A growing literature associates the neuropeptides oxytocin (OT) and arginine vasopressin (AVP) with affiliative and cognitive outcomes. The majority of this work in humans, however, considers these neuropeptides separately. Also, despite evidence that OT and AVP interact with gonadal hormones, still warranted is an examination of sex and age variations in endogenous neuropeptide levels, their interrelations, and their functional relationships with attachment and cognition in humans. This study measured endogenous plasma OT and AVP levels in generally healthy young (18-31 years) and older (63-81 years) men and women to (i) determine levels of and interrelations between OT and AVP; (ii) explore functional relationships with self-reported attachment (attachment anxiety and avoidance) and performance-based cognition (processing speed, verbal memory); and (iii) identify variations in these effects by sex and age. We observed sex- and age-differential patterns of results: Women had higher plasma OT levels than men and older adults had higher plasma AVP levels than young adults. The two neuropeptides were highly negatively intercorrelated across all groups. Functionally, higher AVP levels were associated with greater attachment anxiety and higher OT and lower AVP levels were associated with faster sensorimotor processing speed, with sex and age moderating these effects. This integrated approach identifies variations in endogenous peripheral neuropeptide levels in humans, supporting their sex- and age-specific role as "difference makers" in attachment and cognition.

The role of oxytocin (OT) in close relationships is complex, as both positive and negative associations have been found between OT and relationship processes. Also, with most research focusing on the effects of exogenous OT administration on communication and couple behaviors, our knowledge about the association between endogenous OT and couple dynamics remains limited. This study is the first to assess the link between peripheral OT levels and observed communication behaviors during sexual and nonsexual conflict discussions in romantic relationships. A sample of 126 young, heterosexual couples (Mean age = 23.3, SD = 2.4; average relationship duration = 1.9 years, SD = 0.9) participated in videotaped sexual and nonsexual couple conflict discussions of 7 min each. Communication behaviors were coded using an adaptation of the Specific Affect Coding System (SPAFF) and the System for Coding Interactions and Family Functioning (SCIFF). Blood samples were collected prior to the couple discussions, during a separate lab visit, and OT plasma levels were determined using enzyme-linked immunosorbent assays (ELISA). Plasma OT levels were positively associated with validating behaviors during sexual discussions in both women (r = +.24, p = .008) and men (r = +.18, p = .052). No significant associations were found between OT levels and validating behaviors during nonsexual discussions and between OT and affectionate and negative behaviors during either sexual or nonsexual discussions. Analyses revealed significant associations between OT levels and one's own validating behaviors during sexual discussions (b = 47.82, t(201.16) = 3.81, p < .001) and one's partner's (b = 32.12, t(216.35) = 2.62, p = .009). The results highlight the biobehavioral aspects of couples' sexual communication and may contribute to a better understanding of the processes involved in individual and relational well-being. This study is the first to report an association between peripheral OT levels and validating behaviors during sexual communication, indicating neurophysiological involvement in dyadic sexual communication patterns.

Since its discovery more than a century ago, oxytocin has become one of the most intensively studied molecules in behavioral biology. In the last five years, Psychoneuroendocrinology has published more than 500 articles with oxytocin in the title, with many of these articles including measures of endogenous oxytocin concentrations. Despite longstanding interest, methods of measuring endogenous oxytocin are still in active development. The widely varying oxytocin concentrations detected by different approaches to measurement - and lack of correlation among these techniques - has led to controversy and confusion. We identify features of oxytocin that may help to explain why various approaches may be differentially sensitive to diverse conformational states of the oxytocin molecule. We propose that discrepancies in data generated by different methods of measurement are not necessarily an indicator that some methods are valid whereas others are not. Rather, we propose that current challenges in the measurement of oxytocin may be analogous to the parable of the blind men and the elephant, with different methods of sample preparation and measurement being sensitive to different states in which the oxytocin molecule can exist.