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Biomedical subjects

M M Frojmovic

Publications and source records attributed to M M Frojmovic.

67 records · Page 4Linked to original sources
PubMed1978

Platelets from "giant platelet syndrome (BSS)" are discocytes and normal sized.

A comparison is made between the shape of human platelets obtained from nine normal donors and two BSS donors. Sizes are evaluated from a cinematographic analysis of freely rotating, unfixed, and glutaraldehyde-hardened platelets in citrated PRP and of platelets on blood smear. On blood smeae, the mean diameters of BSS platelets are 1.7 to 1.8 times larger than those of normal platelets, with a major fraction having a diameter greater than 2.5 micrometer. As for normal donors, 80% to 90% BSS platelets in PRP are in the disc form (discocyte). In addition, they are essentially indistinguishable from a normal discocyte. Echinocytes (spherical forms with pseudopods) for BSS have a main body diameter (i.e., excluding pseudopods) 1.6 times larger than normal and in addition a reduced number of pseudopods. The results demonstrate that the giant size of BSS platelets results from abnormal behavior of these platelets during the preparation of the blood smear. It is suggested that this disorder is associated with a defect in the mechanism of platelet shape change.

Adult↗
PubMed1976

Geometry of normal mammalian platelets by quantitative microscopic studies.

The shape distributions of normal and hardened human and rabbit erythrocytes and platelets were obtained for edge-on orientations of a few hundred freely rotating cells from analyses of microphotographs obtained similarly as by Ponder(1930, Q. J. Exp. Physiol. 20:29) by phase-contrast microscopy at 800 X magnification. Major average diameters (d) and thicknesses (t) were estimated for both normal and hardened cells, and were used to calculate an average geometric axis ratio, rp = t/d, which increases to unity as cells become more spherical. Our fixation procedure did not alter these shape parameters: rp was unchanged for erythrocytes, with d and t values similar to those reported by Ponder (1930); platelets had d X t = 3.6 +/- 0.7 mum X 0.9 +/- 0.3 mum and 3.1 +/- 0.4 mum X 0.6 +/- 0.3 mum, respectively, for human and rabbit cells, with rp = 0.26 and 0.20, respectively. Agreement in rp was found with data obtained by a novel rheo-optical method which allows for a direct statistical averaging for large populations (greater than 100 X 10(3) cells). Histograms and linear correlation studies were made of the above three parameters (d,t,rp), as well as volume (V), total surface area are (S), and sphericity index (S.I.) calculated for both "prolate ellipsoid" and "disc with rounded edges" models. Results indicate very high linear correlations between rp - t, rp - S. I., and d -S, with high correlations for t - V,d -V and S. Data are in agreement with the few reports in the literature determined by other methods, with the best model for platelets appearing to be an oblate spheroid.

Animals↗
PubMed1975

Blood cell structure-function studies: light transmission and attenuation coefficients of suspensions of blood cells and model particles at rest and with stirring.

The Beer-Lambert law of light transmission was found valid for suspensions of blood platelets, erythrocytes, and leukocytes, as well as similarly sized model particles (latex spheres and flat guanine crystals), for a DB-G double-bean photometer at 605 and 710 mg, and a Payton aggregometer with red filter (660 to 750 mu). Attenuation coefficients (K) showed a similar dependence on a particle "equivalent sphere" radius as data reported for a "zero-degree photometer," for particles at rest. Size distribution, degree of aggregation, state of contamination, and effects of aldehyde fixation of the cell suspensions, well as optical geometry, were related to the measured K values. Particle optical efficiencies (K) for asymmetric particles were similar whether calculated from cross-sectional areas derived from "equivalent spheres" or from geometric cross-sections accounting for orientation distributions at rest. Appropriate cell and latex models were identified for the erythrocytes (E) and platelets (P) at rest on the basis of similar K,k values. The biphasic change in K occurring with stirring of these asymmetric blood cells (E, HP) was partly explainable by the known variations of K with shear-induced particle alignment to the optic axis. No such effects were observed with spherical particles or "sphered" cells, even when polydisperse as to size an aggregates. This investigation begins to quantitate ongoing light transmission studies of blood cell shape/aggregation changes.

Animals↗
PubMedDate not supplied

The kinetics of thrombin- and SFLLRN-induced aggregation of human platelets in flow through tubes.

The kinetics of aggregation of human platelets activated by alpha-thrombin (0.17-0.35 nM) and the hexapeptide SFLLRN (2-10 microM) was studied in plasma-free washed cell suspensions undergoing Poiseuille flow at 37 degrees C using a previously described double infusion technique. Platelet-rich Tyrodes, prepared from venous blood by multiple centrifugation, and agonist were rapidly mixed in a small chamber and the suspension flowed through various lengths of 1.19 and 0.76 mm diameter polyethylene tubing at mean transit times t from 0.2 to 43 s and mean tube shear rates = 41.9, 335, and 1335 s-1. Effluent was collected in 0.5% glutaraldehyde and single cells and aggregates in the volume range 1-10(5) micron 3 counted and sized using an aperture impedance counter. The rate and extent of aggregation with thrombin increased with increasing [thrombin] and , and although characterized by a small initial lag time, exhibited a very rapid growth of aggregates to macroscopic size, >> 10(5) micron 3, at low and moderate shear rates. With SFLLRN, the initial lag times were appreciably longer, but subsequently aggregates also rapidly grew to macroscopic size. We hypothesize that the initial lag time is due to the time required for sufficient secretion and surface organization of ligands such as vWF (known to be released by the platelet) to occur, in order for cross-bridging of the GPIIb-IIIa receptors on adjacent platelets to take place. It appears that thrombin, which, at the low concentrations used, primarily activates the platelet via binding to the GPIb alpha receptor, can more rapidly facilitate secretion of the ligand than SFLLRN, which activates the cell via binding to the seven transmembrane domain receptor.

Adult↗
PubMedDate not supplied

The effects of calcium antagonism on the epicerebral circulation in early vasospasm.

We have studied the effects of the calcium antagonist verapamil on the epicerebral arteriovenous transit time and regional epicerebral circulation of dogs by direct measurement of arterial diameters, fluorescein angiography, and krypton-85 regional epicerebral blood flow analysis. A large craniectomy was performed and vasoconstriction was induced by the subarachnoid injection of human platelet-rich plasma (PRP) pretreated with 25 mu M of ADP to cause maximum aggregation. Once vasoconstriction was established, verapamil (0.1 mg/kg) was topically applied to the perforated arachnoid. The PRP-ADP produced a mean decrease in the arterial diameters of 38.2 +/- 1.6% (p less than 0.01) at 10 minutes after its injection and verapamil produced a mean dilatation of 19.5 +/- 2.5% (p less than 0.01), compared to control values. Regional epicerebral blood flow was 54.9 +/- 3.4 ml/100 g/min in the control state, 34.8 +/- 3.2 ml/100 g/min (p less than 0.01) during vasospasm, and 78.2 +/- 4.5 ml/100 g/min (p less than 0.01) after verapamil. Fluorescein angiography, after verapamil, demonstrated a mean acceleration of the arteriovenous circulation time of 4.5 +/- 0.8 seconds (p less than 0.01) compared to the spasm value. We concluded that the topical application of verapamil can dilate previously constricted cortical arteries and that this dilatation is associated with acceleration of the epicerebral transit time and increased cerebral blood flow.

Administration, Topical↗