Search PubMed⌕ Search

Biomedical subjects

D Meyer

Publications and source records attributed to D Meyer.

At least 433 records · Page 24Linked to original sources
PubMed1986

Comparison of tryptic fragments of von Willebrand factor involved in binding to thrombin-activated platelets with fragments involved in ristocetin-induced binding and binding to collagen.

Previously we have studied the binding domains on von Willebrand factor (vWF) involved in ristocetin-induced binding to platelets (ristocetin binding domain, RBD) and in the binding of vWF to collagen (collagen binding domain, CBD) using tryptic fragments of 125I-labelled vWF (21, 23). We have also reported on the RBD, CBD and the domain on vWF involved in the binding to thrombin activated platelets (thrombin binding domain, TBD) using vWF-fragments prepared by digestion with staphylococcal protease V8 (25). In the present study, we have digested 125I-vWF with TPCK-trypsin and we have performed at various times of digestion immuno-precipitation with Mab 9, the antibody inhibiting binding of vWF to thrombin activated platelets. The data were compared with the immunoprecipitation patterns simultaneously obtained with CLB-RAg 35 which inhibits binding of vWF in the presence of ristocetin and with CLB-RAg 201, which inhibits binding of vWF to collagen. At 90 min, Mab 9 and CLB-RAg 201 precipitated similar high molecular weight bands, whereas CLB-RAg 35 precipitated bands at 180 and 120 kDa. After 24 h, Mab 9 precipitated bands at 200, 155, 116 and 85 kDa; CLB-RAg 201 precipitated a band at 48 kDa and CLB-RAg 35 a band at 116 kDa. Two-dimensional electrophoresis demonstrated that the high molecular weight bands, precipitated by Mab 9 and CLB-RAg 201 at 90 min, were identical. The 116 kDa fragment recognized by CLB-RAg 35 had a different subunit composition than the 116 kDa fragment precipitated by Mab 9.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Monoclonal↗
PubMed1986

tRNA (adenine-N1)-methyltransferase from Dictyostelium discoideum. Purification, characterization and developmental changes in activity.

An enzyme activity transferring methyl groups from S-adenosylmethionine to endogenous tRNA was detected in the cytosol of aggregative Dictyostelium discoideum amoebae. This enzyme was purified more than 1000-fold and was characterized as a tRNA (adenine-N1-)-methyltransferase. Kinetic analysis yielded a K0.5 for S-adenosylmethionine of 0.27 microM and competitive inhibition by S-adenosylhomocysteine showed an I0.5 of 0.26 microM. The tRNA methyltransferase activity was stimulated by monovalent cations and the pH optimum was 7.3. tRNAs isolated from D. discoideum as well as from other eucaryotic sources could be methylated only to a minor extent. In contrast, Escherichia coli tRNA accepted up to 0.6 mol methyl group/mol tRNA, suggesting that the target nucleotide is unmethylated in procaryotic tRNA, but is commonly methylated in tRNAs from eucaryotic organisms. The activity of the methyltransferase increased 4-6-fold during cell differentiation from the vegetative to the aggregative stage.

Cations↗
PubMed1986

Homozygous variant of antithrombin III: AT III Fontainebleau.

A qualitative defect of antithrombin III (AT III) was demonstrated in four members of a large Tunisian family by the discrepancy between a normal amount of antigen and decreased or absent heparin cofactor activity. The propositus, a 3-year-old girl, died from massive intracardiac thrombosis despite oral anticoagulant therapy. Heparin cofactor activity measured in the presence of thrombin or F. Xa was undetectable in her plasma. Anti-F. Xa activity was also absent when using low molecular weight heparin or a synthetic pentasaccharide, representing the binding site to AT III. The lack of affinity of the propositus AT III for heparin was demonstrated by two-dimensional immunoelectrophoresis and chromatography on heparin-Sepharose. The parents, first cousins, and the sister of the propositus also demonstrated a qualitative abnormality of AT III, with levels of heparin cofactor activity close to 50% of the normal range. Our data support the view that the abnormal protein was present at the heterozygous state in the parents and sister and at the homozygous state in the propositus. None of the affected family members had thrombotic episodes, except for the propositus. The name of AT III Fontainebleau is proposed for this variant.

Antithrombin III↗
PubMed1986

Investigation of a case of subtype IIC von Willebrand disease: characterization of the variability of this subtype.

A variant of von Willebrand disease (vWD) has been identified in a 19-year-old woman with a severe bleeding syndrome. She had a very prolonged bleeding time (over 20 min), 24 U/dl factor VIII coagulant activity (F.VIII:C), 16 U/dl von Willebrand factor antigen (vWF:Ag), no ristocetin cofactor activity, and an anodal mobility of vWF:Ag on crossed immunoelectrophoresis (CIE). vWF:Ag was markedly reduced in her platelet lysate. In plasma and platelets, SDS-agarose electrophoresis consistently demonstrated the absence of large multimers, a relatively increased concentration of the fastest-moving multimer, and gross abnormalities of the internal structure of each vWF multimeric unit. Five members from the maternal side of the family had a double vWF:Ag peak by CIE and a relative increase of the fastest-moving vWF multimer by SDS-agarose electrophoresis; no quantitative or qualitative vWF defects were found in the paternal side of the family. The pattern of the findings in the propositus and her family is similar to those of type IIC vWD. However, there are some unique characteristics suggesting phenotypic variability in this subtype, such as low level of platelet vWF:Ag and the absence of increase of vWF after DDAVP administration.

Adult↗
PubMed1986

Electrocochleography recorded non-invasively from the external ear.

A method is described to record cochlear evoked potentials in humans (ECochG) with a low impedance electrode on the external ear near the opening of the external auditory canal. A piezoelectric click stimulus was delivered to the ear through a polyethylene tube creating diminution of stimulus artifact and a signal delay. Wave forms resembling the cochlear microphonic (CM), summating potential (SP) and the eighth nerve action potential (N1) were differentially accentuated by changes in stimulation and recording parameters. The addition or subtraction of condensation and rarefaction click wave forms further clarified the N1 and SP, or the CM potential, respectively. These responses can be recorded with most contemporary evoked response equipment. This non-invasive method of ECochG lends itself well to the study of hearing loss and possibly other neurologic disorders, and may complement BAER examination especially when wave I is poorly delineated.

Audiometry, Evoked Response↗
PubMed1986

Cloning and developmental expression of the murine neurofilament gene family.

DNA clones encoding the 3 mouse neurofilament (NF) genes have been isolated by cross-hybridization with a previously described NF-L cDNA probe from the rat. Screening of a lambda gt10 cDNA library prepared from mouse brain RNA led to the cloning of an NF-L cDNA of 2.0 kb that spans the entire coding region of 541 amino acids and of an NF-M cDNA that covers 219 amino acids from the internal alpha-helical region and the carboxy-terminal domains of the protein. These cDNA clones were used as probes to screen mouse genomic libraries, and cosmid clones containing both NF-L and NF-M sequences were isolated as well as overlapping cosmids containing the NF-H gene. This strongly suggests that the 3 neurofilament genes are organised in a cluster and derived by gene duplication of a common ancestral gene. RNA blot analyses using specific DNA probes for each of the genes indicate that NF mRNAs are differentially expressed during brain development. The NF-L and NF-M mRNAs are detected early in the embryonal brain, with a progressive increase in their levels during development, while the NF-H mRNA is barely detectable at embryonal stages and accumulates later in the postnatal brain.

Animals↗
PubMed1986

Action of gadolinium complexes on different enzyme systems.

Gadolinium complexes have two advantages: their toxicity is very low and the paramagnetic properties are adequate enough to give a useful signal with magnetic resonance imaging (MRI). The effects of several MRI contrast media on the activity of two brain enzymes, glutamate decarboxylase (GAD) and cholineacetyl transferase (ChAT), were investigated. The study was performed on homogenates of rat striatum with variable concentrations of gadolinium sulphate, EDTA, DTPA, DOTA, Gd-EDTA, Gd-DTPA and Gd-DOTA (from 10(-2) mol/l to 10(-9) mol/l. Gadolinium in its ionic form and the chelators of cation agents such as EDTA, DTPA and DOTA inhibit GAD, a calcium dependent enzyme, whereas they have no inhibiting effect on the activity of ChAT, a calcium independent enzyme. Gadolinium complexes inhibit the GAD activity by about 15 per cent whereas they do not modify that of ChAT. The complex form of gadolinium has the advantage of retaining its paramagnetism while drastically lowering its toxicity.

Animals↗
PubMed1986

Mapping of distinct von Willebrand factor domains interacting with platelet GPIb and GPIIb/IIIa and with collagen using monoclonal antibodies.

We have used monoclonal antibodies (M Abs) and proteolytic fragmentation to localize structurally the functional sites of human von Willebrand factor (vWF) responsible for interaction with membrane glycoproteins GPIb, GPIIb/IIIa, and with collagen. SpII (215 kd) and SpIII (320 kd), the S aureus V-8 protease homodimeric fragments representing the carboxy-terminal and amino-terminal segments of the vWF subunit, competitively inhibited the binding of multimeric vWF to thrombin-stimulated or ristocetin-stimulated platelets, respectively. Specific saturable binding of each fragment was observed to stimulate platelets appropriately and was inhibited only by selected M Abs that both bound to the specific fragment and inhibited the corresponding function. M Ab 9, which blocks thrombin-induced binding of vWF to platelets, inhibited binding of SpII to platelets and bound to SpII as well as to a dimeric, 86-kd thermolysin fragment composed of 42-kd and 23-kd subunits, each possessing the epitope. Binding of SpII was also inhibited by a M Ab to GPIIb/IIIa. Thus, it appears that a portion of the carboxy-terminal end of vWF contains the ligand site for the GPIIb/IIIa receptor. In contrast, M Ab H9, which blocks ristocetin-induced binding of vWF to platelets, inhibited binding of SpIII to platelets and bound to SpIII as well as to monomeric 33-kd and 28-kd subtilisin fragments. Binding of SpIII to platelets was also inhibited by a M Ab to GPIb. Thus, it appears that a small segment of the amino-terminal part of vWF contains the ligand for the platelet GPIb receptor. The collagen binding site of vWF was localized with M Ab B203, which inhibits vWF interaction with collagen. This M Ab also bound to SpIII as well as to monomeric 26-kd and 23-kd subtilisin fragments. Thus, the third functional site responsible for collagen binding appears to be localized on the amino-terminal portion of vWF, in a linear sequence different from those responsible for interaction with either of the platelet receptors. These assignments of functional sites should facilitate the localization of structural defects of vWF in the various forms of vWD and support the role of vWF as an adhesive protein with multiple interactive sites.

Antibodies, Monoclonal↗
PubMed1986

Mediation of platelet adhesion to fibrillar collagen in flowing blood by a proteolytic fragment of human von Willebrand factor.

The effect of purified von Willebrand Factor (vWF) fragments, SpII (dimer of two 110 kd subunits) and SpIII (dimer of two 170 kd subunits) obtained with S aureus V-8 protease was tested upon platelet adhesion to collagen. Purified fibrillar human collagen coated onto cover slips was incubated with SpII, SpIII, or undigested vWF and exposed to reconstituted human blood in a parallel-plate perfusion chamber at a high shear rate. Platelet-collagen interactions were estimated using 51Cr-platelets and quantitative morphometry. When blood was reconstituted with citrated autologous plasma, SpIII and vWF strikingly enhanced platelet adhesion to collagen whereas SpII had no effect. When blood was reconstituted with human albumin and divalent cations, SpIII and vWF again promoted platelet adhesion to collagen. In conclusion, our data suggest that (1) SpIII, the N-terminal portion of vWF which binds to platelet membrane glycoprotein Ib, functionally substitutes for vWF in supporting platelet adhesion to collagen; (2) SpII, the C-terminal portion which binds to glycoprotein IIb/IIIa, has no such effect; (3) in addition to its platelet binding domain, SpIII contains another site for binding to collagen; and (4) the multimeric structure of vWF is not required for platelet adhesion to collagen.

Binding Sites↗
PubMed1986

The family conference: what do patients want?

This study investigated patients' desire for family conferences in a variety of clinical situations encountered in family practice. Two hundred seventy-six family practice center patients were given a questionnaire in which they indicated the likelihood that they would want a family conference in 21 clinical situations. Patients' past experiences with family conferences as well as demographic information were obtained. For serious medical problems and some behavioral problems, patients indicated a high likelihood of wanting a family conference. They showed moderate to low interest in such conferences for guidance for family developmental stages, health promotion, and minor acute problems. Demographic factors and previous experiences with family conferences did not predict patients' interest in future conferences.

Attitude↗
PubMed1985

Multicenter comparison of von Willebrand factor multimer sizing techniques. Report of the Factor VIII and von Willebrand Factor Subcommittee.

A multicenter study of various types of von Willebrand's disease (vWD) was conducted in order to compare the different electrophoretic techniques used to evaluate von Willebrand factor multimers in plasma. Seven laboratories participated in the blind study of eight plasma samples from two healthy subjects and six vWD types and subtypes (Ia, Ib, IIA, IIB, IIC and IID). From the results of the multimeric analysis of these samples, it appears that the differential diagnosis of vWD types and subtypes should be first approached by using a low-resolution electrophoretic technique, where each vWF multimer appears as a single band. Low-resolution techniques differentiate type I from type II, subtype Ia from Ib and also subtype IIA from other type II subtypes. When type II subtypes other than IIA are identified with these techniques, samples should be rerun using high resolution techniques that resolve each of the fastest migrating multimers in at least three subbands, and permit the differentiation of subtypes IIB, IIC and IID.

Electrophoresis, Agar Gel↗
PubMed1985

Common-sense models of illness: the example of hypertension.

Our premise was that actions taken to reduce health risks are guided by the actor's subjective or common-sense constructions of the health threat. We hypothesized that illness threats are represented by their labels and symptoms (their identity), their causes, consequences, and duration. These attributes are represented at two levels: as concrete, immediately perceptible events and as abstract ideas. Both levels guide coping behavior. We interviewed 230 patients about hypertension, presumably an asymptomatic condition. When asked if they could monitor blood pressure changes, 46% of 50 nonhypertensive, clinic control cases said yes, as did 71% of 65 patients new to treatment, 92% of 50 patients in continuing treatment, and 94% of 65 re-entry patients, who had previously quit and returned to treatment. Patients in the continuing treatment group, who believed the treatment had beneficial effects upon their symptoms, reported complying with medication and were more likely to have their blood pressure controlled. Patients new to treatment were likely to drop out of treatment if: they had reported symptoms to the practitioner at the first treatment session, or they construed the disease and treatment to be acute. The data suggest that patients develop implicit models or beliefs about disease threats, which guide their treatment behavior, and that the initially most common model of high blood pressure is based on prior acute, symptomatic conditions.

Attitude to Health↗