Glucocorticoids are steroid hormones that circulate in the blood to coordinate organismal physiology. They have pleiotropic effects, regulating metabolic, cardiovascular, neural, and immune function. While glucocorticoids are classically thought to be secreted exclusively by the adrenal glands, evidence suggests that different organs may be able to autonomously regulate their local glucocorticoid levels via local production. Local production may be important when circulating glucocorticoids are low or absent, such as in early life of altricial young, which are unable to care for themselves. Immune (lymphoid) organs are particularly interesting candidates for tissue-specific regulation of glucocorticoid levels, as glucocorticoids are necessary for early-life immune development in altricial young. In this dissertation, I present a series of studies using birds and mice to examine whether tissue- specific regulation of glucocorticoids occurs in lymphoid organs. In brief, I report that a) glucocorticoids are locally elevated in lymphoid organs of newly-hatched altricial but not precocial birds, b) glucocorticoids are locally elevated in lymphoid organs of neonatal altricial mice, and c) lymphoid organs of both neonatal and adult mice synthesize glucocorticoids from other steroid precursors. Local glucocorticoid production in lymphoid organs may function to ensure production of functional lymphocytes, and factors that alter lymphoid glucocorticoid levels may play a role in programming the overall immune reactivity.Science, Faculty ofZoology, Department ofGraduat
