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Biomedical subjects

J M Horner

Publications and source records attributed to J M Horner.

17 recordsLinked to original sources
PubMed1994

Lead poisoning from paint--still a potential problem.

Regulations were introduced in the UK in the 1970s to limit the lead content of paints. This has greatly reduced the number of children poisoned by ingesting leaded paint. However, it is argued that old paintwork is still a lead poisoning hazard in some older UK properties. Paint collected from a children's nursery classroom in a London school included samples with lead concentrations exceeding suggested safety levels. Lead poisoning from paint is a problem which should not be forgotten in the UK, and may be a more serious problem in countries with less stringent lead in paint regulations.

Child↗
PubMed1993

Tyre disposal--a burning environmental issue ?

Used road vehicle tyres are one of the less publicized environmental impacts of traffic. However, there is increasing concern about the proliferation of fly tipping and large potentially combustible tyre dumps, and a lack of policy for disposing of used tyres in the United Kingdom. Some worn tyres are retreaded, but most are either landfilled, stockpiled, incinerated or converted to crumb. This paper reviews the major tyre disposal methods used with particular reference to environmental implications and health effects. Suggestions are made concerning the future of UK disposal policy and for further monitoring to assess potential environmental problems.

Automobiles↗
PubMed1989

Stochastic choice models: A comparison between Bush-Mosteller and a source-independent reward-following model.

Horner and Staddon (1987) argued that a class of reward-following processes defined by a property they termed ratio invariance is a better model for the probabilistic choice performance of pigeons than competing molecular accounts such as momentary maximizing, melioration, and the Bush-Mosteller model. The critical data were provided by choice distributions-distributions of a variable S, the proportion of Right choices, defined on a moving window typically 32 choices long-obtained under a frequency-dependent schedule. The schedule prescribed equal payoff probabilities, p(S), for both choices. p(S) was a maximum when S = 0.5 and declined linearly for S values above and below 0.5. Pigeons showed generally bimodal choice distributions with the modes at equal p(S) values. These data do not follow easily from melioration or momentary maximizing and are inconsistent with molar maximizing, but they may be consistent with Bush-Mosteller. We present here the results of computer simulations showing that the ratio-invariance model studied yields, as expected, choice modes at equal p(S) values, but that Bush-Mosteller, although capable of generating bimodal choice distributions, does not have choice modes at equal p(S) values.

Journal Article↗
PubMed1981

Growth hormone and somatomedin in insulin-dependent diabetes mellitus.

In order to study the interrelationship of GH, somatomedin (SM), and growth in insulin-dependent diabetes mellitus (IDDM), concentrations of serum glucose, serum GH, and plasma SM were determined at 2-h intervals for 48 h in 19 ambulatory children with IDDM of at least 2-yr duration (mean duration, 6 yr) and in 9 normal age-matched controls. Serum glucose was significantly elevated (P less than 0.001) in subjects with IDDM compared to controls [287 +/- 15 mg/dl vs. 99 +/- 2 mg/dl (mean +/- SEM)] as was the hemoglobin A1C (11.0 +/- 0.40% vs. 4.59 +/- 0.08%) and the serum GH (8.4 +/- 0.4 ng/ml vs. 5.6 +/- 0.6 ng/ml; P less than 0.002). Despite evidence of inadequate diabetes control and elevated GH levels, the subjects with IDDM had normal SM levels (1.82 +/- 0.14 U/ml) compared to their age-matched controls (mean, 1.66 +/- 0.19 U/ml) and normal growth. Furthermore, SM levels did not show any significant diurnal variation in either group. There was no significant correlation in either group between the mean plasma SM concentrations and the mean serum GH or mean serum glucose concentration of each subject. These findings of normal SM levels and elevated GH levels in these children with normal stature and IDDM suggest a partial block in GH action.

Adolescent↗
PubMed1979

Further comparisons of the [125I]somatomedin A and the [125I]somatomedin C radioreceptor assays of somatomedin peptide.

The GH dependency of somatomedin (SM) peptide content in plasma was assessed using the placental membrane radioreceptor assay (RRA) to measure whole and acid-chromatographed plasma using both [125I]SM A and [125I]SM C. Plasmas from 10 normal children and adults, 11 GH-deficient children before and after therapy with 0.1 U/kg GH im daily for 5 days, and 10 acromegalic patients were assayed as well as a standard plasma pool from 20 healthy adult males. The results of these assays revealed that the SM content of plasma is GH dependent and that assay of whole and acid-chromatographed plasma with the [125I]SM A RRA and assay of acid-chromatographed plasma with the [125I]SM C RRA give comparable measurements of SM peptide content. There was a positive correlation of the [125I]SM A RRAs of whole and acid-chromatographed plasma from each patient (r = 0.87; n = 41; P much less than 0.001). An even stronger positive correlation was observed when the [125I]SM A and [125I]SM C RRAs of acid-chromatographed plasma were compared (r = 0.94; n = 41; P much less than 0.001). Furthermore, it was demonstrated that precise measurement of SM peptide content in plasmas from subjects with abnormal GH states and from normal subjects is enhanced by acid chromatography of the plasma before assay in either the [125I]SM A or [125I]SM C RRA.

Acromegaly↗
PubMed1978

Comparison of [125I]somatomedin A and [125I]somatomedin C radioreceptor assays for somatomedin peptide content in whole and acid-chromatographed plasma.

The placental membrane radioreceptor assay was used to measure the levels of somatomedin (SM) peptides in plasma. Displacement of both [125I]somatomedin A ([125I]SM-A) and [125I]somatomedin C ([125I]SM-C) by normal whole plasma, the peptide fraction of acid-chromatographed plasma, and a partially purified, insulin-free SM preparation were compared. The peptide fraction of plasma was isolated by acid chromatography over Sephadex G-50 in 0.25 M formic acid with a yield of greater than or equal to 90%, as determined by bioassay and [125I]SM. In the case of [125I]SM-A, the dose-response curves for whole plasma, acid-chromatographed plasma, and the standard SM preparation were parallel (P less than 0.2). In contrast, for [125I]SM-C, the dose-response curves for acid-chromatographed plasma and the purified SM preparation were parallel (P less than 0.2), but both differed significantly from that of whole plasma (P less than 0.001). In addition, there was less variability in the assay of acid-chromatographed plasma compared to whole plasma. The results indicate that radioreceptor assay of unextracted normal plasma using [125I]SM-A is a valid measure of SM peptide concentration, while radioreceptor assay of unextracted normal plasma using [125I]SM-C, in our hands, is not. Acid chromatography of plasma before its assay is an uncomplicated procedure which allows valid and precise measurement of SM peptide content using either [125I]SM-A or [125I]SM-C.

Adult↗
PubMed1978

Growth deceleration patterns in children with constitutional short stature: an aid to diagnosis.

A retrospective study of 263 children referred for evaluation of short stature revealed that 149 (56.7%) had constitutional short stature (CSS). A typical pattern of growth was observed in these children. As exemplified by 12 children who had complete serial growth measurements, exaggerated growth deceleration first became apparent between 3 and 6 months of age, was greatest in the first two years of life, and resulted in these children falling more than 2 SDs below the mean for height by 3 years of age. After 3 years of age, the growth rate of these children with CSS was essentially the same as that of normal children, and they ran parallel to the growth curve though below the third percentile. The importance of serial measurements and the growth chart is emphasized, and recommendations are made for the evaluation of short stature or abnormal growth deceleration in the first three years of life. Awareness of this typical pattern of growth in children without disease may aid the pediatrician in his evaluation of short stature and allow for watchful waiting when results of screening tests are normal.

Age Determination by Skeleton↗
PubMed1973

Zen macrobiotic diets.

Explore the source record for details and available documents.

Child Nutritional Physiological Phenomena↗
PubMedDate not supplied

Tracer technique to measure in vivo chemical transport rates within an implantable cell transplantation device.

An in vivo tracer technique that uses radiolabeled insulin as the tracer molecule has been developed to assess the rate of chemical transport between the cell transplantation chamber of an implantable bioartificial device and the host's circulatory system. The device considered here employs site-directed neovascularization of a porous matrix to induce capillary growth adjacent to an immunoisolated cell implantation chamber. This device design is being investigated as a vehicle for therapeutic cell transplantation, with the advantages that it allows the cells to perform their therapeutic function without the danger of immune rejection and it avoids damaging contact of blood flow with artificial surfaces. A pharmacokinetic model of the mass transport between the implantation chamber, the vascularized matrix, and the body has been devised to allow proper analysis and understanding of the experimental tracer results. Experiments performed in this study have been principally directed at evaluation of the tracer model parameters, but results also provide a quantitative measure of the progression of capillary growth into a porous matrix. Measured plasma tracer levels demonstrate that chemical transport rates within the implanted device increase with the progression of matrix vascular ingrowth. Agreement between the fitted model curves and the corresponding measured concentrations at different levels of capillary ingrowth demonstrate that the model provides a realistic representation of the actual capillary-mediated transport phenomena occurring within the device.

Animals↗
PubMedDate not supplied

Evaluation of an immunoisolation membrane formed by incorporating a polyvinyl alcohol hydrogel within a microporous filter support.

An immunoisolation membrane formed by incorporating a high water content polyvinyl alcohol (PVA) hydrogel into a microporous polyether sulfone (PES) filter has been investigated in this study. The PVA hydrogel is formed in situ within the filter pores via glutaraldehyde (GA) crosslinking under acidic conditions. The tortuous nature of the microporous filter pores securely anchors the embedded hydrogel to provide excellent structural integrity. The high void fraction of the PES filter support (>80%) and high water content of the PVA hydrogel (>85% water by weight) allow excellent solute transport rates, while an appropriate level of glutaraldehyde crosslinking supplies the required molecular size selectivity. In vitro permeability measurements made with solutes covering a wide range of molecular sizes demonstrate high transport rates for small nutrient molecules with rapidly diminishing permeabilities above a molecular weight of approximately 1,000 Dalton. Implantation experiments show that the membrane properties are not deleteriously affected by prolonged in vivo exposure or common sterilization techniques. Thus, this hybrid hydrogel/filter membrane system offers a promising approach to the immunoisolation of implanted cells.

Animals↗
PubMedDate not supplied

Environmental health implications of heavy metal pollution from car tires.

This paper reviews the potential for environmental pollution by heavy metals from the disposal of used car tires and describes laboratory work and field research exploring the magnitude of the problem. The metals considered here are cadmium, lead, and zinc; their respective mean concentrations for ten makes of tires used in the United Kingdom ranged from 0-3.0, 8.1-22.3, and 2524-6012 ppm. The metals were extracted from tires by simulated acid-rain solutions (pH 2.5); zinc concentrations of the leachate ranged from 169-463 ppm, but cadmium and lead concentrations were negligible. A significant increase in surface soil concentrations of all three metals was measured with increasing proximity to a tire dump in West London. The respective mean concentrations of cadmium, lead, and zinc in soil at the base of the dump were 22, 1160, and 1235 ppm, indicating contamination by each metal.

Acid Rain↗
PubMedDate not supplied

Anthropogenic emissions of carbon monoxide.

Carbon monoxide (CO) is a colorless, nonirritating, odorless and tasteless gas. Carbon monoxide combines with hemoglobin far more readily than does oxygen, leading to tissue hypoxia. Thousands of people die annually from CO poisoning, and those recovering from acute exposure commonly suffer brain damage. Chronic poisoning is of particular concern to sufferers of coronary heart disease, pregnant women, and people with certain hematological disorders. Indoor emission sources, notably fuel-burning heating appliances, cause most unintentional deaths and cases of illness and should be the main focus of concern. Motor vehicle emissions pose a chronic health risk for occupationally exposed groups. Smoking is a major source of personal exposure. Recent exposure to CO is commonly evaluated by measuring blood carboxyhemoglobin levels, which are related to the concentration of atmospheric CO. Monitoring methods are reviewed here, and monitoring is considered in relation to air quality standards and guidelines. Finally, control measures for motor vehicles and indoor heating appliances are suggested.

Adult↗