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Biomedical subjects

M Crook

Publications and source records attributed to M Crook.

68 records · Page 4Linked to original sources
PubMed1991

Electrokinetic properties and surface membrane sialic acid status of platelets in idiopathic thrombocytopenic purpura (ITP).

Continuous flow electrophoresis has been used to investigate heterogeneity in the circulating platelets from patients with idiopathic thrombocytopenia (ITP) and from age- and sex-matched control donors. The ITP patients' platelet counts ranged from 15 to 80 X 10(9)/l and they had much higher mean volumes and significantly higher (two-fold) total cell and neuraminidase-labile surface sialic acid contents expressed per unit cell than normal. After volume normalization the mean difference between the two groups was not statistically significant. The relationships of these findings to abnormal thrombopoiesis and to molecular recognition for reticuloendothelial system (RES) removal are discussed.

Adolescent↗
PubMed1991

Haemoglobin in stools from neonates: measurement by a modified Apt-test.

The Apt test for the detection of fetal haemoglobin in stool samples from neonates is described. This test has been previously reported to be helpful in the diagnosis of the swallowed blood syndrome in neonates, giving rise to 'melena neonatorum'. In this syndrome it is important to distinguish between swallowed maternal blood at the time of delivery from blood derived from the neonatal gastrointestinal tract. A spectrophotometric improvement has been made to the originally described Apt test, with additional recommendations for use.

Feces↗
PubMed1990

Basal and induced prothrombinase expression in platelets from patients with essential thrombocythaemia (ET).

Both the basal and the collagen plus thrombin-stimulated prothrombinase activities have been measured in platelets from eight patients with essential thrombocythaemia (ET). On a mean basis these activities were significantly lower than the values recorded for a group of age and sex matched control subjects. When the Ca2+ ionophore A23187 was substituted for the agonist mixture the induced expression of prothrombinase activity was essentially the same for the patient and control groups. It is suggested that the defect in prothrombinase expression seen with ET platelets may reside in either membrane signal transduction processes concerned with Ca2+ mobilization or in Ca2+ sensitive cytoskeletal control of membrane phospholipid topography.

Adult↗
PubMed1990

Platelet prothrombinase in health and disease.

Platelets play a central role in haemostasis. Not only are they involved in aggregatory and agglutination responses but they are also implicated in the clotting system. The conversion of prothrombin to thrombin, in the presence of coagulation factors Va, Xa and calcium ions, is termed prothrombinase activity. For optimal expression of this process a negatively charged phospholipid surface is required. Platelets can provide such an environment, by exposing negatively charged phospholipids at their external plasma membrane, by a 'flip-flop' process whereby negatively charged phospholipids, predominantly phosphatidylserine, move from the inner plasma membrane leaflet to the outer leaflet upon the activation of platelets by certain agonists. Such agonists include collagen and thrombin and the amount of prothrombinase activity expressed is well correlated with the propensity of the agonist to activate platelet calcium-dependent protease, calpain. This enzyme is then thought to act upon platelet cytoskeletal components, thus breaking the restraining action of the cytoskeleton upon the platelet plasma membrane and facilitating 'flip-flop'. The platelet plasma membrane is therefore a dynamic surface capable of catalytic functions in coagulation systems. Recent research has high-lighted abnormalities in platelet prothrombinase expression in certain disease states. These include Bernard-Soulier syndrome, essential thrombocythaemia and conditions where the lupus anticoagulant may be present.

Blood Platelet Disorders↗
PubMed1989

Electrokinetic, analytical and functional heterogeneity of circulating human platelets: separation of subpopulations by continuous flow electrophoresis after taxol stabilization.

A continuous flow electrophoresis procedure has been developed to study platelet subpopulation heterogeneity with separations based upon surface electrical charge differences. Taxol at low concentrations has been used to transiently stabilize the cells during the separations. At a concentration of 10(-5) M taxol has no effect upon a wide range of physical, analytical and enzymatic properties and does not compromise agonist-induced activation responses (aggregation and secretion). A typical normal platelet subpopulation profile extends over 15-20 fractions with mobilities from -0.97 to -0.78 microns per s per volt per cm. Platelet size (resistive particle counter volumes) differed significantly across the profile, the most electronegative cells being the larger, and the least electronegative the smaller platelets. Total platelet sialic acid content and surface neuraminidase-labile sialic acid correlated positively with electronegativity, but the surface -SH group status had an inverse relationship with the least electronegative smaller platelets, having twice as many surface DTNB-titratable - SH groups as the most electrophoretically mobile and larger cells. Normalisation of analytical and enzymatic data to cell volumes revealed that the smaller less electronegative platelets were substantially richer in all constituents and properties than the larger more electronegative platelets. These smaller cells showed higher activities for lysosomal enzymes, and their functions (capacity to transport 5-hydroxytryptamine and adenosine across the plasma membrane and responsiveness to thrombin expressed by synthesis of thromboxane B2 (TXB2) or release of 5HT) were greater than the larger more electronegative cells. No significant differences were observed, however, in the subpopulations by optical aggregometry using six different agonists each at three different concentrations. This free flow electrophoresis separation of platelets, which can be carried out on a preparative scale, may have some advantages over the conventional density gradient separations of subpopulations for investigating clinical states affecting thrombopoietic regulation or platelet losses from the circulation due to vessel wall disease, prosthetic implants or during extracorporeal circuitry.

Alkaloids↗
PubMed1988

Platelet surface charge heterogeneity: characterization of human platelet subpopulations separated by high voltage continuous flow electrophoresis.

Washed formol-fixed normal human platelets have been separated into surface charge-dependent subpopulations using high voltage continuous flow electrophoresis. The procedure is highly reproducible and the heterogeneity profile extends over 20-25 fraction tubes on the anodal side of the entry port to the separation chamber. Fractions have been subdivided into subpopulation pools A, B and C which have mean mobilities by analytical cytopherometry extending over the range 0.81-0.91 micron/s/V/cm from the least (C) to the most (A) electronegative cells. Coulter volume differences across the profile from 5.0 to 12.8 fl correlated well with electrophoretic mobilities whereas buoyant density appeared to be an independent parameter. Analysis of surface neuraminidase-labile sialic acid of the platelets in pools A and C correlated well with differences in electrophoretic mobility, whereas a similar relationship for the alkaline phosphatase-labile phosphate moieties (also believed to be contributory to cell surface electrokinetic properties) could not be established even though in both cases the profiles of the enzyme-treated platelets showed significant shifts towards the cathode when compared with untreated cells. Titration of surface DTNB-reactive sulphydryl (-SH) groups revealed an inverse relationship between electronegativity and membrane -SH group status. This electrophoretic expression of subpopulation heterogeneity within the circulating platelet pool may have advantages in studying clinical conditions where the profiles may reflect cell surface interactions 'in vivo'.

Blood Platelets↗
PubMed1984

Comparison of the analysis of delta 9-tetrahydrocannabinol capsules by high-performance liquid chromatography and capillary gas chromatography.

The modification of a high-performance liquid chromatography (HPLC) system and the development of a capillary gas-chromatographic (GC) system for the analysis of delta 9-tetrahydrocannabinol, encapsulated in soft gelatin capsules, are described. A photodiode array detector was used to evaluate peak homogeneity after each HPLC system modification. Sesame oil was separated from the extract by Sep-Pak filtration prior to GC analysis. Quantitation by both systems had r values greater than 0.999 and R.S.D. values less than 1.0%. Simultaneous capsule assays by both methods agreed within 1%.

Capsules↗
PubMedDate not supplied

Dormont High School (Pittsburgh, Pennsylvania) blood pressure study.

A cohort of high school students examined in a school health study between 1957-63 were followed to 1977, when as adults still living in the area, 373 (71%) were reexamined. Mean age at 17-year follow-up was 34 years. The mean systolic blood pressure (SBP) at follow-up for men was 125 mm Hg, women 111 mm Hg. The boys' SBP had increased 4.0 Hg while the girls' declined 4.0 mm Hg in 17 years. The boys had gained an average of 37.2 lbs, and 1 inch, the girls 16.7 lbs, and 0.5 inch. Tracking was studied in several ways. The correlation coefficient of the SBP taken 17 years apart ws 0.44 for boys and 0.39 for girls. Current SBP was 115 mm Hg for boys with the lowest tenth of high school SBPs and 131 mm Hg for the boys in the highest tenth. Thirty-nine had hypertension, DBP greater than or equal to 90, or were on antihypertensive medication. They had had substantially higher SBP and weight in high school, and had gained more weight from high school to adult life than controls. After adjusting for high school SBP, weight gain for boys was the major determinant of subsequent high blood pressure (BP).

Adolescent↗
PubMedDate not supplied

Phosphate: an abnormal anion?

In this era of modern medicine it is understandable that medical practitioners can lose sight of the more well-established and perhaps less fashionable biochemical tests. The determination of plasma phosphate concentration, it could be argued, falls into this latter category and is the subject of this review.

Adult↗