Grant: Discovery Grants Program - Individual

The long-term objective of this research program is to realize the mechanisms by which estrogen and progesterone influence human temperature regulation, and relatedly fluid balance, across the lifespan from adolescence, through adulthood, and with ageing. We have previously shown that whilst there are differences in autonomic thermoregulation (i.e. thermal sweating) between normally menstruating and oral contraceptive user women (i.e. higher vs. lower estrogen/progesterone concentrations), no differences exist in their behavioral responses. Further, their behavioral response minimizes autonomic differences in thermoregulation and fluid balance. However, women remain vastly underrepresented in this literature and because it has been understudied our knowledge on and understanding of this topic remains incomplete. Over the next five years we will conduct four challenging human studies to provide sound mechanistic insight into the intra- and inter-individual non-reproductive effects of the primary ovarian hormones on thermoregulation. First we will follow pregnant women as their estrogen/progesterone concentrations continue to increase dramatically during their second and third trimester, measuring their autonomic and behavioral thermoregulatory responses. Next, we will use the menstrual cycle to determine the influence of estrogen on autonomic and behavioral thermoregulation, independent of, and in combination with, increased progesterone (i.e. early vs. late follicular vs. mid-luteal phases). Then, we will compare post-menopausal to pre-menopausal women to determine how the depletion of estrogen/progesterone affects autonomic and behavioral thermoregulation. Finally, we will use the menstrual cycle to determine if the adaptive thermoregulatory responses following heat acclimation differ when participants have low (follicular phase) and high (luteal phase) ovarian hormone concentrations. To achieve these goals we will utilize the same techniques and methods for all studies; exercise in a warm environment to achieve hyperthermia and stimulate increased thermoeffector responses of skin blood flow and thermal sweating, coupled with a discrete behavioral task. This comprehensive approach is unique and will allow a better and more complete understanding of the mechanisms underlying human temperature regulation, especially in women. Changes in estrogen and progesterone characterize a majority of the Canadian (17 million) and global (2.3 billion) female populations. Yet, our understanding of how these ovarian hormones influence human temperature regulation is incomplete despite an increasing threat to humans due to climate change, and increased numbers of women working in physically demanding occupations and enjoying leisure time physical activities. Long-term this ground-breaking but translatable work can provide a foundation for guidelines and policy on how women can safely perform and optimally adapt to activity with heat stress.