TUMOR-NECROSIS-FACTOR-ALPHA INHIBITS ENDOTHELIUM-DEPENDENT RELAXATION

Tumor necrosis factor-alpha (TNF-alpha) stimulates nitric oxide (NO) i n vascular endothelium by induction of the enzyme NO synthase II (NOS II). We examined the effects of TNF-alpha on 1) endothelium-dependent (EDR) and endothelium-independent (EIR) relaxation and 2) contraction of bovine intralobar pulmonary arteries (BPA) and veins (BPV) in vitro . Acetylcholine (ACh), bradykinin (BK), histamine, and A23187 produced EDR of BPA contracted with a 50% effective concentration of U-46619 ( 15 nM), because relaxation was abolished by endothelium-rubbing and at tenuated by L-N(G)-monomethylarginine (L-NMMA; 300 muM). TNF-alpha (0. 00417, 0.0417, 0.417, and 1.25 mug/ml) incubated with BPA for 60 min i nhibited EDR of the BPA to ACh, BK, and histamine. The effects of TNF required 30 min for onset. Recovery of EDR occurred 3-4 h after washou t of TNF-alpha. Pentoxifylline (1 muM) did not affect ACh-induced EDR but selectively reversed TNF-alpha-mediated inhibition of ACh-induced EDR. TNF-alpha-mediated inhibition of EDR was not reversible by L-NMMA , an inhibitor of NOS I and NOS II, the cyclooxygenase inhibitor ibupr ofen, or CV-3908 (1 muM), a platelet-activating factor antagonist. The inhibitory effect of TNF-alpha on EDR was not mediated by nonspecific sensitization of the endothelium to human protein because recombinant human granulocyte colony-stimulating factor (10, 50, and 500 x 10(3) U/ml) did not affect EDR of BPA. The effect of TNF-alpha was specific for release of NO from the endothelium of BPA because TNF-alpha did no t affect 1) EDR of BPV to ACh, BK, or ATP; 2) EIR of BPA or BPV to nit roprusside; and 3) contraction of either BPA or BPV to KCl, U-46619, h istamine, norepinephrine, or serotonin. Thus TNF-alpha appears to sele ctively inhibit receptor-mediated EDR and NO release in BPA. TNF-alpha -mediated inhibition of EDR differs from that of L-arginine-based inhi bitors and may represent an endogenous physiological mechanism of regu lation of NO in the endothelium.