C-type natriuretic peptide in maternal plasma in spontaneous labour, at elective cesarean section and during puerperium.

C-type natriuretic peptide (CNP) is the third member of the natriuretic peptide family that is involved in the regulation of blood pressure, renal function and volume homeostasis. In man CNP is highly expressed in endothelial cells, distinct brain areas and kidney. Maternal CNP plasma concentration remains stable in normal pregnancy with advancing gestational age. Using a radio-immunoassay we measured for the first time CNP plasma levels of women in the active phase of labour, during elective cesarean section in spinal anesthesia and in the postpartum period. Healthy pregnant women in the third trimenon were used as controls (7.36 +/- 3.0 pg/ml). CNP is significantly increased in labour (11.48 +/- 1.2 pg/ml) as well as after volume load before cesarean section (14.25 +/- 4.5 pg/ml). The postpartum concentration (9.3 +/- 2.4 pg/ml) was in the range of the controls. We conclude that CNP in plasma is increased during spontaneous labour. Its possible role in volume regulation with increased levels after rapid volume load but normal levels in puerperium with physiologically enhanced diuresis and natriuresis remains unclear.