An investigation of plasma and salivary oxytocin responses in breast- and formula-feeding mothers of infants.

Oxytocin (OT) is a peptide increasingly studied in relation to human social interactions, affiliation, and clinical disorders. Studies are constrained by use of invasive blood draws and would benefit from a reliable salivary OT assay. Our goals were to examine feasibility of salivary OT measurement, compare salivary to plasma OT responses in 12 breast- and 8 formula-feeding mothers, and assess the degree of correlation between plasma and salivary OT. Using a commercial EIA kit, we measured OT in 5 saliva and 7 plasma samples in a protocol designed to elicit changes in OT (Rest, Infant Interaction, Stress, Feeding). Breast-feeders had higher OT levels than formula-feeders across all conditions in plasma (+36%) and saliva (+23%). OT levels and ranges were similar in saliva and plasma, with slightly greater variance in saliva. Concurrently sampled plasma and salivary OT were correlated at end of Baseline Rest (r=+.59, p=.022) and Post-Stress Recovery (r=+.59, p=.025). These data suggest that salivary OT assay is feasible, and will be of value where plasma samples are not possible. Validation with larger samples is needed.