Evidence that platelet density and volume are not related to aging

Variation in platelet size during recovery from thrombocytopenia following extracorporeal circulation

Serial platelet counts and measurements of mean platelet volume have been performed on patients who became thrombocytopenic during open heart surgery. The results show that large platelets are released from the bone marrow during the 48 hours following the operation as a primary response to an acute increase in demand. During this period there is only a gradual recovery of the platelet count. In the subsequent days there is an acceleration of platelet production and a simultaneous reduction in platelet volume. These results suggest a change in the nature of the stimulus following the initial postoperative period, indicating a close relationship between platelet size and the total platelet count. Platelet size, therefore, may not be wholly dependent upon either megakaryocytic heterogeneity or platelet age.

Increased platelet cholesterol and decreased percentage volume of platelets as a secondary risk factor for coronary artery disease

Platelet hyperactivity is likely to contribute to the progression of atherogenesis and organized thrombus formation on vascular surfaces. The purpose of this study was to examine the effect of hypercholesterolemia on the cholesterol content of platelets, on platelet responsiveness and other platelet indices using platelets from 5 groups of age-matched subjects (n = 30 each), which includes healthy controls. All groups except controls had a high plasma lipid profile. While subjects in group I had only hyperlipidemia, those in groups II and III had hyperlipidemia in conjunction with diabetes mellitus and hypertension, respectively. The fourth group consisted of patients with confirmed coronary artery disease (CAD). The parameters studied include packed cell volume of platelets (platelet crit), platelet distribution width (PDW), platelet cholesterol and platelet aggregation in response to adenosine diphosphate and collagen. All the patient groups showed increased platelet aggregation (p < 0.05) and low platelet crit compared with controls (p < 0.05). In addition, platelet cholesterol was increased in patients with coronary disease, hyperlipidemia and diabetes mellitus (p < 0.05) but not in patients with hypertension (p > 0.05); PDW was high only in CAD (p < 0.05). A higher PDW indicated a prothrombotic tendency in CAD patients. Our data suggest that hyperlipidemia increases the lipid content in platelets and enhances their reactivity. Hyperactive platelets with increased platelet cholesterol may contribute to accelerated atherogenesis associated with CAD.

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.

Recovery of cyclooxygenase activity after aspirin in populations of platelets separated on stractan density gradients

Human platelets obtained before and at intervals up to one week following the ingestion of 650 mg acetylsalicylic acid (ASA) were subjected to fractionation on discontinuous gradients of stractan. Platelets were recovered from the density gradients and incubated with arachidonate. Thromboxane synthesis was estimated by radioimmunoassay (RIA). There were no differences in cyclooxygenase activity among the platelet fractions prior to ASA ingestion. ASA inhibited synthesis of thromboxane B2 (TXB2) by 98% in all subfractions. Twenty-four hours after ASA ingestion the total platelet population exhibited 10% of the control cyclooxygenase activity suggesting that new platelets emerging from the bone marrow within 24 hours of an ASA dose have functional cyclooxygenase enzymes. The pattern of return of TXB2 synthesis differed markedly among the platelet fractions, indicating differences in the distribution of new platelets among these fractions. New platelets with functional cyclooxygenase enzyme were twice as concentrated in the less dense fractions as in the most dense fraction. By 72 hours up to 75% of the platelets in the less dense fractions synthesized thromboxanes, while only 27% of platelets in the most dense fraction were active. Newly formed platelets may increase in density as they age or platelets of low density have a more rapid turnover than platelets of high density.

Platelet density analysis: a tool for the detection of acquired storage pool disease in man

This study was designed to evaluate the usefulness of platelet density analysis in the detection of acquired storage pool defects in human patients. Two groups of patients were investigated: 19 subjects affected with a myeloproliferative disorder (group I) where abnormal platelets are released from the megakaryocytes and 11 patients hospitalized in an intensive care unit (Group II) where normal platelets are injured in the circulation. Platelet density distribution after isopycnic centrifugation on a discontinuous stractan density gradient, dense granule markers (serotonin, ATP and ADP) and alpha granule markers (intraplatelet beta-thromboglobulin and platelet factor 4) were simultaneously determined. An increased proportion of the percentage of light platelets was observed in 16 patients of group I and nine of group II; an increased ATP/ADP ratio was observed in 12 patients of group I and 10 of group II. Both the tests were abnormal in 11 patients of group I and nine of group II. In group I, the level of serotonin was low and was related to the percentage of light platelets. The alpha granule specific proteins were normal in the two groups. These results indicate that platelet density analysis may serve as a screening test to detect exhausted platelets in human diseases.

Estimation of platelet size by measurement of intracellular water space using an oil technique

The intracellular water space of human platelets has been measured after equilibration with tritiated water and then separating these cells by centrifugation through phthalate oil of density 1.042. The mean intracellular water space of platelets in citrated plasma was 0.52 +/- 0.09 microliter/10(8) cells for 19 normal subjects. The gravimetric water content of platelets was 784 +/- 4 mg water/g cells. From these values the mean platelet volume was calculated to be 6.2 fl which agrees closely with values based on Coulter size distribution and thrombocytocrit. Gel filtration alters platelets such that a mean 19% of the platelets could not be centrifuged through phthalate oils of density 1.031 or 1.042. The measurement of tritiated water space of platelets centrifuged from their own plasma through oil provides a simple and reliable estimate of the mean platelet size.

Measurement of the density of human platelets and its relationship to volume

New methods are described for platelet isolation and buoyant density determination using low-speed centrifugation in continuous density gradients of Percoll. The conditions used do not induce loss of granule or cytoplasmic markers and enable reproducible platelet frequency distributions to be obtained in linear density gradients. Such frequency distributions are normal with a mode of 1.0645 +/- 0.0015 g cm-3 (mean +/- SD, n=20). Platelets fixed in 0.1% glutaraldehyde show a modal density of 1.0712 +/- 0.0005 g cm-3. Content of protein, lactate dehydrogenase, beta-thromboglobulin and 3H-serotonin correlate closely with platelet numbers throughout the density distribution. The frequency distribution of platelet volume between 2.2 and 21 fl fits a log normal model and cell volume in density subfractions from the most dense to the least dense also approximate log normality. There is a positive correlation between mean platelet volume and buoyant density with a small increment between the least and the most dense extremes. Platelet subfractions separated by volume using a FACS II cell sorter differ substantially from each other in cell volume but the difference in mean density of four different volume fractions in negligible. In discontinuous density gradients of Stractan factors other than platelet density must influence the separation of platelets, as rebanding of platelets from interfaces shows a wide variation in buoyant density when analysed in continuous gradients. It is concluded that analysis of platelet buoyant density in continuous Percoll gradients supports the view that platelet density, like platelet volume, is determined primarily during thrombocytopoiesis and that volume and density are largely independent elements of platelet heterogeneity.

Serotonin uptake and storage in human platelet density subpopulations

Serotonin uptake and storage were studied in human platelet density subpopulations which were isolated after isopycnic centrifugation on a discontinuous iso-osmolar stractan gradient. Kinetic parameters of the serotonin uptake were calculated (Km, Vi max) and the granular storage capacity was determined by comparing the total amount taken up in the presence or absence of reserpine, a specific inhibitor of the uptake at the granular level. Mean platelet volume and the number of mepacrine-labelled dense bodies were also determined. The results show that the active metabolic process of serotonin uptake is identical whatever the platelet subpopulation but the storage capacity is greater in the densest fraction which contains more dense bodies than the lightest one. Thus active serotonin uptake appears as another well-defined platelet metabolic process which is independent of platelet density; this argues against the conception that light platelets could be old platelets with reduced functional capacities.

Theoretical requirements for the density separation of platelets with comparison of continuous and discontinuous gradients

In continuous density gradients platelets will approach their equilibrium position with exponential deceleration. The time taken to reach an acceptable approximation to equilibrium will depend upon platelet radius, density and medium viscosity. If centrifugation is stopped before equilibrium has been achieved then platelet "subpopulations" produced will not be density dependent. Discontinuous gradients take longer to reach equilibrium. Separation of platelets by density must conform to theoretical physical criteria.

Platelet production time, uricemia, and some hemostasis tests in pre-eclampsia

In order to choose the best adapted test for pre-eclampsia monitoring, platelet production time (PPT) was measured simultaneously with uricemia, factor VIII complex, beta-thrombogobulin, and other tests of platelet activation including platelet volume, density and platelet very dense body content. In the pre-eclamptic group (11 patients). In the PPT was significantly reduced in comparison with normal pregnancies (6 patients). In the pre-eclamptic group, there was good and significant correlation between PPT and the VIIIrAg/VIIIc ration (r = 0.87) and between PPT and uricemia (r = 0.79). The correlations between PPT and the other tests are poor and non-significant. Thus, for clinical purposes, the VIIIrAg/VIIIc ratio and uricemia are convenient parameters, and give very reliable information on the severity of the consumption coagulopathy which characterizes pre-eclamptic pregnancies.

Platelet volume, density and 5 HT organelles (mepacrine test) in acute leukaemia

Qualitative platelet parameters (volume, 5 hydroxy-tryptamine (5 HT) organelles studied by the mepacrine test, and density) were evaluated in 31 patients with acute leukaemia: 11 myelomonocytic (AML), 8 lymphoblastic (ALL), 12 granulocytic (AGL). Macrothrombocytosis was observed in most of the cases of AML, was rare in AGL and was never found in ALL. The 5 HT organelles/volume ratio was normal in AGL and ALL but was significantly decreased in AML. In contrast, platelet density distribution was always abnormal whatever the platelet volume and 5 HT organelle concentration. Thus, using simple new methods, convenient even in cases of thrombocytopenia, we demonstrate that qualitative platelet abnormalities are a constant feature in acue leukaemia and that they are more severe in AML.