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

Abstract

Arginine vasotocin (18-argininel-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.

The Effect of Assisted Ventilation on Creatinine Clearance and Hormonal Control of Electrolyte Balance in Very Low Birth Weight Infants

“…The apparent decrease in renal sensitivity to vasopressin in the AV group on day 1 could reflect, in part, competitive inhibition of the renal vasopressin receptor by another antidiuretic agent known to be secreted by the newborn infant pineal gland, namely, vasotocin. Vasotocin has been found in fetal sheep plasma (30). Because of the nearly 50% cross-reaction of vasotocin on the present vasopressin radioimmunoassay system, we are not able to differentiate between these possible explanations.…”

The unique endocrine milieu of the fetus.

“…During the last trimester of gestation fetal hypothalamic-pituitary responsiveness to both volume and osmolar stimuli for VP secretion are well developed, and an antidiuretic effect of VP on the fetal kidney is well established (33, 37,38). Baseline plasma levels of AVT in fetal sheep during the last trimester approximate values for VP and OT (36). Presumably this AVT is derived from the posterior pituitary.…”

Neuropeptide Cells and Fibers in the Hypothalamus and Pituitary of the Fetal Sheep: Comparison of Oxytocin and Arginine Vasopressin

“…The issue remains controversial. More recent work confirmed the pre sence of arginine vasotocin in ovine fetal blood, urine and amniotic fluid using high-pressure liquid chromatography and a highly specific antibody to vasotocin [10]; however, the site of production of this vasotocin is unknown. The picture is compli cated by the fact that the placenta is the source of an expanding host of neuropeptides [19], including oxytocin [11], Nonethe less, vasotocin, if present in the young fetus, appears to decline as birth approaches [34], Since the distributions of OXY we ob served in fetal lambs are identical to those of postnatal lambs 1 week and I month after birth [Hoffman, unpublished] and the intensity of staining for OXY increases rather than decreases during late gestation (present study), it is unlikely we are local izing mainly vasotocin.…”