ATRIAL-NATRIURETIC-PEPTIDE (ANP) AND N-TERMINAL PEPTIDE OF PROANP (NT-PROANP) IN MATERNAL AND UMBILICAL-CORD PLASMA IN SPONTANEOUS LABOR AND AT ELECTIVE CESAREAN-SECTION

The effects of spontaneous labor and of intravenous volume load at elective cesarean section were studied on concentrations of atrial natriuretic peptide (ANP) and N-terminal portion of ANP precursor peptide (NT-proANP) in maternal and umbilical cord plasma. At the time of delivery, the concentrations (median (range)) of these peptides in maternal plasma were higher at elective cesarean section (25.5 (11.6-54.8) pmol/l and 1080 (366-1920) pmol/l, respectively, n = 15) than during labor (8.4 (4.8-30.8) pmol/l and 778 (229-2290) pmol/l, respectively, n = 20). Concentrations of ANP and NT-proANP in the umbilical cord arterial and venous plasma also were higher after elective cesarean section than after spontaneous delivery by vaginal route. In the subgroup of mothers studied serially during labor (n = 7) mean concentration of ANP increased from 5.5 (2.3-10) pmol/l to 11.5 (3.2-23) pmol/l (P < 0.01) and those of NT-proANP from 430 (183-1610) pmol/l to 508 (325-1690) pmol/l (NS). The intravenous volume load used to prevent the fall of the blood pressure under spinal anesthesia elicited a significant increase in maternal ANP levels [from 8.2 (5.6-25.8) pmol/l to 28.5 (14.5-66) pmol/l, n = 5, P < 0.01] and in the NT-proANP levels (from 293 (147-572) pmol/l to 673 (412-929) pmol/l, P < 0.01). These findings suggest that maternal intravenous volume load and labor stress stimulate the release of ANP and NT-proANP.