Urodilatin and Atrial Natriuretic Peptide Are Present in the Urine of Healthy Neonates and Young Infants

Urine sampling has been proposed as noninvasive monitoring of plasma atrial natriuretic peptide (ANP) in neonates, assuming urine contains only filtered plasma ANP. Recently, urodilatin, another natriuretic peptide, which is cross-reactive to ANP in the ANP radioimmunoassay (ANP-RIA), has been isolated from the urine of adults. We studied the urine of healthy term neonates and young infants for the presence of urodilatin. In all urine samples, we found three peaks of ANP-RIA-reactive material: the first one in the position of urodilatin, the second one coeluting with synthetic ANP and a third late eluting peak, possibly containing degradation products. The physiological significance of these findings remains to be investigated.