IN-VIVO ADMINISTRATION OF ENDOTOXIN AND TUMOR-NECROSIS-FACTOR-ALPHA PRODUCE DIFFERENT EFFECTS ON CONSTITUTIVE AND INDUCIBLE NITRIC-OXIDE SYNTHASE ACTIVITY IN RAT NEUTROPHILS AND AORTA EX-VIVO

Tumor necrosis factor-alpha (TNF-alpha) inhibits release of nitric oxi de (NO) in vitro by stimulating the degradation of constitutive NO syn thase (cNOS III) mRNA. However, TNF-alpha is believed to be the cytoki ne mediator of the hypotension and upregulation of inducible NO syntha se (iNOS II) produced by gram-negative bacterial endotoxin (LPS). Some in vivo effects of TNF-alpha are opposite to those which occur in vit ro. This study tested the hypothesis that in vivo administration of ex ogenous TNF-alpha and endogenously released TNF-alpha induce iNOS II a ctivity and inhibit cNOS III activity, and thereby mediate the acute p hase effects of LPS on blood pressure and the NO system in the rat, We show that LPS produces acute phase hypotension in ketamine anesthetiz ed rats, The hypotension was associated with elevation of biologically active TNF-alpha in plasma, increased production of RNI (NO2- and NO3 - anion) in rat neutrophils (PMN) and suppression of RNI production by A23187(1 mu M) stimulated thoracic aorta (RTA) ex vivo. TNA-alpha (10 (6) U/ml, iv) did not produce acute phase hypotension but initially ra ised arterial blood pressure and heart rate (HR), did not increase RNI production by PMN, and inhibited RNI production by A23187 stimulated RTA ex vivo, Pretreatment of rats with the Immunex monomeric soluble P 75 receptor binding protein for TNF-alpha (TNFsr, 0.5 mg/kg, iv) 15 mi n prior to LPS administration decreased circulating TNF-alpha from 92, 137 +/- 12,456 U/ml to undetectable levels as determined by the L929 b ioassay, However, LPS-induced increases in RNI in PMN was enhanced and LPS-induced decreases in RNI production by RTA was inhibited by TNFsr , Thus, in vivo administration of TNF-alpha does not mimic the hemodyn amic and NO-inducing effects of LPS, However, TNF-alpha mediates in pa rt LPS-induced inhibition of RNI production by RTA, Thus, endogenous T NF-alpha is not required for LPS-induced acute phase hypotension or iN OS II activity, The importance of TNF-alpha in sepsis resides in syste ms other than iNOSII and blood pressure.