James A. Marcum

Acceleration of thrombin-antithrombin complex formation in rat hindquarters via heparinlike molecules bound to the endothelium.

We have examined the role of heparinlike molecules in the regulation of coagulation by perfusing rat hindquarters with purified human thrombin and with its plasma inhibitor, antithrombin. Our data indicate that contact of the hemostatic components with the endothelium enhances the rate of thrombin-antithrombin complex formation by as much as 19-fold over the uncatalyzed rate of enzyme-inhibitor interaction. Heparinlike molecules are responsible for the antithrombin accelerating activity. The amount of thrombin-antithrombin complex generated within the hindlimb preparation after pretreatment of the vasculature with purified Flavobacterium heparinase or with addition of platelet Factor IV to the hemostatic components, was equal to the uncatalyzed levels. These heparinlike molecules appear to be tightly bound to the luminal surface of the endothelium, since they could not be detected within the physiologic buffer that was perfused through the animal. The above mucopolysaccharides function in a manner similar to commercial heparin, since modification of antithrombin at a site critical for heparin-dependent acceleration of the protease inhibitor resulted in a level of interaction product identical to the uncatalyzed amount. Finally, addition of diisofluorophosphate-thrombin to the enzyme perfusion stream reduced the amount of thrombin-antithrombin complex formed in the animal by 30-40%, which suggested that thrombin bound to the endothelium as well as enzyme free in solution are accessible to antithrombin that has interacted with heparinlike molecules present on the endothelium.

Heparinlike molecules with anticoagulant activity are synthesized by cultured endothelial cells

Cultured microvascular endothelial cells isolated from rat epididymal fat pads produce glycosaminoglycans that accelerate thrombin-antithrombin complex formation. The heparinlike nature of these macromolecules was established by complete destruction of their anticoagulant activity employing purified Flavobacterium heparinase. Only 15% of the biologic activity of these complex carbohydrates was expressed when the heparin binding domain on the protease inhibitor was chemically modified at the Trp 49 residue. The anticoagulantly active species contains disaccharides which constitute the unique antithrombin binding region of the mucopolysaccharide. Removal of the biologically active heparinlike components from endothelial cells with 0.05% trypsin suggests that these molecular species are present on the cell surface.

An integrated model of clinical reasoning: dual-process theory of cognition and metacognition

RATIONALE AND AIM Clinical reasoning is an important component for providing quality medical care. The aim of the present paper is to develop a model of clinical reasoning that integrates both the non-analytic and analytic processes of cognition, along with metacognition. METHOD The dual-process theory of cognition (system 1 non-analytic and system 2 analytic processes) and the metacognition theory are used to develop an integrated model of clinical reasoning. RESULTS In the proposed model, clinical reasoning begins with system 1 processes in which the clinician assesses a patients presenting symptoms, as well as other clinical evidence, to arrive at a differential diagnosis. Additional clinical evidence, if necessary, is acquired and analysed utilizing system 2 processes to assess the differential diagnosis, until a clinical decision is made diagnosing the patients illness and then how best to proceed therapeutically. Importantly, the outcome of these processes feeds back, in terms of metacognitions monitoring function, either to reinforce or to alter cognitive processes, which, in turn, enhances synergistically the clinicians ability to reason quickly and accurately in future consultations. CONCLUSIONS The proposed integrated model has distinct advantages over other models proposed in the literature for explicating clinical reasoning. Moreover, it has important implications for addressing the paradoxical relationship between experience and expertise, as well as for designing a curriculum to teach clinical reasoning skills.

Species specificity of streptokinase

Streptokinase, a bacterial protein, forms a complex with human plasminogen which results in a conformational change in the plasminogen molecule and the exposure of an active center. The plasminogen-streptokinase complex is an activator of plasminogen and is rapidly converted to a plasmin-streptokinase complex which, in the human, is also an activator of plasminogen. Species differences have been found in the reaction of streptokinase with plasminogen varying from no active complex formation at one extreme to the rapid formation of an active activator complex at the other, with resultant differences in rates of complex formation and the yield of plasmin. Explanation of these species differences at a molecular level are discussed as well as the possible application of complex formation in a variety of biological systems as a mechanism to produce variation in enzyme activities in proportion to the concentration of substrate available.

Reflections on Humanizing Biomedicine

Although biomedicine is responsible for the “miracles” of modern medicine, paradoxically it has also led to a quality-of-care crisis in which many patients feel disenfranchised from the health-care industry. To address this crisis, several medical commentators make an appeal for humanizing biomedicine, which has led to shifts in the philosophical boundaries of medical knowledge and practice. In this paper, the metaphysical, epistemological, and ethical boundaries of biomedicine and its humanized versions are investigated and compared to one another. Biomedicine is founded on a metaphysical position of mechanistic monism, an epistemology of objective knowing, and an ethic of emotionally detached concern. In humanizing modern medicine, these boundaries are often shifted to a metaphysical position of dualism/holism, an epistemology of subject knowing, and an ethic of empathic care. In a concluding section, the question is discussed whether these shifts in the philosophical boundaries are adequate to resolve the quality-of-care crisis.

Anticoagulantly active heparin from clam (Mercenaria mercenaria).

Heparin was isolated from Mercenaria mercenaria by ion-exchange chromatography and was fractionated into two distinct populations with immobilized antithrombin. The high-affinity glycosaminoglycan accelerated dramatically the inhibition of purified human factors IIa and Xa via purified human antithrombin. Specific anti-factor IIa and anti-factor Xa activities were 363 and 348 U.S.P. units/mg, respectively. The highly active clam heparin exhibited a molecular weight of approximately 18,000 and contained approximately 2.5 sulfate groups per disaccharide. The intrinsic fluorescence of purified human antithrombin was enhanced in the presence of the high-affinity invertebrate glycosaminoglycan to an extent comparable to the level induced by vertebrate heparin. In addition, the critical tetrasaccharides containing 3-O-sulfated glucosamine residues, which constitute part of the unique antithrombin-binding domain of mammalian heparin, were also detected in high-affinity Mercenaria heparin.

The epistemically virtuous clinician

Today, modern Western medicine is facing a quality-of-care crisis that is undermining the patient–physician relationship. In this paper, a notion of the epistemically virtuous clinician is proposed in terms of both the reliabilist and responsibilist versions of virtue epistemology, in order to help address this crisis. To that end, a clinical case study from the literature is first reconstructed. The reliabilist intellectual virtues, including the perceptual and conceptual virtues, are then discussed and applied to the case study. Next, a similar method is employed to examine the responsibilist intellectual virtues, including curiosity, courage, honesty, and humility, and to apply them to the case study. To round out the discussion, the love of knowledge and both theoretical and practical wisdom are explored and applied to the case study. The paper concludes with a brief discussion of how the notion of an epistemically virtuous clinician addresses the quality-of-care crisis, in terms of the connection between ethical and intellectual virtues, and of the notion’s implications for medical education.

‘Soup’ vs. ‘Sparks’: Alexander Forbes and the Synaptic Transmission Controversy

Summary During the twentieth century, a controversy raged over the role of electrical forces and chemical substances in synaptic transmission. Although the story of the ‘main’ participants is well documented, the story of ‘lesser’ known participants is seldom told. For example, Alexander Forbes, who was a prominent member of the axonologists, played an active role in the controversy and yet is seldom mentioned in standard accounts of the controversy. During the 1930s, Forbes incorporated chemical substances into his theory of synaptic transmission, advocating a complementarity model for the role of electrical forces and chemical substances. By focusing on Forbes and the axonologists, the controversy is simply more than a debate over ‘soup’ vs. ‘sparks’ but also involves the relative roles of electrical forces and chemical substances in synaptic transmission. The implications of this case study for the nature of scientific controversies are also discussed.

Metaphysical presuppositions and scientific practices: Reductionism and organicism in cancer research

Metaphysical presuppositions are important for guiding scientific practices and research. The success of twentieth‐century biology, for instance, is largely attributable to presupposing that complex biological processes are reducible to elementary components. However, some biologists have challenged the sufficiency of reductionism for investigating complex biological phenomena and have proposed alternative presuppositions like organicism. In this article, contemporary cancer research is used as a case study to explore the importance of metaphysical presuppositions for guiding research. The predominant paradigm directing cancer research is the somatic mutation theory, in which mutated genes are presumed to be ultimately responsible for explaining carcinogenesis. This reductionistic approach to cancer has been criticised recently, and an organistic approach has been proposed. The article concludes with a discussion of the reciprocal interaction of metaphysical presuppositions and scientific practices for investigating cancers complex nature.

The amino-terminal region of a proteochondroitin core protein, secreted by aortic smooth muscle cells, shares sequence homology with the pre-propeptide region of the biglycan core protein from human bone.

Smooth muscle cells, isolated from rat and bovine aortae and grown in vitro, synthesize chondroitin sulfate proteoglycans which are secreted into the growth media. Analysis of metabolically [35S]-labeled macromolecules, employing ion-exchange chromatography, revealed a single peak of radioactivity, upon elution with a linear salt gradient. Treatment of the material with enzymes that specifically degrade chondroitin sulfate demonstrated that chondroitin-4-sulfate was the predominant species isolated from rat smooth muscle cells and that chondroitin-4-sulfate and dermatan sulfate were the predominant species isolated from bovine aortic smooth muscle cells. Treatment of the native proteoglycans with chondroitinase ABC and subsequent SDS-PAGE analysis of the digestion products resulted in the appearance of a band with an apparent molecular weight of 45,000. Electrotransfer of the core protein to Immobilon-P membrane and gas phase sequencing of the amino-terminal region revealed striking homology between the core proteins of the rat and bovine proteochondroitin with the pre-propeptide region of human bone biglycan.