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S Heptinstall

Publications and source records attributed to S Heptinstall.

At least 73 records · Page 4Linked to original sources
PubMed1991

Measurements of the G-/F-actin equilibrium in ADP-stimulated human platelets.

The amounts of the different forms of actin (G-actin, F-actin) can be measured biochemically following lysis of the cells by the DNase I inhibition assay. The existing methodology for studying G-actin in unstimulated platelets was found to be inappropriate for studies during ADP-induced platelet activation. However, this problem was overcome by a simple modification of the procedure in which formaldehyde was added to the buffer used to lyse the activated platelets. Using this modification the G-actin values obtained immediately after lysis did not change during storage of the lysates on ice for more than 30 minutes. The results show rapid conversion of G-actin to F-actin in association with the shape change during ADP-stimulated activation. Examination of unstimulated platelets using the modified procedure enabled identification of a pool of actin that is rapidly dissociated to G-actin in the absence of formaldehyde, the existence of which had not previously been recognised.

Actins↗
PubMed1990

Glucose increases spontaneous platelet aggregation in whole blood.

Glucose (10-50 mM) added to samples of citrated whole blood increased the spontaneous platelet aggregation (SPA) that was observed upon stirring the samples, in a dose-dependent but time-independent manner. EDTA prevented and also reversed the SPA that occurred in the presence of glucose. Galactose, fructose and 2-deoxyglucose, but not sorbitol and sucrose, had effects on SPA similar to those of glucose. The effect of glucose on SPA in whole blood could not be specifically inhibited by tetramethylene glutaric acid (an inhibitor of aldose reductase). SPA was not affected by pentoxifylline, but was markedly reduced by chlorpromazine. We previously found that glucose, galactose, fructose and 2-deoxyglucose, but not sorbitol and sucrose, render red blood cells more fragile, and the results obtained in the present study provide further evidence that glucose as well as other reducing sugars potentiate SPA in whole blood by liberating ADP or other aggregating material from red blood cells.

Carbohydrates↗
PubMed1990

A cross-sectional study of basal platelet intracellular free calcium concentration in normotensive and hypertensive primigravid pregnancies.

1. The intracellular free calcium concentration ([Ca2+]i) in washed human platelets was measured using the fluorescent indicator, fura-2, in a cross-sectional study of 36 normotensive, primigravid volunteers, 12 in each trimester of pregnancy and a further 12 at 6 weeks post partum. The results were compared with those obtained from 30 normal female volunteers not using oral contraception. 2. The mean basal [Ca2+]i in the platelets of the pregnant women in the first two trimesters (115.6 +/- 6.7 and 120.1 +/- 5.7 nmol/l, respectively) was not shown to differ significantly from that of normal non-pregnant volunteers (112.3 +/- 2.9 nmol/l). However, during the third trimester a significant increase in [Ca2+]i was noted (134.0 +/- 4.9 nmol/l; P less than 0.05), with a return to normal values in the post-partum period (108.2 +/- 6.1 nmol/l). 3. [Ca2+]i was also measured in the platelets of a group of 12 primigravid pregnant women in the third trimester whose pregnancies were complicated by gestational hypertension (pregnancy-induced hypertension and pre-eclampsia). A significant rise in basal [Ca2+]i was noted in the platelets of primigravidae whose pregnancies were complicated by pre-eclampsia (163.6 +/- 8.8 nmol/l) as compared with normotensive, third-trimester primigravidae (P less than 0.02). However, no correlation could be demonstrated between [Ca2+]i and systemic blood pressure.

Adult↗
PubMed1990

A longitudinal study of platelet behaviour and thromboxane production in whole blood in normal pregnancy and the puerperium.

A longitudinal study of platelet behaviour (platelet aggregation and release reaction) in whole blood and of serum thromboxane B2 production was performed before, during and after normal pregnancy. The response of platelets to arachidonic acid and to adrenaline was significantly increased in the third trimester. Six weeks after delivery, values were still modestly increased but return to non-pregnant values was complete by 12 weeks. Serum thromboxane B2 production was unchanged throughout pregnancy and the puerperium.

Arachidonic Acid↗
PubMed1990

A comparison of the effects of an extract of feverfew and parthenolide, a component of feverfew, on human platelet activity in-vitro.

Extracts of the herb feverfew inhibit human blood platelet aggregation and secretion induced by a number of agents in-vitro and this may relate to the beneficial effects of feverfew in migraine. We previously identified several compounds with antisecretory activity in human blood platelets using adrenaline as the stimulant. In the present study, we have compared the inhibitory activity of one of these compounds, parthenolide, with that of crude feverfew extract. The effects of both on [14C]5-HT secretion from platelets and on platelet aggregation induced by a number of different stimulants were determined. The activating agents studied included the phorbol ester PMA, ADP, arachidonic acid, collagen, the thromboxane mimetic U46619, the calcium ionophore A23187, the diacylglycerol analogue OAG and adrenaline. The results show that there are marked similarities between the effects of feverfew extract and of parthenolide on both [14C]5-HT secretion and platelet aggregation, which is consistent with the effects of feverfew extract on platelets being brought about by parthenolide or similar compounds in the extract. Only in one case, when A23187 was used as the stimulatory agent, was there any discrepancy, which may have been due to materials in the extract other than parthenolide. Both feverfew extract and parthenolide were more effective as inhibitors of the [14C]5-HT secretion and aggregation induced by some agents and not others, and were most effective as inhibitors of the [14C]5-HT secretion (but not the aggregation) induced by PMA. This suggests that the effects of feverfew/parthenolide on the protein kinase C pathway warrants further study.

Blood Platelets↗
PubMed1990

Influence of substances affecting cell sulfhydryl/disulfide status on adherence of human monocytes.

An in-vitro model is described for investigating the adherence of human monocytes. Mononuclear cells (MNC) isolated from peripheral blood were incubated in plastic multiwell cell culture plates. The adherence of monocytes was quantified on the basis of their DNA content. The cell adherence proceeds rapidly; after 30 min of incubation about 85% of maximum adherent cells were attached to the plastic surface. On testing the effects of various sulfhydryl-affecting substances on monocyte adherence we found that the thiol-oxidizing compound diamide (0.1-1 mmol/l) inhibited the adherence by about 60%. Incubation with an extract of the plant feverfew, which contains materials that neutralize cellular sulfhydryl groups, also diminished monocyte adherence. The soluble thiol 2-mercaptopropionylglycine, in a concentration range of 0.5 to 10 mmol/l, had no effect on adherence in this system. The results suggest that cellular sulfhydryl groups play an important role in the adherence of monocytes.

Cell Adhesion↗
PubMed1989

Verapamil is a potent inhibitor of 5-HT-induced platelet aggregation.

We have studied the effects of verapamil, diltiazem and amlodipine on 5-HT-induced platelet aggregation and compared the results with those obtained for other platelet aggregating agents. Experiments were carried out using both human whole blood and platelet-rich plasma (PRP). Verapamil (but not diltiazem or amlodipine) inhibited 5-HT-induced platelet aggregation at much lower concentrations (IC50 = about 1 microM) than were required for inhibition of aggregation induced by other aggregating agents. Like some other selective inhibitors of 5-HT-induced platelet aggregation, it was not possible to completely overcome the inhibition by increasing the concentration of 5-HT. The antiaggregatory effects of verapamil were similar, but not identical, in whole blood and PRP. These results show that the Ca2+ channel blocker verapamil has some selectivity as an inhibitor of 5-HT-induced platelet aggregation and that this behaviour as a 5-HT antagonist should be taken into account when interpreting any therapeutic benefit ascribed to this drug.

Adenosine Diphosphate↗
PubMed1989

Feverfew in rheumatoid arthritis: a double blind, placebo controlled study.

Feverfew, reputed by folklore to be effective in arthritis, has in vitro properties that could be beneficial in the control of inflammatory disease. Forty one female patients with symptomatic rheumatoid arthritis received either dried chopped feverfew (70-86 mg) or placebo capsules once daily for six weeks. Allocation was random and not known by patient or observer. Variables assessed included stiffness, pain (visual analogue scale), grip strength, articular index, full blood count, erythrocyte sedimentation rate, urea, creatinine, C reactive protein, complement breakdown products (C3dg), rheumatoid factor titre, immunoglobulins (IgG, IgA, IgM), functional capacity, and patient and observer global opinions. One patient (placebo) withdrew after three days and was not included in the analysis. Treatment and placebo groups (20 patients each) were well matched at entry. No important differences between the clinical or laboratory variables of the groups were observed during the six week period. This study therefore shows no apparent benefit from oral feverfew in rheumatoid arthritis.

Adult↗
PubMed1989

[Cellular chemiluminescence of activated phagocytes of whole blood].

Both, the phagocytic process and the activation of phagocytes with soluble stimuli are accompanied by increased production of reactive oxygen species (ROS). Chemiluminescence (CL) measurement is a simple and sensitive method for the detection of ROS generation. Phagocytes (mainly polymorphonuclear leukocytes, PMNL) were stimulated with soluble stimulus or via phagocytosis in diluted whole blood, and the generation of Luminol-enhanced CL was registered. The time dependence of CL, determined in whole blood, corresponds to the CL from isolated leukocytes. A relationship between peak CL and the number of leukocytes as well as of PMNL was observed. The specific CL, i.e. the CL response related to a defined PMNL number, increases with the age of investigated healthy individuals. No correlations were found between CL and the capacity of PMNL to ingest zymosan particles. Relations between CL and spontaneous platelet aggregation suggest, that reactivity of blood platelets may be a contributing factor to the kinetics of the CL signal in our test system. The inhibition of CL by the sulphydryl reagents diamide and fever few extract indicate the role of cellular sulphydryl groups for phagocyte function. Measurement of CL in whole blood is proved to be a simple assay for assessment of PMNL function and allows measurements in very small blood samples (greater than or equal to 10 ul).

Cell Separation↗
PubMed1989

[The effect of high glucose concentrations on the osmotic and mechanical resistance of human erythrocytes].

Incubation of citrated or heparinized blood samples with 25 or 50 mmoles/l glucose for 1 hour at 37 degrees C results in a decrease in the osmotic and mechanical resistance of red blood cells as well as in an increase in the red blood cell volume measured as increase in haematocrit. Fructose, but not sorbitol or saccharose has effects on red blood cells that are similar to those of glucose. It is discussed that an uptake of glucose into red blood cells with subsequent water influx results in swelling and decreased stability of the cells.

Erythrocyte Volume↗
PubMed1988

Randomised double-blind placebo-controlled trial of feverfew in migraine prevention.

The use of feverfew (Tanacetum parthenium) for migraine prophylaxis was assessed in a randomised, double-blind, placebo-controlled crossover study. After a one-month single-blind placebo run-in, 72 volunteers were randomly allocated to receive either one capsule of dried feverfew leaves a day or matching placebo for four months and then transferred to the other treatment limb for a further four months. Frequency and severity of attacks were determined from diary cards which were issued every two months; efficacy of each treatment was also assessed by visual analogue scores. 60 patients completed the study and full information was available in 59. Treatment with feverfew was associated with a reduction in the mean number and severity of attacks in each two-month period, and in the degree of vomiting; duration of individual attacks was unaltered. Visual analogue scores also indicated a significant improvement with feverfew. There were no serious side-effects.

Adult↗
PubMed1988

Identity of saturable calcium-binding sites on blood platelets and their involvement in platelet aggregation.

Extracellular Ca2+ ions are required for platelet aggregation and we show that they enter two platelet pools. One pool is rapidly filled and easily displaced by EGTA. The second is filled more slowly and is not displaced by EGTA. The EGTA-displaceable pool is believed to be surface-located and was found to contain at least one class of saturable binding sites as well as a class of non-saturable binding sites. The saturable sites were found to be highly selective for Ca2+ (dissociation constant, 3.5 X 10(-7) M) even in the presence of 1 mM Mg2+ ions, and they took up between 261,000 and 307,000 Ca2+ ions/platelet. Full occupancy of the saturable binding sites appeared to be necessary for platelet aggregation to proceed. We also studied platelets that were unable to aggregate normally, either due to the congenital bleeding disorder Glanzmann's thrombastenia or due to experimental manipulation. In both cases we found decreased Ca2+ uptake specifically by the saturable Ca2+ binding sites, and that this was associated with decreased number of GP IIb/IIIa molecules expressed on these platelets. We suggest that the Ca2+ binding sites involved in platelet aggregation are located on the GP IIb/IIIa complexes and may be involved in holding the glycoproteins in the complex together, and that the binding sites need to be fully occupied before aggregation can proceed.

Binding Sites↗
PubMed1988

Pseudo grey platelet syndrome--grey platelets due to degranulation in blood collected into EDTA.

We have studied a woman with a history of mild bruising and bleeding, with a normal platelet count and normal clotting factors, who had platelets that appeared grey when stained and viewed under the microscope. Unlike the grey platelet syndrome, the abnormality was only evident when blood had been collected into EDTA and not when citrate or heparin was used as anticoagulant. This 'pseudo grey platelet syndrome' was associated with platelet dense body and alpha granule secretion with no aggregation and occurred on removal of extracellular Ca2+. We discovered that a plasma factor was responsible which could be an immunoglobulin but which is clearly different from the EDTA-sensitive antibodies which cause platelet aggregation and agglutination. We were not able to demonstrate a relationship between the mild bleeding tendency and the in vitro abnormality.

Adult↗
PubMed1988

Effects of an extract of feverfew on endothelial cell integrity and on cAMP in rabbit perfused aorta.

Extracts of feverfew inhibit platelet aggregation and secretion of granular contents from platelets and other cells. They also modify the interaction of platelets with collagen substrates: feverfew extracts inhibit both platelet spreading and formation of thrombus-like platelet aggregates on the collagen surface. We have now investigated the effect of an extract of feverfew on the vessel wall using rabbit aortas that were perfused with a physiological salt solution in-situ. Addition of feverfew extract to the perfusion medium protected the endothelial cell monolayer from perfusion-induced injury and led to a reversible increase in the cAMP content of aorta segments. The results indicate that feverfew may have a vasoprotective effect in addition to its effects on platelets.

Animals↗