Abstract 59

Introduction: Lipid A is responsible for the endotoxic activities of lipopolysaccharides in gram-negative infection. Since there are no tests to prove direct endotoxic intraction with membranes, we analyzed lipid A by measuring the content of hydroxymyristic acid (HMA). The HMA is not found in human tissues but only in bacterial endotoxins.

Materials: Washed red blood cells (RBC) from 5 neonates and 5 adults were incubated with 100 µg of lipid A for 30 and 60 minutes. RBC membranes were isolated and the hydoxymyristic acid content was qualitatively and quantitatively analysed by gas chromatography.

Results: Lipid A was detectable in all RBC membranes. After 30 min of incubation the HMA content was 459.7 ± 16.8 pmol/ml RBC in neonates and 423.3 ± 12.7 pmol/ml RBC in adults. After 60 min of incubation 518.9 ± 99.9 in neonates and 491.5 ± 99.2 in adults(Means ± SEM).

Conclusion: This study shows, that lipid A interacts directly with RBC membranes. The effect is time dependent. Neonatal RBC are slightly more susceptible for lipid A insertion into their membranes than adult RBC. Approximately 1% of the lipid A was detected in the RBC membranes after incubation indicating that this method is effective to detect minimal amounts of endotoxin in membranes. Further studies should be done to detect lipid A in endothelial cells during infection.