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

Endotoxin added in vitro to plasma of swine and cattle was detected by the Limulus Amoebocyte Lysate (LAL) test in order to evaluate the possible utility of the test for detection of endotoxemia in the veterinary clinic and in research. The inhibitory effect of plasma on the test was diminished in porcine plasma by dilution with saline, by heat-extraction, or by the pH-shift method. The last-mentioned method was not applicable to porcine plasma, whereas the heat-extraction method followed by serial 2-fold dilutions in water admitted the detection of endotoxin at low concentrations in porcine as well as in bovine plasma. The inhibition of the LAL test was more pronounced by bovine than by porcine plasma in that, when the same lysate sensitivity was used, the detection limit of endotoxin was highest in bovine plasma. The detection limit could be lowered by increasing the lysate sensitivity either by prolongation of the incubation or by the use of water instead of saline as diluent for plasma. However, an essential increase in lysate sensitivity demands extreme precautions, and a comparatively greater increase in the clinical applicability of the LAL test would be obtained if the inhibitory effect, that is present at low concentrations of endotoxin even in heat-extracted plasma, could be eliminated. It is concluded, that to get full benefit of the LAL test for detection of endotoxemia in the veterinary clinic and in research, a functional LAL laboratory must be made available and new techniques for the elimination of plasma inhibitors at low concentrations of endotoxin must be developed.