**1. Introduction**

114 Sex Steroids

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We have undertaken a critical analysis of the role of sex and sex steroids in influencing stress responsiveness. We have reviewed the current literature regarding the manner in which the stress-induced activation of the sympatho-adrenal medullary system and the hypothalamopituitary adrenal axis are influenced by the sex of individuals and the sex steroids that are present and how these vary with different types of stress and in different physiological conditions. The chapter focuses predominantly on sheep and human research, although research in rodents is introduced where pertinent. Where appropriate, we draw on our extensive research published over the last two decades using sheep as an experimental model and consider how these data inform and compliment the current findings in human studies. It is clear from the literature reviewed here that there is a major need for research to understand stress responsiveness. The gaps in knowledge requiring this research are highlighted.
