The present findings, while preliminary, indicate that recent self-induced vomiting behavior may negatively impact the correlation of plasma OT with salivary OT, a problem for the use of this non-invasive method for measurement of OT in individuals with eating disorders marked by self-induced vomiting. Although this was a small sample pilot study that precluded hypothesis testing due to sample size and variability, these preliminary findings nonetheless raise concern and encourage further investigation of this observation. With reference to urinary OT, further study is needed to determine the normal range of urinary OT values expected. While this sample included two individuals with extreme urinary OT values, with a sample size of only 18 individuals for this new technique, it is unknown if these values represent true outliers or values in the higher range of a normal distribution. In this pilot sample, exclusion of these two extreme values yielded a larger positive correlation between plasma and urinary OT, supporting further larger studies of this non-invasive option for sampling OT.
Due to the limited scope of this pilot study, blood and saliva samples were collected at only one time point; in future studies it will be important to determine if self-induced vomiting behavior influences the correlation of plasma and salivary OT over time, limiting detection of changes in peripheral OT using saliva alone. Timing of sample collection represented a limitation in the analysis of urinary OT; while blood was collected over 15 minutes, urine was collected over 24 hours. Although a limitation, this was a deliberate aspect of the study design, as our objective at this early stage was to demonstrate proof of concept of collection and assay of OT in urine and gross correlation with plasma measures. Thus, timing may be at least partly responsible for the small positive correlation found between urine and plasma OT, but our results are similar to a recent study in a larger sample of healthy individuals that also found no significant relationship (Feldman, et al., 2011
). Additional investigations into the utility of this sampling approach should determine the timing of urine sampling that most closely approximates plasma levels during experimental tasks (e.g., immediately after the task, thirty minutes later, one hour later, etc.) which may be complicated by interindividual variation in kidney function.
Although salivary measurement of OT is gaining favor (Carter, et al., 2007
; Feldman, et al., 2011
; Grewen, et al., 2010
; White-Traut et al., 2009
) due to less invasive sampling procedures, our findings warrant serious caution when considering salivary OT sampling in individuals with eating disorders marked by self-induced vomiting behaviors. Measurement of OT in urine may be another non-invasive option, but an initial challenge will be determination of appropriate timing of urine collection to produce meaningful results.
We examine correlations of plasma oxytocin with salivary and urinary oxytocin. We compare women with anorexia nervosa with and without self-induced vomiting. Plasma-salivary oxytocin correlation was lower in women with self-induced vomiting. Urinary oxytocin was not well correlated with plasma oxytocin.