REGULATION OF THE RENAL RESPONSE TO ATRIAL-NATRIURETIC-PEPTIDE BY SODIUM-INTAKE IN PREWEANED RATS

The neonate conserves sodium avidly, and sodium intake is normally lim ited to that present in maternal milk. To evaluate the role of atrial natriuretic peptide (ANP) in this adaptation, preweaned rat pups were artificially reared and fed a formula with either normal sodium (25 mE q/L) or high sodium (145 mEq/L) for 7-8 d. To determine whether increa sed dietary sodium decreases ANP clearance receptor activity, animals were anesthetized, and the plasma ANP concentration (ANPp), urine flow (V), urinary sodium (UNaV), and cGMP excretion (UcGMPV) were measured before and after infusion of ANF(4-23), an ANP clearance receptor inh ibitor (C-ANF), at 50 mu g/kg/min. Infusion of C-ANF increased ANPp 10 -fold in both normal and high sodium groups, but V, UNaV, and UcGMPV i ncreased only in animals receiving the high sodium diet (p < 0.05). In cubation of isolated glomeruli with 0.1 mu M ANP increased extracellul ar cGMP more in high sodium than normal sodium groups (p < 0.05). We c onclude that ANP clearance receptors in the neonate are highly activat ed regardless of sodium intake. Increased dietary sodium increases the renal diuretic and natriuretic response to circulating ANP through en hanced generation of cGMP.