Are single peripheral measurements of baseline oxytocin in saliva and plasma reliable biomarkers of the physiology of the oxytocin system in humans?

Abstract

Background: Single measurements of salivary and plasmatic oxytocin are used as indicators of the physiology of the oxytocin system. However, questions remain about whether they are sufficiently stable to provide valid biomarkers of the physiology of the oxytocin system, and whether salivary oxytocin can accurately index its plasmatic concentrations. Methods: Using radioimmunoassay, we measured baseline plasmatic and/or salivary oxytocin from two independent datasets. Dataset A comprised 17 healthy men sampled on four occasions approximately at weekly intervals. We administered exogenous oxytocin intravenously and intranasally in a triple dummy, within-subject, placebo-controlled design and compared baseline levels and the effects of routes of administration. Dataset B comprised baseline plasmatic oxytocin measurements from 20 healthy men sampled on two separate occasions. Additionally, in dataset A, we tested whether salivary oxytocin can predict plasmatic oxytocin at baseline and after intranasal and intravenous oxytocin administration. Results: Single measurements of plasmatic and salivary oxytocin showed poor reliability across visits in both datasets. Intranasal administration of exogenous oxytocin increases salivary oxytocin, but intravenous administration of a considerable dose does not produce any changes. Saliva and plasma oxytocin did not correlate at baseline or after administration of exogenous oxytocin. Conclusions: Our findings question the use of single measurements of baseline oxytocin concentrations in saliva and plasma as valid biomarkers of the physiology of the oxytocin system in humans. Salivary oxytocin is a weak surrogate for plasmatic oxytocin. The increases in salivary oxytocin observed after intranasal oxytocin most likely reflect unabsorbed peptide and should not be used to predict treatment effects.

Salivary oxytocin after play with parents predicts behavioral problems in preschool children

“…However acceptable high levels of reliability (>.70) were achieved through the averaging of at least two samples. This result supports a previous study that found low reliabilities of single measures of both saliva and plasma oxytocin in healthy adult men (Martins et al, 2020). Although saliva sampling is non-invasive and convenient to perform, collecting several samples per individual has increased costs associated with the quanti cation of multiple samples per subject and may not be possible for all protocols.…”

“…While the single measures coe cient applies to the estimated reliability of a single measurement, the average measures coe cient applies to the arithmetical mean of N measurements. This means that in average measures reliability is dependent on the aggregated series of measurements/observations, and not on a single measurement (Martins et al, 2020).…”

“…A power analysis calculation based on the number of saliva samples we collected per individual (seven) for each set suggested that with a sample size of 30 children we should had been able to detect an acceptable ICC of .70 if it did exist with 80% of statistical power. Furthermore, for ICCs of at least .70, the same sample size would allow us to detect a moderate correlations of r = .60 between salivary OXT and behavioural problems in our sample with 80% of statistical power (Martins et al, 2020) Ethical approval…”

Salivary oxytocin after play with parents predicts behavioural problems in preschool children

“…A power analysis calculation based on the number of saliva samples we collected per individual (seven) for each set suggested that with a sample size of 30 children we should had been able to detect an acceptable ICC of .70 if it did exist with 80% of statistical power. Furthermore, for ICCs of at least .70, the same sample size would allow us to detect a moderate correlations of r = .60 between salivary OXT and behavioural problems in our sample with 80% of statistical power (Martins et al, 2020).…”

“…Questions about the reliability of single measurements of peripheral OXT make it yet a controversial topic. Martins et al (2020) have recently reported that plasmatic and salivary OXT are unlikely to be reliably measured using single samples in healthy adult men and suggested the collection of multiple samples per individual as a way of circumventing this low reliability problem. Although there is a scarcity of reliability assessment of salivary OXT measures, some studies in children have reported strong test-retest correlations.…”