四甲基吡嗪对内毒素血症小鼠的保护作用及其与血小板活化因子的关系(英文)

研究四甲基吡嗪（ＴＭＰ）对内毒素血症小鼠的保护作用及其与血小板活化因子（ＰＭ）的关系．方法：给 ＴＭＰ处理的小鼠 ｉｖ　 ＬＰＳ,观察其存活率及血清ＰＡＦ水平．体外用ＬＰＳ刺激小鼠ＰＭφ,测定 ＰＭ及 ＰＬＡ２和乙酰辅酶 Ａ乙酰基转移酶的活性．结果：ＴＭＰ明显提高小鼠存活率和降低血清ＰＡＦ水平．体外,ＴＭＰ（０．０５－５０μｍｏｌ· Ｌ－１）剂量依赖性减少ＰＭφ释放ＰＡＦ［１２．７±１．６）,（８．９±１．２）,（６．９±０．８）,（５．５±１．０）μｇ·Ｌ－１,Ｐ＜０．０１］,降低ＰＬＡ２活性肝（１４９．９±２．８）（１１７．５±２．０）,（８９．６±２．０）,（７５．０±２．８） Ｕ,Ｐ＜０．０１］和乙酰辅酶Ａ乙酰基转移酶活性［ＰＡＦ（９．５±０．７）,（５．２± ０．７）,（２．９±０． ３）,（２．５±０． ３）μｇ· ｇ－１（ｐｒｏｔｅｉｎ）·ｍｉｎ－１, Ｐ＜０．０１］．结论： ＴＭＰ对内毒血症小鼠有保护作用,其机制是通过抑制 ＰＬＡ２和乙酰辅酶Ａ乙酰基转移酶的活性而抑制ＰＡＦ的合成。     

苦参碱对脂多糖／痤疮丙酸杆菌诱导的小鼠肝炎及产生肿瘤坏死因子的影响

用小鼠致死性肝炎模型和ＴＮＦ体外诱生的方法，研究苦参碱（Ｍａｔ）对脂多糖（ｌｉｐｏｐｏｌｙｓａｃｃｈａｒｉｄｅｓ，ＬＰＳ）诱导的经痤疮丙酸杆菌（ｐｒｏｐｉｏｎｉｂａｃｔｅｒｉｔｔｍａｃｎｅｓ，ＰＡ）预刺激的小鼠产生肿瘤坏死因子（ＴＮＦ）以及致死性肝炎的影响。结果表明：Ｍａｔ（１０，５０ｍｇ·ｋｇ￣（－１），ｉｐ，ｂｉｄ×３ｄ）可降低血清ＴＮＦ和ＡＬＴ水平及小鼠对ＬＰＳ致死毒性的敏感性，并可在体外抑制ＬＰＳ诱导的经ＰＡ预刺激的小鼠腹腔巨噬细胞释放ＴＮＦ。提示Ｍａｔ的保肝作用与其抑制ＴＮＦ释放有关。     

氨甲喋呤对类风湿性关节炎患者外周血单个核细胞产生细胞因子的影响

目的研究氨甲喋呤（ＭＴＸ）对类风湿性关节炎（ＲＡ）患者外周血单个核细胞（ＰＢＭＣ）产生细胞因子的影响。方法采用ＥＬＩＳＡ双抗夹心法，观察ＲＡ患者ＴＮＦ－α、ＩＬ－６的自发分泌及ＭＴＸ和ＬＰＳ的影响，以及ＭＴＸ和ＰＨＡ对ＩＬ－１０和ＩＦＮ－γ产生的影响。结果低浓度ＭＴＸ（５ｍｇ·Ｌ－１）有抑制ＲＡ患者ＰＢＭＣ自发分泌ＩＬ－６的作用，并对ＬＰＳ（１０ｍｇ·Ｌ－１）诱导ＩＬ－６的产生具有抑制作用，对ＴＮＦ－α的自发分泌及ＬＰＳ促分泌作用无明显影响；而高浓度ＭＴＸ（１５ｍｇ·Ｌ－１）对ＴＮＦ－α、ＩＬ－６和ＩＮＦ－γ均具有抑制作用；并能促进ＰＨＡ（１０ｍｇ·Ｌ－１）诱导ＩＬ－１０的产生；使ＩＬ－１０／ＩＮＦ－γ的比率上升。结论ＭＴＸ通过调节细胞因子网络（增高Ｔｈ２型细胞产生的细胞因子和降低Ｔｈ１型细胞产生的细胞因子）来发挥免疫调节作用和抑制炎症反应，这可能是其对ＲＡ产生治疗作用机制之一     

Inhibitory effects of nitric oxide and interleukin-10 on production of tumor necrosis factorα,interleukin-1β,and interleukin-6 in mouse alveolar macrophages

目的：观察一氧化氮和ＩＬ１０对肺泡巨噬细胞炎症反应的调节作用．方法：小鼠肺泡巨噬细胞（ＡＭ）受脂多糖（ＬＰＳ）１０ｍｇ·Ｌ－１刺激同时,加入一氧化氮合酶抑制剂Ｓ硫酸甲基异硫脲（ＳＭＴ）或一氧化氮供体Ｓ亚硝基乙酰青霉胺（ＳＮＡＰ）．ＥＬＩＳＡ法测定上清液中ＴＮＦα、ＩＬ１β、ＩＬ６和ＩＬ１０浓度．结果：ＡＭ受ＬＰＳ刺激后,ＴＮＦα、ＩＬ１β和ＩＬ６释放峰值分别在６、１２和２４小时．ＳＭＴ抑制一氧化氮释放,但促进ＩＬ１β和ＩＬ６释放,对ＴＮＦα无影响．ＳＮＡＰ对ＩＬ１β和ＩＬ６释放有明显的抑制作用,呈剂量依赖效应．重组ＩＬ１０抑制ＴＮＦα、ＩＬ１β和ＩＬ６释放,而ＩＬ１０单克隆抗体促进上述因子释放．结论：内源及外源性一氧化氮和ＩＬ１０均对ＬＰＳ诱导的炎症性细胞因子释放有抑制作用．     

牛膝多糖的抗肿瘤活性及其免疫增强作用

牛膝多糖（ＡＢＰ）５０ｍｇ·ｋｇ＾－１ｉｐ或２５０ｍｇ·ｋｇ＾－１ｉｇ显抑制小鼠移植性肉瘤Ｓ１８０生长，提高荷瘤小鼠低下的血清ＩｇＧ含量和抗体形成细胞数量及脾淋巴细胞增殖反应。ＡＢＰ ｉｐ还提高荷瘤鼠ＮＫ细胞活性及ＬＰＳ诱生的血清ＴＮＦ－α产生。ＡＢＰ５０－８００μｇ·ｍｌ＾－１体外对Ｓ１８０细胞无直接细胞毒作用，但能增强ＭФ对Ｓ１８０的杀伤作用。提示ＡＢＰ抗肿瘤作用与其增强宿主免疫功能有关。     

慢性肾功能衰竭患者血清胃动素和胃泌素测定的临床意义

测定慢性肾功能衰竭（ＣＲＦ）患者胃动素（ＭＯＴ）和胃泌素（ＧＡＳ）的水平及其血液透析（ＨＤ）前后变化、并设健康成年人作对比分析。结果示ＣＲＦ患者ＭＯＴ和ＧＡＳ明显高于健康人（Ｐ〈０．００１）。ＨＤ后ＭＯＴ和ＧＡＳ明显降低（Ｐ〈０．０１或０．０５），且ＭＯＴ、ＧＡＳ与血清肌酐（Ｓｃｒ）均呈密切正相关。     

一氧化氮和白细胞介素—10对小鼠肺泡巨噬细胞产生肿瘤坏死因？…

目的 观察一氧化氮和ＩＬ－１０对肺泡巨噬细胞炎症反应的调节作用,方法：小鼠肺泡汇噬细胞（ＡＭ）受脂多糖（ＬＰＳ）１０ｍｇ．Ｌ＾－１刺激同时,加入一氧化氮合酶抑制剂Ｓ－硫酸甲基异硫脲（ＳＭＴ）或一氧化氮供体Ｓ－亚硝基乙酰青霉胺（ＳＮＡＰ）,ＥＬＩＳＡ法测定上清液中ＴＮＦα,ＩＬ－１β,ＩＬ－６和ＩＬ－１０浓度,结果：ＡＭ受ＬＰＳ刺激后,ＴＮＦα,ＩＬ－１β和ＩＬ－６释放峰值分别在６,１２和２４小时,     

白芍总甙对大鼠腹腔巨噬细胞产生肿瘤坏死因子的影响

采用Ｌ９２９细胞株细胞毒检测法，观察了白芍总甙（ＴＧＰ）对ＬＰＳ诱导大鼠腹腔巨噬细胞（ＭΦ）产主肿瘤坏死因子（ＴＮＦ）的影响。结果表明、亚适量ＬＰＳ（５ｍｇ·Ｌ－１）诱导大鼠腹腔ＭΦ培养上清在６ｈ对Ｌ９２９细胞杀伤百分率最大．ＴＧＰ（２．５ｍｇ·Ｌ－１）能促进ＬＰＳ诱导大鼠腹腔ＭＯ产生ＴＮＦ，但不改变其动力学过程。ＴＧＰ（０．５～２５０ｍｇ·Ｌ－１）对ＬＰＳ诱导ＭΦ产生ＴＮＦ量效曲线呈钟罩形．提示ＴＧＰ对ＭΦ产主ＴＮＦ具有浓度依赖性双向调节作用。不同浓度ＴＧＰ对Ｌ９２９细胞无直接杀伤作用，亦无ｒｈＴＮＦ－α拮抗作用。     

多抗甲素对小鼠巨噬细胞功能的影响

对多抗甲素体外影响小鼠腹腔巨噬细胞吞噬中性红染料作用、对Ｌ９２９细胞的细胞毒活性，分泌ＴＮＦ、ＩＬ－１功能等方面进行了探讨。结果表明，ＰＡ能显著增强淀粉刺激的ＭΦ的吞噬功能、细胞毒作用、ＩＬ－１及ＴＮＦ的分泌功能（Ｐ＜０．０５），且呈良好剂量依赖关系。ＰＡ对正常小鼠ＭΦ吞噬功能几乎无明显促进作用（Ｐ＞０．０５），但能明显增强其细胞毒活性（Ｐ＜０．０５）、ＰＡ能协同ＬＰＳ促进ＩＬ－１的分泌（Ｐ＜０．０５），但不能联合ＬＰＳ、ＩＦＮ－ｒ促进ＴＮＦ的分泌（Ｐ＞０．０５）。     

脂质过氧化与血管内皮的关系及培哚普利的影响

研究脂质过氧化在血管内皮损伤中的意义及培哚普利对内皮影响的机理。方法采用ＳａｔｏｈＴＢＡ比色法测定ＬＰＯ,采用Ｐｙｒｏｇａｌｌｏｌ－ＮＢＴ比色法测定ＳＯＤ以及循环内皮细胞计数和验正。结果高血压病组培哚普利治疗前ＣＥＣ、ＬＰＯ、ＭＡＰ、ＳＢＰ、ＤＢＰ明显高于对照组;治疗后ＣＥＣ、ＬＰＯ、ＭＡＰ、ＳＢＰ、ＤＢＰ显著低于治疗前;ＳＯＤ三组间无统计学判别且高血压病组干预前,后ＣＥＣ与ＬＰＯ成正相关,相关系     

血小板活化因子诱导血小板P—选择素表达及相关信号传导机制

AIM: To study the intracellular signal transduction mechanisms of platelet activating factor (PAF)-induced platelet P-selectin expression. METHODS: Human blood platelets were used to test the effect of PAF-induced P-selectin expression using flow cytometry. RESULTS: PAF 20 nmol.L-1 elicited a moderate upregulation of P-selectin expression [(47.5 +/- 1.3)% vs control (3.8 +/- 0.9)%, P < 0.01]. Pretreatment with egtazic acid (EGTA) 2 mmol.L-1 and 5,5'- dimethyl-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetracetic acid (BAPTA) 200 mumol.L-1 to block Ca2+ influx or chelate the intracellular calcium, respectively, reduced P-selectin expression in response to PAF [(13.3 +/- 0.9)% and (16.8 +/- 1.9)% vs (47.5 +/- 1.3)% of PAF group, P < 0.01]. Inhibition of Na+/H+ exchange with amiloride (Ami) 400 mumol.L-1 resulted in an inhibition of P-selectin expression [(37.5 +/- 2.1)% vs (47.5 +/- 1.3)% of PAF group, P < 0.01]. Genistein (Gen) 300 mumol.L-1 to inhibit protein tyrosine phosphorylation showed similar effect [(29 +/- 4)% vs (47.5 +/- 1.3)% of PAF group, P < 0.01]. CONCLUSION: Multiple signal transduction pathways, including protein tyrosine phosphorylation, Na+/H+ exchange, and Ca2+ mobilization, mediated PAF-induced P-selectin expression.     

地塞米松,噻庚啶,山莨菪碱和地诺前列酮对内毒素休克TNFα产？…

目的：研究地塞米松（Ｄｅｘ）噻庚啶（Ｃｙｐ）,山莨菪碱（Ａｎｉ）和地诺前列腺酮（Ｄｉｎ）对脂多糖（ＬＰＳ）诱导的肿瘤坏死因子（ＴＮＦα）,基因表达的影响和抑制ＴＮＦ,产生的抗体休克作用。方法：Ｗｉｓｔａｒ大鼠静脉注射ＬＰＳ（ＥｃｏｌｉＯ１１１Ｂ４,５ｍｇ．ｋｇ＾－１）复制内毒素休克模型,Ｎｏｒｔｈｅｒｎ印迹杂交分析肝脏ＴＮＦαｍＲＮＡ表达,放射免疫法测定血浆ＴＮＦα的含量。结果：ＬＰＳ攻击后２ｈ肝     

金属硫蛋白对大鼠硝酸甘油耐药性的影响(英文)

目的:评价金属硫蛋白(metallothionein, Met)在体内是否能改善硝酸甘油耐药的发生。方法:大鼠给予硝酸甘油(nitroglycerin, Nit)贴剂治疗两天(0.05 mg·h~(-1))以产生耐药。于耐药大鼠预先给予ZnCl_2以诱导内源性Met的合成及给予外源性Met15 mg·kg~(-1)·d~(-1)连续2 d。结果:Nit ZnCl_2组大鼠肝脏、血浆Met明显高于对照组(C组)。Nit组大鼠离体主动脉环的舒张反应最低。Nit ZnCl_2组大鼠及Nit Met组大鼠对SNP的降压反应明显强于Nit组。结论:外源性Met或内源性诱导合成的Met可以改善大鼠Nit耐药的发生。     

Arachidonic acid release and platelet-activating factor formation by staurosporine in human neutrophils challenged with n-formyl peptide.

Staurosporine, a putative protein kinase C (PKC) inhibitor, increased the release of [14C]arachidonic acid dose dependently between 100 nM and 1000 nM in human neutrophils challenged with 100 nM N-formyl-methionine-leucine-phenylalanine (FMLP). Staurosporine also increased the formation of leukotriene B4 (LTB4) and platelet-activating factor (PAF) in a dose-dependent manner. In addition, exogenously added lyso-PAF further augmented [3H]PAF formation in staurosporine-pretreated human neutrophils stimulated by FMLP, thus suggesting an activation of acetyl-CoA: lyso-PAF acetyltransferase by staurosporine. The potentiation of [14C]arachidonic acid release and [3H]PAF formation by staurosporine was further enhanced in the presence of 100 nM phorbol 12-myristate 13-acetate (PMA), which pinpoints a mechanism other than the modulation of PKC in this process, inasmuch as staurosporine antagonizes PMA-induced O2- production and [3H]PAF formation. Additional studies with other putative PKC inhibitors also revealed the potentiating effects of 1-(5-isoquinolinsulfonyl)-2-methylpiperazine (H-7, 20 microM) and sphingosine (2.5 microM) on FMLP-induced [14C]arachidonic acid release and [3H]PAF formation. We therefore conjecture that staurosporine-sensitive protein kinases including PKC are not involved in the activation of phospholipase A2 and acetyl-CoA:lyso-PAF acetyltransferase.     

KATP通道激活介导大鼠小肠的缺血预处理

AIM: To study whether the protective effects of ischemic preconditioning against rat small intestine ischemia/reperfusion injury could be mediated by KATP channel opener. METHODS: Preconditioning (Pc) was induced by 3 cycles of 8-min superior mesenteric artery (SMA) occlusion and 10-min reperfusion before prolonged ischemia. Cromakalim (Cro 75 micrograms.kg-1) and glibenclamide (Gli 8 mg.kg-1) were injected i.v. 10 min before prolonged ischemia and Pc, respectively. RESULTS: Compared with ischemic reperfusion (IR) group, Pc before prolonged ischemia (Pc + IR) decreased LDH release [(380 +/- 55) vs (559 +/- 49) U.L-1, P < 0.05], attenuated intestinal edema [wet weight/dry weight (WW/DW), 5.6 +/- 0.6 vs 6.34 +/- 0.29, P < 0.05], ameliorated intestinal histological damage (grading scale, 3.4 vs 5.7, P < 0.01), and improved reperfusion-induced hypotension. These effects of Pc were mimicked by Cro [LDH, (298 +/- 40) vs (559 +/- 49) U.L-1, P < 0.05; WW/DW, 5.6 +/- 0.4 vs 6.34 +/- 0.29, P < 0.05; grading scale, 3.6 vs 5.7, P < 0.01] and abolished in the presence of Gli [LDH, (624 +/- 44) vs (559 +/- 49) U.L-1; WW/DW, 6.6 +/- 0.6 vs 6.34 +/- 0.29; grading scale, 5.7 vs 5.7; P > 0.05] compared with IR group, respectively. CONCLUSION: Ischemic preconditioning on the rat small intestine is mediated by activation of KATP channels.     

褪黑激素对大脑皮层谷氨酸释放及其神经毒的拮抗作用

AIM: To observe the effects of melatonin (Mel) on glutamate (Glu) release from the cortical synaptosomes in old mice and on neurotoxicity induced by KCl, Glu in cultured cortical cells of fetal rat and to explore the antiaging mechanism of Mel. METHODS: Glu release by the synaptosomes in old mouse cerebral cortex was detected in a spectrofluorophotometer. The neuronal viability in primary cultures from rat cerebral cortex was assessed using MTT stain and lactate dehydrogenase (LDH) efflux in the bathing medium. RESULTS: Mel inhibited the K+ (30 mmol.L-1)-induced Glu release from synaptosomes either in calcium dependent or independent conditions [control (10.6 +/- 1.1), (9.2 +/- 0.7) mumol.g-1 (protein); Mel 0.1 mumol.L-1 (6.5 +/- 0.9), (7.5 +/- 0.6) mumol.g-1 (protein), respectively, P < 0.01 vs control group), increased MTT activity (control 0.67 +/- 0.04, 0.81 +/- 0.03; Mel 0.1 mumol.L-1 0.715 +/- 0.023, 0.925 +/- 0.027, P < 0.01 vs control group] and decreased LDH efflux (control 0.400 +/- 0.016, 0.379 +/- 0.016; Mel 0.1 mumol.L-1 0.345 +/- 0.021, 0.340 +/- 0.012, respectively, P < 0.01 vs control group), therefore, protected the neuronal viability against KCl and Glu-induced injury. CONCLUSION: The inhibitory effect of Mel on Glu release from cortical synaptosome and the protective effect of Mel on cortical neurons against neurotoxicity are its antiaging mechanisms.     

Role for intracellular platelet-activating factor in the circulatory failure in a model of gram-positive shock.

1. This study investigates the effects of two structurally different antagonists of platelet-activating factor (PAF), BN52021 and WEB2086, on the circulatory and renal failure elicited by lipoteichoic acid (LTA) from Staphylococcus aureus (an organism without endotoxin) in anaesthetized rats. 2. Administration of LTA (10 mg kg-1, i.v.) caused hypotension and vascular hyporeactivity to noradrenaline (1 microgram kg-1, i.v.) WEB2086 (5 mg kg-1, i.v., 20 min before and 150 min after LTA) inhibited the delayed fall in mean arterial blood pressure (at 300 min: 99 +/- 6 mmHg vs. 75 +/- 6 mmHg, P < 0.01) and prevented the decrease in pressor response to noradrenaline (at 300 min: 36 +/- 5 mmHg min vs. 17 +/- 5 mmHg min, P < 0.01). Surprisingly, BN52021 (20 mg kg-1, i.v., 20 min before and 150 min after LTA) neither prevented the hypotension (74 +/- 6 mmHg) nor the vascular hyporeactivity (21 +/- 5 mmHg min). However, BN52021 inhibited the hypotension to injections of PAF as well as the circulatory failure elicited by lipopolysaccharides (10 mg kg-1, i.v.). 3. LTA caused an increase in plasma concentration of creatinine from 39 +/- 5 microM (sham-operated) to 70 +/- 8 microM and urea from 4.7 +/- 0.1 to 13.1 +/- 1.6 mM. The renal failure elicited by LTA was significantly inhibited by WEB2086 (creatinine: 45 +/- 4 microM and urea: 5.7 +/- 0.7 mM), but not by BN52021. 4. The induction of nitric oxide synthase activity in lungs by LTA was attenuated by WEB2086 from 98 +/- 17 to 40 +/- 15 pmol L-citrulline 30 min-1 mg-1 protein (P < 0.01), but not by BN52021 (148 +/- 21 pmol L-citrulline 30 min-1 mg-1 protein). Similarly, WEB2086, but not BN52021, inhibited the increase in plasma nitrite concentration associated with the delayed circulatory failure caused by LTA. The release of tumour necrosis factor-alpha (TNF-alpha) after injection of LTA was not attenuated by WEB2086. 5. The induction of nitrite release by cultured macrophages activated with LTA (10 micrograms ml-1 for 24 h) was inhibited by 74 +/- 4% by WEB2086 (3 x 10(-4) M), but not by BN52021, indicating that only WEB2086 acts on intracellular PAF receptors. 6. Thus, the intracellular release of PAF contributes to the circulatory and renal failure and induction of nitric oxide synthase elicited by LTA in anaesthetized rats. The difference between the two structurally different PAF antagonists in our septic shock models using either LTA or lipopolysaccharide (LPS), shows the importance of models for Gram-positive sepsis in the elucidation of the pathophysiology of septic shock and for the evaluation of potential drugs.     

Platelet activating factor, lyso-platelet activating factor and arachidonic acid release in normal human skin and the influence of topical steroid treatment.

1. Previous, in vitro, studies have established the synthesis of platelet activating factor (PAF) by the 're-modelling' pathways in which the activation of a phospholipase A2 (PLA2) enzyme catalyses the hydrolysis of an ether-acyl-phosphocholine to give concomitant release of lyso-PAF, the immediate precursor of PAF, and arachidonic acid, the precursor of the icosanoids. The aim of this study was to investigate the relationship between PAF and eicosanoid release in human skin, and to study the effect of treatment of skin with a topical steroid, on the release of PAF, lyso-PAF and arachidonic acid. 2. A novel assay procedure was developed for the simultaneous assay of PAF and lyso-PAF in skin exudates from abrasions and suction blisters in normal human skin. In addition we assayed arachidonic acid and prostaglandin E2 (PGE2), a representative eicosanoid. 3. The mean amounts of mediator recovered in the first 30 min period following abrasion were PAF 0.43, lyso-PAF 11.9, PGE2 25.7 and arachidonic acid 760 pmol/sample. The molar ratio of PAF:lyso-PAF:arachidonic acid in skin exudates from abrasions was 1:30:1800 and in suction blister exudates was 1:90:3660. 4. Time course studies showed a decline in the recoveries of arachidonic acid and lyso-PAF, of about 50% in 2 h. In contrast, PAF was recovered in exudates at a constant rate over 2 h but PGE2 release decreased by more than 90% after the initial 30 min period. 5. Topical application under occlusion, of 0.05% clobetasol propionate, a potent corticosteroid, significantly reduced lyso-PAF by 30% in suction blister exudates but did not significantly alter the concentrations of PAF or arachidonic acid.(ABSTRACT TRUNCATED AT 250 WORDS)     

血小板释放的ADP通过稳定细胞内钙浓度而稳定PAF诱导的兔血小板 …

AIM: To examine whether platelet-released adenosine diphosphate (ADP) would contribute to the stabilization of rabbit platelet aggregation induced by platelet activating factor (PAF). METHODS: Rabbit platelet aggregation induced by PAF was measured turbimetrically. ADP release from rabbit platelets stimulated by PAF was determined by HPLC. Intracellular Ca2+ was measured using Ca(2+)-sensitive fluorescent indicator Fura 2-AM. RESULTS: PAF > or = 1 nmol.L-1 induced full platelet aggregation, which did not deaggregate over 5 min after aggregation reached peak. Platelet aggregation was deaggregated in a concentration-dependent manner by subsequent addition of ADP scavenger ATP-diphosphohydrolase (apyrase) at 5-100 mg.L-1. PAF 3 nmol.L-1 stimulated release of ADP (29% vs 6% of control), and elicited a rapid rise in intracellular calcium ([Ca2+]i) which peaked at approximately 15 s. Then the [Ca2+]i gradually decayed from 585 +/- 80 nmol.L-1 within 100 s to a low level (364 +/- 82 nmol.L-1). Apyrase 100 mg.L-1, added 2 min after PAF, reduced [Ca2+]i to a lower level (171 +/- 29 nmol.L-1). CONCLUSION: Platelet-released ADP stabilizes PAF-induced rabbit platelet aggregation by stabilizing [Ca2+]i at elevated level.