GRAM-NEGATIVE SHOCK IN RATS DEPENDS ON THE PRESENCE OF CAPSULATED BACTERIA AND IS MODIFIED BY LAPAROTOMY

To develop a hyperdynamic sepsis model in rats, four Escherichia coil strains were used, which differed in the presence or absence of a caps ule or K antigen (K1 and K-, respectively) and/or in O serogroup (O9 a nd O18). Of the two clinical isolates, O9K(-) did not survive in rat s erum, whereas O18K1 and two isogenic laboratory strains (O18K1 acid O1 8K(-)) were able to resist serum bacteriolysis. Pentobarbital-anesthet ized rats (n = 21) received an intravenous bolus of 10(9) bacteria. In contrast to the two noncapsulated strains, both capsulated strains in duced hyperdynamic shock: arterial lactate rose from a mean value of . 91 to 3.09 mmol . L(-1), systemic Vascular resistance dropped from 1.1 5 to .78 mmHg . min . mL(-1), and cardiac output transiently increased from 98 to 115 mL . min(-1); renal plasma flow remained at 3-4 mL . m in(-1), whereas glomerular filtration rate decreased from 1.3 to .7 mL . min(-1) Laparotomy, which is often performed to study kidney functi on, completely abolished the hyperdynamic condition, while glomerular filtration rate was still decreased, We conclude that in rats, in cont rast to humans, capsulated bacteria are required to induce a hyperdyna mic septic shock; the hyperdynamic characteristics of the shock do not occur in animals subjected to a laparotomy.