Intranasal oxytocin attenuates the cortisol response to physical stress: a dose–response study

Rationale/statement of the problem : Intranasal oxytocin attenuates cortisol levels during social stress inductions. However, no research to date has documented the dose–response relationship between intranasal oxytocin administration and cortisol, and researchers examining intranasal oxytocin have not examined the cortisol response to physical stress. We, therefore, examined the effects of 24 and 48 IU of intranasal oxytocin on the cortisol response to vigorous exercise. Methods : Seventeen males participated in a randomized, placebo-controlled, double-blind, and within-subject experiment. Participants engaged in vigorous exercise for 60 minutes following the administration of placebo or intranasal oxytocin on three occasions. Saliva samples and mood ratings were collected at 8 intervals across each session. Results : Salivary cortisol concentrations changed over time, peaking after 60 minutes of exercise [Quadratic: F(1,16) = 7.349, p=0.015, partial η2=0.32]. The 24 IU dose of oxytocin attenuated cortisol levels relative to placebo [F(1,16) = 4.496, p=0.05, partial η2=0.22) and the 48 IU dose, although the latter fell just short of statistical significance [F(1,16) = 3.054, p=0.10, partial η2=0.16). There was no difference in the cortisol response to exercise in participants who were administered 48 IU of intranasal oxytocin relative to placebo. Intranasal oxytocin had no effect on mood. Conclusion : This is the first study to demonstrate that the effect of intranasal oxytocin on salivary cortisol is dose-dependent, and that intranasal oxytocin attenuates cortisol levels in response to physical stress. Future research using exogenous oxytocin will need to consider the possibility of dose–response relations