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At least 343 records · Page 19Linked to original sources
PubMed1980

The effect of orthodontic force application on the pulpal tissue respiration rate in the human premolar.

This study investigates the effect of an orthodontic force on pulpal respiration in the human premolar. The participants in this study required the removal of four first premolars for orthodontic treatment. After written consent was obtained, these teeth were used in the following manner. Randomly, the premolars on one side of the mouth were designated as experimental and the premolars on the opposing side served as controls. The four teeth were removed following a 3-day application of an orthodontic force. The pulp tissue was then extirpated and used for the investigation. A radioactively labeled carbon dioxide production system was used to evaluate the effect on pulpal respiration of the orthodontic force. It is thought that this method has been proved to provide a viable and sensitive biochemical analysis of tissue respiration on very small samples over short observation periods. The data were collected and prepared for statistical analysis. This investigation demonstrated that the pulp tissue respiration in seventeen subjects was depressed an average of 27% as a result of orthodontic force application. A positive correlation between the age of the participant and the amount of tissue respiratory depression was also demonstrated. It was therefore concluded that orthodontic forces of very short duration do cause biochemical and biologic pulpal tissue alterations and that orthodontic forces may be less biologically safe as the age of the patient increases.

Adolescent↗
PubMed2005

Retrospective birth dating of cells in humans.

The generation of cells in the human body has been difficult to study, and our understanding of cell turnover is limited. Testing of nuclear weapons resulted in a dramatic global increase in the levels of the isotope 14C in the atmosphere, followed by an exponential decrease after 1963. We show that the level of 14C in genomic DNA closely parallels atmospheric levels and can be used to establish the time point when the DNA was synthesized and cells were born. We use this strategy to determine the age of cells in the cortex of the adult human brain and show that whereas nonneuronal cells are exchanged, occipital neurons are as old as the individual, supporting the view that postnatal neurogenesis does not take place in this region. Retrospective birth dating is a generally applicable strategy that can be used to measure cell turnover in man under physiological and pathological conditions.

Adult↗
PubMed2005

Radon exhalation of cementitious materials made with coal fly ash: Part 2--testing hardened cement-fly ash pastes.

Increased interest in measuring radionuclides and radon concentrations in fly ash (FA), cement and other components of building products is due to the concern about health hazards of naturally occurring radioactive materials (NORM). The paper focuses on studying the influence of FA on radon exhalation rate (radon flux) from cementitious materials. In the previous part of the paper the state of the art was presented, and the experiments for testing raw materials, Portland cement and coal fly ash, were described. Since the cement and FA have the most critical role in the radon release process relative to other concrete constituents (sand and gravel), and their contribution is dominant in the overall radium content of concrete, tests were carried out on cement paste specimens with different FA contents, 0-60% by weight of the binder (cement+FA). It is found that the dosage of FA in cement paste has a limited influence on radon exhalation rate, if the hardened material is relatively dense. The radon flux of cement-FA pastes is lower than that of pure cement paste: it is about approximately 3 mBq m(-2) s(-1) for cement-FA pastes with FA content as high as 960 kg m(-3).

Air Pollutants, Radioactive↗
PubMed2005

Radon exhalation of cementitious materials made with coal fly ash: Part 1--scientific background and testing of the cement and fly ash emanation.

Increased interest in measuring radionuclides and radon concentrations in fly ash, cement and other components of building products is due to the concern of health hazards of naturally occurring radioactive materials (NORM). The current work focuses on studying the influence of fly ash (FA) on radon-exhalation rate (radon flux) from cementitious materials. The tests were carried out on cement paste specimens with different FA contents. The first part of the paper presents the scientific background and describes the experiments, which we designed for testing the radon emanation of the raw materials used in the preparation of the cement-FA pastes. It is found that despite the higher (226)Ra content in FA (more than 3 times, compared with Portland cement) the radon emanation is significantly lower in FA (7.65% for cement vs. 0.52% only for FA).

Air Pollutants, Radioactive↗
PubMed2005

Positive fallout from the bomb.

Atmospheric isotopes left behind by atomic weapons tests provide the foundation for an unusual method for determining the age and turnover rate of human cells.

Adult↗
PubMed2002

Apolipoprotein E genetic polymorphism, remnant lipoproteins, and nephropathy in type 2 diabetic patients.

BACKGROUND: We previously showed that the apolipoprotein (apo) Eepsilon2 allele is associated with the progression of diabetic nephropathy. The aim of the present study is to further investigate the association between apo E genetic polymorphism, plasma lipid levels (particularly remnant lipoproteins), and diabetic nephropathy. SUBJECTS AND METHODS: One hundred fifty-eight patients with type 2 diabetes who had a duration of diabetes longer than 10 years were divided into the three apo E groups: apo E2 (n = 22), E3/3 (n = 102), and E4 (n = 34). Plasma levels of lipids and remnant lipoproteins were measured. The effect of apo E2 triglyceride (TG)-rich lipoproteins, including remnant lipoproteins, on the accumulation of cholesteryl esters by human mesangial cells (HMCs) was estimated by measuring the stimulation of radioactive carbon-labeled oleate incorporation into cholesteryl esters. RESULTS: The frequency of overt nephropathy was significantly greater in apo E2 patients with diabetes (59.1%) than apo E3/3 (34.3%) or apo E4 patients (8.8%), and the frequency of normoalbuminuria was significantly greater in apo E4 patients with diabetes (67.6%) than apo E3/3 (34.3%) or apo E2 patients (4.5%). Logistical regression analysis showed that odds ratios of apo E2 and apo E4 genotypes for the presence of overt nephropathy were 10.179 (P = 0.0349) and 0.129 (P = 0.0028), respectively. Plasma TG and remnant-like lipoprotein particle cholesterol levels were significantly greater in apo E2 patients and significantly lower in apo E4 patients than apo E3/3 patients. Apo E2 TG-rich lipoproteins stimulated the accumulation of cholesteryl esters by HMCs significantly more than apo E3/3 or apo E4 TG-rich lipoproteins. CONCLUSION: Apo E2 is a positive factor and apo E4 is a negative factor for diabetic nephropathy. Apo E2 TG-rich lipoproteins, including remnant lipoproteins, affected HMCs. Remnant lipoproteins may have an important role in the progression of diabetic nephropathy.

Aged↗
PubMed1980

Cold exposure and mammary glucose metabolism in the lactating goat.

1. [U-14C]glucose was infused intravenously into conscious lactating goats exposed to thermoneutral or cold environments for a total of 24 h. The irreversible loss of glucose from the whole body and uptake of glucose by the mammary gland was measured and glucose utilization in the udder was studied by measuring the incorporation of radioactivity into carbon dioxide in mammary venous blood, into milk lactose and milk triglyceride-glycerol. 2. Exposure to cold increased the circulating level of glucose and slightly though not significantly, increased the non-mammary irreversible loss of glucose. 3. The extraction of glucose from the circulation by the udder fell, the secretion of lactose by the udder also fell and this correlated closely with the reduced secretion of milk in the cold. 4. Simultaneous measurements of the concentrations of insulin, growth hormone and corticosteroids in the arterial plasma were made. 5. The plasma concentration of corticosteroids increased significantly in the cold. 6. It is concluded that reduced glucose uptake and lactose synthesis by the udder are important factors which reduce milk secretion during cold exposure.

Animals↗
PubMed1984

Environmental effects of natural radionuclides from coal-fired power plants.

The assessment of the environmental effects of natural radionuclides contained in fly ash released from a coal-fired power plant was carried out and the following results were obtained. Mean concentrations of U, Th and K in 28 kinds of domestic and foreign coals were 1.0 ppm, 3.3 ppm and 2300 ppm, respectively. A good correlation between U and Th concentrations appears evident. Natural radionuclide concentrations of bottom and fly ashes were approximately equal in both ashes, and the values were the same as those calculated by concentration in coal divided by ash content. Release rates of 40K and radionuclides of each decay chain of U or Th were evaluated in the range of 2 to 40,000 pCi/sec for model coal-fired power plants of 1000 MW and 250 MW. The natural radionuclide concentration in air in a plume at the maximum concentration point was 5 X 10(-9) to 5 X 10(-3) pCi/m3, and these values were below 1/200 of those of natural origin.

Air Pollutants↗
PubMed1985

An evaluation of the external radiation exposure dosimetry and calculation of maximum permissible concentration values for airborne materials containing 18F, 15O, 13N, 11C and 133Xe.

To better understand the dose equivalent (D.E.) rates produced by airborne releases of gaseous positron-emitting radionuclides under various conditions of cloud size, a study of the external radiation exposure dosimetry of these radionuclides, as well as negatron, gamma and x-ray emitting 133Xe, was undertaken. This included a calculation of the contributions to D.E. as a function of cloud radii, at tissue depths of 0.07 mm (skin), 3 mm (lens of eye) and 10 mm (whole body) from both the particulate and photon radiations emitted by these radionuclides. Estimates of maximum permissible concentration (MPC) values were also calculated based on the calculated D.E. rates and current regulations for personnel radiation protection (CFR84). Three continuous air monitors, designed for use with 133Xe, were evaluated for applications in monitoring air concentrations of the selected positron emitters. The results indicate that for a given radionuclide and for a cloud greater than a certain radius, personnel radiation dosimeters must respond acceptably to only the photon radiations emitted by the radionuclide to provide acceptable personnel dosimetry. For clouds under that radius, personnel radiation dosimeters must also respond acceptably to the positron or negatron radiations to provide acceptable personnel dosimetry. It was found that two out of the three air concentration monitors may be useful for monitoring air concentrations of the selected positron emitters.

Air Pollutants↗
PubMed1990

An improved passive activated C collector for measuring environmental 222Rn in indoor air.

A modified version of an activated C monitor has been developed for the time-weighted average measurement of 222Rn for periods ranging from 1-7 d. The new collector consists of a metal can containing 50 g of activated C with a sintered metal filter covering the 3.2-cm diameter sample port in its lid. The new configuration reduces the adsorption and desorption rate of both 222Rn and water vapor by a factor of 4-5, as compared to an open-faced canister. The device measures the average 222Rn concentration accurately, even if the 222Rn concentration varies by more than a factor of 10. For practical situations encountered indoors, the modified collector yields results that are accurate to within +/- 10%. The integration time constant of the collector, tested at relative humidities ranging from 23-75%, is 9-11 d, which is more than three times longer than that of existing diffusion barrier collectors. It is simple to use, inexpensive (total cost of materials is +3.50), maintenance-free, easily sent and returned in the mail (total weight = 100 g), and is reusable for multiple exposures after simple regeneration by heating. The lower limit of detection for a 10-min counting interval is 7 Bq m-3 (0.2 pCi L-1) when counted within 3 d after the end of exposure.

Adsorption↗