ENDOTHELIN-1 STIMULATES THE BIOSYNTHESIS OF TUMOR-NECROSIS-FACTOR IN MACROPHAGES - ET-RECEPTORS, SIGNAL-TRANSDUCTION AND INHIBITION BY DEXAMETHASONE

Endothelin-1 (ET-1) enhances the biosynthesis of interleukin-6 (IL-6) in endothelial cells and bone marrow-derived stromal cells of the rat. This study investigates (i) whether ET-I stimulates the formation of tumour necrosis factor alpha(TNF alpha) or interferon-gamma(IFN gamma) in cultured macrophages or in the anaesthetized rat. Incubation of J7 74.2 macrophages with ET-1 (0.001 - 1 mu M) caused a concentration-and time-dependent increase in the concentration of TNF alpha, but not of IFN gamma, in the culture medium. The increase in TNF alpha caused by stimulation of 5774.2 macrophages was abolished by pretreatment of ce lls with (i) the protein synthesis inhibitor cycloheximide, (ii) with the select:ve ETA-receptor antagonists BQ-123 or BQ-485 the selective ETB-receptor antagonist BQ-788), (iii) the tyrosine kinase inhibitors genistein or tyrphostin AG126, or (iv) with the glucocorticoid, dexame thasone. The inhibition by dexamethasone of the formation of TNF alpha by cells activated with ET-1 is not due to the formation of lipocorti n-l (LC1), as it was not reduced by a monoclonal antibody against LC1. Systemic administration (iv) of ET-1 (1 nmol.kg(-1)) to anaesthetized rats caused a rapid and sustained (maximum: 45 min; return to baselin e: within 180 min) rise in the plasma levels of TNF alpha. This is the first demonstration that ET-1 can release proinflammatory cytokines i n vitro and in vivo. The generation of TNF alpha caused by ET-l involv es (in sequence) the (i) activation of ETA-receptors, (ii) activation of tyrosine kinase resulting in the phosphorylation of intracellular p roteins, (iii) the activation of, hitherto, unknown transcription fact ors, finally resulting in (iv) transcription and translation of the TN F alpha gene. The generation of TNF alpha by cells activated with ET-I points to a pro-inflammatory role of ET-1 in diseases associated with local (e.g. atherosclerosis, heart failure) or systemic inflammation (circulatory shock), which are associated with high ET-I plasma levels .