The Limulus Amoebocyte Lysate test: detection of endotoxin in plasma of swine and cattle. II. In vivo investigations.

Endotoxin was detected by the LAL test in the plasma of swine and cattle following in vivo injection of endotoxin in order to evaluate the applicability of the test in veterinary medicine for detection of endotoxemia. Clinical symptoms of endotoxemia occurred after the injection into 3 swine of 0.10–0.25 mg endotoxin/100 kg bwt and after the infusion during 1–1½ h of 2.0–2.2 mg endotoxin/100 kg bwt into 3 calves. The concentration of endotoxin detected by the LAL test in the experimental animals ranged from 0.15 ng to 6.0 ng endotoxin per ml crude plasma. As positive LAL reactions were obtained only in close connection to the administration of endotoxin, clearance of endotoxin to levels below the sensitivity of the test was fast. In spite of the fast clearance, light symptoms of endotoxemia could be seen as long as 24 h after the last sample showing a positive test result. The applied technique for LAL analysis on blood, therefore, was not adequate for detection of endotoxin at sufficiently low concentrations and some possibilities of improving the technique are discussed. Though leukocytosis were found not to influence the outcome of the LAL test on blood, leukocytic mediators released by endotoxin or endotoxin-derived injuries may still have caused the persistence of the symptoms of endotoxemia, and this question is disputed in relation to the benefit of improving the technique. Especielly in the veterinary clinic, great precautions are necessary to obviate false positive test samples resulting from, e.g., external contamination or transient stress caused by excitement, and it is concluded that the possible application of the LAL test for detection of endotoxemia in veterinary medicine is restricted to surveillance of hospitalized animals and to research purposes.