PubMed Health⌕ Search

Biomedical subjects

R H Wagner

Publications and source records attributed to R H Wagner.

At least 55 records · Page 3Linked to original sources
PubMed1975

Platelets fixed with paraformaldehyde: a new reagent for assay of von Willebrand factor and platelet aggregating factor.

Present methods for assay of platelet aggregating agents use freshly prepared platelets. Much time is spent in daily preparation of platelets and standardization presents problems. The preparation of fixed washed platelets (FWP) and their use in two bioassays are described in this report. Washed human platelets were fixed for 48 hours with 4 per cent paraformaldehyde, washed twice in phosphate buffer, pH 6.4, and stored at 4 degrees C. Aggregation of FWP was studied with a macroscopic test and a light absorbance measurement. FWP did not aggregate with adenosine diphosphate, collagen, adrenalin, and thrombin. FWP aggregated with bovine or porcine plasma, poly-L-lysine, and ristocetin with normal human plasma but not with von Willebrand's disease plasma. These observations confirm the direct aggregating effect of these agents. Macroscopic aggregation times were dependent on the amount of aggregating agent (bovine plasma, normal human plasma). A quantitative assay for bovine platelet aggregating factor (PAF) and von Willebrand factor (vWF) with FWP was developed. The ability of FWP to aggregate remained unchanged after 1 month of storage at 4 degrees C. Ristocetin alone caused a decrease in light transmission of FWP suspensions, depending upon the concentration of ristocetin, but did not cause aggregation. FWP constitute a stable reagent suitable for quantitative measurement of PAF and vWF.

Animals↗
PubMed1974

Von Willebrand factor: gene dosage relationships and transfusion response in bleeder swine--a new bioassay.

Aggregation of human platelets by bovine plasma was recently recognized as a marker for the study of the antihemophilic and von Willebrand factors. A similar marker in porcine plasma is shown to be specific for the platelet-active von Willebrand factor of plasma, but not for the antihemophilic factor (factor VIII). A new quantitative assay for the von Willebrand factor is based on the dose-response relationship observed between the concentration of von Willebrand factor and platelet aggregation times determined macroscopically. Bleeder swine, homozygous for von Willebrand disease, had no detectable platelet aggregating activity, while heterozygotes, carriers of the disease, had reduced levels of approximately 50% of normal. Exact detection of non-obligate carriers, hitherto impossible, becomes readily feasible because of the gene dosage relationship to the von Willebrand factor plasma levels. Transfusion of bleeder swine with normal plasma results in an immediate post-transfusion rise of the von Willebrand factor, followed by a rapid falloff. At 24 hr post-transfusion, no von Willebrand factor is detectable at a time when the factor VIII response is at its maximum. The discordance in plasma levels of this platelet-active von Willebrand factor and factor VIII in carrier animals and in the bleeder animals after transfusion suggests a different molecular and genetic basis for these two biological activities.

Animals↗
PubMed1974

Nature of von Willebrand factor: a new assay and a specific inhibitor.

Platelet-active "von Willebrand factor" is a poorly characterized activity of a plasma-protein macromolecular complex. A new simple assay for von Willebrand factor is based on the dose response relation of the factor and the ristocetin platelet aggregation time. This assay uses the "snowstorm" macroscopic endpoint. A multiply transfused subject with von Willebrand's disease was observed to have a circulating inhibitor that blocks normal ristocetin aggregation of platelets, but not ADP-, epinephrine-, or collagen-induced aggregation. The inhibitor was not adsorbed by normal platelets, and was stable to heating at 56 degrees for 30 min and to repeated freezings and thawings. This inhibitor also prevents action on human platelets by platelet-aggregating factor of bovine plasma, indicating this bovine factor activity is a function of von Willebrand factor. Three inhibitors were compared: (1) the von Willebrand factor inhibitor specifically blocked von Willebrand factor activity, (2) a human antibody from a hemophiliac inhibited only antihemophilic factor activity, and (3) a rabbit antiserum to a preparation of human antihemophilic factor inhibited both activities. The active site for von Willebrand factor on the macromolecular complex appears to be spaced some distance from the antihemophilic factor site.

Adenosine Diphosphate↗
PubMed1974

The defect in hemophilic and von Willebrand's disease plasmas studied by a recombination technique.

Factor VIII in preparations from normal plasma is a large glycoprotein of greater than 2 million molecular weight which elutes in the exclusion volume of 4% agarose gels at an ionic strength of 0.15. Recent studies have demonstrated that the factor VIII in canine and bovine plasma is a macromolecular complex composed of a large inert carrier protein and a noncovalently bound small fragment which contains the procoagulant active site. This complex is dissociable in 0.25 M CaCl(2), and conditions for its recombination have been reported. The present study reports the dissociation characteristics of normal human factor VIII preparations in 0.25 M CaCl(2) and the ability to achieve quantitative recombination of the dissociated fragments of normal human and bovine factor VIII after the removal of Ca(2+). The recombination technique was used to characterize further the defect in hemophilia and von Willebrand's disease. Void volume preparations from human hemophilia A(-), canine hemophilia A, and human von Willebrand's plasma, with no factor VIII procoagulant activity, were mixed with the small active fragment prepared from the normal plasma of their respective species. Chromatography of the three mixtures in agarose gel showed that the fractions from the human hemophilic plasmas contained a molecule that bound the small active normal fragment, but neither the fractions from canine hemophilia A plasmas nor the fractions from the human von Willebrand's plasmas demonstrated evidence of such material. These data suggest that there is present in human hemophilia A plasma a normal functional carrier molecule which is absent or nonfunctional in the plasma of hemophilic dogs and humans with von Willebrand's disease.

Animals↗
PubMed1973

Plasma aggregating factor (bovine) for human platelets: a marker for study of antihemophilic and von Willebrand Factors.

The human-platelet aggregating factor in preparations of bovine plasma and bovine antihemophilic factor has been reported to be an activity of bovine antihemophilic factor. However, we show that activities of aggregating factor and antihemophilic factor are present in varying proportion in different preparations of antihemophilic factor. Aggregating factor activity is more stable on storage than is antihemophilic factor activity and can be selectively adsorbed by human platelets. Further, antihemophilic factor activity free of aggregating activity was eluted from DEAE-Sephadex. The factors were also separated during agarose chromatography in 0.25 M CaCl(2), which yields a small-molecular-weight moiety with antihemophilic factor activity; aggregating factor activity continued to elute in the void volume. Thus, aggregating factor activity is clearly separable from antihemophilic factor activity. The usual physiologic platelet-aggregating reactions require fresh platelets. Fresh, aged, and sonicated platelets, but not platelets that have been frozen and thawed, react with aggregating factor, indicating that the platelet "receptor sites" for the aggregating factor are unusually stable.

Animals↗
PubMed1973

Factor VIII recombination after dissociation by CaCl12.

Factor VIII is a large protein molecule of molecular weight 2,000,000 or larger that elutes in the void volume on agarose gel chromatography. It has been shown previously that high concentrations of alkali halides and, more specifically, 0.25 M Ca(2+) dissociate the molecule into a large carrier protein and a small fragment that retains the factor VIII activity. Factor VIII was prepared from normal canine plasma collected in sodium oxalate and heparin and adsorbed with BaSO(4). Results with Ca(2+) dissociation were the same as those obtained with fraction prepared from canine plasma collected in sodium citrate. The addition of 0.1 M epsilon-aminocaproic acid in the dissociation step had no effect. Fractionation of canine hemophilic plasma produced preparations without activity, and no activity was found when these inert preparations were dissociated with Ca(2+). These results indicate that the Ca(2+) dissociation is a true dissociation and not caused by enzymatic degradation by plasmin, thrombin, or activated factors VII, IX, or X. The apparent molecular weight of the small active fragment of factor VIII determined by gel chromatography was about 100,000. Finally, when the large carrier protein and the small active fragment of factor VIII were separated by gel chromatography, mixed, and dialyzed free of Ca(2+), they recombined to form a large active molecule that appeared in the void volume on agarose gel chromatography.

Aminocaproates↗
PubMed1969

Factor XIII in human plasma and platelets.

Plasma and platelet factor XIII levels were measured in normal human donors and in a patient congenitally deficient in factor XIII. The purpose of these experiments was to study the role of platelet factor XIII in blood coagulation. On polyacrylamide disc electrophoresis, factor XIII activity in extracts of washed normal platelets appeared as a single peak. This peak was missing or very low when factor XIII-deficient platelet extract was used. The patient was also studied before and after transfusion of fresh frozen plasma. Before transfusion, factor XIII activity could not be detected in the patient's plasma or platelet extracts. 24 hr after transfusion the plasma factor XIII level was still at the anticipated value, but factor XIII activity could not be detected in the platelet extracts. These experiments imply that plasma factor XIII was not transported across the platelet membrane in measurable quantities in vivo. This suggests that platelet factor XIII is a true platelet component and originates in the platelet precursor, the megakaryocyte. Thrombelastographic studies suggest that platelet factor XIII participates in the coagulation process. Thrombelastograms of factor XIII-deficient samples had decreased maximum amplitude and clot elasticity values. The abnormalities were fully corrected by the addition of washed normal platelets to factor XIII-deficient plasma; preincubation of the normal platelets in the deficient plasma had no additional effect. This indicates that platelet factor XIII is immediately available during clot formation.

Adolescent↗