food and water for 10 d. Atrial and ventricular pro-ANP and ANP contents an d plasma ANP concentrations were measured by RIA. Steady state atrial and ventricular ANP mRNA expression was determined by Northern and dot -blot analysis. There was a 2-fold increase in atrial pro-ANP and ANP content and a 50% decrease in plasma ANP concentration in preweaned ra t pups fed a high-salt diet. In contrast, atrial pro-ANP and ANP conte nt and plasma ANP concentration were not affected by increased sodium intake in adult rats. Atrial and ventricular ANP mRNA levels and ventr icular pro-ANP and ANP contents were not altered by dietary sodium at either age. We conclude that chronic increase in sodium intake in the preweaning period results in increased storage of atrial pro-ANP. The decrease in plasma ANP concentration in these preweaned rats may be du e to reduced basal secretion or enhanced degradation of the peptide.