Oxytocin in human plasma: correlation with neurophysin and stimulation with estrogen.
RIA for the measurement of oxytocin in human plasma is described. Extraction of oxytocin from larger peptides in plasma used acetone precipitation with a 75% +/- 2 SEM recovery of oxytocin. Nonspecific binding of the assay was less than 4%, and the minimum level of detection was 0.2 microunits/tube. No cross-reactivity was noted with neurophysins, arginine, or lysine vasopressin. The mean basal level (+/- SEM) of oxytocin in men was 1.80 +/- 0.07 microunits/ml and was not different in normal women (1.71 +/- 0.07 microunits/ml). Changes in posture had no effect on the levels of oxytocin. Samples obtained every 15 min over 4 h showed no pulsatile secretion of oxytocin. In women chronically receiving estrogen as an oral contraceptive, oxytocin was greater than normal, (4.59 +/- 0.51 microunits/ml; P less than 0.01). Estrogen-stimulated neurophysin was also elevated (8.45 +/- 1.99 ng/ml; P less than 0.005). Acute ingestion of estrogen caused an increase in the level of oxytocin in plasma by 12 h and a concomitant elevation of estrogen-stimulated neurophysin. When the neurophysin was isolated from plasma obtained from a subject after ingestion of estrogen, the neurophysin from plasma comigrated on a polyacrylamide gel with a human pituitary standard of estrogen-stimulated neurophysin. In the studies in which neurophysin was elevated, the correlation between the level of oxytocin and the level of estrogen-stimulated neurophysin in plasma was significant (P less than 0.01). The observation that estrogen administration stimulates the release of oxytocin and estrogen-stimulated neurophysin provides additional evidence that this neurophysin is the oxytocin-neurophysin of man.
D000818:Animals; D003278:Contraceptives, Oral, Hormonal / Q000494:pharmacology; D004589:Electrophoresis, Disc; D045166:Estradiol Congeners / Q000494:pharmacology*; D005260:Female; D006801:Humans; D008297:Male; D008656:Mestranol / Q000494:pharmacology; D009481:Neurophysins / Q000097:blood*; D010121:Oxytocin / Q000097:blood*; D011187:Posture; D011817:Rabbits
D003278:Contraceptives, Oral, Hormonal; D045166:Estradiol Congeners; D009481:Neurophysins; D010121:Oxytocin; D008656:Mestranol