Confirmation of the inhibitory influence of exogenous oxytocin on cortisol and ACTH in man: Evidence of reproducibility

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Abstract
The influence of low-dose oxytocin perfusion (32 mIU/min) on ACTH and cortisol plasma levels was tested in 8 normal male volunteers (age 18-26). The 1-h oxytocin perfusion periods were preceded and followed by two 1-h saline control periods. During the first period, there was a slight ACTH concentration decrease in 4 individuals. Oxytocin perfusion induced a clear-cut plasma ACTH decrease in 7 out of the volunteers, and a slight decrease in the remaining one. During the second saline infusion, there was a marked ACTH increase in 7 out of the volunteers, and a weak increase in one (P < 0.0001). A similar pattern was observed in the plasma cortisol levels (P < 0.00001). Furthermore, a control saline perfusion was performed in 4 of the 8 volunteers and compared to the 4 corresponding oxytocin perfusion tests: the differences between the 2 sets of tests was highly significant both for ACTH (P < 0.003) and for cortisol (P < 0.007). Lastly, the reproducibility of this inhibitory influence was retested in 4 volunteers: the tests were repeated under the same conditions 7 days later. There were no global differences between the 2 sets of tests either for ACTH (NS) or for cortisol (NS). ACTH and cortisol concentration fluctuations during the period between each set of tests were not significant. The following variations were measured for ACTH (NS) and for cortisol (NS). The present results confirm the inhibitory influence of low-dose oxytocin perfusion on ACTH and cortisol levels in normal males. Moreover, we demonstrate an increase at the end of the oxytocin perfusion (second control saline infusion). The reproducibility of the inhibitory effect at a one-week interval in 4 volunteers brings new argument against a non-specific stress influence on corticotroph function.