Study of Immunoreactive 8-Arginine Vasopressin in Human Plasma During Pregnancy and at Delivery : Utilization of a Highly Sensitive Radioimmunoassay with a Reversed Phase C18 Silica Column

Abstract

Changes in plasma concentration of immunoreactive(IR) 8-arginine vasopressin (AVP) during pregnancy and at delivery were examined using a highly sensitive radioimmunoassay (RIA). The following results were obtained : (1) The maternal plasma concentrations of IR-AVP gradually decreased during pregnancy and reached a plateau after week 28 up to delivery. From week 28, the plasma concentrations of IR-AVP were significantly lower than those before week 15 (2.4 + 0.36 pg/ml). Maternal plasma IR-AVP levels at normal vaginal delivery did not differ from those at delivery by elective cesarean section. (2) The umbilical arterial plasma concentrations of IR-AVP at vaginal delivery (390 + 60.6 pg/ml), which were significantly higher than those of umbilical venous plasma (224 + 34.1 pg/ml), were markedly higher than at delivery by cesarean section (14.1 = 9.1 pg/ml). (3) The fact that the concentrations of IR-AVP in the umbilical arterial plasma at de livery, in cases of asphyxia (505 + 74.1 pg/ml), were significantly higher than those at normal delivery (300 – 13.3 pg/ml) is noteworthy. These results suggest that : (1) In the mother, AVP acts as an antidiuretic hormone to maintain the homeostasis of physiologically increased total body water and decreased body tonicity, associated with pregnancy. (2) In the fetus, AVP acts as a stress hormone to maintain the homeostasis of cardiovascular and metabolic systems, which are subjected to the influence of labour. (Thai J Obstet Gynaecol 1993;4:89-98.)