The effects of endotoxin on platelet-activating factor synthesis in cultured rat glomerular mesangial cells

Platelet-activating factor (PAF), a potent vasoactive phospholipid, may contribute to acute renal failure and septic shock accompanying endotoxemia. Rat glomerular mesangial cells in culture synthesize PAF and contract after the addition of PAF. We thus investigated the potential of mesangial cells to respond to Escherichia coli lipopolysaccharide endotoxin with enhanced PAF synthesis in vitro. The mesangial cells were incubated with [3H]acetate, substrate for lyso-PAF: acetyl-CoA acetyltransferase, and endotoxin at different concentrations for various periods of time at 37 degrees C. Lipids were extracted and PAF was isolated by thin-layer chromatography. Endotoxin stimulated PAF generation in a time- and dose-related manner. Whereas most of the PAF was associated with the cells, endotoxin more than doubled the amount of PAF released into the extracellular medium as compared to control. Furthermore, the PAF-like material obtained from endotoxin-stimulated mesangial cells irreversibly aggregated washed rabbit platelets. This effect was lost after alkaline methanolysis and was totally blocked by L-652,731, a specific PAF-receptor antagonist. Finally, the PAF-like material exerted a hypotensive effect, which was abolished by L-652,731, when infused intravenously into healthy rats. These data indicate that rat glomerular mesangial cells have the ability to synthesize PAF in response to endotoxin. This suggests that PAF, so generated within the glomerulus, may contribute to acute decrements of glomerular filtration rate in endotoxemia.