Battye K M, Evans G, O'Neill C
Human Reproduction Unit, Royal North Shore Hospital, St. Leonards, NSW, Australia.
Biol Reprod. 1996 Feb;54(2):355-63. doi: 10.1095/biolreprod54.2.355.
Explanted endometrial tissue from ovariectomized ewes that had received hormone replacement to mimic the luteal phase released platelet-activating factor (PAF) into medium in vitro. On Day 14, 310.1 (261-2185), and on Day 15, 424.4 (14.1-590.7) pg PAF (median 25th-75th percentile; p > 0.05) was released per 100 mg endometrial tissue after a 20-min incubation. A regulatory and final enzyme in the PAF biosynthetic pathway, lysoPAF:acetyltransferase, was also present with a specific activity of 0.533 +/- 0.124 pmol acetate/50 micrograms protein/30 min in Day 14 endometrial tissue and 0.810 +/- 0.468 in Day 15 tissue (mean +/- SEM; p > 0.05). PAF:acetylhydrolase, the metabolic enzyme regulating PAF's half-life, was present in uterine luminal washings, with a specific activity of 3.78 +/- 1.37 nmol acetate released/min/mg protein on Day 14 and 3.41 +/- 0.34 on Day 15 (mean +/- SEM; p > 0.05). Intrauterine infusion of 50-400 micrograms PAF caused a dose-dependent release of prostaglandin (PG) F2 alpha (measured as venous 14-dihydro-15-keto-prostaglandin F2 alpha, PGFM) within 10 min on Days 13-15. The enantiomeric form of PAF was significantly less effective in inducing a rise in venous PGFM. WEB 2086 is reported to be a competitive receptor antagonist for PAF, but a 10-fold excess of WEB 2086 failed to inhibit PAF-induced release of PGFM. It was observed that this dose of WEB alone induced PGFM release, suggesting that in this model this agent may not work as a true competitive antagonist. Repeat challenges at intervals of 0, 90, and 120 min with either 200 micrograms PAF or micrograms oxytocin resulted in a marked tachyphylaxis of response by the third challenge. This desensitization after repeated PAF challenge suggests a specificity of its actions. Infusion of 200 micrograms PAF on Day 14 or 15 at five 60-min intervals resulted in a tachyphylaxis such that by the fourth and fifth challenges, essentially no response was observed. The tachyphylaxis that was induced by four repeat challenges with PAF had no apparent effect on the capacity of the uterus to respond to a fifth challenge with oxytocin. Thus, PAF and oxytocin both caused homologous desensitization of their own capacity to mobilize uterine PGF2 alpha, but PAF did not cause heterologous desensitization of the response to oxytocin. This failure of heterologous desensitization suggests differences in the mechanism of action of the two ligands. Kinetic binding studies showed that PAF did not compete for the oxytocin receptor in vitro. This result demonstrated that the ovine endometrium produces PAF and responds to it by the release of PGF2 alpha in situ. The dynamics of the response elicited by PAF were similar to those of oxytocin, yet the two mediators apparently act separately. PAF may be a modulator of PGF2 alpha release by the ovine uterus during the luteal phase.
对接受激素替代以模拟黄体期的去卵巢母羊的子宫内膜组织进行体外培养时，其会向培养基中释放血小板活化因子（PAF）。在第14天，每100毫克子宫内膜组织在孵育20分钟后释放310.1（261 - 2185）皮克PAF，第15天释放424.4（14.1 - 590.7）皮克PAF（中位数，第25 - 75百分位数；p>0.05）。PAF生物合成途径中的一种调节性终末酶——溶血PAF：乙酰转移酶，在第14天的子宫内膜组织中也有存在，其比活性为0.533±0.124皮摩尔乙酸盐/50微克蛋白质/30分钟，第15天组织中为0.810±0.468（平均值±标准误；p>0.05）。PAF：乙酰水解酶是调节PAF半衰期的代谢酶，存在于子宫腔冲洗液中，第14天的比活性为3.78±1.37纳摩尔乙酸盐释放/分钟/毫克蛋白质，第15天为3.41±0.34（平均值±标准误；p>0.05）。在第13 - 15天，子宫内注入50 - 400微克PAF会在10分钟内引起前列腺素（PG）F2α剂量依赖性释放（以静脉血中14 - 二氢 - 15 - 酮 - 前列腺素F2α，即PGFM来衡量）。PAF的对映体形式在诱导静脉血中PGFM升高方面效果明显较差。据报道，WEB 2086是PAF的竞争性受体拮抗剂，但10倍过量的WEB 2086未能抑制PAF诱导的PGFM释放。观察到仅该剂量的WEB就可诱导PGFM释放，这表明在该模型中该药物可能并非真正的竞争性拮抗剂。分别以200微克PAF或微克催产素每隔0、90和120分钟重复刺激，到第三次刺激时反应出现明显快速耐受性。重复PAF刺激后的这种脱敏现象表明其作用具有特异性。在第14天或15天每隔60分钟分五次注入200微克PAF会导致快速耐受性，以至于到第四次和第五次刺激时，基本观察不到反应。PAF四次重复刺激诱导的快速耐受性对子宫对第五次催产素刺激的反应能力没有明显影响。因此，PAF和催产素都会引起自身动员子宫PGF2α能力的同源脱敏，但PAF不会引起对催产素反应的异源脱敏。这种异源脱敏的失败表明这两种配体的作用机制存在差异。动力学结合研究表明，PAF在体外不与催产素受体竞争。该结果表明，绵羊子宫内膜可产生PAF，并通过原位释放PGF2α对其作出反应。PAF引发的反应动力学与催产素相似，但这两种介质显然是分别起作用的。PAF可能是黄体期绵羊子宫释放PGF2α的一种调节剂。
