SAT-360 Acute Stress Increases Local Corticosterone Levels in Lymphoid Organs of Neonatal Mice: Analysis Using LC-MS/MS

Abstract Glucocorticoids (GCs) are steroids produced by the adrenal glands and also by lymphoid organs such as bone marrow, thymus, and spleen (Taves et al., 2015). GCs are critical regulators of immune system development. During early development (postnatal day (PND) 2 to 12), mice show decreased adrenal GC secretion at baseline and in response to stressors, which is termed the stress hyporesponsive period (SHRP) (D’Amato et al., 1992). Lymphoid organs locally produce GCs, particularly during the SHRP, suggesting that these organs might increase local GC production in response to stress. Here, using PND1, PND5, PND9, and PND13 mice, we administered 5% isoflurane (an anesthetic) in 21% oxygen as an acute stressor, 21% oxygen as a vehicle control, or neither (baseline). For both isoflurane and oxygen treated groups, pups were removed from their home cage and placed in an induction chamber with a heating pad and nesting material from their home cage. Animals were given either given isoflurane for 3min followed by 27min oxygen or 30min continuous oxygen and rapidly euthanized. Baseline animals were given neither isoflurane nor oxygen and were rapidly euthanized in less than 3min. We then measured a panel of 7 steroids, including corticosterone, in the blood and lymphoid organs using liquid chromatography tandem mass spectrometry (LC-MS/MS). Note that PND1 is pre-SHRP, PND5 and PND9 are within the SHRP, and PND13 is post-SHRP. At PND1, corticosterone levels were generally high in both blood and lymphoid organs and did not differ with treatment. At PND5, corticosterone levels were generally very low, but increased with stress in a tissue-dependent fashion, showing the greatest increase in bone marrow and the least increase in blood. At PND9, baseline corticosterone levels were very low, but increased in both blood and lymphoid organs in response to a stressor. At PND13, corticosterone levels were higher in blood than in lymphoid organs for all treatments and increased with stress. Taken together, these novel data indicate that during the SHRP, an acute stressor produces little to no increase in corticosterone levels in blood but produces a 100-fold increase in bone marrow and a 20-fold increase in thymus and spleen. These data support the exciting possibility that mouse lymphoid organs can locally produce corticosterone, even when the adrenal glands produce little corticosterone. More generally, it is important to recognize that local steroid levels often do not match systemic steroid levels and that local steroid synthesis is particularly important in certain developmental and physiological contexts.