Studies on murine embryo‐derived platelet‐activating factor (EPAF)

Abstract

Studies were carried out using the splenectomized mouse bioassay (SMB) to investigate the nature of embryo-derived platelet-activating factor (EPAF) and its relationship to synthetic platelet activating factor (PAF). While both C16-PAF and embryo conditioned media (ECM) induced a significant platelet decline in the SMB at 15 min postinjection, C18-PAF induced a similar effect at 30 min postinjection. The degree of EPAF activity in ECM was not altered with increasing embryo number from 2 to 40/ml of media. In contrast, PAF (C16/C18 mixture) induced a linear increase in activity with increasing concentration, leading to lethal effects at high concentrations. While EPAF activity was not significantly altered when ECM was diluted 1/1,000, PAF activity was abolished at 1/10 dilution. EPAF in ECM was not inactivated by mouse plasma; however, lipid extracted ECM, like PAF, underwent rapid inactivation in the presence of plasma. Aggregometer studies using horse platelets showed that ECM and lipid-extracted ECM were unable to induce platelet aggregation, while thin-layer chromatography (TLC) purified ECM (Rf 0.23) successfully aggregated horse platelets in vitro. Results suggested that EPAF and PAF are not homologous. EPAF might consist of PAF bound to a regulatory carrier molecule and appears to be associated with EPAF-inhibitor substance(s) in ECM.

Detection and preliminary characterization of two enzymes involved in biosynthesis of platelet-activating factor in mouse oocytes, zygotes and preimplantation embryos: dithiothreitol-insensitive cytidinediphosphocholine: 1-O-alkyl-2-acetyl-sn-glycerol cholinephosphotransferase and acetyl-coenzyme A:1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine acetyltransferase

“…It has been detected using several different methods including a whole-animal bioassay (O'Neill et al, 1987), in vitro bioassays (Collier et al, 1988), radioimmunoassays and mass spectroscopy (Kodama et al, 1989), and has been inde¬ pendently confirmed for the mouse (Adamson et al, 1991) and human (Punjabi et al, 1990) embryo. However, some workers (Amiel et al, 1989;Smal et al, 1990) have failed to demonstrate the release of PAF by embryos.…”

Exogenous platelet-activating factor stimulates cell proliferation in mouse pre-implantation embryos prior to the fourth cell cycle and shows isoform-specific stimulatory effects

“…Embryo-derived PAF (EPAF) may be homologous to PAF and is thought to consist of a family of PAFreceptor ligands composed predominantly of C 16 and C 18 PAF-like molecules that may be coupled to one or more regulatory molecules (reviewed by Adamson et al, 1991). EPAF is secreted by the pre-implantation embryos of several mammalian species (reviewed by O'Neill, 1991) including those of the mouse, rabbit, sheep and human.…”

Intrauterine Signaling and Embryonic Implantation

“…Nev ertheless, the standard used in bioassays was Intrauterine Signaling and Embryonic Implantation an equimolar mixture of C l 6:0 and C l 8:0 PAF. In the splenectomized mouse bioassay, both C16:0-PAF and embryo-conditioned media induced a significant platelet decline at 15 min while C18:0-PAF reacted much more slowly [111]. Also, while EDPAF activity was not significantly altered when conditioned medium was diluted 1:1,000, synthetic PAF activity was abolished at 1:10 dilution.…”

“…Progesterone requirement is absolute. 112 Biol Signals 1996;5: [111][112][113][114][115][116][117][118][119][120][121] Estrogen may also be required, but only tran siently. The coarser (more traumatic) the in duction stimulus, the less stringent the estro gen requirement.…”