Mammalian Blood Platelets Research Articles

Platelet monoamine oxidase-A activity and aging: effect of carnosine

Platelet mitochondrial MAO-A activity of male albino rats (Wistar strain) was significantly inhibited with an inhibition of its only V max during aging. This age-induced inhibition of platelet MAO-A activity became reversed following the application of higher dosages (2.0-2.5μg/kg/day, i.t. for 21 consecutive days) of carnosine. Though carnosine at lower dosage (0.5μg/kg/day, i.t. for 21 consecutive days) was ineffective to platelet mitochondrial MAO-A activity in both young and aged rats, at higher dosages (2.0-2.5μg/kg/day, i.t. for 21 consecutive days) under similar condition this enzyme activity was significantly enhanced. Carnosine at 1.0μg/kg/day, i.t. for 21 consecutive days significantly enhanced MAO-A activity only in aged (18 and 24months) rats. These results suggest that carnosine withdraws the aging-induced inhibition of mammalian blood platelet MAO-A activity and restores its activity towards that (MAO-A activity) observed in young mammalian blood platelets.

Response of Northern Elephant Seal platelets to pressure and temperature changes: A comparison with human platelets

Mammalian blood platelets are activated by physiological agonists such as collagen or thrombin, or by physical stimuli such as cold temperatures and rapid decompression. Marine mammals regularly experience cold temperatures, high pressures and rapid decompression while diving, yet do not appear to suffer from thrombotic events during routine dive activity. We evaluated the effects of cold temperature and high pressure excursions on Northern Elephant Seal (NES) platelets and compared NES platelet response to that of human platelets subjected to identical stimuli. NES platelets undergo cold-induced activation when chilled to 4°C, and 3 distinct phase transitions can be measured using Fourier Transform Infrared Spectroscopy. NES platelet membrane lipid composition was determined using thin layer chromatography and NES platelets were found to have three times the amount of cholesterol (21% by weight) as human platelets. When exposed to high pressure-rapid decompression excursion, NES platelets did not undergo morphological shape change nor bind increased amounts of fibrinogen, while human platelets were significantly activated by the same excursion. These results demonstrate that while NES platelets are activated by the physical stimulus of cold temperatures, they are resistant to decompression-induced activation. We suggest that the composition of NES platelet membranes may play an important role in preventing pressure-related activation.

Localization of Fibrinogen during Aggregation of Avian Thrombocytes

The thrombocyte is the avian equivalent of the mammalian blood platelet and is involved in hemostasis through a fibrinogen-mediated process. Although fibrinogen has been implicated as a molecular bridge between activated cells during aggregation, the location of this molecule and its receptor on thrombocytes has not been characterized. Pigeon fibrinogen, isolated from plasma by precipitation with PEG-1000 and purified over Sepharose 4B, was used to study receptor-ligand interaction. Separation of pigeon fibrinogen on SDS-PAGE resulted in three peptides of molecular mass 62, 55, and 47 kDa, which were comparable to those of human fibrinogen. The role of fibrinogen and its receptor in thrombocyte function was established by turbidimetric aggregation using thrombin as an agonist under conditions requiring Ca 2+ and fibrinogen. Maximum response occurred using 3 m M Ca 2+ and 100 μg/ml fibrinogen. Fibrinogen-dependent aggregation was inhibited by an anti-GPIIb antibody, verifying a role for fibrinogen receptors in thrombocyte function. Fibrinogen-gold conjugates were used to describe receptor and ligand localization on aggregated cells. Computer reconstruction was used to verify relocalization of fibrinogen receptors following activation. Fibrinogen distribution changed from a dispersed state in preactivated cells to focal localization at points of cell contact and along pseudopods following activation. This selective positioning of fibrinogen suggests that a functional relocalization of the receptor occurs upon thrombocyte activation, and this relocation facilitates the role of fibrinogen as a molecular bridge. These studies establish similarities between the avian and the human systems and document the conserved nature of the hemostatic process.

5034409 Pyrrole carboxylic acids and esters for blood platelet aggregation inhibition

Heterocyclic acids and esters useful as inhibitors of mammalian blood platelet aggregation characterized by Formula I are disclosed. HET.sub.1 --(CH.sub.2).sub.n CO.sub.2 R (I) Formula I compounds are those wherein n is 6-9, R is hydrogen, lower alkyl or an alkali metal ion, and HET 1 is the heterocyclic radical 3,4-diphenyl-1H-pyrrol-1-yl.

Molecular mechanisms of platelet activation.

Molecular mechanisms of platelet activation.

Coated Pits and Vesicles Transfer Plasma Components to Platelet Granules

Electron microscopy of mammalian blood platelets after contrast enhancement with tannic acid after an initial fixation in glutaraldehyde and osmium reveals numerous coated pits (c.p.) and vesicles (c.v.), indicating a process of receptor-mediated endocytosis. The c.p. may be located at any site of the plasma membrane or the canalicular, surface connected membrane system. C.v. fuse with platelet granules without losing their coat. Evidence for a continuous transfer of ambient fluid to granules via c.p. and c.v. was obtained by the use of fluid-phase markers. It is proposed that the endocytic process may play a role in blood platelet activation.

Total synthesis of 12-( [formula omitted])-10-hydroxy- [formula omitted]-11,12-epoxyeicosa-5,9,14-( [formula omitted])-trienoic acids, metabolites of arachidonic acid in mammalian blood platelets

The two isomeric hydroxy-11,12-epoxides produced from arachidonic acid in mammalian blood platelets have been identified by comparison with totally synthetic substances as the C(10)-diastereomers of 2 .

Nucleated thrombocytoid cells

The so-called nucleated thrombocytes of the domestic fowl (and mallard) were analyzed intravitally by use of phase- and interference-contrast microscopy with regard to their morphology and functional state, and in comparison to other avian blood cells and mammalian blood platelets. Since nucleated thrombocytoid cells of birds do not differ in size from white blood cells, they are automatically included in differential cell counts. They can easily be confused with other white blood cells and even with erythrocyte ghosts, which also appear to be hemostatically active elements. However, the nucleated thrombocytoid cells displayed a characteristic, definite morphology. The platelet-like spreading process and elongation of aging cells in vitro to spindle forms deserve special attention. A technique of counting live avian blood cells was used to determine their values in chickens of different sexes and ages.

Lack of prostacyclin biosynthesis by aortic tissue of the chicken

The capacity of chicken aorta to produce prostaglandins both from exogenous and endogenous arachidonic acid has been evaluated. The metabolism of arachidonic acid in this tissue is mainly directed to PGE 2 and, in contrast to mammalian species, virtually no prostacyclin synthetase in present. However, the capacity of chicken thrombocytes to generate thromboxane A 2 and 12-L-hydroxy-5,8,10,14-eicosatetraenoic acid is similar to that observed for the mammalian blood platelets.

Association of centrioles with the marginal band of a molluscan erythrocyte.

Continuous circumferential bundles of microtubules, or marginal bands (MBs), are best known as a prominent structural feature of all nonmammalian vertebrate erythrocytes and mammalian blood platelets. Since their discovery in the late 19th century, MBs have been thought to play a cellular morphogenetic role, but no cytological clues to the mechanism of MB biogenesis have been reported. In previous work we have established the presence of MBs in serveral invertebrate blood cell types, including amebocytes and coelomocytes of certain Arthropod species and erythrocytes of a Sipunculan. We report here the occurrence of MBs in erythrocytes of the ark Anadara transversa (Mollusca) and four closely related species. The MBs of these arks have a striking structural feature; each is physically associated with a pair of centrioles. The centrioles are identified as such on the basis of morphological criteria: size, cylindrical shape, right-angle orientation, pairing, and 9-triplet ultrastructure. This intimate association between centrioles and MBs suggests that centrioles may be MB-organizing centers and invites comparative investigation of their possible role in vertebrate erythrocyte and platelet morphogenesis.

Marginal bands in blood cells of invertebrates

Marginal bands (MBs) constructed of microtubules have been observed classically in nonmammalian vertebrate erythrocytes and in mammalian blood platelets. Examination of invertebrate blood cells shows that the MB system has a much wider phylogenetic distribution than previously suspected. MBs are present in erythrocytes of the marine Sipunculan worm Golfingia gouldii and in amebocytes (clotting cells) of the horseshoe crab Limulus polyphemus. The cell types and species in which MBs occur are considered in relation to MB function.

Microtubules and Filaments in Blood Platelets

Within the last decade the mammalian blood platelet has enjoyed a rapidly increasing popularity as a research object. It is widely appreciated that platelets are multifunctional, and that they play a role in a variety of physiological and pathological processes besides their main function: the formation and consolidation of a haemostatic plug (for a recent monograph, and for references, see Gordon, 1976). The platelet is an anucleate piece of cytoplasm, pinched off from megakaryocytes (MK) in the bone marrow or in the circulation (Tinggaard Petersen, 1974). Vital microscopy has shown that in the circulation the platelet is disc-shaped, that it normally does not stick to endothelium or to other blood cells, and that it is the least deformable cell in blood - the latter observation does suggest the presence of a rigid skeleton in the platelet cytoplasm.

The Subcellular Distribution of [3H]-Colchicine-Binding Activity and Tubulin in Pig Blood Platelets

The subcellular distribution of the [3H]-colchicine-binding protein, believed to be tubulin, the subunit protein of microtubules, has been investigated in mammalian blood platelets. Studies on a soluble extract from pig platelets and two particulate fractions (viz. membrane-rich and granule-rich fractions) have shown that about 98% of the colchicine-binding activity in a platelet homogenate is located in the soluble phase. This result is in agreement with polyacrylamide gel electrophoresis experiments which show that the soluble fraction contains a substantial amount of 55,000 MW tubulin, whereas the membrane and granule-rich fractions contain very little of this component. The [3H]-colchicine-binding activity of the platelet soluble phase is largely precipitated by 40-50% ammonium sulphate and also by vinblastine sulphate in millimolar concentrations. Moreover the colchicine-binding protein in the platelet soluble fraction has a sedimentation coefficient of 5.9 S, is eluted in the void volume of a Sephadex G-100 column, and binds to DEAE-Sephadex at low ionic strength and is eluted from this ion-exchanger at an ionic strength of 0.47 M-KCl. In addition, most of the colchicine-binding activity of the platelet soluble phase is associated with protein which will undergo temperature-dependent polymerization in vitro and which has a molecular weight on SDS-polyacrylamide gels of 55,000. All these experimental findings suggest that the colchicine-binding activity of pig platelet homogenates is due to the presence of the microtubule protein, tubulin, which is largely found in the soluble compartment of the cells.

Platelet aggregation: induction by means of a complex between endotoxin and copper (Cu 2+ ).

The presence of a complex formed between bacterial endotoxin and cupric ion (Cu2+) causes mammalian (human, pig, and rabbit) blood platelets to aggregate in suspension. Complexes formed between endotoxin and Zn2+, Co2+, Ni2+, Mn2+, Fe3+, Ca2+, Mg2+, Ba2+, Al3+, Be2+, Pb2+, Cd2+, Ag+, or Hg2+ do not cause aggregation. The initial stage of the aggregation induced by the complex is not inhibited by inhibitors of adenosine diphosphate (ADP) or collagen induced aggregation, and is not accompanied by release of measureable amounts of serotonin or ADP. The potential clinical significance of the phenomenon is noted.

Ultraviolet light: a new stimulus for the induction of platelet aggregation.

Exposure to ultraviolet light (253.7 nanometers) causes mammalian blood platelets to aggregate. Aggregation is markedly enhanced in the presence of extracellular fibrinogen and is followed by the grodual of relatively small amounts of nucleotide and serotonin. Aggregation is inhibited by ethylenediamine tetraacetic acid or a combination of 2-deoxy-D-glucose and antimycin A. Adenosine, apyrase, and prostaglandin E(1) produced slight inhibition. The effect of exposure to ultraviolet light is cumulative and lasting. This agent may be used to study the process of platelet aggregation after the removal of the stimulus, by delaying the addition of fibrinogen until after cessation of irradiation. Thus ultraviolet light is the first agent known which may be used to study platelet aggregation in a period following its removal.

Enzymic formation of serotonin in mammalian blood platelets and red cells.

Throbozyten aus Menschen- und Rinderblut enthalten eine hohe Aktivitat an 5-Hydroxy-tryptophan-Decarboxylase und fur diese enzymatische Reaktion scheint Pyridoxalphosphat als Cofaktor eine Rolle zu spielen.

Incomplete microtubules observed in mammalian blood platelets during microtubule polymerization.

Incomplete microtubules observed in mammalian blood platelets during microtubule polymerization.

Substructure in negatively stained microtubules of mammalian blood platelets

Substructure in negatively stained microtubules of mammalian blood platelets

Demonstration of 5-Hydroxytryptamine in Blood Platelets by Electron Microscope Autoradiography

MAMMALIAN blood platelets are known to contain 5-hydroxytryptamine (5-HT) and to concentrate 5-HT added to platelet rich plasma in vitro1. Hughes and Brodie2 suggested that 5-HT existed in an unbound form in the platelet. The maintenance of increased platelet 5-HT was believed to be best explained by the presence of an active transport system for 5-HT2,3. The finding that the amount of 5-HT in platelets is related to the content of adenosine triphosphate (ATP) has led to the suggestion that the amine is bound to ATP4, and investigations using density-gradient centrifugation of disintegrated platelets have demonstrated a fraction containing most of the 5-HT and ATP5. More recently, in experiments with platelets disrupted ultrasonically and subjected to differential centrifugation 80 per cent of the 5-HT was recovered in the sedimented fraction, suggesting that 5-HT was bound within granules6.

Inactivation of 5-hydroxytryptamine by mammalian blood platelets

When the platelet-rich plasma of rabbit is incubated in vitro with 20 μg/ml of tetrabenazine most of the 5-hydroxytryptamine released from the platelets is inactivated. This inactivation is done by the platelets themselves and not by the plasma outside. It is prevented by monoamine oxidase inhibitors and by incubation in nitrogen atmosphere instead of air. Under similar conditions, the human platelets inactivate about 30 per cent of their 5-hydroxytryptamine released and those of rat less than 10 per cent. It is possible that also when released by other mechanisms, 5-hydroxytryptamine is inactivated in blood platelets and that this inactivation has an important role in the metabolism of the amine.