ACTH, beta-endorphin and met-enkephalin: peripheral modifications during the stress of human labor.

We investigated the psychoneuroendocrine and emotional correlates of the natural stress situation of human labor. State anxiety, subjective pain, plasma ACTH, peripheral plasma beta-lipotropin (Beta-LPH), beta-endorphin (Beta-EP), and met-enkephalin (Met-Enk) were serially evaluated at six predetermined time points before, and after labor in a sample of 14 women with normal pregnancies. State anxiety and subjective pain showed a progressive increase during labor, with a levelling during the final stage. Plasma Beta-EP and ACTH showed a similar progressive increasing from baseline until the end of labor. Beta-LPH showed no significant modification. Met-Enk remained at nearly baseline values throughout labor, with a marked progressive rise in the postpartum stage. The findings of this study seem to confirm the role of plasma Beta-EP as a stress hormone. Possible relationship between pain and anxiety curves and plasma Beta-EP are discussed in light of psychobiological studies on stress, the opioid system and analgesia. Plasma Met-Enk, according to our findings, should probably not be regarded as a stress hormone. Its rise in the postpartum stage might be as one of the psychoneuroendocrine mechanisms maintaining elevated prolactin levels during lactation.