Biochemical and pharmacological characterization of human embryo-derived platelet activating factor.

The soluble platelet activating factor (PAF) produced by mouse embryos was shown to have properties similar to 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphocholine (PAF-acether). In this study PAF was extracted from the medium in which human embryos were cultured for approximately 18 h prior to transfer. The extracted embryo-derived PAF moved on silica thin layer chromatograms with the same RF of 0.26 +/- 0.03 (n = 26) as PAF-acether. Embryo-derived PAF or PAF-acether activity was assayed by monitoring the decrease in the proportion of single platelets in rabbit whole blood due to aggregation on incubation at 37 degrees C. The two agonists were said to be of the same activity, if they induced the same degree of platelet aggregation after 15 min incubation. PAF-acether (93 nM) and embryo-derived PAF of similar activity induced an identical time response of platelet aggregation, the response being maximal by 6 min. PAF-acether, over the range 5.6-200 nM, induced a decrease that was linear when plotted on a log-log scale. Embryo-derived PAF and PAF-acether (184 nM) gave identical dose responses when serially diluted to 16 nM. Pharmacologically, the action of embryo-derived PAF and PAF-acether (46 nM) on platelet aggregation was significantly inhibited by 3.75 microM of the PAF-specific receptor inhibitor, SRI 63-441, and completely inhibited at 15 microM SRI 63-441. Embryo-derived PAF and PAF-acether (184 nM) were inactivated to the same degree by incubation with 5-13 IU/ml phospholipase A2 (pA2).(ABSTRACT TRUNCATED AT 250 WORDS)