Rapid in vivo induction of leukocyte tissue factor mRNA and protein synthesis following low dose endotoxin administration to rabbits
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INTRODUCTION: Disseminated intravascular coagulation in humans is frequently associated with Gram-negative bacterial sepsis. Therefore, to examine the role and time frame of the in vivo induction of tissue factor (TF) by bacterial endotoxin, a reverse transcription polymerase chain reaction and a solid-phase ELISA assay were developed to monitor the in vivo production in rabbits, of TF mRNA and TF antigen by peripheral blood leukocytes (PBL). METHODS: : Healthy rabbits were injected intravenously with either 1, 10 or 50 microg/kg of Salmonella endotoxin. Blood samples were obtained both before endotoxin administration and at various time points thereafter, up to 24 h. Some experiments were also done to determine whether all-trans retinoic acid would ameliorate the signs of the endotoxin-induced disseminated intravascular coagulation. RESULTS: PBL counts dropped significantly within 2 h of rabbits receiving the endotoxin, recovering to baseline levels by 24 h. Platelet counts decreased gradually over this same time frame. Fibrin deposition was noted in renal glomerular capillaries at 24 h. An increase (P<0.001) in PBL-associated TF mRNA levels was observed 2 h post-endotoxin (10 microg/kg, n = 8), followed by a gradual decline over the subsequent 24 h. The average increase in TF mRNA at 2 h was approximately 4.6-fold (P<0.001) over that seen at time 0. The amount of mononuclear cell associated TF antigen demonstrated a peak at 2 h post-endotoxin (10 microg/kg, n = 13), with levels approximately 9.6-fold greater than (P<0.001) baseline. Pre-treatment of rabbits with all-trans retinoic acid significantly (P<0.001) ameliorated the PBL-associated increase in TF mRNA and TF antigen levels. CONCLUSION: These results suggest that low dose endotoxin (10 microg/kg) faithfully reproduces the non-overt activation of coagulation observed in primates and human volunteers, supporting the hypothesis that TF expression is involved in the in vivo initiation and propagation of disseminated intravascular coagulation. Moreover, all-trans retinoic acid may be effective in modulating in vivo the TF transcription induced by endotoxin.
