Lymphocyte responses to stress in postpartum women: relationship to vagal tone

Although women spend their lives in various phases of the reproductive cycl e, including menstrual, pregnancy, postpartum, lactation and menopause, few studies have examined immune responses to stress in women as a function of events associated with reproduction. The objective of this study was to ev aluate differential effects of breastfeeding (n=16), bottlefeeding (n=10) a nd non-postpartum (n=10) status on lymphocyte responses to stressful tasks (public speaking and mental arithmetic). To measure cellular immune respons es, lymphocyte proliferation to plant lectins. poke weed mitogen (PWM) and phytohemagglutinin (PHA) were used. The autonomic measures, heart rate, vag al tent, blood pressure and the hormones of the HPA axis, ACTH and cortisol , were measured and their possible roles in mediating lymphocyte proliferat ion responses were examined. Recently parturient women who were breastfeedi ng or bottlefeeding had attenuated stress-induced change in lymphocyte resp onses to PWM compared with non-postpartum women, tested in the follicular p hase of their cycle (P<0.05). Also, lymphocyte responses to PHA were higher in the breastfeeding group compared with non-postpartum controls (P<0.05). Regression analyses revealed that an index of cardiac vagal tone, but not other autonomic or endocrine measures, was positively predictive of lymphoc yte proliferation to PWM, To summarize, these findings suggest that lactati on and parturition can influence lymphocyte proliferation and that activity in the vagal system may influence lymphocyte responses to stress. (C) 2001 Elsevier Science Ltd. All rights reserved.