Adrenal rather than central dysfunction limits HPA axis recovery after chronic glucocorticoid treatment in male mice

Glucocorticoid-induced adrenal insufficiency (GIAI) can persist for months after discontinuation of chronic corticosteroid therapy, placing patients at risk for life-threatening adrenal crises. This prolonged suppression has been attributed primarily to delayed restoration of hypothalamic-pituitary signaling based on indirect measures of central axis activity. To identify the rate-limiting site of hypothalamic-pituitary-adrenal (HPA) axis recovery, we evaluated the timing of functional and histologic recovery at each node of the axis following 8 weeks of dexamethasone (DEX) treatment in adult, male mice. DEX administration fully suppressed HPA axis activity. Unexpectedly, within one week of DEX withdrawal, hypothalamic Crh mRNA and plasma ACTH rebounded above control levels, whereas corticosterone (CORT) remained suppressed for an additional seven weeks. DEX-treated adrenals were markedly atrophic and contained large clusters of lipid-filled macrophages. Even after adjusting for macrophage content, CORT secretion was disproportionately low relative to the remaining adrenocortical cell mass despite supraphysiologic ACTH stimulation. The adrenal is thus the principal site of post-withdrawal GIAI, involving adrenocortical cell loss and a superimposed defect in steroidogenesis. We next tested whether preserving adrenal trophic signaling during glucocorticoid exposure could prevent GIAI. Adrenal function recovered more slowly in mice treated with DEX and daily cosyntropin (a synthetic ACTH analog) compared to those treated with DEX alone. In contrast, mice with non-suppressible endogenous ACTH due to targeted hypothalamic deletion of the glucocorticoid receptor maintained normal adrenal architecture and steroidogenic capacity despite prolonged DEX treatment. Pharmacologic treatments that mimic sustained trophic signaling to the adrenal during chronic glucocorticoid treatment may thus prevent GIAI.