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J Levin

Publications and source records attributed to J Levin.

At least 163 records · Page 9Linked to original sources
PubMed1989

A modified Limulus amebocyte lysate test with increased sensitivity for detection of bacterial endotoxin.

We have developed a simple modification of the chromogenic Limulus amebocyte lysate test that increases the sensitivity for the detection of bacterial endotoxins. In this assay, free paranitroaniline, cleaved from synthetic chromogenic substrates by proteases that were generated by Limulus lysate after incubation with endotoxin, was then derived. Derivation was with p-dimethylaminocinnamaldehyde in the presence of strong acid, forming a stable Schiff base end product with much greater molar absorbancy than the parent chromogen. Conditions (times and temperatures of incubations, concentrations of reagents) for the augmented chromogenic procedure were optimized. A ten-fold or greater increase in sensitivity for bacterial endotoxin was obtained with the modified assay as compared with the standard chromogenic Limulus test, with unequivocal detection of endotoxin concentrations of less than 100 pg/ml. The greater sensitivity of this modified Limulus test increases its usefulness for a wide range of research applications and clinical investigations.

Colorimetry↗
PubMed1989

The effect of partially purified thrombopoietin on guinea pig megakaryocyte ploidy in vitro.

Enriched populations of guinea pig bone marrow megakaryocytes were prepared by density gradient and velocity centrifugation and maintained in liquid cultures for 24 or 48 h. The resulting megakaryocyte preparations were of 86.1% +/- 5.5% purity. After 24 or 48 h in liquid culture, recovery of viable cells was 77% +/- 11% or 83% +/- 13%, respectively. Megakaryocyte cultures were supplemented with 100-200 micrograms/ml of either a lectin-fractionated preparation of thrombopoietin (TPO) from the plasma of thrombocytopenic rabbits or an identically prepared protein fraction from non-thrombocytopenic animals. Addition of TPO resulted in a significant increase (p less than 0.05) in both the proportion and total numbers of 32N megakaryocytes and a significant decrease (p less than 0.05) in the relative frequency of 8N megakaryocytes. In most experiments, a decrease in the total number of 8N megakaryocytes also was noted. These results indicate that partially purified TPO is able to increase the ploidy (DNA levels) of megakaryocytes in vitro.

Animals↗
PubMed1988

Intervention in detention. Psychological, ethical and professional aspects.

The psychological stressors in detention, besides being a frequent cause of distress, are also significant obstacles to effective intervention. Conditions for detention in South Africa, laid down by law, have been described as psychological torture. These legal conditions for detention conflict with the ethical principles of autonomy, non-maleficence and beneficence and by compromising ethical principles result in inadequate clinical standards. It is therefore not possible to provide an adequate mental health service for detainees. Attempts to formulate minimum standards for the psychological treatment of detainees do not address the problem that the conditions of indefinite detention are incompatible with providing mental health care services. Professional ethics are subverted by legalising unethical practice, and attempts to criminalise ethical practice should be resisted. It is important for the mental health professional to address these issues so as not to abrogate his responsibilities to himself, his patients, and his profession.

Dissent and Disputes↗
PubMed1988

Comparison of absorption measurements of DNA stain content by utilizing video and scanning image cytometers.

After staining with the Feulgen reaction, the DNA stain contents of 155 mouse bone marrow cells and 22 adjacent chicken erythrocytes were measured by absorption image cytometry by utilizing two different systems--a scanning cytometer and a video cytometer. In the scanning cytometer (M85 microdensitometer, Vickers Instruments, Malden, MA), a spot of light was scanned across the cell. In the video cytometer (TAS Plus, E. Leitz, Rockleigh, NJ), the microscope field, which may contain several nuclei, was imaged onto a Plumbicon video camera. With each system, cells were scanned, digitized into their elementary pixels, and analyzed to determine their integrated absorbance. Comparison of the DNA stain contents of the same G0/G1 bone marrow cells and chicken erythrocytes, as measured by video and scanning cytometry, showed that both techniques gave comparable results; scanning cytometry is more precise. The coefficients of variation of the measurements for the G0/G1 bone marrow cells and for the chicken erythrocytes were 5.9% and 7.0%, respectively, when measured by video cytometry at the absorption peak (584 nm), compared to 4.1% and 3.5%, respectively, for the same cells when measured by scanning cytometry off the absorption peak (615 nm). The video-based measurements were relatively lower than the scanning measurements for darkly stained cells; this suggests that glare and other optical errors which increase with stain darkness caused greater systematic errors in the video cytometer than they did in the scanning cytometer.

Animals↗
PubMed1988

Thrombocytopenia associated with repletion of iron in iron-deficiency anemia.

Two patients with iron deficiency experienced rapid decreases in their platelet levels following initiation of replacement therapy with oral ferrous sulfate or ferrous gluconate. The first patient, whose pretreatment platelet count was 168,000 per mm3, developed marked thrombocytopenia (platelet count, 21,000 per mm3) on the sixth day of iron repletion. The second patient's platelet level fell from 725,000 to 105,000 per mm3 on the tenth day of therapy. In both instances, platelet levels gradually returned to normal levels. The data suggest that the administration of oral iron resulted in an acute reduction in platelet production. The mechanism(s), prevalence, and clinical significance of thrombocytopenia following iron repletion in patients with iron deficiency anemia remain unknown.

Adolescent↗
PubMed1988

Plasma cortisol and corticosteroid-binding globulin in essential hypertension.

Plasma concentration of cortisol, total CBG-binding capacity, and blood pressure were measured in control subjects (n = 171), patients with essential hypertension (EH; n = 210) and their first-degree normotensive (NR; n = 84) or hypertensive (HR; n = 66) relatives. Mean (+/- SD) plasma cortisol was significantly (p less than 0.001) decreased in EH (10.1 +/- 4.3 g/dl) patients and HR (11.7 +/- 4.1). Plasma cortisol in NR did not differ from control values (14.3 +/- 4.5) but the distribution of individual values covered the entire control-EH (14.6 +/- 5.5) range. Mean (+/- SD) CBG-binding capacity was significantly (p less than 0.001) lower in EH (14.4 +/- 3.0), NR (17.5 +/- 2), HR (17.6 +/- 2.2) as compared to controls (20.9 +/- 2.1), indicating that the decline in EH and in most relatives was mainly in plasma CBG-bound cortisol. The plasma CBG-binding capacity for cortisol was significantly negatively correlated with mean arterial pressure (MAP) in both controls (p less than 0.001) and NR (p less than 0.01) but not in either HR (r = 0.02) or never-treated EH patients. Total afternoon plasma aldosterone was higher (p less than 0.01 vs. controls) in 93 untreated EH patients (11.2 +/- 4.8 ng/dl) than in either 161 first-degree relatives (8.1 +/- 3.4 ng/dl) or 117 controls (7.6 +/- 3.5 ng/dl). The respective aldosterone-binding globulin (ABG) binding capacities for aldosterone were 21.2 +/- 6.7, 20.1 +/- 9.3 and 9.8 +/- 4.0%. In all these subjects taken together, there was a positive correlation between MAP and ABG-binding capacity (r = 51; p less than 0.001). The association of reduced plasma cortisol and decreased CBG binding capacity in EH may be closely related to altered steroid metabolism, which may be partly explained by an abnormality resembling a relative deficiency in adrenal 17 alpha- and 11 beta-hydroxylation. In some EH patients, hypertension may be the result of the ineffectiveness of plasma cortisol in preventing slightly elevated endogenous ACTH levels leading to an increase in ACTH-sensitive steroids.

Adolescent↗
PubMed1988

Use of arabinogalactan to obtain washed murine platelets free of contaminating plasma proteins and appropriate for studies of function, morphology, and thrombopoiesis.

A simplified procedure for preparing washed murine platelets, free of contaminating plasma proteins, has been developed. Platelet-rich plasma (PRP) was prepared from diluted whole blood from C57BL/6N mice by two centrifugations at 100 x g for 12 minutes. Platelets were concentrated and then washed by centrifugation through isosmolar 10% arabinogalactan (Stractan). Platelet recovery was 85% +/- 6% (1 SD) (n = 10) from whole blood to PRP and 86% +/- 4% (1 SD) (n = 6) from PRP to Stractan-washed platelets. Overall recovery of platelets with this technique was 73% +/- 10% (1 SD). Contamination of platelets with plasma proteins could not be detected with use of unlabeled platelets that had been incubated with radiolabeled plasma proteins followed by washing with Stractan. The Stractan-washed platelets were assessed for function by using aggregometry. The response of Stractan-washed platelets to collagen and thrombin was identical to that of unwashed platelets. Stractan-washed platelets did not respond to 20 mumol/L adenosine diphosphate unless supplemented with 12% platelet-free plasma. The morphology of the Stractan-washed platelets indicated that degranulation had not occurred. With use of antibodies directed against the alpha granule membrane protein GMP-140 or fibrinogen, no evidence of secretion or plasma protein contamination was observed. The use of this method resulted in an improved assay for the rate of thrombopoiesis, based on detection of radioactive proteins in newly synthesized platelets, by eliminating contamination by radioactive plasma proteins. Our results indicate that this procedure is a convenient method for the separation of platelets from platelet-rich plasma, free of plasma proteins, which are suitable for bioassays, functional studies, and morphologic investigations.

Animals↗
PubMed1988

Antidepressant binding to the porcine and human platelet serotonin transporters.

The ability of four antidepressant drugs, imipramine, alaproclate, norzimelidine, and fluvoxamine, to inhibit serotonin transport into platelet plasma membrane vesicles was tested over a range of external Na+ concentrations. Imipramine affinity, as we previously reported [J. Biol. Chem. 258:6115-6119 (1983)] increases sigmoidally with Na+. When measured by inhibition of serotonin transport, the affinity for alaproclate and norzimelidine is much less sensitive to Na+ and fluvoxamine actually inhibits more avidly at lower Na+. All of the drugs competitively inhibit serotonin transport. Moreover, alaproclate, norzimelidine, and fluvoxamine all competitively displace [3H]imipramine from platelet plasma membranes. The Ki for fluvoxamine inhibition of transport is 16-fold higher than its Ki for inhibition of imipramine binding. In contrast, alaproclate inhibits transport at concentrations lower than those required to block imipramine binding. In the case of fluvoxamine, and possibly also alaproclate, these differences are not due to separate sites mediating substrate and imipramine binding but rather to differences in the nature of binding and transport measurements. The results suggest that these antidepressant drugs and serotonin all bind to the same site, or to overlapping sites on the serotonin transporter, or to sites on the transporter whose occupation is mutually exclusive with substrate site occupation. The observation that binding of each ligand reacts differently to changes in Na+ suggests that distinct subsites are involved in each case. As reported previously by Wennogle and Myerson [Eur. J. Pharmacol. 86:303-307 (1983)] serotonin decreases the rate of imipramine dissociation from human platelet membranes. This effect is not observed in porcine platelets, is not Na+ dependent, and requires serotonin concentrations over 100 times the Km for transport. It is likely, therefore, to result from serotonin binding to a site distinct from the transport active site.

Animals↗
PubMed1988

The horseshoe crab: a model for gram-negative sepsis in marine organisms and humans.

The roles of the amebocyte in providing hemostasis and controlling infection, and its reaction to endotoxin, suggest that the response of platelets and the blood coagulation system in various mammals to gram-negative infection or endotoxin is an evolutionary remnant of this ancient mechanism. In humans, this mechanism occasionally subverts its presumed protective function by overresponding in a manner that results in pathophysiologic thrombosis or hemorrhage. (In this regard, it is interesting that human platelets are much more resistant to the effects of bacterial endotoxins than are other species.) Similarly, the rudimentary ability of mammalian platelets to phagocytose particles and kill bacteria may be another remnant of functions that are more important in amebocytes (or the thrombocytes of other invertebrates). Thus, these two cells, one from an ancient invertebrate and the other from mammals, have remarkably similar characteristics, although the relative importance of their various functions has changed as evolution has taken place. Nevertheless, after at least 400,000,000 years of evolution, coagulation and anti-bacterial mechanisms remain at least partially linked.

Animals↗
PubMed1987

Apparent effect of catalase on airway edema in guinea pigs. Role of endotoxin contamination.

The airway edema that develops in guinea pigs after exposure to toluene diisocyanate (TDI) requires the presence of polymorphonuclear leukocytes (PMN). To determine whether this airway edema is mediated by the release of hydrogen peroxide from PMN, we treated animals intravenously with catalase bound to polyethylene glycol and examined the extravasation of Evans blue dye into the tracheal wall after exposure to air or 3 ppm TDI for 1 h. Catalase (25,000, 100,000, and 300,000 IU/kg) caused a dose-dependent inhibition of the TDI-induced increase in dye extravasation. However, treatment with catalase, inactivated at the peroxide binding site with 3-aminotriazole, inhibited dye extravasation after exposure to TDI as effectively as the equimolar 100,000 IU/kg dose of active catalase. Injection of polyethylene glycol alone was without effect. Dose-dependent decreases in extravascular migration of PMN and in circulating PMN also were noted after catalase treatment. These results suggest that the catalase preparations used in these studies inhibited the PMN-dependent airway edema by an effect other than hydrogen peroxide scavenging. Examination of this and other commercially available catalase preparations revealed trace concentrations of endotoxin at levels that could be responsible for the observed effects on PMN function. Treatment of animals with doses of Escherichia coli endotoxin similar to those inadvertantly administered to the catalase-treated groups (0.1 ng/kg to 100 ng/kg, intravenously) inhibited TDI-induced extravasation of Evans blue dye in a dose-dependent manner. These results suggest that contaminating endotoxin may contribute to some of the protective effects of preparations of catalase observed in previous studies of vascular permeability.

Animals↗
PubMed1987

Characterization of soluble cyclic AMP phosphodiesterases and partial purification of a major form in human leiomyoma of the uterus.

Human leiomyoma of the uterus contained seven forms of cyclic AMP phosphodiesterase in the crude cytosol as revealed by a specific activity stain on non-denaturing polyacrylamide gel electrophoresis. The enzymes from human myometrium and normal uterus showed an identical activity pattern. Ferguson plot analysis showed four different molecular weight species of Mr 229,000 +/- 4,000, 186,000 +/- 4,000, 174,000 +/- 4,000 and 162,000 +/- 4,000. The Mr 174,000 species comprised four differently charged forms. Sucrose density gradient centrifugation of the crude cytosol revealed the presence of three molecular weight species sedimenting at 11.8S, 8.1S and 3.6S. The Michaelis constant (Km) for the band 1 form which displayed linear kinetics was 5 microM and the band 2 form which produced non-linear kinetics had Km values of 5.8 and 37 microM.

3',5'-Cyclic-AMP Phosphodiesterases↗