Similar cytokine but different coagulation responses to lipopolysaccharide injection in D-galactosamine-sensitized versus nonsensitized rats

Abstract

To compare cytokine release and coagulation disturbances induced by administration of high versus low doses of endotoxin (lipopolysaccharide [LPS]), we used two endotoxin test systems similar in mortality but different in the degree of endotoxemia. One group of rats (n = 11) randomly received endotoxin (15.0 mg/kg of body weight intraperitoneally [i.p.]) and 1 ml of Ringer's solution (nonsensitized animals). The second group (n = 11) received 1 ml of D-galactosamine (500 mg/kg i.p.) and endotoxin (100 μg/kg i.p.) simultaneously (sensitized animals). Endotoxin levels in the plasma of nonsensitized rats were 1,000-fold higher than those in the plasma of sensitized rats (69.33 x 103 ± 22.42 x 103 versus 75.8 ± 27.08 ng of LPS per ml), leading to a mortality of 91% in nonsensitized rats versus 82% in the sensitized-rat model within 48 h postendotoxemia. Serum transaminase activity increased up to 100-fold in sensitized rats as a sign of hepatocyte damage. Despite the large difference in LPS levels in plasma, the time courses of the plasma tumor necrosis factor (TNF) increase were similar in the two groups, with a peak at 2 h (54 ± 12 ng/ml in nonsensitized rats versus 43 ± 12 ng/ml in sensitized rats), and also similar to that of a group of nonsensitized rats (n = 5) that received a low dose of LPS (100 μg/kg) only (52 ± 21 ng/ml), while D-galactosamine alone did not induce TNF release. Despite similar TNF levels, a more pronounced coagulation disorder was observed at 4 h in nonsensitized rats (with the high LPS dose) as measured by platelet counts, plasma fibrinogen levels, and activated partial thromboplastin time prolongation (191 x 103 ± 107 x 103 cells per μl, 40 ± 24 mg/dl, and 53 ± 15 s, respectively) than in rats with the low LPS dose either sensitized (495 x 103 ± 153 x 103, 95 ± 49, and 38 ± 16, respectively) or nonsensitized (439 x 103 ± 62 x 103, 170 ± 18, and 35 ± 11, respectively). From these data, we conclude that (i) TNF production induced by LPS in rats is not changed by D-galactosamine treatment; (ii) since endotoxin alone (100 μg/kg of body weight) induced a TNF increase in nonsensitized rats similar to that seen in D-galactosamine-sensitized rats but did not produce any lethality, the increased sensitivity to LPS in D- galactosamine-sensitized animals appears to be due to the higher level of sensitization of the animals to LPS-induced mediators; and (iii) similar cytokine responses to high and low doses of LPS (with or without D- galactosamine) but different coagulation disturbances indicate that factors other than TNF also play a role in producing disseminated intravascular coagulation.