HEMODYNAMIC CONTROL OF ATRIAL-NATRIURETIC-PEPTIDE PLASMA-LEVELS IN NEONATAL RESPIRATORY-DISTRESS SYNDROME

To evaluate the contribution of the pulmonary and ductal hemodynamics on the cardiac atrial natriuretic peptide (ANP) synthesis and release in neonatal respiratory distress syndrome, serial blood samples for pl asma C-terminal end, and the more stable N-terminal end (NT-proANP) of the propeptide were obtained. Simultaneous evaluation of the systolic pulmonary artery pressure (PAP) and magnitude of ductal shunting by t he Doppler method were made of 37 distressed infants during the first 4 days of life. Both plasma ANP and NT-proANP rose after birth, peaked at 48 hours of age, and correlated significantly (r = 0.66; p <0.001; n=78) with each other. The initially high systolic PAP and, since the systemic arterial pressure (SAP) did not change, the PAP/SAP ratio de clined slowly during the study period, as did the magnitude of ductal left-to-right shunting after an initial increase during the first hour s after birth. Plasma NT-proANP had a positive correlation to the magn itude of ductal left-to-right shunting both during the first 2 and 4 d ays of life, but did not correlate with PAP, SAP, or PAP/SAP ratio dur ing the same time periods. Eight infants with delayed closure of the d uctus maintained elevated plasma NT-proANP values after the second day of life. Our data thus suggest that in neonatal respiratory distress syndrome the high plasma ANP levels are due to increased cardiac ANP s ynthesis and release and that the main determinant accounting for this high ANP production during the acute phase of the disease is persiste nt ductal left-to-right shunting with left atrial stretch rather than the high right cardiac afterload.