Arginine vasotocin in ovine fetal blood, urine, and amniotic fluid

Arginine vasotocin ([8-arginine]-oxytocin) (AVT), the primary antidiuretic principle in submammalian vertebrates, has been reported to be present in mammalian pituitary and pineal glands. Although the most phyletically ubiquitous of the known neurohypophysial peptides, AVT is still not recognized as a mammalian hormone. We examined plasma, urine, and amniotic fluid from fetal lambs by radioimmunoassay (RIA) for evidence of AVT to assess the possibility of its being such a hormone. Measureable quantities of AVT-like immunoreactivity (irAVT) were observed in fetal plasma (2.4 +/- 0.2 pg/ml), urine (1.4 +/- 0.2 pg/ml), and amniotic fluid (1.9 +/- 0.2 pg/ml). Since the AVT antiserum shows minimal cross-reactivity with arginine vasopressin (AVP) and oxytocin (OT), measurements of AVP and OT concentrations in the same biological fluids also were conducted with specific antisera. The results suggest that the irAVT was not accountable on the basis of cross-reaction. To further verify the identity of the irAVT, a high pressure liquid chromatography system using RIA as a means of detection was developed. This system is sufficiently sensitive to allow the separation and quantitation of picogram quantities of the synthetic peptides AVT, AVP, and OT. In this system, the irAVT in fetal plasma, urine, and amniotic fluid appeared as a single peak coeluting with synthetic AVT. These results indicate that AVT is present in ovine fetal plasma and support the view that the fetus secretes this peptide. The physiological significance of circulating AVT remains to be defined.