Resistin has recently been implicated as an adipocytokine leading to insulin resistance and, therefore, potentially linking obesity and diabetes. To further characterize the regulation of this fat-secreted protein by insulin sensitivity-modulating hormones, 3T3-L1 adipocytes were treated with tumor necrosis factor (TNF) alpha, angiotensin (AT) 2, as well as growth hormone (GH), and resistin gene expression and protein secretion were determined by quantitative real-time reverse transcription-polymerase chain reaction and Western blotting. Interestingly, both, resistin mRNA expression and protein secretion, were inhibited by 70-90% after TNF alpha -treatment whereas AT2 and GH did not have any effect. The inhibitory effect of TNF alpha was time-and dose-dependent with significant inhibition occurring as early as 4 h after effector addition and at concentrations as low as I ng/ml TNF alpha. Pharmacological inhibition of protein kinase A (PKA), p44/42, and p38 mitogen-activated protein (MAP) kinase did not reverse the inhibitory effect of TNF alpha suggesting that neither of these signaling molecules is involved in suppression of resistin gene expression by TNF alpha. Furthermore, suppression of resistin mRNA levels could be completely reversed to control levels by withdrawal of TNF alpha for 24 h. Taken together, these results suggest that TNF alpha is a pivotal negative regulator of resistin gene expression. This may have important implications for the pathogenesis of insulin resistance and its link to obesity.