Do plasma oxytocin and vasopressin indicate effects of bonding therapy and interpersonal trust?

Oxytocin (OT) has been found to be involved in many kinds of social closeness and trust and to reduce stress, whereas vasopressin (AVP) is claimed to be associated with aggression or anxiety. Although it is unclear, if plasma OT and AVP reflect brain levels of these peptides, it seemed worthwhile to test changes in plasma levels of both peptides elicited by social stimuli. A natural setting for inducing close physical contact is bonding therapy. Therefore blood samples from 40 psychosomatic inpatients treated for 7 weeks by bonding therapy were obtained before and after the first and last bonding session. They filled in the attachment style questionnaire RSQ and rated their accompanying emotional experiences after each session. Results: Increases of both peptides and significant positive relationships between OT and AVP responses were found after the last but not after the first session. Correlations between values of sessions 1 and 7 indicated stability of both peptide responses, and an increase in size of treatment responses demonstrated “learning” the release of peptides by bonding. No relations were found with bonding induced emotional states, but RSQ trust scores at session 7 were associated with high baseline VAS levels, less with OT values. Conclusions: AVP and OT responses in plasma seem to co-vary, to be fairly stable biomarkers, and susceptible to changes by long term bonding treatment. Moreover, AVP seems to be an indicator of trust rather than of aggression.