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Biomedical subjects

R W Mayes

Publications and source records attributed to R W Mayes.

At least 19 recordsLinked to original sources
PubMed2005

Alcohol discovered in the urine after death: ante-mortem ingestion or post-mortem artefact?

A study was undertaken of blood and urine alcohol levels in 44 cases where the bodies had been immersed in water, following accidents, for at least one day after death. In no case was there any ante-mortem evidence of ingested alcohol. In 15 cases there was a raised urine alcohol. The average urine-to-blood alcohol ratio in these cases was 0.56:1. This is dramatically less that that seen after ingestion. It is suggested that the alcohol, following its initial post-mortem production in the abdomen, enters the urine by diffusion from surrounding tissues. The presence of alcohol in the urine from bodies that have not been recovered and examined until several days after death cannot always be taken to indicate ante-mortem ingestion. Urine-to-blood alcohol ratios of less than 1:1 are strongly suggestive of post-mortem production.

Artifacts↗
PubMed2002

A simple method for the estimation of the bioavailability of radiocaesium from herbage contaminated by adherent soil.

Adherent soil may contribute a large proportion of the radiocaesium content of sampled vegetation. Consequently, inadvertent ingestion of adherent soil can contribute significantly to the radiocaesium intake of grazing animals, and needs to be accounted for within radiological assessments. However, accurate estimation of the degree of soil adhesion on vegetation is acknowledged to be difficult. To determine the relative contributions of vegetation and soil to the radiocaesium contamination of milk and tissues, soil-specific estimation of radiocaesium bioavailability values would be required. Here we suggest that a previously developed in-vitro bioavailability assay (involving a 2 h extraction with 0.1 M stable CsCl) can be used to estimate the true absorption coefficient of radiocaesium associated with sampled vegetation directly. Using this technique, seasonal trends in bioavailability are demonstrated to vary in accordance with estimations of the degree of soil adherent to vegetation collected from an upland pasture. The use of this technique would negate the need for detailed measurements of the amount of soil adhering to sampled vegetation and soil-specific radiocaesium bioavailability assessments.

Biological Availability↗
PubMed2000

A model of radioiodine transfer to goat milk incorporating the influence of stable iodine.

Previously reported models for radioiodine in ruminants cannot account for the effect of variations in stable iodine intake including large countermeasure doses of stable iodine on the transfer of radioiodine to goat milk. A metabolically based model of radioiodine transfer in goats has been parameterised using new experimental data on the effect of countermeasure doses of stable iodine on radioiodine transfer to milk. To account for the effect of dietary stable iodine levels, the model represents the transfer of iodine from the extracellular fluid to milk with Michaelis-Menten kinetics. The model shows good agreement with the experimental data, and the estimated parameters compare favourably with values which can be estimated from the literature. The parameterised model accounts for 95% of the variation in the observed data for milk, faeces, urine and thyroid (n=199). The model has been used to predict the effects of variation in stable iodine intake and the extent of consequent chemical contamination of milk by stable iodine. The time taken for radio-iodine to reach peak concentrations in milk following a deposition event is predicted to vary significantly (ca. 2 days) over a range of expected stable iodine intakes. Doses of stable iodine sufficient to reduce the radioiodine transfer to milk will result in stable iodine concentrations in milk greatly in excess of internationally advised limits. Therefore, we recommend that stable iodine supplementation not be used as a countermeasure to reduce radioiodine transfer to milk. Indeed, model predictions suggest that reductions in stable iodine intake would be a more effective countermeasure. However, this is unlikely to be feasible since the short physical half-life of 131I may not allow adequate time to implement changes in feed manufacture. The model described in this paper is freely available in ModelMaker 3.0 format (http://www.notingham.ac.uk/environmentalmodelling+ ++/).

Animals↗
PubMed2000

Radiocaesium variability within sheep flocks: determination of 137Cs intake in free-ranging sheep.

A study is described in which 137Cs intake by free-ranging sheep was estimated at two farms in the area of west Cumbria (northwest England) which received some of the highest amounts of fallout from the Chernobyl accident within the United Kingdom. The faecal excretion of 137Cs was estimated from faecal 137Cs activity concentrations and the use of intraruminal controlled release devices containing Cr2O3 to determine faecal dry matter output. The intake of 137Cs was estimated by assuming an apparent absorption coefficient appropriate to the herbage grazed. The methodology has the advantage that sampling of herbage representative of that ingested by study animals is not required. Caesium-137 dietary intake explained >60% of the observed variability in the 137Cs activity concentration determined in the muscle of sheep. Resultant transfer coefficient (Ff) values to describe the transfer of 137Cs from the diet to muscle were in agreement with previously reported values. At one farm, there was a positive correlation between the 137Cs activity concentration in muscle and Ff whilst at the other farm there was a negative correlation between Ff and 137Cs dietary intake. Potential reasons for these observations are discussed.

Animals↗
PubMed1998

A metabolic approach to simulating the dynamics of C-14, H-3 and S-35 in sheep tissues.

The results of a study in which groups of sheep were given single oral administrations of 14C, 3H and 35S and then slaughtered over a period of 1 year are reported. The experimental data were used to investigate the potential of metabolically based models for describing the transfer of the three radionuclides to sheep tissues. The structure of these models is based upon a simplified understanding of the transfer of the macro-elements C, H and S by processes such as respiration and protein synthesis/degradation. A consequence of this approach is that the three models have many common parameters. The models reproduced the general trends of the observations, accounting for 74%, 66%, and 58% of the observed variation in the 14C, 3H and 35S data, respectively, suggesting that they may provide a useful alternative approach to modelling the transfer of these radionuclides. The models presented are limited to the particular experimental situation for which they were developed, and further experimental work would be required to extend them. However, such metabolically based models have great potential: for example, they should be able to account for the influence of dietary intake, physiological status or the form of the radionuclide in the animals diet (e.g. tritiated water or organically bound tritium).

Administration, Oral↗
PubMed1998

Generic relationship between calcium intake and radiostrontium transfer to the milk of dairy ruminants.

The hypothesis is tested that there is a generic relationship between the calcium intake and the transfer of radiostrontium to milk which can be used for all dairy ruminants. In addition to the daily calcium intake, the relationship also requires values for the strontium to calcium observed ratio, which describes the discrimination in transfer of the two elements to milk (a value of 0.11 is used), and the calcium concentration in milk. The relationship had previously only been validated for dairy cattle as there were insufficient data for other ruminant species. Here, we present recently available data for dairy goats, and also a limited amount of data for sheep derived from the literature. From the comparison between these data and predicted values, we conclude that it is possible to derive a generic model of the transfer of radiostrontium to the milk of dairy ruminants.

Animals↗
PubMed1998

Variation in the metabolism of radiocaesium between individual sheep.

Considerable variability has been recorded in the radiocaesium activity concentration of muscle between individual sheep in the same flocks in upland areas that received fallout from the Chernobyl accident. In a previous paper we demonstrated that there is a propensity for certain sheep within a flock to be always amongst the most contaminated and others to be consistently the least contaminated. Here we report a study to determine the extent to which variation in the metabolism of radiocaesium by individual sheep may contribute to the observed variability within sheep flocks. The transfer coefficient and biological half-life of orally administered ionic radiocaesium in muscle were determined under controlled conditions in 22 ewes from an upland farm in an area of the UK which received comparatively high levels of Chernobyl fallout. There was considerable variation between individuals in both the transfer coefficient (0.19-0.56 day x kg(-1); mean 0.34 day x kg(-1)) and biological half-life in muscle (5.2-18.7 days; mean 9.8 days). Changes in liveweight during the study and feed intake together accounted for 72% of the variation in the derived transfer coefficients; liveweight change also accounted for 56% of the observed variation in biological half-life. In a subsequent study, the true absorption coefficient of radiocaesium was determined in 12 of the ewes. There was a positive correlation between transfer and true absorption coefficients (R = 0.57). We conclude that differences in the metabolism of radiocaesium will contribute to the observed variability in radiocaesium activity concentrations within sheep flocks in areas which were contaminated by Chernobyl fallout. We also suggest that for growing animals, the influence of liveweight change and feed intake on radiocaesium transfer may be greater than observed here. Similarly, in dairy cattle, for which feed intake changes considerably during the course of a lactation, large temporal variation in radiocaesium transfer to milk could be expected.

Animals↗
PubMed1998

A model of radiostrontium transfer in dairy goats based on calcium metabolism.

A model for the transfer of radiostrontium (90Sr) in dairy goats is presented. The novel feature of the model is that it is based on the current understanding of Ca metabolism and assumes that the transfer of radiostrontium is driven by Ca transfer. Previously published models of radiostrontium transfer in animals have ignored the influence of Ca metabolism. Unknown model parameters were obtained by fitting the model to data from a study of radiostrontium and Ca transfer in goats. The model accounted for 95 and 97% of the observed variation in the data for Ca (n = 22) and radiostrontium (n = 43), respectively. Unlike previously reported models, the model presented here could be applied to simulate the effect of additional dietary Ca as a countermeasure to the contamination of milk by radiostrontium under different circumstances.

Absorption↗
PubMed1997

The use of dietary calcium intake of dairy ruminants to predict the transfer coefficient of radiostrontium to milk.

Transfer coefficients (the equilibrium ratio between radionuclide activity concentration in milk or meat and the daily intake of radionuclide) are widely used to predict the contamination of animal products following the release of radionuclides into the environment. For a transfer coefficient to be generally applicable, its value must be constant for a range of circumstances. However, this is not the case for radiostrontium, the behaviour of which is strongly influenced by that of the homeostatically controlled nutrient, calcium. In this study, a relationship is derived between radiostrontium transfer coefficients and dietary calcium intake which takes into account the observed ratio for strontium:calcium transfer to milk. This relationship is tested against a range of observed data collated from the literature (n = 30) and found to account for 93% of the variability in transfer coefficient values. Model calculations show that a reduction in Fm of at least 40%-60% would be expected if dairy cattle, fed rations typical for well-managed herds, were supplemented with 100-200 g per day. Larger reductions would be predicted when dietary calcium intake is low.

Animal Feed↗
PubMed1996

Development and testing of a revised dynamic model of radiocaesium transfer to sheep tissues.

The model of radiocaesium transfer to sheep presented by Galer et al. provides reliable predictions only for sheep of a similar body weight to those used in the development of the model (approximately 30 kg). To extend the applicability of the model, it was necessary to re-parameterise it in terms of activity concentrations in tissues rather than total activities within them (although for gut compartments the use of activity has been retained). The rate coefficients for the new model have been estimated by fitting the model to the data used by Galer et al. which was derived from a single "calibration" experiment. The new model was found to account for 94% of the observed variation in the data (n = 42), a result similar to that obtained by Galer et al. The model has also been tested against data not used in its development but obtained from four separate experiments undertaken by three different laboratories. Good agreement between the predictions of the new model and observations was found for most circumstances and for several breeds of sheep with different body weights. It is concluded that the new model provides a useful dynamic description of radiocaesium transfers to the tissues of sheep of different breeds and under different contamination scenarios.

Administration, Oral↗
PubMed1996

Use of the true absorption coefficient as a measure of bioavailability of radiocaesium in ruminants.

Limitations of existing methods to describe the bioavailability of dietary radionuclides to ruminants (the transfer coefficient and apparent absorption coefficient) have led to the alternative suggestion of using the true absorption coefficient (A(t)). Various approaches to estimating A(t) for radiocaesium, involving the intravenous administration of a second isotope, are presented and discussed with reference to results from studies in which a range of radiocaesium sources were examined in sheep. Although estimates of A(t) differed between the sources, they were reasonably consistent between measurement techniques. Those methods which involved the estimation of endogenous faecal excretion of radiocaesium could be used with previously contaminated animals and did not require continuous administrations of radiocaesium isotopes, but gave unreliable results for sources of low bioavailability. Methods based on estimating the turnover rate of dietary radiocaesium through blood plasma were sufficiently sensitive to measure A(t) for the range of sources studied. However, they require previously uncontaminated animals and continuous administration of both isotopes for approximately 7 days. Bioavailability is more effectively measured as A(t) than as the transfer or apparent absorption coefficients since A(t) does not incorporate factors relating to the metabolism of radiocaesium in the tissues of the animal. The results of these studies show that differences in transfer coefficients between sheep and cattle and between sheep of differing ages are not due to variation in absorption across the gut. The potential for applying these approaches to other radioactive elements is discussed.

Animals↗
PubMed1996

Plant wax components: a new approach to estimating intake and diet composition in herbivores.

The nutrient status of the herbivore depends on the nutritive value of the plants available, the botanical composition of the consumed diet and the intake of the animal. It has always been difficult to quantify these last two. At present, intake is usually calculated from separate estimates of fecal output and diet digestibility. In this review we discuss the errors inherent in this approach, especially those associated with the determination and application of digestibility in vitro. We then critically evaluate a new approach to the estimation of intake, based on the use of plant cuticular wax alkanes as markers. Plant alkanes are predominantly odd-chain and substantially indigestible. They can be used, in combination with orally dosed even-chain alkanes, to obtain an intake estimate which is essentially independent of marker recovery in feces and which is more truly "individual" because it accommodates the level of digestibility occurring in individual animals. We present published data which indicate that the method is accurate and can be extended to measure diet composition as well. Previous approaches to estimating diet composition have been based on the laborious microscopic examination of esophageal extrusa, stomach contents or feces. However, most plant species have a characteristic pattern of alkane concentrations in their cuticular wax. This permits the estimation of diet composition from the pattern of alkanes in the feces and in the plants available. We present data to show that this approach can provide accurate estimates of diet composition in terms of either plant species or plant parts. A major advantage of the approach is that, if the animals are also dosed with even-chain alkanes, estimates of total intake and diet composition can be obtained simultaneously. The method is equally applicable to domestic and wild herbivores and to animals receiving supplementary feeds. In future work, the method will be extended to the simultaneous estimation of plant species and plant parts in the diet, and to the use of other wax components as markers.

Alkanes↗
PubMed1995

The use of an in vitro technique to predict the absorption of dietary radiocaesium by sheep.

The validity of an in vitro extraction technique to predict the availability for absorption of radiocaesium in the sheep gut has been assessed. The technique (a 2-h extraction with caesium chloride) was found to be valid for sources with a low availability for transfer across the gut, but inappropriate for ionic radiocaesium or radiocaesium incorporated internally within herbage. For such radiocaesium sources, which have a high in vitro availability, no correlation was found between in vitro extraction and true absorption measurements. A true absorption value of 0.80 is recommended for these sources, although values for individual sheep in the range 0.60 to 1.00 should be expected.

Animal Feed↗
PubMed1994

Novel approaches to the estimation of intake and bioavailability of radiocaesium in ruminants grazing forested areas.

It is difficult to measure transfer of radiocaesium to the tissues of forest ruminants because they can potentially ingest a wide range of plant types. Measurements on undomesticated forest ruminants incur further difficulties. Existing techniques of estimating radiocaesium intake are imprecise when applied to forest systems. New approaches to measure this parameter are discussed. Two methods of intake estimation are described and evaluated. In the first method, radiocaesium intake is estimated from the radiocaesium activity concentrations of plants, combined with estimates of dry-matter (DM) intake and plant species composition of the diet, using plant and orally-dosed hydrocarbons (n-alkanes) as markers. The second approach estimates the total radiocaesium intake of an animal from the rate of excretion of radiocaesium in the faeces and an assumed value for the apparent absorption coefficient. Estimates of radiocaesium intake, using these approaches, in lactating goats and adult sheep were used to calculate transfer coefficients for milk and muscle; these compared favourably with transfer coefficients previously obtained under controlled experimental conditions. Potential variations in bioavailability of dietary radiocaesium sources to forest ruminants have rarely been considered. Approaches that can be used to describe bioavailability, including the true absorption coefficient and in vitro extractability, are outlined.

Animal Feed↗
PubMed1994

Dynamic behavior of 110mAg in sheep tissues.

The transfer coefficient of 110mAg to a range of sheep tissues and its biological half-life in these tissues has been determined. Liver was shown to be the major site of 110mAg deposition and retention, with a transfer coefficient of Ff 7.1 d kg-1 and a biological half-life of 79 d. These results also suggest that previous estimates of the transfer of silver to muscle were too high, although further work would be required to confirm this. There is a need for accurate data which can be used to predict the transfer of 110mAg to food-producing animals.

Animals↗