A Novel Oxytocin-Like and Vasotocin-Like Peptide in Human Plasma after Administration of Estrogen*

Abstract

Using three antisera to oxytocin (OT Pitt Ab-1, OT Pitt Ab-2, and TOR OT Ab), we found comparable levels of OT in response to infant suckling and during infusion of synthetic OT, and identical standard curves with biological and synthetic standards of OT. Pitt Ab-1, but not Pitt Ab-2 or TOR OT Ab, measured increased OT in response to estrogen. Using an arginine vasotocin RIA (TOR AVT Ab), we found an increase in AVT immunoreactivity after estrogen treatment. Mean basal OT levels measured with OT Pitt Ab-2 in plasma of men [0.75 +/- 0.06 (+/- SEM) microU/ml] and women (0.8 +/- 0.09 microU/ml) were lower than OT measured with Pitt Ab-1 (1.7 +/- 0.09 microU/ml in men and 1.7 +/- 0.07 microU/al in women; P less than 0.001). Mean OT measured with Pitt Ab-2 in the plasma of women given estrogen chronically (0.8 +/- 0.04 microU/ml) and acutely (0.6 +/- 0.15 microU/ml) were not significantly different from basal levels. OT levels measured with Pitt Ab-1 in the same samples were 4.6 +/- 0.5 and 4.3 +/- 0.5 microU/ml, respectively, both significantly increased from basal levels (P less than 0.001) and significantly higher than OT measured with Pitt Ab-2 (P less than 0.001). Mean OT measured with Pitt Ab-1 in the plasma of pregnant women was 8.6 +/- 1.02 microU/ml, significantly higher than OT measured with Pitt Ab-2 (1.0 +/- 0.3 microU/ml; P less than 0.001). Men given 25 mg diethylstilbestrol had significant increases in OT measured with Pitt Ab-1 and in AVT measured with TOR AVT (P less than 0.01), but not in OT measured with Pitt Ab-2. Plasma from a man given diethylstilbestrol was prepared for high performance liquid chromatography and applied to a C18 muBondapak reverse phase column. The plasma contained two peaks of immunoreactivity detected as OT with Pitt Ab-1 and as AVT using TOR AVT Ab. The material was not detected by Pitt Ab-2 or TOR OT Ab and did not coelute with standards of OT, AVT, or AVP. Pregnancy plasma, thioglycolic acid, chymotrypsin, and trypsin reduced Pitt Ab-1, Pitt Ab-2, and TOR OT immunoreactivity of synthetic OT. The percent recovery of OT immunoreactivity was not significantly different with Pitt Ab-1 vs. Pitt Ab-2. A novel peptide, which is increased in response to administered estrogen, is present in human plasma and is detected by some antisera to OT and AVT. The observation explains the wide variability in OT levels in the estrogen-primed state and provides a new mechanism to study estrogen-related physiology and pathophysiology.

Deficits in plasma oxytocin responses and increased negative affect, stress, and blood pressure in mothers with cocaine exposure during pregnancy

“…Oxytocin was first extracted from plasma and then assayed using a specific oxytocin antibody (Pittsburgh Antibody 2) by Dr. Janet Amico of the University of Pittsburgh following previously published techniques (Amico et al, 1985;Amico, Johnston, & Vagnucci, 1994). The standard curve was linear between 0.5 and 10 pg/tube, and any sample less than 0.5 pg was designated as zero.…”

Effect of Estradiol and Progesterone Administration upon the Circadian Rhythm of Oxytocin in the Cerebrospinal Fluid of Rhesus Monkeys

“…Furthermore, this oxytocin-like peptide is detected only with Pittsburgh oxytocin an tibody 1, which was not used in the present study. Pittsburgh oxytocin antibody 2, which was used in the present study and in our prior studies of oxytocin in CSF, is specific for oxytocin as validated by HPLC and bioassay [23,24,41]. Therefore, the oxytocin immunoreactivity measured in CSF in the present study is likely authentic oxytocin.…”

“…We previously found that the oxytocin immunoreactivity in extracts of monkey and human CSF as well as monkey spinal cord eluted from an HPLC column in the position of synthetic oxytocin [5,40]. Although we had previously also found that humans and monkeys administered estrogen released an oxyto cin-like peptide into plasma [23], this oxytocin-like peptide was not found in CSF of Ei-treated primates. Furthermore, this oxytocin-like peptide is detected only with Pittsburgh oxytocin an tibody 1, which was not used in the present study.…”

Intracerebroventricular administration of the prolactin (PRL) receptor antagonist, S179D PRL, disrupts parturition in rats

“…This assay has been described previously (Amico et al 1981(Amico et al , 1985. Briefly, a starting volume of 300-400 ml plasma was extracted using the acetone-ether method.…”