Patients with glucocorticoid excess develop central obesity, yet in simple obesity, circulating glucocorticoid levels are normal. We have suggested that the increased activity and expression of the enzyme 11 beta -hydroxysteroid dehydrogenase type 1 (11 beta HSD1) generating active cortisol from cortisone within adipose tissue may be crucial in the pathogenesis of obesity. In this study primary cultures of human hepatocytes and adipose stromal cells (ASC) were used as in vitro models to investigate the tissue-specific regulation of 11 beta HSD1 expression and activity. Treatment with tumor necrosis factor-alpha (TNF alpha) caused a dose-dependent increase in 11 beta HSD1 activity in primary cultures of both sc [1743.1 +/- 1015.4% (TNF alpha, 10 ng/ml); P <0.05 vs. control (100%)] and omental [375.8 +/- 57.0% (TNF alpha, 10 ng/ml); P <0.01 vs. control (100%)] ASC, but had no effect on activity in human hepatocytes [90.2 +/- 2.8% (TNF alpha, 10 ng/ml); P = NS vs, control (100%)]. Insulin-like growth factor I (IGF-I) caused a dose-dependent inhibition of 11 beta HSD1 activity in sc [49.7 +/- 15.0% (IGF-I, 100 ng/ml]; P <0.05 vs. control (100%)] and omental [71.6 +/- 7.5 (IGF-I, 100 ng/ml); P <0.01 us. control (100%)] stromal cells, but not in human hepatocytes [101.8 +/- 15.7% (IGF-I, 100 ng/ml); P = NS vs, control (100%)]. Leptin treatment did not alter 11 beta HSD1 activity in human hepatocytes, but increased activity in omental ASC [135.8 +/- 14.1% aeptin, 100 ng/ml); P = 0.08 vs, control (100%)]. Treatment with interleukin-1 beta induced 11 beta HSD1 activity and expression in sc and omental. ASC in a time-and dose-dependent manner. 15-Deoxy-Delta 12,14-PGJ2, the putative endogenous ligand of the orphan nuclear receptor peroxisome proliferator-gamma, significantly increased 11 beta HSD1 activity in omental cells [179.7 +/- 29.6% (1 muM); P <0.05 vs. control (100%)] and sc [185.3 +/- 12.6% (1 muM); P <0.01 vs, control (100%)] ASC, and it is possible that expression of this ligand may ensure continued cortisol generation to permit adipocyte differentiation. Protease inhibitors used in the treatment of human immunodeficiency virus infection are known to cause a lipodystrophic syndrome and central obesity, but saquinavir, indinavir, and neflinavir caused a dose-dependent inhibition of 11 beta HSD1 activity in primary cultures of human omental ASC. 11 beta HSD1 expression is increased in human adipose tissue by TNF alpha, interleukin-1 beta, leptin, and orphan nuclear receptor peroxisome proliferator-gamma agonists, but is inhibited by IGF-I. This autocrine and/or paracrine regulation is tissue specific and explains recent clinical data and animal studies evaluating cortisol metabolism in obesity. Tissue-specific 11 beta HSD1 regulation offers the potential for selective enzyme inhibition within adipose tissue as a novel therapy for visceral obesity.