A Study on blood levels of Oxytocin and Neurophysins during labor and lactation

Plasma oxytocin (OT) and serum neurophysins (Nps), during labor and nursing, were measured by specific radioimmunoassay for the study of the physiological role of this hormone in human reproduction. OT levels markedly increased to 217.3 + 36.02 pg/ml (Mean + S.E) during labor as compared to 119.2 + 21.29 pg/ml in the third trimester. At delivery OT was 176.3 + 30.92 pg/ml in maternal venous blood and 207.5 + 62.90 pg/ml in the umbilical vein, respectively. Blood ESN (Estrogen Stimulated Neurophysin) levels during the third trimester were almost twice as high as during the first trimester. Serum NSN (Nicotine Stimulated Neurophysin) levels at delivery were higher than during pregnancy, especially the NSN concentration in the umbilical artery was higher than that in the umbilical vein. One month after delivery, ESN returned to the level of the first trimester. Both ESN and NSN levels during nursing were higher than the values found before and after nursing. These results clearly indicate that the hypothalamo-posterior pituitary system plays some roles during labor and lactation, and that useful interpretations of concomitant analysis of both OT and Nps could be made for the study of this system.