Concentrations and Origin of Oxytocin in Breast Milk

Abstract

Samples of human milk obtained from lactating women in the early post-partum period were assayed for oxytocin concentrations by specific RIA, following extraction procedures with Florisil. Mean oxytocin concentrations in human milk at postpartum day 1 to 5 were 4.5±1.1, 4.7±1.1, 4.0±1.3, 3.2 0.4, 3.3±0.6 μu/ml (±SE), respectively. Oxytocin levels in milk were significantly increased by nursing (3.1 ± 0.6, 5.3±1.0 μu/ml, respectively). 3H-oxytocin in human milk was stable even after incubation at 37°C for 2 hours. The dilution curve for milk was parallel to the curve for the standard oxytocin. The chromatographic fraction of immunoreactive oxytocin was identical to that of 3H-oxytocin. 3H-oxytocin was administered to lactating rats. Radioactivity in the neonatal gastric contents and plasma were 12.8% and 4.4% of the counts in the maternal plasma. It was made clear that oxytocin is stable in milk and that oxytocin in maternal blood can be transferred to mik and then to neonates. © 1986, The Japan Endocrine Society. All rights reserved.