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Biomedical subjects

M S Read

Publications and source records attributed to M S Read.

At least 55 records · Page 3Linked to original sources
PubMed1989

Role of botrocetin in platelet agglutination: formation of an activated complex of botrocetin and von Willebrand factor.

Botrocetin (venom coagglutinin) induces binding of von Willebrand factor (vWF) to platelet glycoprotein Ib (GPIb), resulting in platelet agglutination. A mechanism whereby botrocetin causes vWF to change to an active platelet-agglutinating form is proposed. Incubation of native vWF with botrocetin yielded an increasingly active vWF with slower migration in two-dimensional immunoelectrophoresis but with no apparent change in vWF multimer pattern. The "activated" vWF eluted mainly in the void volume (Vo) (Bio-Gel A-15m column chromatography). Botrocetin eluted in the included volume (Vi). Vo peaks appeared to contain a vWF-botrocetin complex, based on bioassays and immunoassays. 125I-Botrocetin mixed with vWF eluted in two peaks: in the Vo, coincident with active vWF, and in the Vi. With von Willebrand disease (vWD) plasma lacking vWF, 125I-Botrocetin eluted in the Vi only. It did not bind to platelets without vWF. In aggregometric studies, antibodies (Ab) against botrocetin, vWF, and GPIb prevented botrocetin-induced platelet agglutination and caused dissolution of preformed platelet agglutinates. Immunostaining of aggregates with antibotrocetin Ab revealed a positive reaction. Botrocetin appears to act in a two-step manner, first binding with vWF to form a complex, which then binds to GPIb to cause agglutination. All three components, vWF, botrocetin, and GPIb, appear to be required for maintenance of stable platelet agglutinates.

Animals↗
PubMed1989

Effect of recombinant factor VIIa on the hemostatic defect in dogs with hemophilia A, hemophilia B, and von Willebrand disease.

Recombinant factor VIIa (rF.VIIa) is a two-chain procoagulant enzyme (Mr, approximately 50,000) active only when complexed with tissue factor in the extrinsic clotting system. We administered human rF.VIIa to hemophilic and von Willebrand disease (vWD) dogs to determine its hemostatic effectiveness and survival in the circulation. Hemophilia A dogs lacking factor VIII demonstrated an immediate increase in plasma rF. VIIa and prompt stoppage of hemorrhage at bleeding time (BT) sites. In seven studies in two dogs, the range of dose of rF. VIIa was 50-220 micrograms/kg, with an apparent 7- to 11-fold increase in plasma factor VII and a mean recovery in plasma of 34%. The t1/2 was 2.8 +/- 0.5 hr. The BT was normalized except in an animal given the minimum dose. In four studies in two hemophilia B dogs lacking factor IX, BT was normalized. The elevation in plasma factor VII was by a factor of 8-30, with a mean recovery of rF.VIIa in plasma of 44%. In two studies in a homozygous vWD dog lacking von Willebrand factor, which is needed for platelet function, BT was not corrected even though large doses of rF. VIIa were given. The human rF. VIIa protein was immunogenic for dogs. These studies indicate that factor VIIa corrects the hemostatic defect in dogs with hemophilia A and B, diseases primarily of the intrinsic clotting system, but does not correct the hemostatic defect in vWD.

Animals↗
PubMed1989

Creation of a regional medical-nutrition education network.

The Southeastern Regional Medical-Nutrition Education Network (SER-MEN) was developed to coordinate and improve nutrition education in a consortium of the medical schools in Alabama, Florida, Georgia, and South Carolina. SERMEN's central office is at the Medical College of Georgia with the testing office at the University of Alabama at Birmingham. Students, faculty, and consultants in nutrition, education, and computer networking work together on projects on each campus that are coordinated and planned through semiannual meetings. A standardized examination was developed with the Nutrition Test-Item Bank to assess nutrition knowledge at various years of medical students from network schools. Each SERMEN school is connected to a microcomputer system at the central office that provides access to a data base of nutrition education and resources on each campus for developing curricula and syllabi. Funding has been provided by societies, foundations, and government agencies.

Computer Communication Networks↗
PubMed1988

A comparison of nutrition knowledge of freshmen and senior medical students: a collaborative study of southeastern medical schools.

It has been documented previously that nutrition knowledge of senior medial students at ten southeastern medical schools varies and is positively correlated with student assessment of the quantity and quality of nutrition education. To determine whether the differences in knowledge are related to the medical educational experience or are simply a reflection of differences in the students' knowledge on entry to medical school, the same examination was administered to entering freshmen at eight of the medical schools. The knowledge scores of freshmen were remarkably homogeneous from school to school (53 +/- 1%, range 51-55%), and nutrition knowledge was significantly higher for seniors than for the freshmen at all schools (mean 69 vs 53%, p less than 0.0001). On the basis of responses to survey items on the examination, the freshman medical students were more inclined than senior students to take a nutrition elective (62 vs 34%, p less than 0.0001), and more freshman rated nutrition as being important to their careers (74 vs 59%, p less than 0.05). These data indicate that 1) entering freshman medical students at the different schools studied have comparable levels of nutrition knowledge and are receptive to nutrition education, and 2) differences in medical training programs most likely explain the previously documented variability in nutrition knowledge of graduating medical students. These findings have important implications for professionals planning curricula for medical-nutrition education.

Education, Medical, Undergraduate↗
PubMed1988

Cross-sectional study of nutrition knowledge and attitudes of medical students at three points in their medical training at 11 southeastern medical schools.

Eleven southeastern medical schools cooperated to evaluate nutrition knowledge and attitudes of medical students. This study complements previous reports of an examination of entering freshmen and seniors. Average knowledge scores for 165 students tested after basic sciences (preclinical) training in this study were 67 +/- 7% compared with 53 +/- 6% for freshmen and 69 +/- 8% for seniors. The upperclassmen's scores were higher than the freshmen's (p less than 0.001) and varied with the amount of required nutrition teaching. Only 13% of preclinical students perceived nutrition as important to their careers compared with 74% of entering and 59% of graduating students, suggesting that preclinical teaching reduces their sense of relevance of nutrition to medicine. These findings suggest that nutrition knowledge can be increased through preclinical coursework and that the knowledge level can be maintained through the clinical years. However, the positive attitude of freshmen toward nutrition is lost after preclinical training and is only partially regained after the clinical years.

Attitude of Health Personnel↗
PubMed1988

Thrombotic thrombocytopenia with von Willebrand factor deficiency induced by botrocetin. An animal model.

Thrombotic thrombocytopenia with severe von Willebrand factor (vWF) depletion was induced in rats by intraperitoneal injection of botrocetin, a Bothrops factor requiring vWF for platelet aggregation. The vWF deficiency state with thrombocytopenia was produced in 12 animals by single or multiple injections of botrocetin. Single botrocetin injection (450 units/kg) reduced plasma vWF activity to less than 0.01 mu/ml for 24 hours and less than 0.2 units/ml up to 72 hours. During this period, multimeric analysis of plasma vWF:Ag revealed loss of intermediate and high molecular weight forms. A moderate reduction in vWF:Ag (Laurell) and FVIII:C was observed. Bleeding time remained prolonged during the deficiency state. Recovery of plasma vWF and platelet count occurred in 4 to 5 days. Multiple botrocetin injections (450 units/kg/injection) at 48-hour intervals produced a sustained severe vWF depletion (less than 0.2 units/ml) for 1 week. On the 8th day, vWF and platelet count had recovered to preinjection levels. Recovery was associated with the appearance of increased levels of very high molecular weight multimers of vWF:Ag in the plasma. After each botrocetin administration (single or repeat), a transient thrombocytopenia developed which was most severe at 1 to 5 hours postinjection. Another group of 10 animals was given a single botrocetin injection and specimens of lung, liver, kidney, and spleen were obtained at varying time intervals postinjection. Transmission electron micrographs of the lung and spleen 2 hours after botrocetin administration showed platelet aggregates and platelet microthrombi in the lung and spleen. The platelet thrombi in the lung had disappeared within 24 hours, and in the spleen by 48 hours. Liver sinusoids and kidney glomeruli were free of thrombi. A comparison is made of the thrombocytopenia and the ultrastructure of the platelet microthrombi induced by botrocetin with that of other agents.

Animals↗
PubMed1987

Prevention of occlusive coronary artery thrombosis by a murine monoclonal antibody to porcine von Willebrand factor.

A murine monoclonal antibody (mAb) against porcine von Willebrand factor (vWF) induced an antithrombotic state in normal pigs. Thrombosis was induced by a standard procedure of stenosis and mechanical injury of the artery. The mAb was an IgG1 kappa that inhibited vWF-induced platelet aggregation at a titer of 1:6250 and bound to immobilized vWF at a maximal dilution of 1:512,000. The antibody did not affect two other vWF functions, platelet adhesion and binding of coagulant factor VIII (factor VIII:C). The antithrombotic state was characterized by a prolonged bleeding time and lack of plasma vWF activity, but with near-normal levels of factor VIII:C and von Willebrand antigen. The circulating Ag.mAb complex demonstrated a multimeric distribution comparable to that of native plasma vWF. Three groups of pigs were studied: group A consisted of nine untreated animals, eight of which developed occlusive coronary thrombosis; group B, four treated animals with a long bleeding time, none of which developed occlusive thrombosis; and group C, two animals with preexisting thrombosis treated with mAb, in which stable blood flow was reestablished. Morphologically, the group B animals showed adherent platelets covering the injured intima but no thrombosis. This mAb is an antithrombotic agent that prevents platelet thrombosis without affecting intrinsic platelet function.

Animals↗
PubMed1986

A paradoxical effect of antibody concentration on vWF-dependent platelet agglutination distinguishes between botrocetin and ristocetin-induced agglutination.

Several heterologous antisera directed against either human or porcine von Willebrand factor (vWF), inhibited botrocetin-induced vWF-dependent agglutination at high concentrations but were found to enhance this reaction at low concentrations. Purified IgG from these immune sera also potentiated botrocetin-induced agglutination as did its F(ab)'2 fragments. However, monovalent Fab fragments of the purified IgG did not. The requirement for a divalent antigen combining region suggests that one possible mechanism of enhanced agglutination may involve intra or inter-molecular cross-linking of vWF multimers by the antibody. Another possible mechanism could be a conformational change in the vWF molecule induced by antibody binding. Such a conformational change may provide additional active sites on the vWF molecule that, in the presence of botrocetin, lead to enhancement of the agglutination reaction. Antisera to human vWF that showed this paradoxical inhibitory/enhancing effect on botrocetin-induced agglutination also inhibited ristocetin-induced platelet agglutination at high concentrations, but failed to enhance agglutination at any concentration. The different effects of these antisera on botrocetin and ristocetin-induced platelet agglutination suggest that no single mechanism can explain the action of both of these mediators.

Adjuvants, Immunologic↗
PubMed1986

Nutrition knowledge of senior medical students: a collaborative study of southeastern medical schools.

The Southeastern Regional Medical-Nutrition Education Network (SERMEN) comprises 11 medical schools with varied nutrition training programs. A faculty representative from each school rated 41 topics in nutrition as to their importance for medical practice. From the seven topics unanimously chosen, a 90-item examination was prepared using the University of Alabama School of Medicine's Nutrition Test-Item Bank. Thirteen additional items surveyed student attitudes toward their nutrition training. Twenty-one percent of senior students from 10 SERMEN schools took the examination. Results showed significant variation in knowledge levels among the schools on the overall examination and on the seven topics. Eighty-five percent were dissatisfied with the quantity and 60% with the quality of their medical-nutrition education. Knowledge scores correlated with the students' assessments with r values of 0.28 and 0.35, respectively (p less than 0.001). Findings indicate significant variation in nutrition knowledge of US medical students.

Attitude of Health Personnel↗
PubMed1985

Determinants of von Willebrand factor activity elicited by ristocetin and botrocetin: studies on a human von Willebrand factor-binding antibody.

The three main probes for functional vWF activity--ristocetin, botrocetin, and the PAggF test--and similarities and differences in their elicited vWF activities have been reviewed. Emphasis has been placed on the technologies dependent on these probes, with a brief description of a series of relatively simple and sensitive tests developed in this laboratory. These tests include the development of the PAF test for vWF in certain animal plasmas; the development and use of fixed lyophilized platelets that retain receptor activity for vWF; the purification of botrocetin (venom coagglutinin) freed of thrombinlike enzymes and its use in vWF assays; the development of macroscopic platelet aggregation tests for screening and assay of vWF; and the application of the macroscopic test for rapid screening and quantitation of human plasmas for acquired inhibitors of vWF utilizing each of the three probes. Historically, the similarities of the ristocetin and botrocetin probes were first observed. For normal human plasmas and for patients with classic vWD, both homozygous or heterozygous, similar values for vWF were obtained with these two probes. Similar platelet binding of vWF in the presence of the two probes was likewise noted. However, further studies of these two probes revealed striking differences. Especially important for study of animal plasmas generally as well as a canine model of vWD was the observation that the vWF in all animal plasmas tested with botrocetin was highly reactive, whereas with ristocetin nearly all plasmas were resistant. Similarly, all animal platelets tested for vWF-dependent aggregation with the two probes were highly reactive with botrocetin, but inactive with ristocetin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Purified human factor VIII procoagulant protein: comparative hemostatic response after infusions into hemophilic and von Willebrand disease dogs.

The procoagulant protein F.VIII:C is noncovalently bound to von Willebrand factor (vWF) to give the factor VIII macromolecular complex. New highly purified preparations of isolated human F.VIII:C, devoid of vWF and about 500,000-fold purified, were administered to hemophilia A and von Willebrand disease (vWD) dogs to determine their hemostatic effectiveness and survival in the circulation. Two preparations of F.VIII:C were used: peak 1, with active components of Mr 185,000-280,000, and peak 2, with a single component of Mr 170,000. In hemophilic dogs, with no plasma F.VIII:C but normal vWF, both preparations immediately elevated plasma F.VIII:C to expected levels, promptly stopped induced and spontaneous hemorrhages, and gave sustained plasma levels of F.VIII:C. The isolated F.VIII:C immediately complexed with endogenous vWF in hemophilic plasma and was eliminated exponentially, with a half-life (t1/2) of about 9 hr. Survival of peak 2 F.VIII:C was longer than that of peak 1 material. In contrast, F.VIII:C complexed to vWF in a therapeutic concentrate administered to hemophilic dogs was eliminated biexponentially with first-phase t1/2 of 3.2 hr and second-phase t1/2 of 9 hr. In vWD dogs with no vWF and reduced F.VIII:C levels, the isolated F.VIII:C produced supernormal levels of F.VIII:C without effect on induced bleeding. It was rapidly eliminated from plasma with a t1/2 of about 1 hr, as was the complexed F.VIII:C in the concentrate. These data indicate that isolated F.VIII:C promptly complexes with vWF and in this form is highly effective in controlling hemophilic hemorrhages with good survival in plasma. Without endogenous vWF with which to complex, the F.VIII:C is promptly eliminated.

Animals↗
PubMed1983

Botrocetin (venom coagglutinin): reaction with a broad spectrum of multimeric forms of factor VIII macromolecular complex.

Botrocetin, originally called venom coagglutinin, is a Bothrops factor that causes aggregation of blood platelets in the presence of the von Willebrand component of the factor VIII macromolecular complex. The complex consists of a series of multimers with a molecular weight of about 1-20 x 10(6). Ristocetin, another agent that causes platelet aggregation dependent on von Willebrand factor, reacts with only the higher molecular weight multimers. We report on the reactivity of botrocetin in relation to the multimeric structure of the factor VIII complex. Several plasmas or plasma fractions with abnormal distribution of the multimeric sizes were examined, including variant von Willebrand disease type IIA with lack of the higher molecular weight forms, commercial antihemophilic factor concentrates with a preponderance of lower molecular weight forms, cryoprecipitate-free plasma containing mainly the smaller multimers, and a chromatographic fraction of plasma containing only the highest molecular weight polymers. Factor VIII-related antigen content was adjusted to 25-100%. All of the preparations lacking the high molecular weight forms caused prompt platelet aggregation with botrocetin, but none of them caused aggregation in the ristocetin test made isochronal with the botrocetin test. The very high molecular weight polymers were equally effective with botrocetin and ristocetin. These findings indicate that the Bothrops factor is reactive with a broad spectrum of high to low molecular weight forms of the factor VIII complex, suggesting that bioassays of von Willebrand factor with botrocetin should correlate better with immunoassays for factor VIII-related antigen and could reflect better the full platelet-aggregating function of the complex than do ristocetin determinations.

Adolescent↗