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PubMed2002

Thermal-field propagation in an exocontact zone of a magmatic body and its impact on radiogenic isotope concentrations in minerals.

In application of radioactive isotope systems (K-Ar, Rb-Sr etc.) during the last decades, experience was gained not only on their geochronometrical uses, but also on estimations of some important parameters of geological processes, especially temperatures and durations of superimposed thermal events. In this paper, the formation of an exocontact thermal field of a magmatic intrusion is considered as a spreading of a thermal source delta-function. Appropriate solutions of the heat-transfer equation are deduced and correlated with diffusion parameters of the radiogenic argon, coupling radioactive, thermal and kinetic parameters in an exocontant zone of a magmatic body. These solutions were used for quantitative reinterpretations of data taken from Hart's classical paper [The petrology and isotopic mineral age relations of a contact zone in the Front Range, Colorado. J. Geol., 1964, v. 72, pp. 493-525]. Theoretic and measured radiogenic argon and strontium concentrations within exocontact aureoles are found to be in good concordance.

Geological Phenomena↗
PubMed2002

A new approach to evaluate magnesium status: determination of exchangeable Mg pool masses using Mg stable isotope.

Magnesium (Mg) status is difficult to evaluate using conventional status markers. Radioactive isotopes and, less commonly, stable isotopes have been used as research tools to assess the size of the exchangeable pools of minerals as a new approach to evaluate mineral status. The present paper is a report concerning the exploration of exchangeable Mg pools characteristics with the use of radioactive and stable isotopes and its validation as a method to evaluate Mg status. Recent data obtained in our laboratory using stable isotope of Mg in animals and in humans are presented. Animal studies demonstrated clearly that the exchangeable Mg pools is an interesting approach to evaluate Mg status, as the size of Mg pool 1, 2 and 3 decreased in proportion to Mg deficiency. However more studies are still necessary to better appreciate the relationship between Mg status and exchangeable Mg pool size in humans.

Animals↗
PubMed1978

[Use of tests based on the analysis of expired air in nutritional studies].

Tests based on the analysis of the gaseous components of expired air have been developed to study intestinal absorption and intermediary metabolism of various nutrients. This paper reviews the breath-analysis tests based on the measurement of CH4, H2, and isotopically-labelled CO2 for studying the intestinal absorption of carbohydrates, fats, and bile salts, and intrahepatic metabolism. New technology employing mass spectrometry allows the use of the stable isotope, carbon-13, instead of the radioactive isotope, carbon-14, for CO2 breath tests. The nutritional application of the breath-analysis tests is discussed, and the advantages of the non-radioactive, non-invasive procedures, especially for use in children and pregnant women in whom standard investigational methods represent a discomfort or a radioactive hazard, are emphasized.

Bile Acids and Salts↗
PubMed1998

13C breath test in gastroenterological practice.

Breath tests (BTs) are used in gastroenterological practice to study (patho)physiological and metabolic processes in an indirect way. In these tests the appearance in breath of a metabolite of a specific test substance is studied. The assumption underlying each BT is that one step-the process of interest-in the absorption and metabolism of the tracer is rate-limiting. Both hydrogen gas excretion and carbon dioxide appearance in breath can be studied. When a carbon-labelled test substance is used. the stable isotope 13C is preferred to the radioactive isotope 14C. Measurements of 13C in expired air are performed by mass spectrometry. Because of the indirect nature of BTs, involving a sequence of reactions and metabolic pools, they usually supply semiquantitative data. The tests are nevertheless useful because they often replace invasive techniques with a simple procedure that is safe because there is no radioactivity involved. BTs have been used to measure gastric emptying, the presence of Helicobacter pylori in the stomach, small-bowel bacterial overgrowth, exocrine pancreatic function as well as liver metabolic capacity; other potential applications of BTs are being studied.

Breath Tests↗
PubMed2006

(137)Cs and (90)Sr uptake by sunflower cultivated under hydroponic conditions.

The (90)Sr and (137)Cs uptake by the plant Helianthus annuus L. was studied during cultivation in a hydroponic medium. The accumulation of radioactivity in plants was measured after 2, 4, 8, 16 and 32 days of cultivation. About 12% of (137)Cs and 20% of (90)Sr accumulated during the experiments. We did not find any differences between the uptake of radioactive and stable caesium and strontium isotopes. Radioactivity distribution within the plant was determined by autoradiography. (137)Cs was present mainly in nodal segments, leaf veins and young leaves. High activity of (90)Sr was localized in leaf veins, stem, central root and stomata. The influence of stable elements or analogues on the transfer behaviour was investigated. The percentage of non-active caesium and strontium concentration in plants decreased with the increasing initial concentration of Cs or Sr in the medium. The percentage of (90)Sr activity in plants decreased with increasing initial activity of the nuclide in the medium, but the activity of (137)Cs in plants increased. The influence of K(+) and NH(4)(+) on the uptake of (137)Cs and the influence of Ca(2+) on the uptake of (90)Sr was tested. The highest accumulation of (137)Cs (24-27% of the initial activity of (137)Cs) was found in the presence of 10 mM potassium and 12 mM ammonium ions. Accumulation of about 22% of initial activity of (90)Sr was determined in plants grown on the medium with 8 mM calcium ions.

Cesium Radioisotopes↗
PubMedDate not supplied

Comparison of the action of an organophosphorus insecticide and its metabolite on chloride and sulfate transport in erythrocyte membrane.

The effect of the organophosphorus insecticide methylparathion and its main metabolite methylparaoxon on chloride and sulfate equilibrium exchange in pig erythrocytes was investigated using an isotope labelling technique. Efflux of both radioactive isotopes with time followed a single exponential. Methylparathion and methylparaoxon inhibited the chloride equilibrium exchange in erythrocyte ghosts in a dose- and time-dependent manner. There was no difference between effects evoked by these two compounds. Methylparathion and methylparaoxon inhibited sulfate efflux from resealed ghosts. The effect was also dose- and time-dependent. Again, there was no difference between the action of both agents. Dixon analysis revealed a non-competitive character of the inhibition of the exchange of both anions with apparent Ki values 183 and 184 microM for methylparathion and methylparaoxon, respectively in the case of chloride transport; for sulfate exchange these values were 675 and 648 microM. It was suggested that structural similarity between the parent agent and its metabolite accounts for their identical effects. Methylparathion and methylparaoxon might inhibit the anion exchange indirectly by changing the fluidity of the erythrocyte membrane or directly by binding to the band 3 protein and evoking conformational changes that lead to the inhibition of the anion transport. The insecticides, due to their ability to phosphorylate, might also disturb some regulation processes in the band 3 protein and affect anion transport in this way.

Animals↗
PubMedDate not supplied

[Genetic action of 131I and 125I on the germ cells of male mice].

A study was made of the genetic effects of iodine radioactive isotopes in male germ cells of (CBA X C57Bl)F1 hybrid mice. After a single intraperitoneal administration of Na131I (1.48 to 740 kBq/g) or Na125I (148 to 7400 kBq/g) to males the occurrence of dominant lethal mutations (DLM), reciprocal translocations (RT), and abnormal sperm heads (ASH) was studied. The radioactive iodine isotopes induced DLM at the postmeiotic spermatogenesis stages only. After the effect of the isotopes, the frequency of RT increased insignificantly with dose. The frequency of ASH was only increased with the highest 131I dose. Relative biological effectiveness of 131I and 125I was less than 1 with a reference to the indices under study.

Animals↗
PubMed1997

Brachytherapy for non-small cell lung cancer and selected neoplasms of the chest.

This article reviews the indications, techniques, and results of brachytherapy in the treatment of non-small cell lung cancer (NSCLC) and selected chest neoplasms. Various isotopes and techniques are used to place radioactive sources directly into a tumor, tumor bed, or the chest. Brachytherapy techniques can be tailored to the clinical situation and can be in the form of permanent interstitial volume or planar implants (radioactive sources permanently imbedded into the tumor or tumor bed) or in the form of temporary interstitial or endoluminal implants (where radioactive sources irradiate a tumor bed over a certain length of time and then are removed). These treatments can be delivered over a short interval (high-dose rate [HDR]) or over a more protracted time (low-dose rate). HDR treatments can be used intraoperatively to deliver a large dose of radiation to a determined target area with selective sparing of surrounding normal structures. Different methods of delivering HDR intraoperative radiation are under investigation. Most reports on brachytherapy for chest malignancies are retrospective and come from a few single institutions. Most of the published data relate to the treatment of NSCLC, but other intrathoracic malignancies, such as malignant pleural mesothelioma and malignant thymoma, have been treated with brachytherapy. To our knowledge, no major randomized trials accurately assess or confirm these retrospective studies yet, complicating the interpretation of these results. Nevertheless, brachytherapy is of value in selected situations and offers the clinician and the patient an innovative method of delivering conformal high-dose radiation to a defined target with preferential sparing of normal surrounding structures. With continued innovations in the development of radioactive isotopes, computerized treatment planning and targeting, and source delivery, brachytherapy should continue to offer an attractive alternative and complement to conventional treatment approaches, and may offer patients improved local control and survival.

Brachytherapy↗
PubMed2000

Exogenous surfactant kinetics in infant respiratory distress syndrome: A novel method with stable isotopes.

Little is known about surfactant metabolism in newborn infants, since radioactive isotopes cannot be used in humans. We describe here a new method for studying exogenous surfactant pharmacokinetics in vivo. We measured surfactant half-life, pool size, and turnover time in eight preterm infants (gestational age: 30 +/- 2 wk; birth weight: 1,416 +/- 202 g) who were mechanically ventilated because of infant respiratory distress syndrome. We administered two doses of 100 mg/kg each of a natural porcine surfactant with (13)C-labeled dipalmitoylphosphatidylcholine as a tracer. The (13)C enrichment of surfactant disaturated phosphatidylcholine (DSPC) was measured in serial tracheal aspirates by gas chromatography-mass spectrometry. The DSPC half-life was 34.2 +/- 9.4 h (mean +/- SD; range: 21.8 to 45.9 h). The apparent DSPC pool sizes were 5.8 +/- 6.1 mg/kg (range: 0.1 to 17.0 mg/kg) and 17.3 +/- 13.6 mg/kg (range: 3.3 to 41.0 mg/kg) at the time of the first and second surfactant doses, respectively. We present a novel and safe method that allows the tracing of exogenous surfactant phosphatidylcholine, the major lipid component of pulmonary surfactant, in infants who receive exogenous surfactant. This method could be a valuable tool for studying: (1) therapies that enhance lung/surfactant maturation; (2) the dosing and timing of surfactant therapy in different lung diseases; and (3) the comparison of different surfactant preparations.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1998

Simultaneous time-varying systemic appearance of oral and hepatic glucose in adults monitored with stable isotopes.

The rates (and extent) of appearance of glucose in arterialized plasma from an oral glucose load and from liver (RaO, RaH) can be estimated in humans using radioisotopes, but estimates vary among laboratories. We investigated the use of stable isotopes and undertook 22 primed intravenous infusions of D-[6,6-2H2]glucose with an oral load including D-[13C6]glucose in healthy humans. The effective glucose pool volume (VS) had a lower limit of 230 ml/kg body weight (cf. 130 ml/kg commonly assumed). This VS in Steele's one-compartment model of glucose kinetics gave a systemic appearance from a 50-g oral glucose load per 70 kg body weight of 96 +/- 3% of that ingested, which compared with a theoretical value of approximately 95%. Mari's two-compartment model gave 100 +/- 3%. The two models gave practically identical RaO and RaH at each point in time and a plateau in the cumulative RaO when absorption was complete. Less than 3% of 13C was recycled to [13C3]glucose, suggesting that recycling errors were practically negligible in this study. Causes of variation among laboratories are identified. We conclude that stable isotopes provide a reliable and safe alternative to radioactive isotopes in these studies.

Administration, Oral↗