Radioactive Tracer Studies Research Articles

X-ray diffraction investigation of the sulphur induced 4 × 1 reconstruction of Ni(110)

The atomic structure of the Ni(110)4 × 1-S reconstruction has been determined on the basis of surface X-ray diffraction measurements. An analysis of the in-plane diffraction data shows that the model consists of Ni rows along the [001] direction, two for every 4 × 1 unit cell, corresponding to 0.5 ML Ni coverage. The S is chemisorbed in pseudo two-fold hollow sites both on the Ni rows and in the troughs between the rows with a S coverage of 0.75 ML. Furthermore, rod-scans along fractional-order reflections reveal sub-surface relaxations. The results are in good agreement with recent STM and previous AES and radioactive tracer studies.

Mechanisms of Viability in Rabbit Flank Venous Flaps

Venous flaps may become more versatile in reconstruction and offer different opportunities to reconstructive surgeons if the mechanisms of their viability is clarified. In this study, axial pattern flank flaps in rabbits were converted into venous flaps by dividing the cutaneous pedicles and ligating the artery. Fluorescein and radioactive tracer studies were performed to elucidate the mechanisms of possible circulation. It is hypothesized that the venous flaps do not have a capillary circulation, but veins transport the fluid out, which is drawn into the capillaries from the interstitium, and that the nutrients and oxygen for flap viability diffuse from the wound bed. Venous drainage plays an important role by draining the metabolites away until revascularization offers a more direct supply.

Applications of emission tomography to radioactive tracer studies on an experimental high-pressure boiler

Applications of emission tomography to radioactive tracer studies on an experimental high-pressure boiler

A new continuous hydride generator for the determination of arsenic, Antimony and tin by hybride generation atomic absorption spectrometry

A new continuous hybride generator is described. Its characteristics are compared with a conventional hybride generator for the determination of arsenic, antimony and tin by using flame atomic absorption spectrometry. This simple hybride generator combines hybride production and gas-liquid separation in one unit, obviating the use of a separate mixing/reaction coil and gas-liquid separator. Radioactive tracer studies show that a hybride generation efficiency of over 95% is achieved with the new hybride generator and that approximately 90% of monomethylarsonic acid (MMA) is converted to its hybride (methylarsine) within the first 10 s of the hybride generation reaction. Compared to a conventional hybride generator, an improved signal-to-noise ratio is achieved and comparable or less interference from transition metal ions is observed. Cysteine (1% in the sample solution) is effective in reducing interferences during the hybride generation processes. In the presence of cysteine, 10–1000 fold higher amounts of Ni 2+, Co 2+ and Cu 2+ are tolerated in the determination of arsenic, antimony and tin. Cysteine also enhances the signals of arsenic, antimony and tin by 60, 200 and 40%, respectively. Reaction conditions were optimized by using both the simplex optimization method and one-factor-at-a-time method and results are in good agreement.

Simplification of complex kinetic models used for the quantitative analysis of nuclear magnetic resonance or radioactive tracer studies

A method for simplifying the mathematical models describing the dynamics of tracers (e.g.13C, 31P, 14C, as used in NMR studies or radioactive tracer experiments) in (bio-)chemical reaction systems is presented. This method is appropriate in the cases where the system includes reactions, the rates of which differ by several orders of magnitude. The basic idea is to adapt the rapid-equilibrium approximation to tracer systems. It is shown with the aid of the Perron–Frobenius theorem that for tracer systems, the conditions for applicability of this approximation are satisfied whenever some reactions are near equilibrium. It turns out that the specific enrichments of all of the labelled atoms that are connected by fast reversible reactions can be grouped together as ‘pool variables’. The reduced system contains fewer parameters and can, thus, be fitted more easily to experimental data. Moreover, the method can be employed for identifying non-equilibrium and near-equilibrium reactions from experimentally measured specific enrichments of tracer. The reduction algorithm is illustrated by studying a model of the distribution of 13C-tracers in the pentose phosphate pathway.

Ion diffusivity from the growth rate of crystalline complex PEO 3NaSCN

The growth rate of the crystalline complex PEO 3NaSCN from an undercooled liquids is used to measure the mutual diffusion coefficient of NaSCN and poly (ethylene oxide) (PEO). Useful results were obtained between 65°C and 95°C for complexes containing 11 mole% NaSCN in PEO with molecular weights ranging from 3500 to 600000g/mole. The observed diffusivity is in the range (0.6−3.2)×10 −8 cm 2/s and is independent of polymer molecular weight, indicating that the polymer is effectively static and that the growth rate method yields the chemical diffusion coefficient of Na and SCN species. The absolute values of D compare well with those from radioactive tracer studies.

Enzymology of the Acetyl-CoA Pathway of CO2Fixation

We know of three routes that organisms have evolved to synthesize complex organic molecules from CO2: the Calvin cycle, the reverse tricarboxylic acid cycle, and the reductive acetyl-CoA pathway. This review describes the enzymatic steps involved in the acetyl-CoA pathway, also called the Wood pathway, which is the major mechanism of CO2 fixation under anaerobic conditions. The acetyl-CoA pathway is also able to form acetyl-CoA from carbon monoxide. There are two parts to the acetyl-CoA pathway: (1) reduction of CO2 to methyltetrahydrofolate (methyl-H4folate) and (2) synthesis of acetyl-CoA from methyl-H4folate, a carboxyl donor such as CO or CO2, and CoA. This pathway is unique in that the major intermediates are enzyme-bound and are often organometallic complexes. Our current understanding of the pathway is based on radioactive and stable isotope tracer studies, purification of the component enzymes (some extremely oxygen sensitive), and identification of the enzyme-bound intermediates by chromatographic, spectroscopic, and electrochemical techniques. This review describes the remarkable series of enzymatic steps involved in acetyl-CoA formation by this pathway that is a key component of the global carbon cycle.

Static and dynamic computerised radioactive tracer studies, vital dye staining and theoretical mathematical calculations to ascertain the mode of survival of single cephalad channel venous island flaps

Experiments were performed to ascertain the perfusion and drainage of single cephalad channel saphenous venous flaps in dogs. In the first experiment a standard saphenous flap and a single cephalad channel saphenous venous island flap were dissected on contralateral thighs of dogs. A radioactive tracer, 99mTc, was injected into a foreleg vein and its appearance in both flaps was monitored with the use of a static and dynamic scanner. After this experiment, Evans blue, a vital dye, was injected into the foreleg vein of the dog. Five minutes later both flaps were excised and the dye in the flaps was assayed quantitatively. In the third experiment radioactive tracer was injected into the single cephalad channel venous flap subcutaneously and its decay in the flap as well as its uptake in the rest of the body were measured dynamically. The experiments show that the single cephalad channel venous island flap is perfused by and drains through its single cephalad vein. A mathematical model to justify the above conclusion was worked out independently, based on standard values involved in mammalian circulatory mechanisms as in dog and man.

Energy balance and diabetes. The effects of cold exposure, exercise training, and diet composition on glucose tolerance and glucose metabolism in rat peripheral tissues.

The effects of cold exposure, exercise training, and diet (high fat versus high carbohydrate) on glucose tolerance and glucose metabolism in rat peripheral tissues will be briefly reviewed. Stimulation of energy expenditure by cold exposure (4 degrees C) or exercise training generally leads to decreased plasma insulin levels and to an improvement in glucose tolerance, suggesting that insulin action on peripheral tissues is increased when energy expenditure is stimulated. On the contrary, feeding high-fat diets to sedentary rats living in the warm (25 degrees C) induces hyperinsulinemia and insulin resistance resulting in a marked deterioration of glucose tolerance. Nevertheless, cold exposure reverses the diabetogenic effects of high-fat feeding, demonstrating that nutrition-induced insulin resistance is amplified in sedentary animals living at temperatures close to thermoneutrality. Radioactive tracer studies of 2-deoxyglucose uptake in peripheral tissues revealed that cold exposure synergistically potentiates the effects of insulin on glucose uptake in skeletal muscles as well as in white and brown adipose tissues. However, more recent data showed that cold exposure improves glucose tolerance and stimulates glucose uptake in starved animals (ie., in the virtual absence of circulating insulin) nearly by the same order of magnitude as in fed animals. It is therefore concluded that cold exposure, and possibly also exercise, improve glucose tolerance and stimulate glucose uptake in peripheral tissues primarily by enhancing glucose oxidation via insulin-independent pathways, and secondarily by increasing the responsiveness of peripheral tissues to insulin.

ISOLATION AND IN VITRO CHARACTERIZATION OF A NOVEL IMMUNOSUPPRESSIVE CYCLOSPORINE METABOLITE

A novel metabolite (M-E) was identified by high-performance liquid chromatography in the serum of cyclosporine-treated renal transplant recipients during a second wave of immunosuppressive activity after disappearance of the initial wave due to the direct effect of CsA. M-E was identified in human serum and porcine bile both by HPLC and by a preparative thin-layer chromatography (TLC). It demonstrated homogeneity with characteristic retention times on C8 and C18 column HPLC systems using a variety of elution systems, and distinctive TLC mobility (Rf 0.35). Metabolite E (M-E) was documented to be a CsA metabolite by radioactive tracer studies, by crossreactivity with a polyclonal sheep antibody in radioimmunoassay, and by the presence of a characteristic mass spectrum. Further, in vitro immunosuppressive assays documented effects of M-E similar to those of CsA. The relative activity of M-E versus CsA was quantitated by potency ratios: for inhibition of normal human mixed lymphocyte culture reactions, the ratio was 0.79 +/- 0.23. Interindividual differences were observed in patient susceptibility to MLR inhibition not only by CsA, as previously reported by others, but also by M-E. There was a lesser effect of M-E compared with CsA in inhibiting proliferation of, and IL-2 generation by, C3H murine splenocytes stimulated with concanavalin A: the potency ratios for both systems were about 0.5, possibly reflecting an interspecies variability in generation of or susceptibility to M-E. These studies suggest that heretofore unidentified metabolites--including, but not limited to, M-E--may play an important role in the immunosuppressive effect of CsA in man.

Wave influence on coastal sand transport paths in a tidally dominated environment

Detailed physical oceanographic and sedimentological data, collected from a coastal embayment and adjoining inner continental shelf, are used to exemplify the changes in sediment transport vectors which take place when wave action is superimposed upon that of tidal currents. The area selected for study is one which is subjected to large tidal ranges (10.2 m on spring tides) and occasional storm-induced swell waves (with a predicted 50-year maximum wave height of 15 m). Bedload transport vectors are determined, on the basis of self-recording current meter observations combined with transport formulae and fluorescent or radioactive sand tracer studies, for: 1. (i) an ‘open’ area of the inner shelf, with regular bathymetry running parallel to the coastline; 2. (ii) a ‘near-coastal’ location, where current flow is constricted by the coastline itself; and 3. (iii) in the vicinity of a linear sandbank, which rises some 10m above the surrounding sea bed. On the basis of analyses carried out for various tidal and wave conditions, the outer (‘open’) area is considered to be one through which sedimentary material passes from the offshore deep water areas to adjacent beaches. Here, the net transport paths are susceptible to wave action and can reverse during storms, in comparison to tidal currents alone. Inshore, the sandbank is at the ‘distal’ end of the transport system: sand is concentrated onto the bank by recirculating tidal currents, but is removed from its crestline by wave action. Wave action also intensifies sand transport rates around such an effectively ‘closed’ system, enhancing the hydrodynamically controlled maintenance process.

Technetium Tc 99m Uptake in Postpartum Thyrotoxicosis-Reply

All patients at our institutions in the past ten years are given iodine 123 as the tracer dose for radioactive iodine uptake studies. No patients at our institution are given any radioactive tracers while nursing. Those patients who have postpartum thyroiditis resulting in hyperthyroidism with enough clinical problems requiring treatment need to stop breast-feeding to be given appropriate medications, all of which are secreted into the milk. Radioactive iodine uptake tracer studies can then be done after breast-feeding has been stopped. In our own institution, technetium Tc 99m uptake studies are usually but not always similar to iodide studies. Absolute uptakes may be altered in breast-feeding women because some of the isotope goes into the milk. Women who become hypothyroid, of course, require no isotopic studies prior to treatment. A small amount of thyroxine is secreted in the milk, but this

The accumulation of phenylpropanoid and capsaicinoid compounds in cell cultures and whole fruit of the chilli pepper, Capsicum frutescens Mill

The accumulation of the phenylpropanoid precursors of capsaicin in suspended and immobilised cell cultures of C. frutescens has been studied and compared with accumulation in whole pepper fruit. The use of HPLC techniques has revealed that the phenolic precursors of capsaicin are present in chilli pepper cells at extremely low levels, irrespective of the source of tissue or the developmental state. Radioactive tracer studies have indicated that the majority of the phenolic derivatives of phenylalanine are ultimately bound to the insoluble fraction of the cells. Results from experiments where immobilised cell cultures were grown under conditions which enhance capsaicin yield would suggest that the ‘diversion’ of compounds into this bound fraction has a considerable influence upon capsaicin biosynthesis in this system.

Effect of MON-0585 on sclerotization of Aedes aegypti cuticle

The effect of MON-0585, an insecticide affecting sclerotization, on mosquito cuticle was investigated. Since the lethal effect of MON-0585 is elicited during cuticle development, cuticular compoments such as structural proteins, chitin, phenoloxidase, and phenols were analyzed from both control and insecticide-treated larvae. Soluble cuticular proteins isolated from both groups of animals did not show any difference in electrophoretic mobility nor in amino acid composition. Cuticle bound proteins also failed to show any differences in amino acid composition. Transmission electron microscopic and radioactive tracer studies indicated that neither chitin synthesis nor chitin fiber assembly in cuticle was affected by MON-0585 treatment. Significant reductions in the levels of covalently bound catechols were observed in MON-0585-treated animals. Moreover, these animals exhibited reduced phenoloxidase activity as compared to controls. Scanning electron microscopic studies revealed malformations in the exoskeleton and in the breathing tubes of poisoned mosquito pupae. These results indicate that MON-0585 interferes with cuticular stabilization indirectly and disrupts the structure of the breathing tubes causing early pupal death.

A Preliminary Evaluation of the Use of the EM Algorithm for Estimating Parameters in Dynamic Tracer-Studies

The iterative, estimation-maximization algorithm for numerically generating maximum-likelihood estimates of parameters is investigated for use in processing data acquired in dynamic radioactive-tracer studies. This algorithm compared favorably to the best known alternative.

Microbial Ecology of Volcanic Sulphidogenesis: Isolation and Characterization of Thermodesulfobacterium commune gen. nov. and sp. nov.,

Microbial sulphate reduction was examined in thermal waters, sediments and decomposing algal-bacterial mats associated with volcanic activity in Yellowstone National Park. In vivo radioactive tracer studies which demonstrated biological [35S]sulphkie production from [35S]sulphate at temperatures higher than 50 C but less than 85 C, correlated with the presence of a unique sulphate-reducing bacterium. This new species proliferated at temperatures above 45 C but below 85 C, and had an optimum growth temperature of 70 C. The organism was a small Gram-negative, straight rod which displayed an outer-wall membranous layer in thin sections. This obligate anaerobe utilized pyruvate, lactate or H2 as electron donors and sulphate or thiosulphate as electron acceptors for growth and sulphide formation. Pyruvate alone was fermented during growth to hydrogen, acetic acid and CO2. Cell extracts contained cytochrome c 3 but lacked a desulphoviridin-type bisulphite reductase. The DNA guanosine plus cytosine content was 34.4 1.0 mol%. Other unusual biochemical features of this extreme thermophile are discussed. Strain YSRA-1 is described as the type strain of the new genus and species Thermodesulfobacterium commune.

Determination of organic-bound chlorine and bromine in human body fluids by neutron activation analysis.

The levels of organic-bound chlorine and bromine in human milk and serum are determined by neutron activation analysis. Desalted milk and serum fractions are irradiated with neutrons in a nuclear reactor and the resulting ..gamma..-rays of /sup 38/Cl and /sup 80/Br are measured. The desalting procedure, achieved by using Bio-Gel molecular sieves, virtually removes all ionic chloride and bromides from milk and serum. Radioactive tracer studies with polychlorinated biphenyl-/sup 14/C indicate a recovery of 90% through the Bio-Gel column. The total organic chlorine in 2.2-(4-chlorophenyl)-1,1-dichloroethane spiked milk and heptachlor spiked milk, determined after being desalted and irradiated according to this procedure, substantiates a good recovery of the added spike. The lower limits of detection of organic-bound chlorine and bromine in milk or serum are 50 and 5 parts per billion (ppb), respectively.

A simple small-scale culture vessel suitable for comparative studies on facultative anaerobes growing under aerobic and anaerobic conditions

A procedure is described for comparing bacteria growint under aerobic and anaerobic conditions in identical small-scale, magnetically stirrable culture vessels. Cultures, 5–15 ml, can be sampled easily and the technique lends itself to radioactive tracer studies with any number of parallel incubations. The whole procedure uses equipment which is readily available in any laboratory.

Uroporphyrin I stimulation of collagen biosynthesis in human skin fibroblasts. A unique dark effect of porphyrin.

Porphyria cutanea tarda and erythropoietic porphyria are disorders of heme synthesis that originate in the liver and bone marrow, respectively. Each is characterized by increased accumulation of uroporphyrin, I, by cutaneous photosensitivity, and in some patients by indurated plaques and scarring that resemble scleroderma. These scleroderma-like lesions occur in light-exposed and light-protected body areas. In these studies we evaluated the role of uroporphyrin I and of light in evoking the scleroderma-like cutaneous changes. Normal human skin fibroblasts were exposed to uroporphyrin I and to 400 nm radiation and the effect of these agents on collagen accumulation by the cells was determined. Radioactive tracer studies showed that uroporphyrin I caused a specific increase in the accumulation of newly synthesized collagen by fibroblast monolayer cultures, as verified by [(3)H]hydroxyproline and collagenase digestion assays. Collagen accumulation was stimulated 1.5- to 2.7-fold by uroporphyrin I, whereas noncollagenous protein accumulation was unchanged. The increased collagen accumulation was time and uroporphyrin I-concentration-dependent, and occurred both in the presence or absence of ultraviolet light exposure. Further studies demonstrated that the increased accumulation was not the result of decreased rates of collagen degradation nor was it due to changes in cell population growth parameters (generation times and saturation densities). No changes in morphology of the treated cells occurred. These studies indicate that porphyrins possess previously undemonstrated biological effects that are independent of their photosensitizing properties. This novel dark effect of uroporphyrin I may account for the sclerodermatous lesions seen in the skin of patients with porphyria cutanea tarda and erythropoietic porphyria.

Body composition in cachexia resulting from malignant and non-malignant diseases.

The body composition of 23 patients with cachexia resulting from malignant or benign inflammatory disease was studied. Skinfold thickness and radioisotope tracer measurements enabled us to estimate total body fat, lean body mass, the ratio of fat loss to lean body loss, erythrocyte and plasma volumes, total body water, extra-, and intracellular water volumes, total body potassium, and intracellular potassium concentration. The total body fat and lean body mass information suggests that the body composition in cancerous cachexia differs from that in cachexia caused by benign inflammatory disease, in that lean tissue appears to be better conserved in the former. The radioactive tracer studies showed that the cachectic patients were anemic, potassium-deficient, and overhydrated; however, fluid partitioning into extra- and intracellular compartments was normal.