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Background Tumor necrosis factor alpha (TNF-α) is important in promoting relative adrenal insufficiency (RAI) due to systemic inflammatory response syndrome (SIRS).We identified the TNF-α receptor involved in the inhibition of adrenal corticotrophin (ACTH)-stimulated hydrocortisone release by studying the expression of TNF-α receptors in adrenal cortex Y1 cells and the effect of downregulating TNF receptors on ACTH-stimulated hydrocortisone release.Methods We used real-time PCR and immunocytochemistry to evaluate the expression of TNF receptors on Y1 cells.TNF-receptor 1 (TNF-R1) DNA fragments corresponding to the short hairpin RNA (shRNA)-sequences were synthesized and cloned into pcDNATM 6.2-GW/EmGFP expression vector.Knockdown efficiency of TNF-R1 expression was evaluated in miRNA transfected and mock-miRNA transfected Y1 cells by quantitative real-time PCR (Q-PCR).Hydrocortisone expression levels were determined in TNF-R1-knockdown and control Y1 cells treated with TNF-α and ACTH.Results Mouse adrenal cortex Y1 cells were positive for type I TNF-R1,but not type Ⅱ TNF-receptor (TNF-R2).Blocking TNF-R1 expression resulted in loss of TNF-α-mediated inhibition of ACTH-stimulated hydrocortisone expression,suggesting a role for the TNF-R1 related signaling pathway in ACTH-stimulated hydrocortisone synthesis.Conclusion The inhibitory effect of TNF-α on ACTH-stimulated hydrocortisone synthesis was mediated via TNF-R1 in adrenal cortex.