An exploratory study into the effect of exhausting bicycle exercise on endocrine and immune responses in post-menopausal women: relationships between vigour and plasma cortisol concentrations and lymphocyte proliferation following exercise.

It is well-established that bicycle exercise alters the endocrine and immune responses in men, but little information is available for women, especially middle-aged, post-menopausal women. The purpose of our study was to document the endocrine and immune reactivity to exhausting bicycle exercise in post-menopausal women, and to explore whether complaints of fatigue or low vigour are related to these exercise-induced responses. Thirteen healthy post-menopausal women participated in this study. We used a graded exercise protocol to study the kinetics of activation of the endocrine and immune system. We chose to examine hormones related to the hypothalamus-pituitary-adrenal (HPA) system such as adrenocorticotropin hormone (ACTH) and cortisol and hormones related to the pituitary such as prolactin (PRL) and growth hormone (GH). With regard to the immune system, we examined the natural killer (NK) cell activity and pokeweed (PWM)-induced lymphocyte proliferation in addition to changes in peripheral blood cell counts. Our results demonstrate that acute physical stress results in a strong release of ACTH, cortisol, GH and PRL. The bicycle test significantly increased the number of CD3+, CD4+, CD16/56+ (NK cells) and CD8+ cells in our group of post-menopausal women. Interestingly, NK activity did not increase significantly despite an increase in NK cell numbers. PWM-induced lymphocyte proliferation did not change either. In addition, our data support the hypothesis that low vigour in post-menopausal women interferes with the endocrine and immune responses to exhausting exercise. In women with complaints of low vigour we found lower cortisol responses and higher increments in the proliferative capacity of lymphocytes as compared to those with high vigour scores. NK activity was unrelated to exhaustive mood states. These data indicate that endocrine as well as immune system activity changes in response to exhausting exercise in middle-aged, post-menopausal women. In addition, exhaustive mood states may contribute to cortisol responses and function of peripheral immune cells in post-menopausal women following exhausting exercise.