Effects of suckling on hypothalamic-pituitary-adrenal axis responses to psychosocial stress in postpartum lactating women.
In several studies lactation has been shown to be associated with a hypothalamic-pituitary-adrenal axis hyporesponsiveness to physical and psychological stressors. As it is not known whether the marked blunting of endocrine stress reactivity in women can be ascribed to suckling as a short-term effect or to lactation in general, the acute effects of suckling on the hypothalamic-pituitary-adrenal axis and the sympathetic-adrenal-medullary system responses to mental stress were investigated in lactating women. Forty-three lactating women were randomly assigned either to breast-feed or to hold their infants for a 15-min period with the onset 30 min before they were exposed to a brief psychosocial stressor (Trier Social Stress Test). Both breast-feeding and holding the infant yielded significant decreases in ACTH, total plasma cortisol, and salivary free cortisol (all P < 0.01). There were no significant differences in baseline hormone levels between the groups 1 min before the stress test. In response to stress exposure, ACTH, total plasma cortisol, salivary free cortisol, norepinephrine, and epinephrine were significantly increased in all lactating women (all P < 0.001). However, total cortisol and free cortisol responses to stress were attenuated in breast-feeding women (P = 0.001 and P = 0.067, respectively), who also showed significantly decreasing PRL levels during the stress test (P = 0.005). In addition, there was no change in plasma oxytocin or vasopressin in response to the stressor. Breast-feeding as well as holding led to decreased anxiety (P < 0.05), whereas, in contrast, stress exposure worsened mood, calmness, and anxiety in the total group (all P < 0.001). From these data we conclude that lactation in women, in contrast to that in rats, does not result in a general restraint of the hypothalamic-pituitary-adrenal axis response to a psychosocial stressor. Rather, suckling is suggested to exert a short-term suppression of the cortisol response to mental stress.
Heinrichs
M
M
Center for Psychobiological and Psychosomatic Research, University of Trier, D-54286 Trier, Germany. mhein@klipsy.unizh.ch
Meinlschmidt
G
G
Neumann
I
I
Wagner
S
S
Kirschbaum
C
C
Ehlert
U
U
Hellhammer
D H
DH
D000324:Adrenocorticotropic Hormone / Q000097:blood; D000328:Adult; D000339:Affect; D001942:Breast Feeding / Q000523:psychology*; D005260:Female; D006801:Humans; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology*; D007774:Lactation / Q000378:metabolism*; D010913:Pituitary-Adrenal System / Q000502:physiology*; D011388:Prolactin / Q000097:blood; D013315:Stress, Psychological / Q000378:metabolism*
D000324:Adrenocorticotropic Hormone; D011388:Prolactin