Atrial natriuretic peptide in renal development.

Although discovered little more than a decade ago, atrial natriuretic peptide (ANP) has been shown to play a significant role in the maintenance of sodium homeostasis. Immediately after birth, plasma ANP concentration is very high concurrent with right atrial dilatation and a high urinary excretion of cyclic GMP (cGMP), the second messenger for ANP. Following postnatal diuresis and natriuresis, atrial volume, plasma ANP concentration, and urinary cGMP excretion decrease to baseline levels. In the ensuing suckling period, the diuretic and natriuretic response to acute saline volume expansion are attenuated, an effect which is offset by the lower hematocrit at this age. Increase in hematocrit by isovolemic exchange transfusion results in a greater rise of plasma ANP concentration following volume expansion, but a reduced excretion of cGMP. Intravenous infusion of ANP results in greater plasma ANP concentration, and greater urinary excretion of cGMP and sodium, in adult than in young rats. This increased metabolic clearance of ANP during early development is due at least in part to increased activity of clearance receptors. In addition, neutral endopeptidase contributes to removal of circulating ANP in maturing as well as adult rats. Infusion of ANP in neonatal or adult rats results in accumulation of cGMP in glomerular podocytes, with a higher threshold for activation in immature animals. Despite the similar response of intracellular generation of cGMP following exposure to ANP in neonatal and adult rats, egression of ANP out of glomeruli is low in neonates, an effect that is due to immaturity of an organic acid transporter.(ABSTRACT TRUNCATED AT 250 WORDS)