Lipopolysaccharide inhibits rat ovarian thecal-interstitial cell steroid secretion in vitro

Lipopolysaccharide (LPS), a major component of gram-negative cell walls, is a potent immunostimulator. Treatment of monocytes/macrophages in vitro with LPS induces the secretion of cytokines such as tumor necrosis factor-alpha and interleukin-1 alpha, -1 beta, and -6. LPS is thought to require LPS-binding protein or CD14 to act at low concentrations (< 100 ng LPS/ml). In the present study, rat ovarian thecal-interstitial cells (TIC) were cultured in a serum-free culture system (in the absence of LPS-binding protein or soluble CD14) and challenged with LPS. Treatment with LPS led to a dose-dependent (1-100 ng LPS/ml) decrease in LH-stimulated progesterone and androstenedione secretion. LPS had no effect on radiolabeled hCG binding to TIC homogenates or cAMP accumulation in culture medium. LPS treatment was associated with an increase in interleukin-6 bioactivity in the medium of thecal-interstitial cell cultures; however, tumor necrosis factor-alpha bioactivity was undetectable. Herbimycin A, an src tyrosine kinase inhibitor, blocked the actions of LPS and was associated with an increase in cAMP accumulation in TIC culture medium. The results suggest that LPS can act directly on ovarian thecal-interstitial cells and that this can occur in a LPS-binding protein/CD14-independent manner. The actions of LPS appear to be specific and require a nonreceptor tyrosine kinase.