Citations

SummaryWhen 125I-labeled canine prothrombin was given to normal adult dogs intravenously, it was calculated that 240% of the plasma prothrombin crossed the capillary barrier per day, 410% of the interstitial prothrombin returned to the blood stream daily, and 79% of the plasmatic prothrombin was catabolized per day. These data are in close agreement with those observed for bovine prothrombin in calves by Takeda (1970).When derived from normal dog prothrombin, prethrombin-1 is a mixture of 2 polypeptides, one larger than the other, and both present in about equal amounts. The longer peptide, “prethrombin-1-long,” was catabolized twice as fast as prothrombin, and the shorter, “prethrombin-1-short,” 4 times faster. Prothrombin fragment-1 was catabolized by the normal dog still more rapidly.The catabolism of prothrombin was not accelerated in 3 dogs receiving continuous infusions of a thromboplastic emulsion of dog brain. Nor was the level of prothrombin in their plasma remarkably altered.

SummaryReversibility in vivo of acute platelet thrombosis in response to specific anticoagulants is analyzed with thrombi that develop in segments (1 cm) of porcine carotid arteries externally crushed with a hemostat. Most thrombi fill the lumens of the injured segments (ca. 1 cm × 3 mm, 1 × w) within 30 min and comprise masses of platelets interpenetrated with neutrophil-lined seepage channels of blood. Continuous quantitative assay of thrombus mass is provided by a gamma detector placed over the injured segments to collect counts from 111In-labeled platelets. Thrombi established 30 min after injury, otherwise stable for 6 h, clear during 30-60 min of continuous infusion of either hirudin, tick anticoagulant or activated porcine protein C, or intermittent activation of endogenous protein C with a latent thrombin reagent. Anticoagulant dose-dependence of thrombus clearance is established for hirudin between 0.01 and 1.0 mg/kg/min. Thrombi become progressively refractory to hirudin between 0.5 and 6 h after injury. Neither heparin nor low-molecular-weight heparin in full (clinical) anticoagulant doses yield significant dethrombosis. It is concluded that, within time limits, controlled thrombin generation in platelet thrombi maintains platelet cohesion without catalyzing irreversible platelet aggregation or clotting of fibrinogen.

An automated method for specific factor assays has been developed using a novel thrombin-specific chromogenic substrate (developed by A. Aiyappa, Ph. D., Abbott Labs). For factors VIII, IX, XI and XII, the test system includes an ellagic acid activator and brain phospholipid in a calcium containing tris buffer pH 7.4. These are mixed with a plasma sample consisting of a mixture of specific factor deficient substrate and test plasma for 5 minutes and then the chromogenic substrate is added. After another 5 minutes the increase in optical density ΔOD is recorded. Normal plasma serially diluted in specific factor deficient substrate is used to construct a standard graph and test plasma results are interpolated from this.Fifty-four comparative assays have been done for factors VIII and IX and correlated with the results obtained from conventional clotting assays. For factor VIII the correlation coefficient (r)=0.935 (N=35) and for factor IX r=0.941 (N=19). While insufficient data exists to date for factors XI and XII, these assays appear to be comparable to the VIII and IX results.The assays for factors V, VII and X use a simplified system in that the chromogenic substrate and phospholipid are added together. The ΔOD is again recorded after 5 minutes. Test plasma results are interpolated from a standard graph constructed using serially diluted normal plasma as before. To date only the factor V assay has enough data to do a correlation with the clotting assays and r=0.953 (N=13) which is similar to the r value for the VIII and IX assays.Because of the widespread availability of the automated analyzer used in the assay and the standardization of end point determination it provides, specific factor assays might be made more widely available outside specialized coagulation centers.

Measuring the release of small amounts of a clotting factor from an isolated perfused rat liver is difficult if the perfusate already contains some of the factor. Further, platelet-containing perfusates generate a coagulant activity that may invalidate clotting assays.We have successfully employed a completely synthetic blood substitute for rat liver perfusions. The perfusate is “Fluosol-43” generously furnished by Alpha Therapeutic Corporation. The oxygen-carrying perfluorochemical is FC-43 (perfluorotributylamine) and the substitute for albumin is hydroxyethyl starch. Using the Brauer perfusion technique, we found that rat livers in 5 hours released an average of 2.3% of the normal plasma concentration of prothrombin, 8.4% factor V, 16.2% factor VII, 7.0% factor IX, 3.7% factor X, 28.3% factor XI and 12.3% factor XII. Antithrombin III and plasminogen were also generated.Only minute amounts of factor VIII were released unless serum, cryoprecipitate or cryoprecipitate-free plasma was added; then the yield was 8.8% on average. The more “venom factor” (platelet aggregability with Bothrops alternata venom) added to the synthetic perfusate, the more factor VIII was released.

SummaryThe relative contribution of plasmin, miniplasmin, PMN-elastase and cathepsin G to the fibrin-gel dissolution is studied. The global kcat/KM ratios are determined as a measure of the fibrinolytic catalytic efficiency using spectrophotometric kinetic analysis of the competition between fibrin and synthetic peptide substrates for the proteases, turbi-dimetric assay for fibrin dissolution and gel-filtration of the partially degraded fibrin. When the substrate is fibrin polymerized in the presence of 3 mM Ca2+, the value of this ratio is 4.3 × 105 M-1·s-1 for plasmin, 1.9 × 105 M-1·s-1 for miniplasmin, 5.0 × 104 M-1·s-1 for PMN-elastase and 2.2 × 103 M-1·s-1 for cathepsin G. When fibrin is polymerized without addition of Ca2+, the kcat/KM values are increased by a factor of 2.3 for plasmin, 2.0 for miniplasmin and 1.6 for cathepsin G, whereas that of PMN-elastase is unchanged. Progressive crosslinking of fibrin decreases the catalytic action of all studied proteases, but no change in their relative contribution to fibrinolysis is observed. When plasmin inhibitor (at physiological concentration) is also crosslinked to fibrin, the most efficient fibrinolytic enzymes are miniplasmin and PMN-elastase. The effect of 6-aminohexanoate on the formation of fibrin degradation products by plasmin and miniplasmin suggests that the high-affinity lysine binding site in the N-terminal kringle domain of plasmin is involved in the interactions with the native polymerized fibrin, whereas the fifth kringle found in both enzymes participates in binding to newly exposed lysine residues. These results provide a quantitative basis for the evaluation of fibrinolytic efficiency and support the concept of synergistic fibrinolysis.

SummaryThe plasmin substrate, H-D-norleucyl-hexahydrotyrosyl lysine-p-nitroanilide (Spectrozyme-PL), was found to be equiva lent to 6-aminohexanoate as an enhancer of porcine and human plasminogen activation by urokinase and of removal of the 1-77 peptide of plasminogen by plasmin. Activation of plasminogen lacking kringles 1-4, on the other hand, was not influenced by Spectrozyme PL. Although the rate of activation of human plasminogen and the modification of human plasminogen by plasmin are faster by an order of magnitude than that of the activation and modification of porcine plasminogen, both reactions in the human zymogen, the hydrolysis at arg561-val562 and at lys77lys78, are accelerated by Spectrozyme PL. The findings indicate that kinetic interpretation of plasminogen activation in solutions containing substrates, where the substrate has been incorporated to inhibit feedback proteolysis by plasmin, must account for the cofactor activity as well as the inhibitory activity of the substrate.

AbstractIntroductionType 2 diabetes mellitus and obesity may increase risks for cognitive decline as individuals age. It is unknown whether this results in different prevalences of cognitive impairment for women and men.MethodsThe Action for Health in Diabetes, a randomized controlled clinical trial of a 10‐year intensive lifestyle intervention, adjudicated cases of cross‐sectional cognitive impairment (mild cognitive impairment or dementia) 10–13 years after enrollment in 3802 individuals (61% women).ResultsThe cross‐sectional prevalences of cognitive impairment were 8.3% (women) and 14.8% (men): adjusted odds ratio 0.55, 95% confidence interval [0.43, 0.71], P < .001. Demographic, clinical, and lifestyle risk factors varied between women and men but did not account for this difference, which was limited to individuals without apolipoprotein E (APOE)‐ε4 alleles (interaction P = .034).ConclusionsAmong overweight and obese adults with type 2 diabetes mellitus, traditional risk factors did not account for the lower prevalence of cognitive impairment observed in women compared with men.

Sudden unexpected death is typically diagnosed in infants, children, teenagers, and young adults following completion of an autopsy that fails to identify a cause of death or when autopsy suggests a potentially genetic cause of death in an individual less than 40, such as cardiomyopathy or aneurysm. Such deaths may be a result of genetic abnormalities that are unable to be diagnosed by gross or microscopic inspection, but may be detectable by molecular studies. Unfortunately, the ability to perform postmortem genetic testing is frequently hindered by lack of an appropriate specimen following completion of an autopsy. This paper provides recommendations developed by the National Association of Medical Examiners with the assistance of genetic counselors. The recommendations establish procedures to facilitate postmortem genetic testing and DNA banking by health care professionals assisting families who have experienced sudden death in young relatives by clarifying proper sample acquisition and storage. Additionally, recommendations for discussion with surviving family members and test planning are provided. The objective of these recommendations is to ensure that postmortem samples suitable for DNA banking are retained, allowing at risk family members improved detection of potentially treatable genetic diseases.