Platelet-activating factor stimulates arachidonic acid release and enhances thromboxane B2 production in intact fetal rat brain ex vivo.
The ability of brain preparations from 20-day-old rat fetuses to synthesize eicosanoids in the presence of platelet activating factor (PAF) was investigated. A rise (49%) in thromboxane B2 (TxB2; the stable thromboxane A2 metabolite) was observed after 30 min in the presence of 0.6 microM PAF. Repetitive administration of PAF did not rise TxB2 production above a certain level, suggesting desensitization. 1-O-alkyl, sn-glycero-3-phosphocholine (lyso-PAF) at 0.6 microM had no effect, whereas selective PAF antagonists, i.e., BN52021, BN50739 and BN50727, or indomethacin, a general cyclooxygenase inhibitor, blocked completely TxB2 synthesis. The calcium ionophore A23187 (10 microM) stimulated production of TxB2, prostaglandin E2 and 6-keto-prostaglandin F1 alpha eicosanoids, whereas extracellular calcium deprivation did not impair eicosanoid release. The effects of PAF and A23187 on TxB2 synthesis were not additive and were not dependent on extracellular calcium. Chelation of intracellular Ca++ by Fluo-3/AM reduced production of TxB2 and prostaglandin E2 eicosanoids. Fluo-3/AM also blocked effectively PAF-dependent TxB2 release, indicating that production of TxB2 was almost entirely dependent on free intracellular calcium levels. PAF-dependent changes in brain phospholipids, prelabeled with [3H]arachidonic acid, were examined. One hour after in vivo injection of the isotope, fetal brains were removed and incubated in vitro for 30 min with carbamyl-PAF. Radioactivity in arachidonic acid and diglyceride fractions increased (35% and 30%, respectively), whereas radioactivity in phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol decreased. BN50726 antagonist abolished the effect of PAF. The radioactivity in poly-phosphoinositides was diminished (30-40% decrease) after PAF addition.(ABSTRACT TRUNCATED AT 250 WORDS)
Kunievsky
B
B
Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel.
Yavin
E
E
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D001923:Brain Chemistry; D002118:Calcium / Q000378:metabolism; D005333:Fetus / Q000378:metabolism*; D006801:Humans; D010743:Phospholipids / Q000378:metabolism; D010972:Platelet Activating Factor / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013687:Telencephalon / Q000187:drug effects* / Q000378:metabolism; D013929:Thromboxane B2 / Q000096:biosynthesis*
D010743:Phospholipids; D010972:Platelet Activating Factor; D016718:Arachidonic Acid; D013929:Thromboxane B2; D002118:Calcium