The lazaroid, U-74389G, inhibits inducible nitric oxide synthase activity,reverses vascular failure and protects against endotoxin shock

The aim of our study was to investigate the effect of the 21-aminosteroid U -74389G [21-< 4-(2,6-di-1-pyrrolidinyl-4-pyrimidinyl)-1-piperazinyl-pregna- 1,4,9,(11) triene-3,20-dione( z)-2-butenedionate] on the I-arginine-nitric oxide (NO) pathway in a rat model of endotoxin shock. Endotoxin shock was p roduced in male rats by a single intravenous (i.v.) injection of 20 mg/kg o f Salmonella Enteritidis lipopolysaccharide (LPS). Rats were treated with U -74389G (7.5, 15 and 30 mg/kg i.v.) or vehicle (1 ml/kg i.v.)5 min after en dotoxin challenge. Lipopolysaccharide administration reduced survival rate (0%, 72 h after endotoxin administration) decreased mean arterial blood pre ssure, enhanced plasma concentration of bilirubin and alanine aminotransfer ase and increased plasma nitrite concentrations. Lipopolysaccharide injecti on also increased the activity of inducible NO synthase in the liver and in the aorta. Furthermore aortic rings from shocked rats showed a marked hypo reactivity to phenylephrine (1 nM-10 mu M). In addition lipopolysaccharide (50 mu g/ml for 4 h) in vitro stimulation significantly increased nitrite p roduction in peritoneal macrophages harvested from normal rats. Treatment w ith U-74389G (15 and 30 mg/kg i.v., 5 min after endotoxin challenge) signif icantly protected against lipopolysaccharide-induced lethality (90% surviva l rate 24 h and 80% 72 h after lipopolysaccharide injection, respectively, following the highest dose of the drug), reduced hypotension, ameliorated l iver function, decreased plasma nitrite levels, restored the hyporeactivity of aortic rings to their control values and inhibited the activity of indu cible NO synthase in the liver and in the aorta. Finally, U-74389G in vitro (12.5, 25 and 50 mu M) significantly inhibited nitrite production in endot oxin stimulated peritoneal macrophages. The data suggest that U-74389G may exert beneficial effects in an experimental model of septic shock by inhibi ting the activity of the inducible NO synthase. (C) 1999 Elsevier Science B .V. All rights reserved.