Platelet-leukocyte cross talk in whole blood.

Thrombosis and inflammation involve complex platelet-leukocyte interaction, the details of which are not fully elucidated. Therefore, we investigated cross talk between platelets and leukocytes in whole blood, under the following physiological conditions: at 37 degrees C, with normal calcium concentrations, and with shear force. Platelet P-selectin and leukocyte CD11b expression were used to monitor platelet and leukocyte activation, respectively, and platelet-leukocyte aggregation (PLA) was analyzed. The leukocyte-specific agonist N:-formyl-methionyl-leucyl-phenylalanine (10(-6) mol/L) increased P-selectin-positive platelets from 2.5+/-0. 1% to 5.1+/-0.6% (P:<0.05). The increase was inhibited by either the platelet-activating factor (PAF) antagonist SR27417, the superoxide anion scavenger superoxide dismutase, the 5-lipoxygenase inhibitor Zileuton, or the 5-lipoxygenase-activating protein inhibitor MK-886, suggesting the involvement of PAF, superoxide anion, and 5-lipoxygenase products in leukocyte-induced platelet activation. The platelet-specific agonist collagen (1 microg/mL) increased leukocyte CD11b expression from 2.94+/-0.52 to 3.81+/-0.58 (P:<0. 05); this was not inhibited by the thromboxane A(2) receptor antagonist ICI 192.605 or the PAF antagonist SR27417. Platelet P-selectin expression induced by N:-formyl-methionyl-leucyl-phenylalanine and leukocyte CD11b expression induced by collagen could be suppressed by glycoprotein IIb/IIIa blockade or P-selectin blockade. This study documents platelet-leukocyte cross talk under conditions that mimic a physiological state and suggests that this involves multiple mediators and mechanisms. Furthermore, new evidence of integrin and selectin involvement in intracellular and intercellular signaling during platelet-leukocyte cross talk is provided.

Agonist and antagonist activities of the leukotriene analogue BAY u9773 in guinea pig lung parenchyma.

BAY u9773(6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11( Z),14(Z)-eicosatetraenoic acid) is a leukotriene E4 analogue used to define 'atypical' receptors for cysteinyl-leukotrienes. The aims of this study were first to characterise the intrinsic properties of BAY u9773 in guinea-pig lung parenchyma in vitro and second to study the influence of BAY u9773 on the concentration-response relation for leukotriene D4 in the same preparation. BAY u9773 in itself caused a concentration-dependent contraction, which was not inhibited by the cyclooxygenase inhibitor indomethacin nor by the 5-lipoxygenase inhibitor zileuton (N-(1-benzo-(12)-thien-2-ylethyl)-N-hydroxyurea). The CysLT1 receptor antagonist ICI 198,615 [(1-((2-methoxy-4-(((phenylsulfonyl)amino) carbonyl)phenyl)methyl)-1H-indazol-6-yl)carbamic acid cyclopentyl ester] alone blocked the contractile response to BAY u9773 1 microM, whereas a combination of the TP receptor antagonist BAY u3405 ((3R)-3-(4-fluorophenylsulfonamido)-1,2,3,4-tetrahydro-9-carbaz olepropanoic acid) and ICI 198,615 was required to block the contraction induced by BAY u9773 10 microM. Together the findings suggest that BAY u9773 acted as a CysLT1 receptor agonist and in the higher concentration also as a TP receptor agonist. The CysLT1 receptor antagonist ICI 198,615 partly inhibited the contractile response to leukotriene D4. Pretreatment with BAY u9773 or leukotriene D4, caused concentration-dependent rightward displacement of the concentration-response curve for leukotriene D4. The inhibition by BAY u9773 was partial, and not greater than that produced by ICI 198,615. Combination of BAY u9773 and ICI 198,615 did not produce additive inhibition, suggesting that the major part of the leukotriene D4 induced contraction in guinea pig lung parenchyma is mediated by a CysLT receptor with properties distinct from those of previously described CysLT1 and CysLT2 receptors.