Increased concentration of circulating atrial natriuretic peptide during normal pregnancy

Atrial natriuretic peptide (ANP) is a recently discovered cardiac hormone involved in blood-volume homeostasis. Known stimulating factors for ANP release are rise in atrial pressures or atrial distension, suggesting that blood volume regulates ANP release. This study was undertaken to test the hypothesis that plasma levels of ANP are high and increase during normal pregnancy secondary to the expanding plasma volume. In a cross-sectional study plasma concentrations of ANP were measured in 99 normal pregnant women at different gestational ages and compared with the values found in an age-matched non-pregnant control group. Mean plasma ANP was already significantly increased in the first trimester as opposed to the non-pregnant women, but despite a continuously expanded plasma volume there was no further increase during pregnancy. Our findings suggest that other factors must interact with plasma volume in regulating plasma ANP during pregnancy.