Intranasal oxytocin attenuates the cortisol response to physical stress: A dose-response study

Introduction: Intranasal oxytocin attenuates cortisol levels during social stress inductions. However, no research to date has documented the dose response relation between intranasal oxytocin administration and cortisot, and researchers examining intranasal oxytocin have not examined the cortisol response to physical stress. We therefore examined the effects of 24IU and 48IU of intranasal oxytocin on the cortisol response to vigorous exercise. Method: Seventeen males participated in a randomized, placebo-controlled, double-blind, and within-subject experiment. Participants engaged in vigorous exercise for 60 min following the administration of placebo or intranasal oxytocin on three occasions. Saliva samples and mood ratings were collected at eight intervals across each session. Results: Salivary cortisol concentrations changed over time, peaking after 60 min of exercise (quadratic: F(1,16) = 7.349, p = .015, partial eta(2) = .32). The 24IU dose of oxytocin attenuated cortisol levels relative to placebo (F(1,16) = 4.496, p = .05, partiale eta(2) = .22) and the 48IU dose, although the latter fell just short of statistical significance (F(1,16) = 3.054, p = .10, partial eta(2) = .16). There was no difference in the cortisol response to exercise in participants who were administered 48IU 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. (C) 2012 Elsevier Ltd. All rights reserved.