SUN-207 Modelling Long Term Glucocorticoid-Induced HPA Axis Suppression in Mice

Glucocorticoids are prescribed for >3 months to 1% of the UK population. 10-50% of these long-term glucocorticoid treated patients develop persistent HPA axis suppression associated with mortality and morbidity. We have developed a mouse model of glucocorticoid-induced HPA axis dysfunction to determine the mechanisms resulting in persistent HPA axis suppression. Experiment 1: 36 C57BL/6 adult male mice received Dexamethasone (DEX,~10µg/day) or vehicle (CTL) via drinking water for 28 days, following which treatment was stopped and tissues were harvested at 0, 7 and 28 days. DEX suppressed waking serum corticosterone at days 0 and 7, recovering by day 28. Adrenal size remained lower 28 days following DEX withdrawal. DEX had no effect on whole pituitary pomc, nr3c1 or crhr1 expression, although avpr1b was increased at day 0. In the adrenal, hsd3b2 and cyp11a1 expression were reduced at time 0; normalising by 28 days. Experiment 2: 24 POMC-GFP male mice were treated as above. Tissues were collected at day 0 (n=6), 7 (n=3) and 10 (n=3) following withdrawal. Pooled corticotrophs (groups of 3) were isolated by FACS and RNA extracted for qPCR. DEX reduced corticotroph pomc expression at time 0 (x20 fold reduction), with x5 fold suppression at day 7, which recovered with evidence of compensation by day 10. DEX increased expression of avpr1b but not crhr1. CONCLUSION: 28 days dexamethasone treatment in mice suppresses the HPA axis. HPA suppression is evident 7 days following withdrawal of dexamethasone in the adrenal, corticotroph population and corticosterone production. Further analysis will determine mechanisms for delays in HPA axis recovery.