Oxytocin secretion is pulsatile in men and is related to social-emotional functioning

The hypothalamic hormone oxytocin (OXT) plays an important role in a range of physiological processes and social-emotional functioning in both sexes. In women, physiological stimuli, such as suckling and parturition, result in pulsatile release of OXT into the peripheral circulation via the posterior pituitary gland. However, data regarding OXT secretory patterns in men during a state of rest are limited. Further, the relationship between secretory dynamics of OXT and emotional measures has never been evaluated. We hypothesized a pulsatile pattern of OXT secretion in men, and explored the relationship between OXT secretory patterns and social-emotional functioning.

Deconvolution analysis was performed on serum OXT levels obtained every 5min over a period of 10h in 5 healthy normal weight men. Area under the curve (AUC), average OXT values, and pulse characteristics [pulse number, inter-pulse interval, pulse height and mass (area under each pulse)] were calculated. State Adult Attachment Measure (SAAM) assessed types of human attachment. Interpersonal Support Evaluation List (ISEL) assessed perception of social support. Toronto Alexithymia Scale (TAS-20) measured the ability to express and identify one's own emotions.

Mean age was 22.8±1.2years, and BMI was 21.7±0.4kg/m² (mean±SEM). Assuming a basal secretion of zero and a half life of five to seven minutes, we demonstrated the following: OXT AUC: 5421±1331pg/ml, mean OXT level: 9.1pg/ml, mean pulse number: 22±3/10hr, mean pulse height: 1.81±0.48pg/ml, mean pulse mass: 30.34±10.29pg/ml and mean inter-pulse interval: 27±4min. The SAAM Avoidant scale correlated negatively with mean OXT pulse height (r=-0.90, p=0.04) and pulse mass (r=-0.95, p=0.01). The ISEL Belonging score correlated positively with OXT AUC (r=0.89, p=0.04) and average OXT (r=0.93, p=0.02). ISEL Appraisal score also had a positive association with mean OXT pulse height (r=0.99, p=0.0006) and pulse mass (r=0.98, p=0.003). Finally, ISEL total score had a significant correlation with average OXT values (r=0.90, p=0.04). While none of the subjects had a score in the alexithymia range, TAS-20 Difficulty describing feelings score had an inverse correlation with OXT pulse height (r=-0.96, p=0.01) and pulse mass (r=-0.99, p=0.001). TAS-20 total score also had an inverse correlation with OXT pulse height (r=-0.94, p=0.02) and pulse mass (r=-0.96, p=0.009).

We demonstrate a pulsatile pattern of peripheral OXT secretion in healthy men at rest. Subjects with lower OXT pulse height and pulse mass had a more avoidant style of attachment, felt less supported, and expressed greater difficulty in describing their feelings. Our findings support the concept that OXT is a key mediator of social-emotional functioning. Future studies to determine causality are warranted.