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Biomedical subjects

M J Silver

Publications and source records attributed to M J Silver.

At least 55 records · Page 3Linked to original sources
PubMed1981

Effects of any epoxymethano stable analogue of prostaglandin endoperoxides (U-46619) on human platelets.

U-46619 is a stable epoxymethano analogue of cyclic endoperoxide PGH2. We studied platelet aggregation, 14C-5HT release, LDH extrusion and prostaglandin and thromboxane production induced by this compound in platelet-rich plasma samples from 15 healthy volunteers. Each subject was tested both before and 90 min after aspirin (500 mg) ingestion. The threshold aggregating concentration (TAC) of U-44619 ranged between 0.18 and 0.90 micro M. Aggregation was maximal between 40 and 60 min after venipuncture and was concentration-dependent. At concentrations below the TAC, U-44619 induced primary reversible aggregation with minimal 14C-5HT release. At TAC or higher concentrations aggregation and release proceeded as parallel events. Neither prostaglandin or thromboxane production nor LDH loss could be detected in any of the situations tested. Aspirin ingestion did not modify the pattern of platelet responses. In unstirred, not aggregated platelet samples 14C-5HT release by U-46619 occurred to a similar extent as in stirred, aggregated platelet samples. Addition to citrated PRP of 0.3 mM Na2 EDTA blocked both aggregation and release induced by U-46619. This compound, however, aggregated washed platelets resuspended in Ca++-free-tyrode-albumin containing fibrinogen. The mechanism by which U-46619 activates platelets differs from that of all other common aggregating agents.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1981

Plasma and platelet lipid composition and platelet aggregation by arachidonic acid in women on the pill.

Sensitivity to induction of platelet aggregation by arachidonic acid (AA) and changes in plasma and platelet polyunsaturated fatty acid distribution were studied in seven women before and after six months of oral contraceptive (OC) treatment with a combination of d-norgestrel (0.25 mg) and ethinylestradiol (0.05 mg). Special interest was focused on AA because certain metabolites of fatty acid induce platelets to aggregate and are considered to play a crucial role in thromboembolic processes. In plasma, AA concentrations increased slightly, but significantly, in both the free fatty acid (FFA) and phospholipid fractions; in platelets AA increased in the phospholipid and neutral lipid fractions. The threshold aggregating concentration (TAC) of AA was significantly reduced in platelets of women after six months of OC treatment (0.65 +/- 0.08 versus 0.30 +/- 0.04 mM). This suggests that changes in platelet fatty acid composition may be associated with in vitro changes in platelet sensitivity to AA. Such changes may contribute to the thrombotic tendency associated with OC treatment.

Adolescent↗
PubMed1981

Formation of lysophosphatidylcholine by human platelets in response to thrombin. Support for the phospholipase A2 pathway for the liberation of arachidonic acid.

Significant increases in lysophosphatidylcholine from a basal level of 4.2 +/- 0.36 nmol/mg of platelet protein to 6.4 +/- 0.46 nmol/mg of protein occur within 20 s after the addition of thrombin (5 units/ml) to washed human platelets. The increases are essentially complete by 1 min, at which time levels of 8.5 +/- 0.53 nmol of lysophosphatidylcholine/mg of platelet protein are reached. Decreases in phosphatidylcholine and also phosphatidylethanolamine occur within 20 s after stimulation of platelets by thrombin. These changes were detected by quantitative measurements of endogenous phospholipid phosphorus after extraction and thin layer chromatography of the platelet lipids. The concomitant increases in lysophosphatidylcholine and decreases in phosphatidylcholine, as well as the decreases in phosphatidylethanolamine, can only be explained by the stimulation of phospholipase A2 activity in platelets by thrombin.

Animals↗
PubMed1981

Prostacyclin production in rabbit arteries in situ: inhibition by arachidonic acid-induced endothelial cell damage or by low-dose aspirin.

The central artery of the rabbit ear was perfused in situ and effluent fractions from the artery were assayed for 6-keto-prostaglandin F1 alpha (6-K-PGF1 alpha) and thromboxane B2 (TxB2), the stable metabolites of prostacyclin (PGI2) and TxA2, using specific radioimmunoassays. These metabolites of arachidonic acid (AA) were not detected in the effluent during infusion of Tyrode's solution but both metabolites were detected when small amounts of AA were infused into the artery. Examination of the arteries by scanning electron microscopy revealed that high concentrations of AA which caused a short burst of 6-K-PGF1 alpha and TxB2 production damaged the endothelial cells while lower concentrations which stimulated continuous production did not cause damage. When a non-damaging concentration of AA was infused into an artery that had previously received a damaging concentration, PG production was greatly reduced. Pretreatment of the rabbits with 4 mg/kg acetyl-salicylic acid (ASA) inhibited 6-K-PGF1 alpha production by the rabbit ear artery in response to AA and 70% inhibition was still evident 18 hours after ASA.

6-Ketoprostaglandin F1 alpha↗
PubMed1981

Inhibition of platelet lipoxygenase by toluene-3,4-dithiol and other ferric iron chelators.

Arachidonate lipoxygenase, obtained from the soluble, cytoplasmic fraction of sonicated human platelets was strongly inhibited by toluene-3,4-dithiol and dithizone, agents which form strong complexes with ferric but not ferrous ions. Weak inhibition was noted with the less specific iron chelator ortho-phenanthroline and with potassium cyanide. There was not inhibition with the ferrous iron chelating agents 2,2' dipyridyl nor with bathophenanthroline or EDTA. These findings suggest that platelet lipoxygenase activity depends on ferric iron.

Arachidonate Lipoxygenases↗
PubMed1981

Bovine endothelial cells in culture produce thromboxane as well as prostacyclin.

Bovine aortic endothelial and smooth muscle cells in culture were incubated with arachidonic acid or prostaglandin H2. The amount of prostacyclin nd thromboxane A2 synthesized ws then determined by specific radioimmunoassay for 6-keto-prostaglandin F1 alpha and thromboxane B2. Although smooth muscle cells produced only 6-keto-prostaglandin F1 alpha and thromboxane B2 in a ratio of 5:1 to 10:1. The same ratio of these metabolites of arachidonic acid ws also found when prostaglandin production from endogenous arachidonic acid was stimulated in endothelial cells by the ionophore A23187. Cyclooxygenase inhibitors inhibited the production of both metabolites equally, whereas thromboxane synthetase inhibitors selectively inhibited the production of thromboxane B2. Cells in culture were also incubated with [1-14C]arachidonic acid and the extracted products were identified by two-dimensional thin-layer chromatography. 6-Keto-prostaglandin F1 alpha was the only metabolite produced by smooth muscle cells, but endothelial cells synthesized 6-keto prostaglandin F1 alpha, thromboxane B2, prostaglandin E2, and prostaglandin F2 alpha.

Animals↗
PubMed1980

Model system for the study of inital damage to arterial endothelial cells in situ by scanning electron microscopy.

The central artery of the rabbit ear was injected with either 1 ml of control or test solutions in a model system which allowed for the study of effluent fractions coming from a segment of the artery and for the examination of the vessel by electron microscopy. The procedure allowed for either mixing of blood with the test solution ("flow by") or injection of the solutions in the absence of blood ("no flow by"). Effluent fractions were collected and assayed for 6-keto-PGF1 alpha, and indicator of PGI2 production. After the collection of effluent fractions, the artery was perfused with 1% glutaraldehyde to begin fixation. Ultrastructural damage to endothelial cells was seen, by SEM, in a graded response to sodium arachidonate solutions at concentrations between 6.6 and 3.3 mM ("flow by"); and between 3.3 and 0.83 mM ("no flow by"). Lower concentrations of arachidonate did not cause damage. Damage included enucleation, separation or denudation of endothelial cells. Sodium linoleate produced similar damage. A burst of PGI2 production appeared to be associated with arachidonate-damaged endothelium. Injection of sodium arachidonate at lower concentrations (0.33 mM and 0.165 mM) resulted in continuous production of PGI2 over a period of 1 to 5 minutes.

Animals↗
PubMed1980

A model system for studying initial events in atherosclerosis.

A model system has been developed which employs the central artery of the rabbit ear, and allows for the study of 1) ultra-structural changes in the arterial endothelium and 2) formation and release of prostacyclin and thromboxane from the arteries in situ. Use of the model should be helpful in evaluating the initial events in atherosclerosis. Both prostacyclin and thromboxane (detected by radioimmunoassay) were formed by arteries in situ in response to infusion of sodium arachidonate.

Animals↗