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J Clin Endocrinol Metab. 1995 Oct;80(10):2954-9.

Suppression of hypothalmic-pituitary-adrenal axis responses to stress in lactating women.

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Division of Intramural Research Programs, National Institute of Mental Health, Bethesda, Maryland 20892, USA.


In the rat, lactation suppresses a variety of physiological responses to stress. We investigated whether stress-responsive neurohormonal systems are also restrained during breast feeding in humans. We chose treadmill exercise as a stressor because this stimulus produces an exercise intensity-dependent activation of the hypothalamic-pituitary-adrenal axis and the sympathomedullary system that is independent of differences in physical conditioning among subjects. Ten lactating and ten nonlactating women who were between 7 and 18 weeks postpartum performed 20 min of graded treadmill exercise. The final 5 min of exercise was set to elicit 90% of the maximal oxygen uptake of each subject. Plasma ACTH, cortisol, and glucose responses to exercise were significantly attenuated in lactating women (P < 0.001, P < 0.05, and P < 0.001, respectively). Basal norepinephrine levels were also reduced in lactating women (P < 0.05). These results indicate that stress-responsive neurohormonal systems are restrained in lactating women.

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