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Biomedical subjects

J M Gerrard

Publications and source records attributed to J M Gerrard.

At least 91 records · Page 5Linked to original sources
PubMed1986

Allopurinol can act as an electron transfer agent. Is this relevant during reperfusion injury?

The xanthine oxidase inhibitor allopurinol markedly enhances myocardial function and decreases ventricular irritability during myocardial reperfusion. In the present report, we have evaluated the molecular mechanism of allopurinol action. First, allopurinol was shown to be a weak radical scavenger. Second, allopurinol was found to act as an electron transfer agent from ferrous iron to ferric cytochrome c. The results suggest that the beneficial effect of allopurinol might partially result from its facilitated electron transport during reperfusion when the lipid components of the chain can be expected to be disordered.

Allopurinol↗
PubMed1986

An enzyme-linked immunosorbent assay for 6-keto PGF1 alpha.

An enzyme-linked immunosorbent assay for 6-keto prostaglandin F1 alpha, a stable metabolite of prostacyclin, has been developed. The assay allows quantitation of 6-keto PGF1 alpha in the range 1-200 pg/0.1 ml and shows very low cross reactivity to nine other prostaglandins. Dose dependent stimulation by thrombin of 6-keto PGF1 alpha formation in human endothelial cells in culture has been used to verify the assay. Quantitation by the enzyme linked immunosorbent assay agrees closely with determination by radioimmunoassay.

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Activation of permeabilized platelets by inositol-1,4,5-trisphosphate.

The effect of inositol 1,4,5-trisphosphate (IP3) was studied using human platelets permeabilized with saponin and suspended in a high potassium, Ca2+-free buffer containing 40 microM EGTA and 1.2 mM magnesium. Under these conditions IP3 stimulated aggregation at a concentration of 0.5 microM with maximum aggregation at 5.0 microM. Aggregation was associated with phosphorylation of myosin light chain and a 47,000 dalton protein, and with a change in platelet shape including granule centralization and pseudopod formation similar to changes seen when cytoplasmic calcium is raised by other means. IP3 stimulated [14C]-serotonin release from platelet dense granules, [14C]-arachidonic acid release from platelet phospholipids and production of thromboxane B2. Preincubation of platelets with aspirin which blocked thromboxane formation also inhibited protein phosphorylation, serotonin secretion and partially inhibited aggregation. These results support the concept that IP3 is a major intracellular messenger in platelets and suggests that its effects are mediated both through Ca2+ flux and thromboxane formation.

Arachidonic Acid↗
PubMed1985

Mepacrine (quinacrine) inhibition of thrombin-induced platelet responses can be overcome by lysophosphatidic acid.

Addition of thrombin to human platelets results in production of lysophosphatidic acid. Such synthesis of lysophosphatidic acid can be inhibited by mepacrine, an inhibitor of the phospholipase A2 which attacks phosphatidic acid to give lysophosphatidic acid. In the present study, mepacrine was used at a concentration of 2.5-20 microM, sufficient to block aggregation and lysophosphatidic acid formation induced by 0.1 U/ml thrombin. Mepacrine, at this concentration, also blocked thrombin-induced phosphorylation of platelet myosin light chain and a 47 kDa protein, thrombin-induced secretion and thrombin-induced release of arachidonic acid from platelet phospholipids. However, mepacrine also partly inhibited the formation of phosphatidic acid in response to thrombin, consistent with some simultaneous inhibition of phospholipase C. Lysophosphatidic acid (2.5-22 microM) overcame the mepacrine block in thrombin-stimulated aggregation, protein phosphorylation and secretion without stimulating the release of arachidonic acid from platelet phospholipids or the formation of lysophosphatidic acid, and only slightly increasing phosphatidic acid formation. The results suggest that lysophosphatidic acid primarily acts distal to mepacrine inhibition of phospholipase A2 and phospholipase C and are consistent with the possibility that lysophosphatidic acid might be a mediator of part of the effects of low-dose thrombin on human platelets.

Arachidonic Acid↗
PubMed1985

Platelet protein phosphorylation.

As can be seen from this review, protein phosphorylation appears involved in both positive and negative regulation of platelets. To date, good evidence has been presented for the involvement of protein phosphorylation in the regulation of granule centralization (i.e. myosin light chain phosphorylation). It is probable that protein phosphorylation may also be involved in granule labilization, pseudopod formation and ATP synthesis. Protein phosphorylation in association with platelet activation appears mediated through calcium flux, in the case of myosin light chain phosphorylation, and through diglyceride or other substances in the case of 47P phosphorylation. A summary scheme is shown in Figure 1.

Actin Cytoskeleton↗
PubMed1985

Reciprocal transmembranous receptor-cytoskeleton interactions in concanavalin A-activated platelets.

Concanavalin A (Con A) has been used to activate platelets, inducing a specific interaction between the glycoprotein IIb-IIIa complex and the cytoskeleton of the activated platelet. In agreement with this, we have shown that Con A activates human platelets, initiating phosphorylation, secretion, and cytoskeletal formation. Con A and cytochalasin B were used to demonstrate a reciprocal interaction of the glycoprotein complex with the platelet cytoskeleton. Additionally, we have shown that a similar reciprocity is provided by the multivalent fibrin-fibrinogen platelet interaction found in the thrombin-induced clot. Con A differs from other activators in precipitating an apparent cytoskeletal core despite a complete inhibition of platelet activation by prostaglandin E1. We suggest, from this result, that Con A may be cross-linking a membrane-associated cytoskeletal complex present in the unactivated platelet.

Actins↗
PubMed1985

Disulfide-linked and transglutaminase-catalyzed protein assemblies in platelets.

Energy depletion induces the formation of disulfide-linked and transglutaminase-catalyzed protein assemblies in platelets. The disulfide type polymers, formed following incubation at 37 degrees C in the absence of adenosine triphosphate (ATP)-generating precursors, are composed of cytoskeletal proteins and are associated with a decrease of reduced glutathione levels accompanying ATP depletion. The maintenance of ATP and reduced glutathione levels to, respectively, 34% and 47% of their original values is sufficient to prevent the formation of both polymer types. The transglutaminase-type cross-links are formed in the presence of calcium in either "energy-depleted" or thrombin stimulated platelets. 125I-surface-labeled membrane proteins, presumably transmembrane proteins, are incorporated into the transglutaminase-catalyzed cross-linked polymer of thrombin-stimulated platelets. Glycoproteins IIb and IIIa are not essential to the polymer formation, since thrombasthenic platelets treated with thrombin exhibit the same type of labeled polymer. The transglutaminase-catalyzed polymer formation following thrombin stimulation of platelets is inhibited by a calcium channel blocker, an intracellular calcium antagonist, as well as other inhibitors such as indomethacin, dibutyryl cyclic AMP, and prostaglandin E1. Although the evidence points to the formation of transglutaminase-catalyzed cross-linking in the cytoplasmic compartment, additional cross-linking of extruded components cannot be excluded.

Acyltransferases↗
PubMed1985

The effects of 1-oleoyl-2-acetylglycerol on platelet protein phosphorylation and platelet ultrastructure.

1-oleoyl-2-acetylglycerol (OAG), an activator of protein kinase C and a synthetic diglyceride, was used in an investigation of the role of diglycerides in platelet stimulus-activation coupling. OAG (20-100 micrograms/ml) added to platelets resulted in rapid phosphorylation of the 47,000-dalton protein as well as a gradual dose dependent disappearance of alpha granules and dense bodies and the appearance of vacuolar structures containing remnants of granule matrix material. These morphologic changes occurred more slowly than the phosphorylation of 47K, which suggests that if these are related the phosphorylated 47K serves to activate some other mechanism, which is ultimately responsible for the changes observed. These results are most consistent with the role for the phosphorylation of 47K to promote granule labilization. Myosin light chain (MLC) phosphorylation also occurred. An absence of granule centralization suggests that MLC phosphorylation by protein kinase C may not trigger effective actin-myosin contraction.

Blood Platelets↗
PubMed1985

Protein phosphorylation and platelet secretion.

Platelet secretion in response to physiologic stimuli appears to result from the complementary stimulation of two processes--granule centralization and granule membrane fusion. Granule centralization is produced by actin-myosin contraction which is initiated by a movement of calcium ions into the cytoplasm. The calcium binds to calmodulin to form a complex which activates myosin light chain kinase to phosphorylate myosin light chain (MLC). Once phosphorylated in this fashion, actin-myosin contraction occurs. Granule membrane fusion can be produced selectively by phorbol myristate acetate and oleoyl-acetyl diglyceride, both of which activate protein kinase C. Phosphorylation of a 47,000 dalton intracellular protein (47K) by protein kinase C may be critical to granule membrane fusion. The mechanism of action of 47K is presently unknown. The combined phosphorylation of MLC and 47K in response to most physiologic agonists which cause granule secretion, and the synergistic effects on granule secretion of agents which independently stimulate MLC and 47K phosphorylation, suggests secretion usually results from the interaction of granule centralization and granule membrane fusion.

Actin Cytoskeleton↗
PubMed1984

Lysophosphatidic acid can activate platelets without increasing 32P-labelling of phosphatidic acid.

Stimulation of platelets by thrombin produced a rise in [32P]phosphatidic acid labelling of platelets which was greater in medium without added calcium than in medium with 2.5 mM calcium. A rise in [32P]lysophosphatidic acid was also seen in platelets stimulated by thrombin in the presence of 2.5 mM extracellular calcium, though it was of lesser magnitude (average 35%) than the rise in phosphatidic acid. In platelets resuspended without added calcium no change in [32P]lysophosphatidic acid was seen in response to thrombin. Lysophosphatidic acid can itself induce platelet aggregation. Similarly to the calcium ionophore A23187, lysophosphatidic acid produced minimal change (in medium with no added calcium) to no change (in medium with 2.5 mM external calcium) in [32P]lysophosphatidic acid. The endoperoxide analog U46619 produced changes in 32P-labelling of platelet phosphatidic and lysophosphatidic acid similar to those produced by thrombin but of lesser magnitude. The results of these studies show that the action of lysophosphatidic acid on platelets differs from the action of thrombin, U46619 and platelet-activating factor, which produce a rapid rise in [32P]phosphatidic acid, and suggests that lysophosphatidic acid, like A23187, largely bypasses the initial receptor-coupled breakdown of phosphoinositides leading to formation of diacylglycerols and phosphatidic acid.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1984

Shortening of bleeding time by 1-deamino-8-D-arginine vasopressin in various bleeding disorders.

To evaluate the effect of 1-deamino-8-D-arginine vasopressin (DDAVP) in various bleeding disorders, 10 micrograms/m2 DDAVP was administered to subjects with von Willebrand disease (13), platelet function defects (12), von Willebrand disease and platelet defects together (8), or isolated prolongation of the bleeding time (5). DDAVP shortened the bleeding time similarly in all patient groups. Shortening of the bleeding time was also observed in 2 patients with aspirin-induced platelet defects and in 2 normal subjects. DDAVP administration was associated with falls in the platelet count, mean platelet volume, and partial thromboplastin time, and rises in platelet adhesion, factor VIII coagulant activity, factor VIII related antigen, and von Willebrand factor activity. The basal bleeding time was the only predictor of the magnitude of the bleeding-time correction. Normal haemostatis was achieved with DDAVP plus epsilon-aminocaproic acid and no blood product support during operations in 18 patients with bleeding disorders.

Adolescent↗
PubMed1983

The influence of amines on various platelet responses.

Four amines, galactosamine, mannosamine, histamine and arginine were studied for their effects on platelet aggregation, platelet morphological changes, platelet protein phosphorylation and platelet secretion. Galactosamine inhibited platelet aggregation in response to arachidonic acid and ionophore A23187 but did not inhibit changes in platelet morphology, or in platelet protein phosphorylation in response to these agents and only partially inhibited platelet secretion. The results suggest that galactosamine can be used as a selective inhibitor of platelet-platelet attachment without having a significant effect on intracellular processes. Mannosamine was similar to galactosamine except that it partially suppressed phosphorylation of myosin light chain. Histamine was similar to mannosamine except that some platelet damage was seen in platelets exposed to histamine and arachidonic acid or ionophore A23187. Arginine was non-selective: it suppressed platelet aggregation, secretion and phosphorylation of myosin light chain and a 40 kDa protein (40P) in response to arachidonic acid and ionophore A23187. Arginine was also potent in suppressing platelet morphological changes. When the same four amines were evaluated for their effects on thrombin-induced aggregation; secretion was inhibited concomitantly with inhibition of aggregation. Inhibition of myosin light chain and 40P phosphorylation was evident with galactosamine, suggesting that when thrombin is used as the agonist, galactosamine is not a specific inhibitor of platelet-platelet attachment. These amines therefore have various effects on platelet responses. Under some conditions and with arachidonic acid or ionophore A23187 as agonist, one of them, galactosamine, can be used as a selective inhibitor of platelet-platelet attachment.

Arachidonic Acid↗
PubMed1983

Evidence that the peroxidase of the fatty acid cyclooxygenase acts via a Fenton type of reaction.

Addition of ferrous sulfate to a solution containing peroxy-methyl arachidonate resulted in cleavage of the peroxy group on the methyl arachidonate as assessed by absorption at 232nm. The results suggest that ferrous iron can be involved in the reduction of fatty acid peroxides and supports the possibility that the peroxidase component of the fatty acid cyclooxygenase occurs via a Fenton type reaction.

Arachidonic Acids↗
PubMed1983

Arachidonic acid deficiency in streptozotocin-induced diabetes.

Fatty acid compositions of phospholipids of heart, liver, kidney, aorta, and serum from rats having streptozotocin-induced diabetes were determined and compared with those of nondiabetic controls. Linoleic and dihomo-gamma-linolenic acids were increased whereas arachidonic acid was decreased in most tissues, suggesting an impairment of delta 5-desaturase activity. Acids derived from linolenic acid were increased in some diabetic tissues from diabetic animals although the linolenic content was normal, indicating less impairment in the desaturation of the omega 3 series of fatty acids. Diabetes suppressed all polyunsaturated acids in the whole animal, but the competition between omega 3 and omega 6 acids favored the excessive suppression of long-chain omega 6 acids and an increase in the proportion of omega 3 acids in lipids of vital tissues. These changes in fatty acid composition of the phospholipids may have significant effects on cellular functions and vasoregulatory control mechanisms in diabetes.

Animals↗