THE MULTIPLE ORGAN DYSFUNCTION SYNDROME CAUSED BY ENDOTOXIN IN THE RAT - ATTENUATION OF LIVER DYSFUNCTION BY INHIBITORS OF NITRIC-OXIDE SYNTHASE

1 We have investigated whether (i) endotoxaemia caused by E. coli lipopolysaccharide in the anaesthetized rat causes a multiple organ dysfunction syndrome (MODS; e.g. circulatory failure, renal failure, liver failure), and (ii) an enhanced formation of nitric oxide (NO) due to induction of inducible NO synthase (iNOS) contributes to the MODS. In addition, this study elucidates the beneficial and adverse effects of aminoethyl-isothiourea (AE-ITU), a relatively selective inhibitor of iNOS activity, and N-G-methyl-L-arginine (L-NMMA), a non-selective inhibitor of NOS activity on the MODS caused by endotoxaemia. 2 In the anaesthetized rat, LPS caused a fall in mean arterial blood pressure (MAP) from 117 +/- 3 mmHg (time 0) to 97 +/- 4 mmHg at 2 h (P<0.05, n=15) and 84 +/- 4 mmHg at 6 h (P<0.05, n=15). The presser effect of noradrenaline (NA, 1 mu g kg(-1), i.v.) was also significantly reduced at 1 to 6 h after LPS (vascular hyporeactivity). Treatment of LPS-rats with AE-ITU (1 mg kg(-1), i.v. plus 1 mg kg(-1) h(-1) starting at 2 h after LPS) caused only a transient rise in MAP, but significantly attenuated the delayed vascular hyporeactivity seen in LPS-rats. Infusion of L-NMMA (3 mg kg(-1), i.v. plus 3 mg kg(-1) h(-1)) caused a rapid and sustained rise in MAP and attenuated the delayed vascular hyporeactivity to NA. Neither AE-ITU nor L-NMMA. had any effect on either MAP or the presser effect elicited by NA in rats infused with saline rather than LPS. 3 Endotoxaemia for 6 h was associated with a significant rise in the serum levels of aspartate or alanine aminotransferase (i.e. GOT or GPT), gamma-glutamyl-transferase (gamma GT), and bilirubin, and hence, liver dysfunction. Treatment of LPS-rats with AE-ITU significantly attenuated this liver dysfunction (rise in GOT, GPT, gamma GT and bilirubin) (P<0.05, n=10). In contrast, L-NMMA reduced the increase in the serum levels of gamma GT and bilirubin, but not in GOT and GPT (n= 5). Injection of LPS also caused a time-dependent, but rapid (almost maximal at 2 h), increase in the serum levels of urea and creatinine, and hence, renal dysfunction. This renal dysfunction was not affected by either AE-ITU (n=10) or L-NMMA (n=5). In rats infused with saline rather than LPS, neither AE-ITU (n=4) nor L-NMMA (n=4) had any significant effect on the serum levels of GOT, GPT, gamma GT, bilirubin, creatinine or urea. 4 Endotoxaemia for 6 h resulted in a 4.5 fold rise in the serum levels of nitrite (9.13 +/- 0.77 mu M, P<0.01, n=15), which was significantly reduced by treatment with AE-ITU (6.32 +/- 0.48 mu M, P<0.05, n=10) or L-NMMA (5.10 +/- 0.40 mu M, P<0.05, n=5). In addition, endotoxaemia for 6 h was also associated with a significant increase in iNOS activity in lung and liver homogenates, which was significantly reduced in lung or liver homogenates obtained from LPS-rats treated with either AE-ITU or L-NMMA. 5 Thus, AE-ITU or L-NMMA (i) inhibits iNOS activity in LPS-rats without causing a significant increase in MAP in rats infused with saline and, hence inhibition of endothelial NOS activity, and (ii) attenuates the delayed circulatory failure as well as the liver dysfunction caused by endotoxaemia in the rat. Thus, an enhanced formation of NO may contribute to the development of liver failure in endotoxic shock.