Actions of synthetic leukotrienes on platelets and blood vessels in the anesthetised pig: the release of a platelet derived vasodilator

The actions of leukotrienes (LT's) C4, D4, E4 and F4 have been investigated in the perfused hind-limb of the anesthetized pig. In the blood perfused hind limb LTC4, D4 and E4 increased the perfusion pressure in a dose-dependent fashion whereas LTF4 decreased perfusion pressure. In the Tyrode perfused hind limb all LT's increased perfusion pressure (rank order potency LTC4 = LTD4 much greater than LTF4). The actions of LTF4 were not affected by a wide variety of pharmacological treatments, including indomethacin, methysergide and FPL-55712. The LT's aggregated porcine platelets (rank order potency LTC4 greater than LTF4 greater than LTD4) and induced the release of a platelet-derived vasodilatory mediator. The results provide pharmacological evidence of specific leukotriene receptors in vivo and that leukotrienes can independently modulate blood flow. These data suggest that important interactions may occur between platelets, the arachidonate lipoxygenase products and platelet-derived substances in response to inflammatory stimuli in the cardiovascular system.     

Effect of synthetic TRH on prolactin release in the pig

Artificial hyperprolactinemia was produced by intravenous administration of synthetic TRH to ovariectomized sows. The prolactin response varied markedly between individual animals. In the range of 25 to 400 mug TRH, the prolactin response was not related to the intravenous dose of TRH. Repetitive administration of 50 mug TRH over a 24-hour period resulted in a prolactin secretory pattern which decreased over time. Prolactin responses to intramuscular doses of TRH were less than those observed after intravenous administration.     

Effect of ergoline derivatives on platelet and blood vessels]

The influence of dihydrogenated ergot alkaloids on vessels and blood platelets was studied in vitro and in vivo. At low concentrations they cause contraction of isolated vein strips via a stimulation of alpha-adrenoceptors, at higher concentrations they antagonize the action of noradrenaline on arteries and veins and inhibit the adrenaline-induced platelet aggregation in vitro. In volunteers, intravenous and subcutaneous administration of dihydroergotamine (Dihytamin) caused a decrease in blood volume of the capacitance vessels and inhibition of the adrenaline-potentiated platelet aggregation "ex vivo". The selective venoconstrictor and antiaggregating effects of dihydroergotamine are utilized in the postoperative prophylaxis of thrombosis.     

Effect of cisplatin on lipid peroxidation in pig blood platelets.

The effect of cisplatin (cis-diamminedichloroplatinum II) on the activities of the blood platelet antioxidative enzymes (glutathione peroxidase, superoxide dismutase) as well as on the peroxidation of blood platelet lipids was investigated. Cisplatin was found to cause a significant inhibition of platelet free radical scavering enzyme activity and an increase of malonyldialdehyde levels in blood platelets incubated with cisplatin in vitro.     

Biosynthesis of major platelet proteins in human blood platelets

We studied de novo protein biosynthesis in platelets of normal adult donors and in newly formed platelets isolated from splenectomized patients with idiopathic thrombocytopenic purpura (ITP). After metabolic labelling of platelet proteins, performed with different radiolabelled amino acids or carbohydrates, a tenfold increase in incorporation of radioactivity into trichloroacetic-acid-precipitable material was obtained with ITP platelets compared to control platelets. Electron microscopic studies of ITP platelets revealed the presence of rough endoplasmic reticulum and polyribosomes, providing morphological evidence for protein synthesis. SDS-PAGE of radiolabelled ITP platelet proteins followed by autoradiography showed that [35S]methionine and [3H]leucine were incorporated into almost all Coomassie-blue-stained proteins whereas [3H]carbohydrates only labelled a few bands. Using crossed-immunoelectrophoresis we identified some of the labelled platelet compounds and demonstrated that major membrane glycoproteins (GPIb, IIb, IIIa) and alpha-granule proteins, such as fibrinogen, thrombospondin, albumin and von Willebrand factor, were synthesized in newly formed circulating platelets.     

Lipid composition of guinea pig platelets and megakaryocytes the megakaryocyte as a probable source of platelet lipids

Platelets are formed by fragmentation of the cytoplasm and plasma membrane of the megakaryocyte in the bone marrow. This study has compared the lipid composition of guinea pig platelets and megakaryocytes. Phospholipids were quantitated by TLC and measurement of lipid phosphorus. Cholesterol and fatty acids were quantitated by GLC. The cholesterol/phospholipid molar ratio was 0.35 in megakaryocytes and 0.55 in platelets. The phospholipid distribution in megakaryocytes was: 9.8% phosphatidylserine, 6.7% phosphatidylinositol, 14.2% sphingomyelin, 40.0% phosphatidylcholine and 29.3% phosphatidy lethanolamine. Platelets contained 11.2% phosphatidylserine, 5.1% phosphatidylinositol, 16.1% sphingomyelin, 38.6% phosphatidylcholine and 29.0% phosphatidylethanolamine. The major megakaryocyte fatty acids were 20.0% palmitic, 16.4% stearic, 20.6% oleic, 13.2% linoleic and 8.2% arachidonic. The major platelet fatty acids were 17.4% palmitic, 17.5% stearic, 11.6% oleic, 12.4% linoleic and 14.6% arachidonic. The minor fatty acids were found in similar proportions in both cells. The major and minor fatty acid compositions of the individual platelet phospholipids reflected those of the megakaryocyte counterparts. The increased arachidonic acid and decreased oleic acid in platelets relative to megakaryocytes were found in all four glycerophospholipids. The similarity of the phospholipid and fatty acid composition of megakaryocytes and platelets suggests that the lipid composition of the platelet is determined by the megakaryocyte.     

Soluble factors differ in platelets derived from separate niches: a pilot study comparing the secretome of peripheral blood and bone marrow platelets

Background aimsPlatelet-rich plasma (PRP) and bone marrow aspirate are commonly used in orthobiologics for their anti-inflammatory, anabolic/regenerative and immunomodulatory characteristics via platelet degranulation and cell secretions. Although platelets are derived from megakaryocytes in the bone marrow, no attention has been paid to the potential benefits of bone marrow platelets and whether their contents differ from aging platelets in peripheral blood.MethodsIn the present study, leukocyte-poor peripheral blood-derived platelets in plasma (LPP) and leukocyte-poor bone marrow platelets in plasma (BMP) were prepared from six donors, activated with calcium chloride, incubated and sampled at day 0, day 3 and day 6. LPP and BMP are platelet preparations intended to evaluate the respective platelet secretomes but are not classified as conventional PRPs, as they are not concentrated to the extent necessary to meet the qualifying criteria. At each time point, 15 growth and immunomodulatory factors were quantitated in LPP and BMP: platelet-derived growth factor AA, basic fibroblast growth factor/fibroblast growth factor 2, granulocyte-macrophage colony-stimulating factor, hepatocyte growth factor, macrophage colony-stimulating factor, stem cell factor, vascular endothelial growth factor, tumor necrosis factor alpha, IL-1β, interferon gamma, IL-4, IL-10, IL-1 receptor antagonist protein, IL-12p40 and arginase-1.ResultsThe results illustrate that platelets derived from bone marrow have a unique secretome profile compared with those derived from peripheral blood, with significant differences in anti-inflammatory cytokines, which are associated with monocyte polarization.ConclusionsUltimately, bone marrow-derived platelets may be useful as a stand-alone orthobiologic or as an effective adjuvant to autologous cell therapies where anti-inflammatory and anabolic processes are desired, especially with respect to monocyte function.     

Functional damage of blood vessels and intravascular platelet aggregation in burns

A study was made of the effect of burn injury on aggregation properties of the vascular wall and platelet aggregation capacity. Maximal accumulation of malonic dialdehyde during thrombin-induced aggregation, maximal rise of the spontaneous intravascular platelet aggregation index, and the most remarkable functional lesions of the vascular wall were observed in the early period (within the first hours), at the disease height (day 7), and during the recovery (day 30). Variation of the homestatic balance between the prostacycline- and thromboxane-generating systems of the blood vessels and platelets in the disease early period is linked with stress reaction and release of biologically active substances (adrenaline, cortisone) to the circulation, whereas at the disease height with marked inflammation and emergence in the blood of endotoxin and break down products of cell membrane phospholipids.     

Comparative effects of selenite and selenite on the glutathione-related enzymes activity in pig blood platelets

The effects of inorganic selenium (Se) compounds (sodium selenite and selenate) on the activities of glutathione-related enzymes (glutathione peroxidase, glutathione-S-transferase [GST] and glutathione reductase [GR]) in pig blood platelets were investigated in vitro. GST activity in blood platelets treated with 10⁻⁴ M of selenite was reduced to 50%, whereas no decrease GST activity was observed after the treatment of platelets with the same dose of selenate. In platelets incubated with physiological doses (10⁻⁷, and 10⁻⁶ M) of Se compounds, the activity of glutathione peroxidase (GSH-Px) was enhanced (about 20%). GR activity after the exposure of platelets to tested Se compounds was unaffected.     

Cooling is a potent vasodilator of deep vessels in the rat.

The objectives of this study were to determine the effect of cooling on smooth muscle tone of the pulmonary artery and aorta and to clarify the basic mechanism of these responses. We recorded isometric tension in smooth muscle strips of rat pulmonary artery and aorta in organ baths during stepwise cooling. Cooling responses were tested before and after the addition of various standard agents that interfere with known neurogenic (autonomic blockers, tetrodotoxin) and myogenic mechanisms (calcium channel blockers) of relaxation. We also examined the hypothesis of the presence of a cooling-released substance. Stepwise cooling (37degrees C to 4 degrees C) of aortic smooth muscle induced reproducible graded relaxations that were inversely proportional to temperature. Cooling-induced relaxation was not dependent on a neural mechanism nor the release of neurotransmitters or a cooling-released substance such as NO or CO. Cooling of pulmonary arterial and aortic smooth muscle preparations induced a graded myogenic relaxation inversely proportional to the cooling temperature. The mechanism is not dependent on local nervous or known mediators but related to a direct physico-chemical effect of cooling.     

Mechanism of action of leukotrienes on the guinea pig bronchus

The pharmacological activity of leukotrienes (LT) A4, C4, D4, E4, and histamine was investigated on guinea pig upper and lower bronchi. The contractions of the upper bronchi to histamine, LTA4, C4 and D4 were enhanced by cyclooxygenase inhibitors aspirin (1.67 X 10(-5) and 1.67 X 10(-6) M) and indomethacin (2.8 X 10(-6) and 2.8 X 10(-5) M) whereas the responses to LTE4 were not affected. The myotropic activity of the lower bronchi to all agonists were either very slightly or not at all modified by the presence of cyclooxygenase inhibitors. The thromboxane synthetase inhibitor OKY-046 (1.77 X 10(-5) and 1.77 X 10(-6) M) did not change the responses of higher bronchi to the agonists which suggested that the response of the upper bronchi may be mediated by prostaglandins but not by thromboxanes. The responses of the lower bronchi to leukotrienes A4, C4, D4 and E4 were inhibited by compound OKY-046. Blockade of thromboxane receptors together with inhibition of lipoxygenases by compound L-655,240 (2.53 X 10(-8) to 2.53 X 10(-5) M) had a slight effect on the stimulation of upper and lower bronchi by leukotrienes and histamine. The compound FPL-55712 (1.92 X 10(-6) and 1.92 X 10(-5) M) strongly reduced the contractions of the upper and lower bronchi to leukotrienes but did not affect the responses to histamine. These results suggest that the contractile effects of leukotrienes on upper bronchi is modulated by bronchorelaxant prostaglandins whereas the responses of the lower bronchi are mediated by thromboxanes.(ABSTRACT TRUNCATED AT 250 WORDS)