ACCUMULATION OF PLATELET-ACTIVATING-FACTOR ACETYLHYDROLASE IN THE PERITONEAL-CAVITY OF GUINEA-PIG AFTER ENDOTOXIN-SHOCK

We examined the production of PAF, a mediator of shock, and LysoPAF, a n inactive metabolite of PAF, in the guinea pig peritoneal cavity afte r i.p. administration of Escherichia coli LPS. Within 1 h of LPS admin istration, the level of PAF in the peritoneal fluid increased from 4.9 to 37.2 pmol/animal and decreased to the control value thereafter. In contrast, the level of lysoPAF gradually rose from 63.5 to 268 pmol/a nimal for upto 6 h. The activity of acetylhydrolase, which converts PA F to lysoPAF, in the peritoneal cavity increased in parallel with the increase in the lysoPAF level. The enzyme was distinguishable from pho spholipase A(2), because p-bromophenacylbromide (p-BPB), Ca2+, and eth ylenediaminetetraacetic acid (EDTA) did not affect its enzymatic activ ity. In addition, this acetylhydrolase revealed similar biochemical pr operties to that detected in plasma. Both acetylhydrolases were resist ant to trypsin treatment and had the same apparent molecular weight, a s shown by gel-filtration column chromatography. These results suggest that the acetylhydrolase, which accumulates in the peritoneal cavity, infiltrates from the plasma in response to LPS, and then participates in the exclusion of PAF during endotoxin shock.