thromboxane-a2 and arginyl-glycyl-aspartic-acid

Stretch-induced contraction of rabbit pulmonary artery depends on endothelium-derived vasoactive prostanoids. We investigated which prostanoid(s) was responsible for the stretch-induced contraction of the artery, and whether integrin was involved in this mechanotransduction process. Stretch increased productions of untransformed prostaglandin H(2), prostaglandin E(2), prostaglandin F(2alpha), and thromboxane A(2) in the pulmonary artery with intact endothelium. A blocking peptide for integrins (RGD peptide) significantly inhibited productions of thromboxane A(2) and prostaglandin F(2alpha), but the peptide did not affect productions of untransformed prostaglandin H(2) and prostaglandin E(2), as well as contraction in response to stretch. SQ29,548, a prostaglandin H(2)/thromboxane A(2) receptor antagonist, inhibited the contractile response to not only stretch but also exogenous prostaglandin H(2). Acetylcholine (up to 30 microM) also contracted the artery in an endothelium-dependent manner. Ozagrel (10 nM-1 microM), an inhibitor of thromboxane synthase, abolished the production of thromboxane A(2), in response to both stretch and acetylcholine, whereas the inhibitor mostly inhibited acetylcholine-induced contraction, but it did not suppress stretch-induced contraction. The results suggested that prostaglandin H(2) and thromboxane A(2), either released from endothelium by mechanical stretch or by acetylcholine, produced contraction of rabbit pulmonary artery in a RGD-independent manner.

Topics: Acetylcholine; Animals; Bridged Bicyclo Compounds, Heterocyclic; Dinoprost; Dinoprostone; Endothelium, Vascular; Fatty Acids, Unsaturated; Hydrazines; In Vitro Techniques; Isometric Contraction; Methacrylates; Oligopeptides; Prostaglandin Antagonists; Prostaglandin H2; Pulmonary Artery; Rabbits; Receptors, Thromboxane A2, Prostaglandin H2; Stress, Mechanical; Thromboxane A2; Thromboxane-A Synthase; Vasoconstriction; Vasodilator Agents

The role of platelet-activating factor (PAF) in heterotypic cell to cell interactions in a rabbit neutrophil-platelet mixture model was investigated. Platelets were exposed to each of three chemotactic agonists: PAF, leukotriene B4 (LTB4), or FMLP. Only PAF stimulated aggregation, [3H]serotonin secretion, and cytosolic Ca2+ mobilization in platelets alone. However, platelets were stimulated by LTB4 and FMLP in the presence of neutrophils. This neutrophil-dependent platelet activation was blocked by pretreatment of platelets with PAF receptor antagonists, and was prevented by desensitization of platelets to PAF. Furthermore, the time-course of platelet activation showed a positive correlation with PAF production by neutrophils stimulated with either LTB4 or FMLP. The PAF-mediated neutrophil-platelet interaction was dependent on direct cell to cell contact, as demonstrated by experiments in which the majority of newly formed PAF was neutrophil associated (rather than released). Platelet activation did not occur when the neutrophil-platelet mixture was not stirred, minimizing cell to cell contact, or when platelets were challenged with a cell-free supernatant prepared from neutrophils activated with LTB4 or FMLP. Finally, the neutrophil-platelet interaction was abolished by SC-49992, a peptidomimetic of the fibrinogen binding sequence Arg-Gly-Asp-Phe, indicating a Arg-Gly-Asp-specific recognition mechanism. Our results demonstrate that neutrophil-generated PAF plays a crucial role in neutrophil-dependent platelet activation in this model system. This type of intercellular signaling event may be important in certain inflammatory or thrombotic processes.

Topics: Amino Acid Sequence; Animals; Azepines; Blood Platelets; Cells, Cultured; Fibrinogen; Molecular Sequence Data; N-Formylmethionine Leucyl-Phenylalanine; Neutrophils; Oligopeptides; Platelet Activating Factor; Platelet Activation; Platelet Aggregation; Platelet Membrane Glycoproteins; Rabbits; Signal Transduction; Thromboxane A2; Triazoles