Dietary Sodium Modulates Neonatal but Not Adult Cardiac Atrial Natriuretic Peptide in Rats

Abstract

After an initial postnatal diuresis, neonates are in positive sodium balance. Because atrial natriuretic peptide (ANP) contributes to sodium homeostasis, this study was designed to evaluate the maturational effects of increased dietary sodium intake on cardiac ANP production. Preweaned Sprague-Dawley rat pups were artificially reared by feeding them either a normalsodium or high-sodium diet for 7 d and were compared with maternally reared rat pups. Adult rats were divided into three groups: the first group was given ad libitum rat food and 1% sodium chloride to drink, the second group was pair-fed with this group but given 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 and 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 Zfold increase in atrial pro-ANP and ANP content and a 50% decrease in plasma ANP concentration in preweaned rat pups fed a high-salt diet. In contrast, atrial pro-ANP and ANP content and plasma ANP concentration were not affected by increased sodium intake in adult rats. Atrial and ventricular ANP mRNA levels and ventricular pro-ANP and ANP contents were not altered by dietary sodium at either age. We conclude thal 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 due to reduced basal secretion or enhanced degradation of the peptide. (Pediutr Res 37: 310-315, 1995) Abbreviations AH, adult high-sotlium diet AL, adult ad libitum diet AN, adult normal-sodium diet ANF, atrial natriuretic factor ANP, atrial natriuretic peptide GAPDH, glyceraltlehyde 3-phosphate dehydrogenase PWH, preweaned high-sodium diet PWM, preweaned maternally reared PWN, preweaned normal-sodium diet C-receptor, clearance receptor ANP, secreted primarily from atrial myocytes, exhibits natriuretic, diuretic, and vasorelaxant properties. Since 1981, when ANP was first described by de Bold et al. (I), the production, secretion, and actions of the peptide have been further elucidated. Although atrial stretch is generally recognized as the major stimulus for ANP release, recent studies suggest an important role for sodium ingestion in ANP regulation (2-4).In term and preterm infants, there is an initial diuresis and natriuresis that occur in conjunction with an increase in plasma