Plasma levels of atrial natriuretic peptide during labour and in puerperium.

Atrial natriuretic peptide (ANP), a new cardiac hormone, has potent natriuretic, diuretic and vaso-relaxant properties in animals and humans. Plasma ANP levels increased in response to volume expansion, atrial distension or postural change. The present investigation was designed to examine the effect of labour on plasma ANP in normotensive pregnant women. The results show that plasma ANP in pregnant women (n = 9) increased significantly in active phase of first stage of labour from 19.5 +/- 4.6 pg/ml to 74.5 +/- 15.1 pg/ml. The magnitude of the increase in ANP levels in active phase varied among the patients. During and after delivery, plasma ANP decreased in all instances towards control level. The cause for the increase in plasma ANP levels in the active phase remains to be determined.