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Biomedical subjects

C R Prentice

Publications and source records attributed to C R Prentice.

At least 73 records · Page 4Linked to original sources
PubMed1984

A comparative study using immunological and biological assay of the haemostatic responses to DDAVP infusion venous occlusion and exercise in normal men.

In a group of six normal male volunteers, infusion of DDAVP, venous occlusion and exercise were shown to increase plasma levels of factor VIII and plasminogen activator, activity and antigen, to different extents and at differing rates. Any mechanisms suggested to explain release of these proteins by various stimuli should account for such differences. All three stimuli could also increase plasma levels of prostacyclin metabolites, although this was only significant for high doses of DDAVP. Other potential endothelial markers, such as fibronectin and thrombospondin, showed no specific increase after any of the stimuli.

Arginine Vasopressin↗
PubMed1984

Utilization of the platelet release reaction in the blood compatibility assessment of polymers.

The release reaction is directly associated with platelet adhesion and aggregation, which are primary events leading to thrombus formation following contact of blood with artificial surfaces. This investigation examined the release reaction from the alpha granules of platelets after blood-polymer interaction, and utilized the measurement of beta-thromboglobulin (BTG), a platelet-specific protein, in the assessment of the in vitro blood compatibility of polymers. A radioimmunoassay was used, to determine the release of BTG following contact of blood with tubes of siliconized glass and polypropylene and flat sheets of poly(vinyl chloride) and silicone rubber. Polypropylene tubes caused less release of BTG than those of siliconized glass and silicone rubber induced less BTG release than poly(vinyl chloride). The investigation indicates a role for BTG measurement in blood compatibility assessment.

Beta-Globulins↗
PubMed1984

Blood rheology in pre-eclampsia and intrauterine growth retardation: effects of blood pressure reduction with labetalol.

Blood viscosity ( Contraves L S 30) and its determinants were measured in 23 patients with mild/moderate pre-eclampsia, 10 patients with intrauterine growth retardation and 22 control subjects, matched for age and gestation. Both abnormal groups had a significantly increased blood viscosity at high shear rate (94 s-1) associated with increased haematocrit. Fibrinogen levels were also increased, but there were no significant differences between groups in plasma viscosity, low shear viscosity (0.94 s-1) or red cell deformability, measured by a low-shear washed cell system of filtration through 5-micron pore diameter Nuclepore filters. In the pre-eclamptic group, measurements were repeated after 1-2 weeks in nine patients treated with labetalol (a combined alpha and beta adrenergic blocker) and in 10 patients treated with bed rest. Labetalol reduced blood pressure but no change in rheology was seen in either group. Control of blood pressure by labetalol does not adversely affect rheology, in contrast to diuretics which are known to cause haemoconcentration and increased blood viscosity.

Adult↗
PubMed1984

Blood coagulation and platelet function following maximal exercise: effects of beta-adrenoceptor blockade.

Alterations of platelet function and blood coagulation may occur with exercise or beta-adrenoceptor blockade. To determine if beta-blockade could modify exercise-induced changes in haemostatic factors we performed a double-blind study of acute strenuous exercise in normal males with and without beta-blockade. Exercise increased prostacyclin and plasminogen activator levels but there was no evidence of thrombin generation as indicated by unchanged platelet aggregation responses, beta-thromboglobulin and fibrinopeptide A levels. The only alteration in coagulation by beta-blockade was a reduction in the factor VIII:C and VIII:RAg rise after exercise and this modification may be relevant to the protective effect of these drugs in patients with coronary artery disease.

Adrenergic beta-Antagonists↗
PubMed1983

The novel effect of a new prostacyclin analogue ZK36374 on the aggregation of human platelets in whole blood.

Platelet aggregation was studied at 37 degrees C in citrated whole human blood, using the Ultra Flo 100 Whole Blood Platelet Counter. Aggregation was measured as a fall in the number of single platelets following addition of an aggregating agent. At peak aggregation, the fall in the number of platelets induced by ADP (10 microM), collagen (1 microgram/ml) or thrombin (0.2 U/ml) was about 90%. When blood was incubated with the prostacyclin-analogue ZK36374, the aggregation responses to ADP, collagen and thrombin were reduced with IC50's = 0.5, 1.5 and 3 nM respectively and the corresponding IC100's were: 1, 3 and 12 nM. When ZK36374 was added at peak aggregation, the number of single platelets increased significantly due to disaggregation of preformed platelet aggregates. It is concluded that the present technique represents a rapid, sensitive and more physiological approach for investigating the effects of pharmacological agents on platelet aggregation.

Adenosine Diphosphate↗
PubMed1983

Plasma fibrinopeptide A and beta-thromboglobulin in patients with chest pain.

Plasma levels of beta-thromboglobulin (BTG) and fibrinopeptide A (FPA), markers of platelet release and thrombin generation respectively, were measured in 48 patients within 3 days of admission to hospital for acute chest pain. Twenty-one patients had a confirmed myocardial infarction (MI); 15 had unstable angina without infarction; and 12 had chest pain due to noncardiac causes. FPA and BTG were also measured in 23 control hospital patients of similar age. Mean plasma BTG levels were not significantly different in the 4 groups. Mean plasma FPA levels were significantly higher in all 3 groups with acute chest pain when compared to the control subjects (p less than 0.01), but there were no significant differences between the 3 groups. Increased FPA levels in patients with acute chest pain are not specific for myocardial infarction, nor for ischaemic chest pain.

Adult↗
PubMed1983

Prognostic value of beta-thromboglobulin in patients with transient cerebral ischaemia.

Plasma levels of beta-thromboglobulin (BTG) and fibrinopeptide A (FPA), markers of platelet alpha-granule release and thrombin generation respectively, were measured in 27 subjects with transient cerebral ischaemic attacks (TIA), 43 age-matched controls, and 32 young controls. BTG and FPA were both higher in elderly controls than in young controls. BTG was higher in TIA subjects than in age-matched controls and higher in the 12 TIA subjects who had further vascular events in the next year than in those who had no further events. FPA was not significantly associated with TIA or with further events. These results support a relationship between platelet activation and TIA and suggest that BTG levels indicate a group at higher risk of further vascular events.

Adult↗
PubMed1983

Blood viscosity and haemostasis in the nephrotic syndrome.

Blood viscosity and its major determinants (haematocrit, plasma viscosity and fibrinogen) as well as several haemostatic variables were measured in 21 patients with the nephrotic syndrome, and 21 controls matched for age, sex, smoking habit and serum creatinine. Blood viscosity was significantly increased in the nephrotic group, measured at a low shear rate (mean increase 41%, p less than 0.01) and at a high shear rate (mean increase 25%, p less than 0.01). Haematocrit was not significantly increased, but plasma viscosity was significantly higher (p less than 0.01), associated with increased plasma macroglobulins especially fibrinogen, which was increased to double the plasma concentration of the control group (p less than 0.01). Nephrotic subjects also had increased plasma levels of alpha 2-macroglobulin, factor VIII activity, factor VIII antigen and beta-thromboglobulin; differences in antithrombin III, fibrin degradation products, plasminogen, and platelet count were not significant. We suggest that increased blood and plasma viscosity may play a role in the vascular complications of the nephrotic syndrome.

Adult↗
PubMed1983

Platelet aggregation studies in whole human blood.

Since the development of the photometric aggregometer, platelet aggregation studies are routinely performed on platelet-rich plasma (PRP). We have studied platelet aggregation in fresh citrated whole human blood using the recently developed Ultra Flo 100 Whole Blood Platelet Counter. Aggregation of platelets in whole blood was induced with adenosine 5'-diphosphate (ADP; 0.25-10 microM), collagen (0.25-1.0 microgram/ml) and thrombin (0.05-0.2U/ml). Platelet aggregation induced by ADP and thrombin was maximum within 1 min, and that of collagen within 3 mins. Aggregation responses to low concentration of ADP and thrombin were rapidly reversible, whereas responses to collagen and high concentrations of ADP and thrombin were virtually irreversible. The aggregation of platelets was indicated by a fall in platelet count; confirmed by scanning electron micrographs which revealed the presence of large aggregates of platelets, and was prevented when blood was treated with EDTA as anticoagulant. The present technique appears to be rapid, sensitive and reliable; and allows direct measurement of platelet aggregation and disaggregation in whole blood in vitro and ex-vivo.

Adenosine Diphosphate↗
PubMed1983

Intermittent epoprostenol (prostacyclin) infusion in patients with Raynaud's syndrome. A double-blind controlled trial.

Two groups of outpatients (7 in each group) with Raynaud's syndrome, matched for severity of illness, were randomly allocated to receive at weekly intervals for three weeks either a 5 h intravenous infusion of buffer or epoprostenol (prostacyclin, PGI2) in buffer (7.5 ng/kg/min after the first hour). PGI2 reduced the frequency and duration of ischaemic attacks (both p less than 0.01). Hand temperature measurements with a thermocouple were significantly improved at 1 week; 6 weeks after the last infusion hand temperatures had returned to baseline. There was a corresponding loss of clinical response 8-10 weeks after the last infusion.

Clinical Trials as Topic↗
PubMed1983

Epoprostenol (prostacyclin) and severe arterial disease. A double-blind trial.

A 96 h infusion of epoprostenol (prostacyclin) or placebo was given as a treatment for rest pain to 28 patients with severe peripheral arterial disease. 24 h after the end of the infusion patients given epoprostenol had significantly less pain and took fewer analgesics tablets than did the controls. In some patients the epoprostenol effect lasted for over 1 month.

Arterial Occlusive Diseases↗
PubMed1983

Dazoxiben, a thromboxane synthetase inhibitor, in the treatment of Raynaud's syndrome: a double-blind trial.

1 UK-37248 (dazoxiben), an orally active thromboxane synthetase inhibitor, was evaluated in a double-blind trial of patients with severe Raynaud's syndrome. 2 Twenty patients were enrolled in the study. Eleven of these patients received dazoxiben 400 mg day and nine received matching placebo capsules. Treatment was given for 6 weeks and the patients reviewed at 2 weekly intervals during the study. 3 Assessment of response was judged by clinical symptoms and hand temperature measurements. Haematological and haemostatic studies were also carried out. 4 Results show a significant clinical improvement in patients receiving dazoxiben for six weeks. Hand temperature measurements, and haematological and haemostatic blood tests remained unchanged, however, apart from the expected lowering in plasma thromboxane B2 levels. 5 The mechanism of action of the drug would appear not to be mediated through increased prostacyclin production and further studies are under way to determine how improvement has been obtained in these patients.

Adult↗
PubMed1983

Coronary artery disease in severe haemophilia.

It has been suggested that the coagulation defect in haemophilia A protects these patients from coronary artery disease. We report two patients with severe haemophilia, who each had severe atheroma localised to the coronary arteries. Both patients had received only small amounts of factor VIII concentrates in their lifetime because of various social reasons. In one case death resulted from myocardial infarction secondary to an occlusive thrombus in a coronary artery. The implications of these findings to the pathogenesis of vascular disease are discussed.

Arteriosclerosis↗
PubMed1983

Freeze dried cryoprecipitate: a clinical evaluation.

Freeze dried cryoprecipitate was used in the treatment of 14 patients with haemophilia A. The in vivo recovery was 91.2% which is comparable to that reported from other parts of Europe. The product was efficacious and no adverse effects were reported. Freeze dried cryoprecipitate is the high yield product of a low technology process and as such may be of value in reducing any possible shortfall in the factor VIII requirements of the haemophiliac population of the UK.

Chemical Precipitation↗
PubMed1983

Total knee arthroplasty in haemophilic arthritis.

The results of total knee replacement in five patients aged between 22 and 37 with severe haemophilia A or B are described. All patients had been managed conservatively without success. Frequent bleeds, severe pain and limitation of movement were the indications for operation. Despite close haematological surveillance, bleeding problems occurred in three of the patients and large quantities of plasma concentrates were required. Review of the patients over a period of 25 to 48 months after operation showed dramatic lessening of pain and maintenance of a satisfactory range of movement. The frequency of haemarthrosis diminished markedly and the requirements for factor concentrate in the years after operation fell substantially. Two patients returned to employment. Total knee replacement led to marked clinical improvement in all the patients, but the long-term results are not yet known.

Adult↗