Independence of serum lipid levels and dietary habits. The Tecumseh study

Serum cholesterol and triglyceride levels were correlated with dietary habits of 4,057 adult participants in a prospective epidemiologic survey of cardiovascular disease in Tecumseh, Mich. Frequency of consumption of 110 different food items was determined for each participant and average weekly consumption rates of foods high in fat, sugar, starch, and alcohol content were calculated. Frequency of consumption of these nutrients was then correlated with serum cholesterol and triglyceride levels of individual subjects. Serum cholesterol and triglyceride values were not positively correlated with selection of dietary constituents. Positive correlations between serum lipid levels and adiposity were statistically significant. These findings suggest that serum cholesterol and triglyceride levels among Americans are more dependent on degree of adiposity than on frequency of consumption of fat, sugar, starch, or alcohol.     

Systematic analysis of the direct methanol fuel cell

The dynamic operating behaviour of the direct methanol fuel cell (DMFC) is governed by several physico-chemical phenomena which occur simultaneously: double layer charging, electrode kinetics, mass transport inside the porous structures, reactant distributions in the anode and cathode flowbeds etc. Therefore it is essential to analyse the interactions of these phenomena in order to fully understand the DMFC. These phenomena were initially analysed independently by systematic experiments and model formulations. Electrode kinetics were determined by fitting models of varying complexity to electrochemical impedance spectroscopy (EIS) measurements. Reaction intermediates adsorbed on the catalyst seem to play a key role here. To describe mass transport across the DMFC a one-dimensional model was formulated applying the generalised Maxwell–Stefan equations for multi-component mass transport and a Flory–Huggins model for the activities of mobile species inside the membrane (PEM). Also swelling of the PEM as well as heat production and transport were considered. Finally, the anode flowbed was analysed by observing flow patterns in different flowbed designs and measuring residence time distributions (RTDs). Detailed CFD models as well as simpler CSTR network representations were used to compare to the experimental results. Even the simpler models showed good agreement with the experiments. After these investigations the results were combined: the electrode kinetics model was implemented in the mass transport model as well as in the CSTR network flowbed model. In both cases, good agreement, even to dynamic experiments, was obtained.     

E.s.r. measurements on asphaltene and resin fractions from various separation methods

Asphaltenes and resins obtained from Athabasca and Cold Lake bitumens (Alberta, Canada) have been fractionated by adsorption, ion-exchangers, and gel permeation chromatography. These fractions have been investigated by electron spin resonance (e.s.r.) of their organic paramagnetic components and vanadium (IV) content. The correlation between number of spins, vanadium content and fractions sequence is discussed.     

Structural Studies of Catalytic Antibodies

A panel of catalytic antibodies which catalyze ester hydrolysis, transesterification, porphyrin metallation, Diels-Alder, and redox reactions has been selected for crystallographic study. While these examples are only a handful of the catalytic antibodies generated to date, they represent distinct and important aspects of antibody catalysis. Since the first reports of catalysis, a great deal of progress has been made with respect to the scope, selectivity, and efficiency of antibody catalysis and strategies for generating catalytic antibodies. However, it is clear that further progress in the field will benefit greatly from a detailed understanding of the molecular interactions occurring in the combining site. High-resolution crystallographic data should allow the importance of general base catalysis, entropy effects, electrophilic catalysis, and transition-state stabilization to be evaluated. Antibody and enzyme active sites have been shown to share considerable structural and mechanistic similarity, and ongoing structure-function studies of catalytic antibodies may enhance our understanding of the mechanisms and evolution of enzymatic catalysis. Structural studies of antibodies which perform a biological or highly selective reactions should enhance our ability to generate catalysts for important synthetic applications. Finally, the combination of high-resolution crystallographic analysis with rational mutagenesis should provide a basis for engineering antibodies with enhanced properties.     

Using creep and recovery to study flow behavior of fresh cement paste

A controlled stress rheometer has been used to determine the creep and recovery behavior of flocculated cement pastes. The behavior was found to depend on the level of applied stress. At a lower applied stress, the creep curve of each paste was characteristics of a nonlinear viscoelastic solid, with an instantaneous strain superimposed on an elastic strain; the recovery, on the other hand, was characteristics of a viscoelastic liquid, with little or no instantaneous strain, but some retarded strain and a substantial unrecovered strain. At a higher applied stress the behavior was strikingly different. In this case, the behavior was characteristics of a viscous liquid, with a nearly linear increase in strain throughout the duration of the stress and no recovery when the stress was released. This transition from solid-like behavior to liquid-like behavior occurred over a very narrow stress increment, and the transition stress corresponded to the yield stress estimated from flow curves and from oscillatory shear measurements.     

Claude H. Organ, Jr. Honorary/Sandoz Nutrition Lectureship. Ethics in research and surgical practice

The topic "Ethics in Research and Surgical Practice" appears most appropriate for the 1997 Claude H. Organ, Jr. Honorary Sandoz Nutrition Lecture. With the increasing numbers of ethical problems facing clinicians today, greater emphasis on ethics is demanded. This lecture focuses primarily on the clinical applications of basic science and ethics certainly plays a major role in this regard. Ethical principles espoused by the American College of Surgeons and the American Medical Association will be emphasized. Further, the results of the deliberations of the Advisory Committee on Human Radiation experiments will be discussed. Certainly, the Tuskegee experiment debacle will be mentioned. Ethics remains important if we are to give our patients the best care. We must always keep in the vanguard of our thinking that the welfare of our patients comes first. High ethical principles emphasize our obligations and responsibilities to our patients.     

Linear epitope mapping of humoral responses induced by vaccination with recombinant HIV-1 envelope protein gp160

Ischemic preconditioning of the myocardium with repeated brief periods of ischemia and reperfusion prior to prolonged ischemia significantly reduces subsequent myocardial infarction. Following ischemic preconditioning, two "windows of opportunity" (early and late) exist, during which time prolonged ischemia can occur with reduced infarction size. The early window occurs at approximately 4 hours and the late window at 24 hours following ischemic preconditioning of the myocardium. We investigated if ischemic preconditioning of skeletal muscle prior to flap creation improved subsequent flap survival and perfusion immediately or 24 hours following ischemic preconditioning. Currently, no data exist on the utilization of ischemic preconditioning in this fashion. The animal model used was the latissimus dorsi muscle of adult male Sprague-Dawley rats. Animals were assigned to three groups, and the right or left latissimus dorsi muscle was chosen randomly in each animal. Group 1 (n = 12) was the control group, in which the entire latissimus dorsi muscle was elevated acutely without ischemic preconditioning. Group 2 (n = 8) investigated the effects of ischemic preconditioning in the early window. In this group, the latissimus dorsi muscle was elevated immediately following preconditioning. Group 3 (n = 8) investigated the effects of ischemic preconditioning in the late window, with elevation of the latissimus dorsi muscle 24 hours following ischemic preconditioning. The preconditioning regimen used in groups 2 and 3 was two 30-minute episodes of normothermic global ischemia with intervening 10-minute episodes of reperfusion. Latissimus dorsi muscle ischemia was created by occlusion of the thoracodorsal artery and vein and the intercostal perforators, after isolation of the muscle on these vessels. Muscle perfusion was assessed by a laser-Doppler perfusion imager. One week after flap elevation, muscle necrosis was quantified in all groups by means of computer-assisted digital planimetry. Our results show that ischemic preconditioning resulted in a significant reduction (p < 0.05) in muscle-flap necrosis immediately and 24 hours following ischemic preconditioning. Perfusion changes after flap elevation were similar among the three groups. Ischemic preconditioning of skeletal muscle prior to flap creation significantly reduces subsequent muscle-flap necrosis caused by the ischemia of flap creation immediately and 24 hours following ischemic preconditioning. Further elaboration of the mechanisms of ischemic preconditioning may allow pharmacologic preconditioning to be used in the augmentation of skeletal muscle-flap survival in the clinical setting.     

The influence of poly-(L-lysine) and porin on the domain structure of mixed vesicles composed of lipopolysaccharide and phospholipid: an infrared spectroscopic study

Fourier transform infrared (FTIR) spectroscopy has been used to study the thermotropic phase behavior of binary lipid mixtures composed of deuterated phospholipids (PLs) and lipopolysaccharides (LPSs). Furthermore, the influence of an extrinsic high-molecular, polycationic polypeptide (poly-(L-lysine), PLL(500)) and an intrinsic membrane protein (outer membrane protein F, OmpF) on these binary mixtures was investigated by FTIR spectroscopy. "Deep rough" mutant LPS (ReLPS), isolated from Salmonella minnesota R595, and perdeuterated 1,2-dimyristoylphosphatidylethanolamine (DMPEd54) were used as model lipids. Deuteration of one of the lipids permitted the detection of lipid protein interaction with each lipid component separately. For this purpose, the symmetric >CH2 and >CD2 stretching bands were utilized as specific monitors to scrutinize the state of order of the membranes. From the individual phase transition temperatures Tm and the shape of the phase transition profiles, it is established that ReLPS and DMPEd54 are molecularly immiscible. In addition to the two domains of the pure lipid components, a third, domain-like structure is detected that may coexist with these pure domains. This domain-like structure undergoes a gel to liquid-crystalline L1 (beta <--> alpha) phase transition at temperatures distinctly different from that of the respective pure lipid domains. The nature of this type of domain is discussed in terms of a "border region" model that adequately explains the experimentally observed complex phase transition profiles. It is further demonstrated that the extrinsic polycationic polypeptide PLL(500) and the intrinsic, pore-forming protein OmpF isolated from Escherichia coli interact preferentially and highly specifically with the negatively charged ReLPS. Both the synthetic polypeptide and the pore-forming protein increased the tendency of ReLPS and DMPEd54 to segregate into distinct, well-separated domains. Whereas the transition profiles of the ternary system ReLPS/DMPEd54/PLL(500) showed the features of a phase segregation phenomenon not affecting the transition temperatures of the pure lipid components, the ternary system composed of ReLPS/DMPEd54 and OmpF exhibited phase transition curves that were characterized by an unspecific (DMPEd54/OmpF) and a strong and unique (ReLPS/OmpF) type of lipid-protein interaction. Furthermore, semiquantitative estimations supported the supposition that OmpF might be able to induce bilayer asymmetry in preformed symmetrical ReLPS/DMPEd54 vesicles.