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Biomedical subjects

C N Barton

Publications and source records attributed to C N Barton.

At least 19 recordsLinked to original sources
PubMed2002

The Autosow raised miniature swine as a model for assessing the effects of dietary soy trypsin inhibitor.

Toxicological effects of dietary soy trypsin inhibitor (TI) were assessed in male miniature swine, a model chosen for its similarities to human digestive physiology and anatomy. The TI preparation was extracted from defatted raw soy flour. From 1 through 5 weeks of age, piglets were automatically fed either a TI liquid diet [Autosow TI group (ASTI)] or a control liquid diet [Autosow control group (ASC)]. From 6 to 39 weeks of age, these animals received either swine chow and TI or swine chow and control article. The TI diets were formulated to contain a TI activity of approximately 500 mg TI/100 g dry matter. A sow control (SC) group suckled from birth to 6 weeks of age and then fed as the ASC group with swine chow plus control article from 6 to 39 weeks of age. The SC piglets grew faster than ASC piglets during postnatal weeks 1 and 2; however, the ASC piglets were significantly heavier than the SC piglets (P=0.001) at 6 weeks of age. Compared with the ASC group, TI caused a moderate decrease in feed consumption and a moderate but reversible decrease in growth from 2 to 5 weeks of age, but not thereafter. Some control and TI-fed Autosow-reared piglets had loose stools until 6 weeks of age; the effect was significantly greater in the TI-fed group. Otherwise, all swine were active and had normal appearance and behavior.

Administration, Oral↗
PubMed2002

Pathological evaluation, clinical chemistry and plasma cholecystokinin in neonatal and young miniature swine fed soy trypsin inhibitor from 1 to 39 weeks of age.

The potential toxicity of dietary soy trypsin inhibitor (TI) was evaluated in neonatal miniature swine. From 1 to 6 weeks of age, two groups of male piglets were artificially reared in an Autosow and automatically fed either TI or control liquid diet. From 6 to 39 weeks of age, these two groups were fed either TI or control chow diet. A third group, sow control (SC), suckled from birth to 6 weeks of age, were also weaned to control chow from 6 to 39 weeks of age. Clinical chemistry and plasma cholecystokinin (CCK) determined at 6, 18, 30 and 39 weeks of age, and serum amylase activity with gross and histopathological analyses of major organs at 6 and 39 weeks of age are reported. TI had no effect on plasma CCK, serum amylase activity, or numerous clinical chemistry values. TI-fed piglets had a larger relative liver weight at 6 weeks of age. Relative pancreas weight decreased with age but was not affected by TI. Gross and histopathological analyses of major organs, except the spleen, were within normal limits. Increased incidence of extramedullary hematopoiesis was noted in the spleen of the TI group at 6 but not at 39 weeks of age. There was no consistent pattern in immunohistochemical foci for secretin, gastrin releasing polypeptide or CCK, and no change in DNA, RNA, mitotic index or nuclear density of pancreatic cells. At 6 weeks of age, TI increased pancreatic protein and amylase activity but not trypsin or chymotrypsin activity. None of the effects suggested that this dose of TI was toxic to either the neonatal or sexually mature miniature male swine.

Administration, Oral↗
PubMed2000

Effectiveness of food fortification in the United States: the case of pellagra.

OBJECTIVES: We evaluated the possible role of niacin fortification of the US food supply and other concurrent influences in eliminating the nutritional deficiency disease pellagra. METHODS: We traced chronological changes in pellagra mortality and morbidity and compared them with the development of federal regulations, state laws, and other national activities pertaining to the fortification of cereal-grain products with niacin and other B vitamins. We also compared these changes with other concurrent changes that would have affected pellagra mortality or morbidity. RESULTS: The results show the difficulty of evaluating the effectiveness of a single public health initiative such as food fortification without controlled experimental trials. Nonetheless, the results provide support for the belief that food fortification played a significant role in the elimination of pellagra in the United States. CONCLUSIONS: Food fortification that is designed to restore amounts of nutrients lost through grain milling was an effective tool in preventing pellagra, a classical nutritional deficiency disease, during the 1930s and 1940s, when food availability and variety were considerably less than are currently found in the United States.

Adolescent↗
PubMed1998

Peroxidation of membrane lipids and oxidative DNA damage by fumonisin B1 in isolated rat liver nuclei.

Fumonisin B1 (FB1), a contaminant of corn, has been reported to be a hepatocarcinogen in rats. In an attempt to understand its mechanisms of action, a model system of isolated rat liver nuclei was used to determine what effects, if any, FB1 might have on nuclear membrane lipids and DNA. The data suggested that FB1 induced lipid peroxidation concurrently with DNA strand breaks in this in vitro system. Iron and copper had no statistically significant stimulatory effects on these reactions. In addition, the active oxygen scavengers catalase, superoxide dismutase (SOD), mannitol and sodium azide had no significant inhibitory effects on the FB1-induced DNA strand breaks. However, a small but significant reduction in lipid peroxidation by catalase and mannitol was observed. These results suggested that hydroxyl radicals may be the initiators of the nuclear membrane lipid peroxidation, which results in production of peroxyl radicals. In turn, the peroxyl radicals may be responsible for the DNA strand breaks. An alternative explanation is that the hydroxyl radicals, produced close to the DNA-bound metal ions, may induce direct site-specific strand breaks, which are insensitive to the scavengers of active oxygen.

Animals↗
PubMed1996

Use of in vitro skin penetration data and a physiologically based model to predict in vivo blood levels of benzoic acid.

A physiologically based pharmacokinetic (PB PK) model was developed to predict plasma levels of benzoic acid (BA) in the hairless guinea pig after topical exposure at three finite dose levels. The PB PK model consisted of four compartments: (1) rapidly perfused tissues; (2) slowly perfused tissues; (3) liver, representing the route of elimination of BA from the plasma after biotransformation to hippuric acid; and (4) plasma. The predictive capacity of the PB PK model was assessed by comparing plasma BA levels measured experimentally with those predicted by the model. The percutaneous absorption of finite doses of BA in the model was described by a transdermal input function, which was derived from in vitro percutaneous absorption studies in which viable hairless guinea pig skin in flow-through diffusion cells was exposed to BA. Physiological parameters used in the model were calculated from previously published values. Biochemical parameters, including partition coefficients and metabolic constants, were measured experimentally in vitro. The PB PK model predictions were generally in good agreement with measured plasma levels for each of the dose levels studied. The predicted plasma BA levels and the measured values were closer for the highest dose (120 microg/cm2) than for either of the other two doses used (12 and 40 microg/cm2). The effects of optimizing the metabolic constants and the transdermal input function parameters on the predicted curve shape and fit to that of the measured plasma BA levels were assessed. Varying the transdermal input parameters produced closer agreement between predicted and measured values.

Administration, Topical↗
PubMed1996

Neurobehavioral dysfunctions associated with dietary iron overload.

Excessive dietary Fe is known to be toxic, but the extent of neurobiological involvement is not clear. In the present study male weanling rats were fed diets containing Fe at 35 (control), 350, 3500, or 20000 ppm for 12 wk. An Fe-deficient group (4 ppm) was included for comparison. Rats were tested for behavioral and body weight changes at various times after initiation of diets, and liver and brain nonheme Fe were measured at term. Excess dietary Fe, primarily at 20000 ppm, significantly decreased activity, habituation, reflex startle, and conditioned avoidance response performance, and enhanced prepulse modulation of startle. Body weights were also markedly decreased. Fe-deficient animals showed similar behavioral effects but more moderate body weight changes. Liver nonheme Fe varied directly with dietary levels. Whole-brain nonheme Fe was significantly reduced in Fe-deficient animals but increased only at the 20000-ppm level. Homeostatic mechanisms appear to regulate whole-brain Fe more effectively under conditions of dietary Fe overload than under conditions of Fe deficiency. The behavioral changes associated with dietary Fe overload may represent secondary consequences of systemic toxicity.

Anemia, Iron-Deficiency↗
PubMed1995

Upper bound risk estimates for mixtures of carcinogens.

The excess cancer risk that might result from exposure to a mixture of chemical carcinogens usually is estimated with data from experiments conducted on individual chemicals. An upper bound on the total excess risk is estimated commonly by summing individual upper bound risk estimates. The degree to which this approach might overstate the true risk associated with the mixture has not been evaluated previously. This paper reports the results of a Monte Carlo simulation study on the degree of reduction in conservation that might be achieved using alternative methods for calculating mixture upper bounds. An unexpected finding is that for chemicals that exhibit strongly linear dose-response relationships, the summing of multistage-model-based upper bounds on excess risk can be anti-conservative, that is, it can provide less than the nominal 100(1-alpha)% coverage.

Animals↗
PubMed1994

Interaction of citrinin and ochratoxin A.

The mycotoxins citrinin and ochratoxin A are produced in common by some molds and have been found together in a number of foods and animal feeds. We used in vitro tests to determine if the same effects are produced by these two mycotoxins when they act both independently and together. Renal cortical cubes prepared from kidneys of young adult Hormel-Hanford miniature swine were cultured in the presence or absence of the toxins for 1 h at 37 degrees C. The concentration of the toxins both singly and in combination ranged from 10(-6) to 10(-3) M. The tissues were incubated, removed, rinsed, and reincubated to measure transport of either tetraethylammonium (TEA) or paraminohippurate (PAH) ions and protein synthesis, using 3H-leucine. The transport data were analyzed by a recently developed logistic function test to ascertain whether the effects were additive, synergistic, or antagonistic. The significance of deviation was tested after a potency multiplier was added to the mixture. Data for three of the five experiments measuring TEA transport indicated a synergistic effect; for the other two, the results were not significantly different from additivity. The same was true for PAH transport. For protein synthesis, one experiment showed synergism; for the other, nonadditivity was not significant. None of the measurements showed antagonism between the two toxins. As with several other systems, tests of biochemical effects showed that administration of citrinin and ochratoxin A together did not elicit either consistent or strong synergistic responses.

Animals↗
PubMed1993

Nonlinear statistical models for the joint action of toxins.

A general approach using nonlinear regression models is presented for evaluating additivity, synergism, and antagonism of mixtures of toxins for proportions and ratio-scale response measures. This approach provides several advantages over the analysis methods typically used, which involve linear regression with logits or probits. A single model fit is performed, rather than a multistep procedure. Nonadditive alternative models can be easily constructed and tested against the appropriate additive models. The approach avoids the use of data "adjustments" for nonzero background response rates. The analyses are performed in the natural response metric, making interpretation straightforward. Also, the nonlinear regression model can be reparameterized to provide more meaningful primary parameters.

Animals↗
PubMed1988

Babble and random-noise masking of speech in high and low context cue conditions.

"Perceptual" masking of speech by multitalker speech (babble) has been widely reported but poorly quantified. Furthermore, the validity of the construct of perceptual masking is questionable. This report describes an experiment using a newly standardized test of speech perception in noise (SPIN) with both babble and spectrally matched random-noise maskers. Classical psychophysical ogive curves were used to model speech recognition as a function of signal-to-noise ratio (S/N). The two maskers yielded speech recognition functions of the same steepness but different locations on the S/N axis. The high-context items of SPIN yielded speech recognition curves with steeper slope and different locations on the S/N axis than the low-context items. These data are used to argue that perceptual masking was not documented (under certain assumptions) and that the superior masking of babble may be explained in purely acoustical terms. Speculations are offered about the possible acoustical differences that could be responsible for the differences in masking effect.

Acoustics↗
PubMed1984

Toluene levels in blood and brain of rats as a function of toluene level in inspired air.

The relationship of toluene concentration in blood and brain to the concentration of toluene in inspired air has not been explicitly studied. Sixty rats were exposed by inhalation to 50, 100, 500, or 1000 ppm toluene for 3 hr. Immediately following exposure, venous blood samples and whole brains were collected and assayed for toluene levels. For several empirical reasons, the natural logarithm (log) of toluene tissue levels were predicted in a linear model from log toluene levels in air. An additional 10 rats were exposed to 550 ppm toluene for 8 hr in order to verify that the 3-hr exposure was sufficient to produce near-asymptotic levels of toluene in blood and brain. Log brain toluene concentration was significantly higher than log blood concentration by an additive constant. The ratio of brain to blood toluene level was estimated as 1.56/1. Three- and eight-hour exposure results did not differ, thus indicating that these results would hold for toluene exposures of 3 hr or greater.

Animals↗
PubMed1984

Toluene blood level following subcutaneous injection of toluene in the rat.

A model of toluene level in blood following subcutaneous injection of toluene mixed with polyoxyethylated-vegetable-oil vehicle was developed. The purpose was to provide a means of predicting dose received for subsequent toxicologic studies for any time and dose combination. The pharmacokinetics were of secondary interest. Using data from 111 rats, a four-parameter equation was devised to predict the time course of toluene blood level from 20-480 min post dosing, for dose levels of 50-1000 mg/kg. Blood concentrations rose at a rate which was independent of dose level. Maximum blood levels were uniquely determined by dose level. Blood levels fell at different rates depending upon dose level. Injection exposure, when compared to inhalation, has the advantages of (a) low expense, (b) low equipment requirements, and (c) simplicity. The disadvantage is, for some experiments, poor temporal stimulation of the normal route of administration, inhalation.

Animals↗
PubMed1984

Recommendations for appropriate statistical practice in toxicologic experiments.

Appropriate statistical practice in toxicologic research is reviewed. The problem centers on the antagonistic needs to discover toxic effects and avoid false indictments of harmless compounds. Specific problems which distort error rates include having many dependent variables, conducting many tests on a variable, data snooping, lack of statistical power and 5) violations of statistical assumptions. Solution strategies include top down planning, designing efficient experiments, balancing type I and type II error rates, selecting hypotheses and 5) using appropriate statistical analysis methods. Top down planning and the "leapfrog" design strategy are particularly emphasized.

Research Design↗
PubMed1981

Effects of age and body lead burden on CNS function in young children. I. slow cortical potentials.

The effects of body Pb burden on slow cortical potentials were studied in 63 children aged 13-75 months. Slow wave (SW) voltage during sensory conditioning varied as a linear function of blood lead (PbB) level. The slope of this function, moreover, changed systematically with age. For children under 5 years of age, SW voltage tended to be positive at low PbBs and to be negative above 30 micrograms/dl. For children over 5 years of age, SW voltage tended to be negative at low PbBs and to be less negative (or positive) above 30 micrograms/dl. These results provide evidence of altered CNS function at the lowest Pb effect level ever reported.

Aging↗
PubMedDate not supplied

Effects of intermittent exposures of aflatoxin B(1) on hepatic and testicular glutathione S-transferase in rats.

Glutathione S-transferase (GST) plays a major role in the detoxification of the potent hepatocarcinogen aflatoxin B(1) (AFB(1)). This study evaluated the effects of intermittent exposures to AFB(1) on hepatic and testicular GST in rats. Male Fischer 344 rats were fed diets containing AFB(1) (0, 0.01, 0.04, 0.4 and 1.6 ppm) intermittently at 4-week intervals up to 20 weeks. The control animals were fed an AFB(1)-free NIH-31 diet. Rats consuming diets with 0.01 ppm AFB(1) did not show the induction of hepatic or testicular GST activity. Intermittent exposures to AFB(1) at concentrations of 0.04-1.6 ppm significantly increased the GST activities. The increase of the enzyme activity was proportional to the dose and length of AFB(1) exposure.

Aflatoxin B1↗
PubMedDate not supplied

Effect of low level carbon monoxide on compensatory tracking and event monitoring.

Experiments by Putz et al. concerning the effect of carbon monoxide (CO) exposure on compensatory tracking and monitoring in healthy young men were replicated. Task and procedural variables were reproduced as closely as practical. Subjects were exposed to either room air or 100 ppm CO. Mean carboxyhemoglobin (COHb) levels in the high CO exposure groups were 5.1% for Putz et al. (70 ppm exposure), and 8.24% for the present study (100 ppm exposure). In both studies elevated COHb produced a statistically significant increase over time in log mean absolute deviation scores (tracking error) with respect to control groups. The magnitude of the effect was smaller in the present study, perhaps because of subtle methodological or training differences between studies. The relationship between task difficulty and magnitude of CO-induced dysfunction remains unresolved. In contrast to Putz et al., no statistically significant effect of COHb in monitoring behavior was found. The failure to replicate this feature of may reflect the large differences in baseline performance, and higher variance in the present study.

Adult↗
PubMedDate not supplied

The effects of low-level carbon monoxide exposure upon evoked cortical potentials in young and elderly men.

The neurophysiological effects of acute, low-level carbon monoxide (CO) exposure are not well known. This experiment investigated the effects of a 5% carboxyhemoglobin level upon two indices of neurophysiological function, reaction time and the late positive component of the visual evoked potential in young and elderly men. Results indicated (1) no effects of CO upon any of the neurophysiological indices and (2) greater absorption of CO by young than by elderly men. These results, along with those of other studies, indicate that acute, low-level CO exposure is probably not neurotoxic, in normal, healthy men.

Adolescent↗