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J Levin

Publications and source records attributed to J Levin.

At least 145 records · Page 8Linked to original sources
PubMed1990

Splenic thrombopoiesis after bone marrow ablation with radiostrontium: a murine model.

Murine platelet production is normally supported by high-ploidy bone marrow megakaryocytes without significant contribution from splenic megakaryocytes with predominantly low-ploidy levels. We produced sustained bone marrow ablation using radiostrontium, and examined the processes by which splenic platelet production is initiated and maintained in the absence of bone marrow function. Bone marrow hematopoiesis, measured by total nucleated cell number and viability, megakaryocyte colony-forming cells, and granulocyte-macrophage colony-forming cells, was rapidly ablated in mice by using yttrium 90-free strontium 90. Platelet count declined from normal (1224 x 10(3)/microliters) to a nadir (98 x 10(3)/microliters) 11 days after 90Sr, and then rose to a stable level (705 x 10(3)/microliters) on days 20 through 115. Peripheral leukocyte concentration decreased rapidly and remained below 25% of normal in contrast to hemoglobin levels, which were minimally lowered. Mean spleen weight rose rapidly after 90Sr to 66% above normal. Splenic megakaryocyte frequency, measured by two-color fluorescence-activated flow cytometry, rose from basal levels (0.09% +/- 0.06%) to 0.15% +/- 0.07% (p less than 0.001), total spleen nucleated cells fell to 71% of normal, and the absolute number of spleen megakaryocytes was unchanged. Total spleen megakaryocyte colony-forming cells were not significantly increased above normal whereas total spleen granulocyte-macrophage colony-forming cells increased abruptly after day 13 to 10 times normal levels. Splenectomy after hematopoietic recovery from 90Sr bone marrow ablation resulted in a rapid decline of platelet levels, followed by death. Although the spleen became the sole site of platelet production, the splenic megakaryocyte ploidy distribution was only minimally changed from normal, and the modal ploidy class remained 2N. In contrast to experimental thrombocytopenia in mice with intact bone marrow, in which megakaryocyte ploidy is increased, thrombocytopenia associated with sustained bone marrow ablation does not result in upward regulation of splenic megakaryocyte ploidy as a compensatory mechanism.

Animals↗
PubMed1990

Sustained thrombocytopenia in mice: serial studies of megakaryocytes and platelets.

We studied thrombopoiesis in mice after the experimental induction of sustained, immune thrombocytopenia with platelet antiserum (PAS). Utilizing light and electron microscopy and a digital image analyzer to determine platelet sectional areas, we examined platelets and megakaryocytes (MK) after 120 h of sustained, severe thrombocytopenia (120CT) and during recovery from thrombocytopenia at 48 h (48R), 72 h (72R), and 120 h (120R) after cessation of administration of PAS. Mean platelet volume (MPV), determined by electrical impedance, also was measured at each time point. Platelets at 120CT (platelet count less than 50,000/microliter), 48R (platelet count 100-200,000/microliter), and 72R (platelet count approximately 1 x 10(6)/microliter) were significantly larger in sectional area than control platelets and contained increased profiles of endoplasmic reticulum and Golgi cisternae, a lower concentration of surface-connected canalicular system, and occasional membrane complexes. The largest median platelet sectional area was detected at 48R and was the largest median value observed in response to either chronic or acute thrombocytopenia. At 120R, most platelets were normal in size and cytoplasmic appearance, although some large cells remained present in the circulation. MPV paralleled the morphometric changes in platelet sectional area. MK were increased in number at 120CT, 48R, 72R, and 120R. In addition, at least half of the MK examined at 48R contained small areas of cytoplasm, devoid of organelles, that were interspersed between larger areas of organelle-filled, undemarcated cytoplasm. The modal bone marrow megakaryocyte ploidy class, determined using two-color fluorescence-activated flow cytometry, shifted from 16N to 32N in response to sustained thrombocytopenia. In contrast, during recovery and development of rebound thrombocytosis, the relative frequency of 8N megakaryocytes was significantly increased. Because there was no consistent correlation between megakaryocyte cytoplasmic characteristics and platelet morphology, these data support the hypothesis that platelet formation is not determined by compartmentalization of MK cytoplasm into platelet areas as MK mature in the bone marrow, but involves a rearrangement of MK cytoplasm immediately prior to platelet release.

Animals↗
PubMed1990

Regulation of platelet heterogeneity: effects of thrombocytopenia on platelet volume and density.

We have examined the effects of variable degrees of acute thrombocytopenia on platelet levels, mean platelet volume (MPV), and buoyant density after induction of thrombocytopenia by platelet antiserum (PAS) in mice with or without spleens. Mice were studied serially 10-16, 36, 48, 60-64, 84, 108, 144, 180, 228, 276, 348-360, 372, and 516 h after PAS treatment. MPV and platelet count (PC) x 10(6)/microliters for normal intact mice (n = 136) were 4.7 +/- 0.3 fl (SD) and 1.69 +/- 0.52 (SD), respectively. Twelve hours after PAS-induced severe thrombocytopenia (PC less than 0.05 x 10(6)/microliters), MPV increased significantly (p less than 0.01) to 6.4 fl, was maximal at 36 h (8.2 fl), remained elevated until 144 h following PAS treatment, and then returned to normal. Platelet density decreased significantly (p less than 0.05) 64 h after PAS treatment and returned to normal at 144 h. Hematocrits of repeatedly bled intact control mice decreased from 45% to 30%, accompanied by thrombocytosis (maximal PC 2.24 x 10(6)/microliters) without significant changes in either MPV or platelet density. Moderate thrombocytopenia (PC 0.1-0.2 x 10(6)/microliters) in intact mice produced significantly (p less than 0.05) increased MPV, at 5.7 fl 12 h after PAS treatment, with a peak MPV of 7.6 fl (p less than 0.001) at 36 h; MPV returned to normal at 84 h. Platelet density decreased (p less than 0.001) 12 h after PAS treatment and returned to baseline at 228 h. Control splenectomized mice (n = 185) had an MPV of 5.0 fl +/- 0.7 fl and a PC of 2.14 +/- 0.6 x 10(6)/microliters. Comparably severe and moderate thrombocytopenia in splenectomized mice produced alterations in platelet count, MPV, and density similar to those in intact mice, although maximal MPV and the degree of rebound thrombocytosis after severe thrombocytopenia were more marked in splenectomized mice. In response to reduction of the platelet mass in both intact and splenectomized mice, MPV increased in proportion to the severity of thrombocytopenia, occurred as early as 4 h after induction, and persisted during early rebound thrombocytosis. Previous observations that megakaryocyte ploidy did not shift until 48 h after onset of thrombocytopenia confirm that both initial and maximal changes in MPV in response to this stimulus are regulated by processes other than alterations of megakaryocyte DNA levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

The relationship between megakaryocyte ploidy and platelet volume in normal and thrombocytopenic C3H mice.

Previous studies have suggested that platelet volume may be primarily regulated by the ploidy distribution of mature bone marrow megakaryocytes. However, earlier investigations from this laboratory using C57/BL mice have shown that in response to acute, severe, or moderate thrombocytopenia, platelet volume is regulated independently of megakaryocyte ploidy. Murine strains, including C57/BL, usually have a modal bone marrow megakaryocyte ploidy class of 16N. In contrast, the C3H mouse has a 32N modal bone marrow megakaryocyte ploidy class. We have examined the platelet count, platelet volume distribution, and bone marrow megakaryocyte ploidy distribution of C3H mice during steady-state thrombopoiesis and after depletion of platelets by antiplatelet serum. The platelet count and volume of normal C3H mice were not substantially different from those of C57/BL mice, but megakaryocyte frequency was marginally greater (p less than 0.05), and the ploidy distribution exhibited a a marked reduction in the proportion of 16N cells (p less than 0.001) and increased relative frequencies of 32N (p less than 0.001) and 64N (p less than 0.01) megakaryocytes. In response to acute severe thrombocytopenia, C3H mice demonstrated an increase in platelet volume equivalent to that previously reported for C57/BL mice, without a subsequent shift in the modal megakaryocyte ploidy class. The relative frequencies of 64N and 128N megakaryocytes increased significantly (p less than 0.005) compared to normal C3H mice, without a change in the frequency of 32N megakaryocytes. These studies indicate that during steady-state thrombopoiesis, a greater proportion of higher ploidy megakaryocytes (32N plus 64N) does not necessarily alter peripheral platelet count or platelet volume. Therefore, it appears that neither platelet volume nor count are primarily regulated by bone marrow megakaryocyte ploidy and that the magnitude of upward regulation of megakaryocyte ploidy is limited.

Animals↗
PubMed1989

Stability of gels formed following coagulation of Limulus amebocyte lysate: lack of covalent crosslinking of coagulin.

Incubation of lysates prepared from amebocytes of the horseshoe crab (Limulus polyphemus) with bacterial endotoxin results in coagulation and formation of a solid gel. Although Limulus gels remained solid indefinitely, if undisturbed, they were easily disrupted by mechanical agitation. Chemical solubility studies of gelled lysates demonstrated rapid solubilization of gels in monochloroacetic acid, a property of clots that have not been covalently stabilized; but in contrast demonstrated resistance to solubilization by urea, a property of stabilized clots. Analysis of solubilized proteins by polyacrylamide gel electrophoresis in SDS demonstrated coagulin, the designation for the activated form of coagulogen (the clottable protein) that forms a gel, only in samples derived from clotted lysate that had been previously incubated with monochloroacetic acid, but not in samples following incubation with urea, confirming the results of the chemical solubility studies. Enzymatic assays for transpeptidase (Factor XIII-like) activity in either native or gelled Limulus lysates were negative. Furthermore, analysis for covalently crosslinked peptides in gelled coagulin confirmed the absence of intermolecular gamma-glutamyl-epsilon-lysyl bonds. Therefore, the stable gels formed following coagulation of Limulus lysate by bacterial endotoxin are not covalently crosslinked.

Animals↗
PubMed1989

Heparin inhibition of endotoxin-dependent Limulus amebocyte lysate coagulation.

Addition of commercial heparin to preparations of the coagulation system obtained by hypotonic lysis of Limulus amebocytes, prior to the addition of endotoxin from gram-negative bacteria, inhibited gelation. Activation of the cell-lysate proclotting enzyme, utilizing a diluted lysate preparation and synthetic substrates, was inhibited to a comparable extent with either anticoagulantly active or inactive heparin. Other glycosaminoglycans, including heparan sulfate, dermatan sulfate, chondroitin 4-sulfate, and chondroitin 6-sulfate, did not inhibit the generation of clotting enzyme activity. Experiments conducted with preparations of proactivator(s) and proclotting enzyme, obtained by fractionation of lysate with heparin-Sepharose, revealed that inhibition of endotoxin-dependent activation of amebocyte lysate by heparin is mediated by precipitation of the proactivator(s) and can be prevented by increasing the salt concentration.

Animals↗
PubMed1989

The use of a monoclonal antibody against alpha-fetoprotein for the radioimmunodetection of hepatocellular carcinoma.

The purpose of this study was to investigate the use of a radiolabeled mouse monoclonal antibody (and its F(ab')2 fragment) against alpha-fetoprotein in the scintigraphic diagnosis of hepatocellular carcinoma. Twenty-six southern African Blacks and one Caucasian with hepatocellular carcinoma and four patients with other malignant tumors of the liver were studied. Although six hepatocellular carcinomas appeared to selectively concentrate alpha-fetoprotein antibody, one of these tumors was not producing alpha-fetoprotein. Moreover, in another 18 patients with alpha-fetoprotein-producing hepatocellular carcinomas, uptake of alpha-fetoprotein antibody was at best only equal to that in nontumorous hepatic tissue, and three hepatocellular carcinomas that were not producing alpha-fetoprotein concentrated the antibody to the same extent as did the alpha-fetoprotein-producing tumors and hepatic tissue. All four tumors other than hepatocellular carcinoma concentrated alpha-fetoprotein antibody as well as did hepatic tissue. These findings suggest that the penetration of hepatocellular carcinomas by alpha-fetoprotein antibody is a passive and nonselective process. This conclusion is supported by an in vitro study in which a non-alpha-fetoprotein-producing hepatic metastasis took up as much radiolabeled alpha-fetoprotein antibody as did three of four alpha-fetoprotein-producing hepatocellular carcinomas. A likely explanation for the failure of alpha-fetoprotein monoclonal antibody to be selectively concentrated by hepatocellular carcinomas is that alpha-fetoprotein is an export protein and is not expressed on the cell membranes of malignant hepatocytes.

Adult↗
PubMed1989

Ultrastructural analysis of acute immune thrombocytopenia in mice: dissociation between alterations in megakaryocytes and platelets.

Thrombopoiesis was studied in mice after the induction of acute immune thrombocytopenia with platelet antiserum (PAS). Utilizing electron microscopy, we examined platelets and megakaryocytes (MK) obtained 4, 8, 12, 24, 48, 72, and 120 hr after administration of PAS. Four to 24 hr after injection of PAS, the majority of bone marrow MK were normal in size and organelle distribution. The demarcation membrane system (DMS) extended normally throughout the mature cell cytoplasm at these times. However, approximately 50% of MK observed 48 hr and 72 hr after injection of PAS were significantly larger than normal, and often had demarcation membranes confined to an area between a peripheral organelle-deficient zone and a central nuclear zone. The median values for sectional areas of platelets obtained 8-72 hr after administration of PAS were significantly greater than the median value for sectional areas of platelets in a pooled control sample. The proportion of cytoplasm to surface-connected canalicular system appeared greater than normal in most large platelets from the PAS samples; and increased numbers of profiles of Golgi complex and endoplasmic reticulum were observed. By 48 hr post-injection of PAS (at which time the modal ploidy class of MK has shifted from 16N to 32N; Corash et al., Blood 70:177, 1987), most platelets were normal in size and cytoplasmic appearance. At 120 hr post-injection of PAS, virtually all platelets exhibited a normal size and complement of organelles, and MK also had returned to normal. Our data indicate that in response to acute thrombocytopenia, MK prematurely release platelets which differ from normal platelets in size and cytoplasmic appearance. There was a marked dissociation between alterations in platelets and MK, since a statistically significant increase in platelet sectional area occurred 40 hr before the shift in modal ploidy class of MK, and platelet size subsequently decreased toward normal during the period that has been shown to be associated with the maximum shift in MK ploidy. These results strongly suggest that the characteristics of platelet release do not depend on the ploidy or cytoplasmic characteristics of MK.

Acute Disease↗
PubMed1989

Model-building of Fnr and FixK DNA-binding domains suggests a basis for specific DNA recognition.

The DNA-binding C-terminal domains of the regulatory proteins Fnr from Escherichia coli and FixK from Rhizobium meliloti have been modelled on the basis of their homologies to the CAP protein from E. coli. Residues Glu181, Thr182 and Arg185 of CAP, which are exposed residues of the DNA-recognition helix alpha F, are conserved in Fnr and FixK. However, Arg180 and Gly184 are substituted by Val and Ser respectively in Fnr. We propose that this valine makes a Van der Waals' contact with the first thymine in the Fnr consensus TTGA-N6-TCAA, and that the serine contributes to the binding by displacing a thymine-bound water molecule. The corresponding residues in FixK, Ile and Ser allow the same interactions with a thymine. Therefore we predict that FixK may recognize the same sites as Fnr. This is supported experimentally by showing that Fnr can substitute for FixK in activating the fixN gene in E. coli.

Amino Acid Sequence↗
PubMed1989

Solitary thick intra-uterine membranes not associated with the amniotic band syndrome; three case reports.

Three cases in which a single intra-uterine membrane with a free and thickened edge was identified by ultrasound antenatally are presented. The bands turned out to be thickenings of the fetal membranes. In one case intra-uterine adhesions were documented by hysterosalpingography (HSG) and hysteroscopy before conception. One infant suffered from hypospadias. The diagnosis of intra-uterine bands or membranes should turn our attention to a possible intra-uterine pathology.

Adult↗
PubMed1989

Adverse effects of antibiotics.

Adverse reactions to antibiotics comprise a number of classes of reactions, including toxicity, side effects, and allergy. Each one of these differs in its implication for treatment of the patient. The authors discuss some of the more common and unusual reactions to antibiotics frequently used in the practice of podiatric medicine.

Anti-Bacterial Agents↗
PubMed1989

Measurement of megakaryocyte frequency and ploidy distribution in unfractionated murine bone marrow.

Measurement of megakaryocyte frequency, ploidy distribution, and maturation stage have been complicated by the low frequency of megakaryocytes in either bone marrow or spleen. Due to harsh labeling conditions, previous studies utilizing flow cytometry have not quantified cell recovery or megakaryocyte frequency. We have modified our two-color fluorescence-activated cytometric technique in order to identify megakaryocytes in unfractionated murine bone marrow with a fluoresceinated cell surface immunologic probe (heterologous polyclonal platelet antiserum) and to selectively measure megakaryocyte DNA content with propidium iodide using isosmolar conditions. Under these conditions, total nucleated cell recovery from unfractionated normal murine bone marrow, after all preparative procedures, averaged 68.0% +/- 5.0% (SD) with 93.5% +/- 2.0% DNA staining efficiency. Mean megakaryocyte frequency (n = 30) was 0.14% +/- 0.04%. Using both our previously described gating technique with single parameter analysis and our modified dual parameter technique, the modal megakaryocyte ploidy class was 16N. Low ploidy megakaryocytes, 2N and 4N, constituted 9.8% and 10.8%, respectively, of the total megakaryocyte population. Analysis of the megakaryocyte population with respect to cell surface fluorescence intensity demonstrated that the dimly fluorescent population contained an increased proportion of lower ploidy class cells (2N + 4N + 8N) compared with brightly fluorescent cells, which contained an increased proportion of higher ploidy cells (16N + 32N). Our modifications of the two-color technique yielded improved recovery of total nucleated bone marrow cells from unfractionated bone marrow and provided more precise measurements of megakaryocyte frequency and ploidy than previously available.

Animals↗
PubMed1989

A randomized clinical trial of 10% pentastarch (low molecular weight hydroxyethyl starch) versus 5% albumin for plasma volume expansion after cardiac operations.

Pentastarch is a hydroxyethyl starch similar to hetastarch, but with a lower average molecular weight (264,000 versus 450,000) and fewer hydroxyethyl groups (molar substitution ratio = 0.45 versus 0.70). These characteristics result in enhanced enzymatic hydrolysis, faster renal elimination (initial intravascular half-life = 2.5 versus 25.5 hours), and less effect on coagulation. We report on a randomized clinical trial comparing the clinical efficacy and safety of 10% pentastarch (group P) for plasma volume expansion after cardiac operations with that of 5% serum albumin (group A). During the first 24 hours after arrival of the patient in the intensive care unit, colloid was infused to maintain a cardiac index of 2.0 L/m2 or more and a mean arterial pressure within 10% of the preinduction value. Group P (n = 50) received 1706 +/- 393 ml of colloid (mean +/- standard deviation) during this period, and group A (n = 44), 1794 +/- 341 ml (p = no significant difference). Hemodynamic responses to infusion were similar for both groups, although in group P a greater increase in both cardiac index (0.5 +/- 0.5 versus 0.3 +/- 0.5 L/min/m2 in group A, p less than 0.01) and left ventricular stroke work index (10.8 +/- 8.0 versus 5.8 +/- 6.0 gm-m/m2, p less than 0.01) was observed during infusion of the first 500 ml. There were no significant differences in any of the measured respiratory parameters (alveolar-arterial oxygen gradient, estimated shunt fraction, and effective pulmonary compliance). Hemodilution with colloid significantly reduced serum protein levels in group P by 24 hours postoperatively (4.0 +/- 0.6 versus 5.0 +/- 0.7 gm/dl in group A, p less than 0.05), although mean serum colloid osmotic pressure was similar (15.4 +/- 2.6 [P] versus 15.5 +/- 2.7 mmHg [A], p = no significant difference). There were no significant between-group differences in prothrombin time, activated partial thromboplastin time, platelet count, bleeding time, or coagulation factors (fibrinogen, V, VII, VIII, or IX) on postoperative days 1 and 7. Perioperative fluid balance, weight change, chest tube output, red blood, platelet, or fresh frozen plasma usage, reexploration for bleeding, and clinical outcome were also similar. These findings indicate that pentastarch is as safe and effective s 5% albumin for plasma volume expansion after cardiac operations with no apparent adverse effects on coagulation. If commercially available at a lower cost than albumin, it would appear to be a reasonable first choice for colloid therapy in this setting.

Aged↗
PubMed1989

Effect of detoxification processes on the interferon-inducing activity of bacterial endotoxins.

The interferon (IFN)-inducing activity of detoxified lipopolysaccharide (LPS) was tested in rabbits treated with LPS preparation derived from Escherichia coli, Salmonella typhi, Salmonella enteritidis and Shigella dysenteriae serovar 1. Of the detoxification procedures used, alkaline hydrolysis, hydroxylaminolysis, formalization, treatment with sodium deoxycholate and the radiodetoxification (fast or slow) methods had no appreciable effects on the IFN-inducing potential of LPS. In contrast, acetylation or prolonged alkaline hydrolysis of LPS resulted in up to a 9-fold reduction of IFN-induction capacity and effects of Cu++ or Fe++ cations bound to LPS were clearly inhibitory (Fe more than Cu).

Acetylation↗
PubMed1989

Ciliary sulcus reconstruction for posterior implantation in the absence of an intact posterior capsule.

Secondary implantation of a posterior chamber intraocular lens in an aphakic eye devoid of an intact posterior capsule requires a special surgical approach. When lens capsule remnants remain in the periphery, the ciliary sulcus can be reconstructed to accommodate a posterior chamber lens. The fibrotic lens or capsular residues that often remain adherent to the posterior surface of the iris are divided with sharp intraocular scissors, and a shelf is created that is sufficient to support the lens haptics. A series of 28 cases, including 16 involving young children, demonstrates the feasibility and the favorable visual results obtainable with this surgical technique.

Adolescent↗
PubMed1989

Mechanisms of platelet production.

The precise mechanism by which platelets are formed from megakaryocytes (MK) remains unclear, despite numerous studies which have been performed during this century. Models have been proposed that attempt to account for platelet formation from disruption of elongated processes of MK cytoplasm, designated proplatelets, or by fragmentation of MK cytoplasm. MK demarcation membranes are hypothesized by some investigators to delineate platelet territories in the MK cytoplasm, and by others to act as a membrane reservoir for MK process formation. Platelet production has been variously speculated to occur primarily in the bone marrow or lung. Each theory or model has attempted to elucidate the phenomenon of size heterogeneity of circulating platelets and the changes that occur under conditions of altered thrombopoiesis. In this article, we have analyzed and compared the characteristics of previously proposed models for platelet production and suggested additional techniques for future studies of thrombopoiesis.

Animals↗