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Biomedical subjects

E F Grabowski

Publications and source records attributed to E F Grabowski.

At least 37 records · Page 2Linked to original sources
PubMed1991

Anticoagulant effects of nonionic versus ionic contrast media in angiography syringes.

To determine whether nonionic contrast media present a clotting hazard when plastic or glass injection syringes are contaminated with aspirated blood, we evaluated two nonionic (iohexol and iopamidol) and two ionic (ioxaglate and diatrizoate) contrast agents. We used a blood:contrast media ratio of 2 mL:5 mL and ten normal donors, each studied at 10, 20, 30, and 60 minutes, a parallel study of clotting and fibrinopeptide A (FPA) generation in plastic tubes, and life table analysis to estimate more accurately donor-based early clotting probabilities. While ionic contrast media are stronger anticoagulants, both nonionic and ionic media retard clotting in plastic tubes, and clotting in plastic and glass angiography syringes in comparison to saline controls. A clotting probability of 1% for nonionic agents in plastic syringes was not reached until a time (mean +/- SD) of 21.5 +/- 3.2 minutes. This contrasts with a time of 8.7 +/- 2.5 minutes for saline control. With plastic syringes, no clotting at all was observed at 10 and 20 minutes with either class of agents. Neither class of agents hastened the generation of FPA. We found no evidence, therefore, that nonionic agents either cause clots or are procoagulant.

Angiography↗
PubMed1990

A hematologist's view of contrast media, clotting in angiography syringes and thrombosis during coronary angiography.

While ionic contrast media (CM) are stronger anticoagulants and antiplatelet agents, both nonionic and ionic CM retard clotting, fibrinopeptide A generation and platelet aggregation (at least by Born-O'Brien aggregometry). Thus, nonionic CM do not cause clots and thrombi. Rather, the driving force for clot or thrombus formation, when it occurs, is blood contact with and activation by the foreign surface of a syringe or catheter itself. A marked enhancement of clotting by glass syringes in comparison to plastic ones supports this view. Blood in any syringe or catheter, therefore, will clot more slowly in the presence of nonionic or ionic CM, the inhibitory effects of the latter being more profound. With respect to models of thrombosis at sites of vascular injury or stenosis, the antithrombotic effects of CM may either be transient owing to the dynamic nature of blood flow (local endothelial cell denudation model), or as in the case of ionic CM, actually to enhance local platelet aggregation (stenosis model). In these situations, preservation of the antithrombotic functions of endothelium with nonionic CM may be quite critical.

Angiography↗
PubMed1990

Platelet aggregation in flowing blood at a site of injury to an endothelial cell monolayer: quantitation and real-time imaging with the TAB monoclonal antibody.

Epifluorescence videomicroscopy permits real-time imaging of platelet adhesion/aggregation to a defined microinjury of a monolayer of endothelial cells exposed to flowing blood. The fluorescent label is the TAB murine monoclonal antibody directed against human platelet GP IIB, together with a fluorescein-conjugated goat F(ab')2 against murine immunoglobulin. The combination assures specificity for platelet membranes, yet leaves platelet function intact. TAB is first added to gently mixed, citrated human blood; the second antibody is added 1 hour after the first, mixing continuing for a second hour. Bovine aortic endothelial cell monolayers (ECMs), grown on rectangular cover glasses precoated with microfibrillar collagen, comprise one wall of a flow chamber mounted on a vertical microscope stage. A loop of 6-0 sterile suture is drawn across the ECM in order to create microinjuries of width 70 +/- 15 microns (mean +/- SD) oriented in a direction transverse to flow. Platelet adhesion/aggregation is virtually absent on intact and confluent regions of the monolayer. On micro-injury sites and at shear rates of 60 to 1,080 sec-1, however, computer-enhanced images obtained by means of videomicroscopy show arrival and adherence of single platelets resulting in the formation of platelet aggregates elongated in the flow direction. When the monolayers are pretreated with 1.0 mmol/L lysine acetylsalicylate, the mean aggregate thickness increases (2P less than .05) to 260 +/- 58% (mean +/- SE, N = 6) of control, aggregates are regularly shed downstream, and the surface area of the injury site covered by platelets is augmented (2P less than .05) from 14.8 +/- 3.9% to 49.2 +/- 4.7% (mean +/- SE, N = 6). Donor ingestion of aspirin, on the other hand, leads to an increase (2P less than .01) in percent surface coverage to 42.7 +/- 8.5 without a concomitant increase in mean aggregate thickness. In parallel with the above, outflow levels of serum thromboxane and prostacyclin are measured by radioimmunoassays (RIAs) for thromboxane B2 and 6-Keto-PGF1 alpha, respectively. Thromboxane B2 is increased (2P less than .01) by monolayer pretreatment with lysine acetylsalicylate from 5.08 +/- 1.47 to 9.35 +/- 2.42, but decreased (2P less than .05) after oral aspirin to 1.21 +/- 0.38 ng/mL (mean +/- SE, N = 6). Levels of 6-Keto-PGF1 alpha were reduced (2P less than .05) by monolayer pretreatment from 0.48 +/- 0.046 to 0.36 +/- 0.016 ng/mL. Platelet adhesion/aggregation at a site of injury to an endothelial cell monolayer, therefore, can be imaged in flowing blood in real time using a monoclonal antibody approach.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Effects of contrast media on endothelial cell monolayers under controlled flow conditions.

To compare the biocompatibility of nonionic and ionic intravascular contrast media in a more physiologic in vitro system, key aspects of blood flow through a microvessel were simulated. Toward this end, monolayers of endothelial cells placed in a specially designed flow chamber, real-time imaging of the monolayers by brightfield and phase videomicroscopy, and real-time imaging and computer-aided quantitation at normal hematocrit levels of platelet adhesion/aggregation to sites of monolayer injury by means of epifluorescence videomicroscopy were used. At a concentration in culture medium of 20% by volume, it was found that monolayer morphology was least altered by iohexol when compared with diatrizoate and ioxaglate; monolayer production of prostacyclin was enhanced (p less than 0.001) by ioxaglate compared with saline controls; and at a concentration in citrated blood of 20% by non-red-cell volume, platelet adhesion/aggregation was reduced by all 3 contrast agents in the order diatrizoate greater than ioxaglate greater than iohexol.

Adult↗
PubMed1988

Effects of contrast media on erythrocyte and platelet interactions with endothelial cell monolayers exposed to flowing blood.

Although there have been reports of clot formation in angiographic syringes containing nonionic contrast agents, these clots are now believed to be aggregates of red cells that form in the low ionic strength, low pH, zero shear rate environment of contrast media syringes. In an in vitro controlled flow system that stimulates blood flow through a microvessel, we found that large (100 microns or more) red cell aggregates are not seen with any of the media tested (iohexol, sodium methylglucamine diatrizoate, and ioxaglate); aggregates that form under shear conditions are rouleaux. The degree of rouleau formation, compared with saline controls, is greatest with ioxaglate, least with diatrizoate, and intermediate with iohexol. Platelet adhesion/aggregation at a site of injury to vascular endothelium is not significantly affected by iohexol. Rouleaux formation, a potential determinant of local levels of thrombin and other platelet-activating substances, is shown to occur in the lee of mural platelet thrombi.

Blood Circulation↗
PubMed1987

Endothelial cell modulation of primary platelet hemostasis.

Rheology has profound effects on the rate, structure, and modulation of primary hemostasis. Many of these effects can be studied via real-time, epifluorescence videomicroscopy of platelet adhesion-aggregation to a site of injury to an endothelial cell monolayer exposed to flowing blood. In particular, with the model described, endothelial cells can be shown to be a significant modulator of platelet function at an injury site.

Blood Platelets↗
PubMed1987

Intraocular and extraocular retinoblastoma.

Retinoblastoma, the most common primary ocular malignancy of childhood, is a tumor in which the pediatrician and pediatric oncologist can now play a much more significant role in therapy. Developments in molecular biology have now made carrier testing and prenatal diagnosis feasible. In the near future, these developments should greatly augment the pediatrician's and pediatric oncologist's ability to offer accurate and appropriate genetic counseling for affected families. A practical staging system for extraocular retinoblastoma together with stage-related effective chemotherapy and radiation therapy was presented in this chapter. These modalities now make possible long-term survival for the majority of the 1 out of 8 children with retinoblastoma who would otherwise die from metastatic disease. Finally, 40 per cent of all children with retinoblastoma (those with the germinal mutation) are at lifelong risk for second, nonocular malignancies. The recognition that more than half of these children will actually develop second tumors by the fourth decade of life makes vigilant follow-up care for these patients a necessity.

Bone Neoplasms↗
PubMed1987

Sickle erythrocytes adhere to endothelial cell monolayers (ECM's) exposed to flowing blood.

In order to determine whether the phenomenon of sickle erythrocyte adherence to cultured vascular endothelium exists under conditions of blood flow, we exposed monolayers of bovine aortic endothelial cells to flowing sickle cell blood under controlled conditions in a specially designed flow chamber. Individual red cells were imaged by means of epifluorescent videomicroscopy, five percent of the total number of red cells in an aliquot of blood having been labelled by the passive uptake of sodium fluorescein isothiocyanate. At a shear rate of 270 sec-1 at the blood-monolayer interface, red cells from sickle cell blood frequently adhered to the monolayer for periods ranging from 100's of m sec to greater than 30 sec. With adhesion defined as the average number of adherent red cells during the sixth minute of blood flow (corrected upward to account for unlabelled erythrocytes), adhesion with sickle cell blood was of the order of 10(4) erythrocytes/cm2 ECM and exceeded (p less than 0.001) that for normal blood by a factor of 5.6. Further studies utilizing in situ displacement of blood with culture medium followed by brightfield microscopy indicate that the adherent cells were predominantly discocytes having single points of tethering to unknown sites on the monolayer. Adhesion of sickle cell erythrocytes to endothelium, therefore, is a very real phenomenon under physiologic conditions of blood flow; this phenomenon may contribute to the pathophysiology of vaso-occlusive events seen in sickle cell disease.

Anemia, Sickle Cell↗
PubMed1986

Prostacyclin production by internal mammary artery as a factor in coronary artery bypass grafts.

Long-term patency of coronary artery bypass grafts (CABG) with internal mammary artery (IMA) is better than with saphenous vein (SV) grafts. To determine if vascular prostacyclin (PGI2) produced by IMA might contribute to the improved outcome, we compared PGI2 generated by IMA and SV fragments from 26 patients undergoing CABG and tested the effect of preoperative, long-term ingestion of of aspirin. Fresh tissues were incubated in buffer +/- 25 mumol/L of sodium arachidonate at 37 degrees C for 5 minutes to stimulate PGI2 production, measured by radioimmunoassay of its major hydrolytic product, 6-keto-PGF1 alpha. Results were expressed in picograms of 6-keto-PGF1 alpha per milligram tissue wet weight for total PGI2 production by vascular segments and picograms per cm2 surface area for endothelial PGI2 production. Endothelial PGI2 production was compared for IMA and SV in template-stirring chambers that exposed only the luminal surface of the vessel, excluding underlying smooth muscle. Endothelial PGI2 production by IMA was significantly higher than production by SV under both basal (mechanical stimulation only 1436 +/- 224 versus 842 +/- 227 pg/cm2, mean +/- SEM, p greater than 0.05) and stimulated (25 mumol/L sodium arachidonate: 3343 +/- 347 versus 2032 +/- 465 pg/cm2, p less than 0.025) conditions in patients not receiving aspirin. For patients receiving aspirin, endothelial PGI2 production by IMA was significantly higher than production by SV in stimulated conditions (1382 +/- 526 versus 683 +/- 124 pg/cm2, p less than 0.05). Histologic examination of the tissue segments revealed intact endothelium after incubation in both IMA and SV. Thus a high capacity for PGI2 synthesis and diminished inhibition of PGI2 after aspirin were demonstrated for IMA compared with SV tissue and may be a factor in the improved patency of IMA grafts.

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Prostacyclin production in vitro by rabbit aortic endothelium: correction for unstirred diffusional layers.

The degree of mixing in fluid layers immediately adjacent to the endothelial surface is a major variable in assessment of prostacyclin (PGI2) production by cultured endothelial cells or intact vessel endothelium in vitro. Lack of adequate mixing should lead to underestimation of true production because PGI2 immediately adjacent to endothelium would be only poorly sampled upon buffer collection. Thoracic aortas from 38 New Zealand white rabbits were therefore excised, opened longitudinally, and mounted endothelial side uppermost in a buffer-filled chamber which excluded cut tissue edges from study. Production of PGI2 under unstirred and magnetically stirred conditions was measured by radioimmunoassay (RIA) for 6-keto-PGF1 alpha. For animals pretreated with the combination of papaverine and heparin (see below), unstimulated and arachidonate-stimulated 6-keto-PGF1 alpha increased with stirring rate toward limits of 2.9 and 28.5 ng/cm2/min, respectively. Unstimulated and stimulated 6-keto PGF1 alpha measured at 650 rpm, for example, were greater than their values at 0 rpm by factors of 3.5 (2P less than .01) and 3.7 (2P less than .001), respectively. The process of vessel excision, however, produces another variable: degree of injury to endothelium caused by such factors as secondary vessel contraction and thrombin generation. Vessel contraction and thrombin generation can be minimized, respectively, by the use of a smooth muscle relaxant and heparin administered prior to killing of the animals. The rabbits were, therefore, grouped according to intravenous (IV) treatment, prior to killing, with saline, papaverine (4 mg/kg), heparin (200 U/kg) or the combination of papaverine and heparin (same doses). As compared with pretreatment with saline, papaverine alone, or heparin alone, pretreatment with the combination of papaverine and saline led to increases in stimulated 6-keto-PGF1 alpha of 1.6- to 2.8-fold. By transmission electron microscopy, endothelium from animals pretreated with saline showed ultrastructural changes, including disruption of cytoplasm, separation without detachment of most endothelial cells from subendothelium, and focal areas of denudation. In contrast, ultrastructural integrity of endothelium was preserved in aortas of animals pretreated with combined papaverine and heparin. These results support the hypothesis that unstirred diffusional layers lead, in vitro, to underestimation of PGI2 production, especially when vessels are protected from excisional injury.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Prostacyclin production by cultured endothelial cell monolayers exposed to step increases in shear stress.

While fluid shear stress is an important cardiovascular factor in vivo, it has generally been ignored in in vitro assays of endothelial cell function. We quantified the influence of shear stress on the production of prostacyclin by confluent monolayers of bovine aortic endothelial cells placed in a lucite flow chamber and exposed to flowing culture medium at constant shear stress at 37 degrees C and pH 7.4. Continuous inverted-phase microscopy (x 300) of the monolayers showed no significant contraction or detachment of cells under these conditions. Step increases in shear stress from zero to 14 dyne/cm2 caused rapid rises in prostacyclin production, from a baseline (n = 4) of 0.17 +/- 0.062 ng/cm2.min (mean +/- SEM) to peak values within 2 minutes, followed by a decline over several minutes. Peak prostacyclin production increased (p less than 0.005) with shear stress, from 0.60 +/- 0.13 ng/cm2.min at 0.9 dyne/cm2 (n = 14) to 2.33 +/- 0.67 ng/cm2.min at 14 dyne/cm2 (n = 10). The time integral of production or total production, however, did not significantly change with shear stress at least for shear stresses above 0.9 dyne/cm2. Once stressed, cell monolayers produced additional prostacyclin in response to stimulation by Na arachidonate or the calcium ionophore A23187, but not to repeat mechanical stimulation. We conclude that endothelial cells produce bursts of prostacyclin in response to suddenly imposed arterial-like shear stress, and that the peak rate, but not the time integral, of this production increases with shear stress.

Animals↗