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

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Abstract
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 ∼ 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°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 μM of the PAF-speeific receptor inhibitor, SRI 63-441, and completely inhibited at 15 μM 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) Thus, the embryo-derived PAF from the human was shown on the basis of biochemical and pharmacological characterization to be homologous to PAF-acether.

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