Inhibitory effect of exogenous oxytocin on ACTH and cortisol secretion during labour.

Complex mechanisms which are still not completely defined, are responsible for the spontaneous onset of labour: an essential role is attributed to endocrine factors. A massive increase, even three times higher than normal physiological values of ACTH and cortisol, has been reported during labour. Similar behaviour has also been recorded for oxytocin at the end of pregnancy as well as during labour. The relationship between oxytocin and the adrenal axis are still debated thus the goal of our study was to attempt to clarify this rapport. Sixty-two women at the end of a term-pregnancy agreed to participate in this study: 46 were innoculated with oxytocin (syntocinon) every 20 minutes for 1 hour; 16 were administered a natural placebo every 20 minutes for 1 hour (control group). ACTH and cortisol values from plasma samples were taken every 20 minutes and analyzed. Our results demonstrated an inhibitory effect of exogenous oxytocin on ACTH and cortisol release. This inhibitory effect, as shown by our results, is time and dose-related. High oxytocin levels, as during exogenous infusion, could induce an effect opposite a normal physiologic one.