Biological responses of sheep treated with endotoxin-contaminated superoxide dismutase and endotoxin preparations.

The purpose of this study was to evaluate the biological response of sheep to different doses of endotoxin and endotoxin-contaminated enzyme preparations. The enzyme used in this experiment was superoxide dismutase (SOD), as it is currently being used in many different experiments and because several preparations were found to be heavily contaminated with endotoxin. A group of ewes were injected intravenously with a variety of different treatments. Peripheral blood was used to determine the total number of leukocytes, a differential cell count to find out the numbers of polymorphonucleocytes (PMN) and monocytes (M), and to measure the concentration of 15-ketodihydro-PGF2 alpha. In addition, rectal temperature was recorded. Treatments included saline (control), Pharmacia-Chiron's Cu/Zn-SOD (r-hSOD, 8 mg/kg), Sigma's bovine SOD (bSOD, 8 mg/kg), Grünenthal's bSOD (8 mg/kg), various doses of Salmonella typhimurium endotoxin (1000, 200, 100, 50, 20, 10, 5, and 1 ng/kg), and a mixture of endotoxin (200 ng/kg) plus r-hSOD (8 mg/kg). Results indicate that sheep react to endotoxin-contaminated SOD preparations with an endotoxemia which is similar to that seen in animals receiving endotoxin alone. This endotoxemia includes, among other things, a rise in rectal temperature, a peak in the PGF2 alpha metabolite, and an increased PMN/M ratio. Endotoxin administered at doses of 50 to 200 ng/kg also caused the expected signs of endotoxemia. At 1000 ng/kg endotoxin actually led to a decreased rectal temperature. This may be due to a type of endotoxemic shock, resulting in a decrease in peripheral blood circulation. Low doses of endotoxin (10, 5, and 1 ng/kg) caused a leukocytosis via increases in PMN; no greater changes in rectal temperature or the PGF2 alpha metabolite were noted. The combination of r-hSOD with 200 ng/kg of endotoxin caused an endotoxemia similar to that caused by 200 ng/kg of endotoxin alone. In conclusion, if an endotoxin-contaminated SOD-preparation was used to study the efficacy of SOD, there would be a serious risk of interaction by the endotoxins. In such a case it would be impossible to distinguish the effects of the endotoxin from those of the preparation itself. It is therefore important that researchers are alert to the problem of endotoxin contamination.