Tetramethylpyrazine prevents inducible NO synthase expression and improvessurvival in rodent models of endotoxic shock

This study is to investigate the possible mechanism of beneficial effects o f tetramethylpyrazine (TMP) on endotoxic shock which we showed in our preli minary study (Liao et al. 1998; Proc Natl Sci Counc Repub China B 22:46-54) . Here, we have confirmed the beneficial effects of TMP on the hypotension, vascular hyporeactivity to noradrenaline (NA), release of tumour necrosis factor-a (TNF-alpha) and nitric oxide (NO) in a rat model of circulatory sh ock induced by bacterial endotoxin (E. coli lipopolysaccharide, LPS), In ad dition, we further examined the expression of inducible NO synthase in the lung and in the aorta from these rats and evaluated the effect of TMP on th e 36-h survival rate in a murine model of endotoxaemia, Male Wistar-Kyoto r ats were anaesthetised and instrumented for the measurement of mean arteria l pressure (MAP) and heart rate (HR). Injection of LPS (10 mg kg(-1), i.v.) resulted in an acute fall followed by a substantial fall in MAP within 4 h and an increase in HR. In contrast, animals pretreated with TMP (10 mg kg( -1), i.p.; at 30 min prior to LPS) maintained a significantly higher MAP bu t the tachycardia was further enhanced at 1-2 h when compared to rats given only LPS (LPS rats). The presser effect of NA (1 mu g kg(-1), i.v.) was al so significantly reduced after the treatment of rats with LPS. Similarly, t he thoracic aorta obtained from rats at 4 h after LPS showed a significant reduction in the contractile responses elicited by NA (1 mu M). Pretreatmen t of LPS rats with TMP partially, but significantly, prevented this LPS-ind uced hyporeactivity to NA in vivo and ex vivo. The injection of LPS resulte d in a bell-shaped change in plasma TNF-alpha level which reached a maximum at 1 h, whereas the effect of LPS on the plasma level of nitrate (an indic ator of NO formation) was increased in a time-dependent manner. This increm ent of both TNF-alpha and nitrate levels was significantly reduced in LPS r ats pretreated with TMP. Endotoxaemia for 4 h caused a significantly increa sed protein expression of iNOS in the lung and the aorta. Ln LPS rats pretr eated with TMP, iNOS protein expression in lung and aorta homogenates was a ttenuated by 75 +/- 3% and 57 +/- 6%, respectively. In addition, the lack o f evidence of presser effect of TMP on rats with endotoxaemia for 4 h sugge sted that TMP inhibits the induction of iNOS rather than directly inhibitin g NOS activity. Treatment of conscious ICR mice with a high dose of endotox in (60 mg kg(-1), i.p,) resulted in a survival rate of only 15% at 36 h (n = 20), However, therapeutic application of TMP (10 mg kg(-1), i.p.; at 0, 6 , 15 and 24 h after LPS) increased the 36-h survival rate to 55% (n = 20). Thus, TMP inhibits the expression of iNOS and mitigates the delayed circula tory failure caused by endotoxic shock in the rat. In addition, TMP also im proves survival in a murine model of severe endotoxaemia.