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Biomedical subjects

J J Powell

Publications and source records attributed to J J Powell.

At least 73 records · Page 4Linked to original sources
PubMed1997

Mechanisms of aluminum absorption in rats.

Aluminum has become a dietary toxin in modern times but its mechanism of absorption is poorly understood. After ingestion, the systemic transfer of aluminum is small but it is greatly affected by the coingestion of certain dietary agents, such as citrate, that complex with the metal in the intestinal lumen or transiently alter the permeability of the mucosa. Here, mechanisms of aluminum absorption were studied by using freshly prepared aluminum hydroxide and aluminum citrate. Everted sacs of rat gut were used to investigate the site of absorption, effect of chemical charge on absorption of aluminum citrate, and presence of active or passive absorption with use of the metabolic inhibitor ouabain. Absorption was biphasic with a large tissue uptake that was consistent with adhesion to mucus-mucosal surface but little tissue transport, which was consistent with passive paracellular permeation. Citrate reduced the uptake-transport ratio both by competing with the mucosal uptake and by increasing mucus-mucosal permeation but not by affecting the charge of the luminal aluminum species. Despite the potential for hydroxypolymerization of aluminum at intestinal pH, the small bowel and colon absorbed aluminum passively and paracellularly but the stomach did not. The predominantly proximal absorption of aluminum observed in vivo is a reflection of the proximal absorption, and therefore removal, of dietary constituents (eg, citrate) that enhance mucosal permeation of aluminum. The colon should be investigated further as a site of significant paracellular permeability.

Aluminum↗
PubMed1996

Characterisation of inorganic microparticles in pigment cells of human gut associated lymphoid tissue.

Macrophages at the base of human gut associated lymphoid tissue (GALT), become loaded early in life with dark granular pigment that is rich in aluminium, silicon, and titanium. The molecular characteristics, intracellular distribution, and source of this pigment is described. Laser scanning and electron microscopy showed that pigmented macrophages were often closely related to collagen fibres and plasma cells in GALT of both small and large intestine and contained numerous phagolysosomes, previously described as granules, that are rich in electron dense submicron sized particles. Morphological assessment, x ray microanalysis, and image electron energy loss spectroscopy showed three distinct types of microparticle: type I - spheres of titanium dioxide, 100-200 nm diameter, characterised as the synthetic food-additive polymorph anatase; type II - aluminosilicates, < 100-400 nm in length, generally of flaky appearance, often with adsorbed surface iron, and mostly characteristic of the natural clay mineral kaolinite; and type III - mixed environmental silicates without aluminium, 100-700 nm in length and of variable morphology. Thus, this cellular pigment that is partly derived from food additives and partly from the environment is composed of inert inorganic microparticles and loaded into phagolysosomes of macrophages within the GALT of all human subjects. These observations suggest that the pathogenicity of this pigment should be further investigated since, in susceptible individuals, the same intracellular distribution of these three types of submicron particle causes chronic latent granulomatous inflammation.

Aluminum Silicates↗
PubMed1995

Analysis of copper and lead in hair using the nuclear microscope; results from normal subjects, and patients with Wilson's disease and lead poisoning.

We have recently developed a technique utilizing the nuclear microscope to analyse accurately the trace element content of hair at concentrations of ppm and to differentiate between the levels within hair and those due to surface contamination. Hair was analysed from four patients with Wilson's disease (systemic copper overload), one patient with sub-acute lead poisoning, and three control subjects, and the concentrations and distributions of lead and copper across the hair shafts were shown. However, there was no increase in the copper content of hair from patients with Wilson's disease compared with those of normal subjects, indicating that the high copper levels of many tissues in this disease are not reflected in hair. In contrast, hair samples from the patient with lead poisoning showed maximum concentrations of 14 (+/-2) micrograms g-1, compared with normal levels of less than 1 micrograms g-1. Further, the composition of the hairs along the shaft reflected the temporal changes of lead levels in the patient during lead elimination.

Adolescent↗
PubMed1995

Assessment of toxic metal exposure following the Camelford water pollution incident: evidence of acute mobilization of lead into drinking water.

Following the incident of acidic pollution of water by aluminium sulfate centred around Camelford in July 1988, we have carried out a retrospective analysis of the mobilization of toxic metals to residents of the area. An advanced nuclear technique was used to measure trace levels of elements within hair, thus, avoiding surface contamination. In contrast to controls, lead, but no other toxic metals, was consistently found within sections of hair that dated to mid-1988 from four residents; they must, therefore, have consumed this metal around the time of the incident. The source of this lead was probably local water pipe residue, and this was found on analysis to have a matrix specific to such soft-water areas that, prior to the incident, had slowly accumulated certain toxic metals such as cadmium and uranium and particularly lead. Lead is mobilized from such residues by acidic water and could, therefore, have heavily contaminated mains water after the incident. However, analyses of residents' plasma and whole blood, and of urine following a lead-chelation test, showed no evidence of either long-term increased body burdens of toxic metals or depletion of essential elements. In addition, we found no evidence of continued poor water quality in the area. In conclusion, during a short period following the pollution, some residents who consumed mains water would have been acutely exposed to lead and other toxic metals. Prediction of the scale of metal exposure to individuals was not possible owing to heterogeneity of the water distribution network, but long-term effects to residents from lead are not anticipated.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1994

Vitamin A and related essential nutrients in cord blood: relationships with anthropometric measurements at birth.

Following the advice given by the Department of Health to women who are, or may become pregnant, not to eat liver and liver products because of the risk of vitamin A toxicity, the concentrations of vitamins A and E, and copper, magnesium and zinc in cord blood were investigated. The study was conducted in Hackney, an inner city area of London. Esters of vitamin A were not detected in any of the samples, indicating that there was no biochemical evidence of a risk of toxicity. Indeed, vitamin A correlated significantly with birthweight, head circumference, length, and gestation period. There was also a significant positive relationship between zinc and birthweight. In contrast, copper showed a negative correlation with birthweight and head circumference. Vitamin E and magnesium were not associated with any of the anthropometric measurements, although magnesium showed an increasing trend with birthweight. The data suggest that most of the mothers of the subjects studied may have been marginal with respect to vitamins A and E and zinc. In those with low birthweight babies. a higher intake would have improved their nutritional status and possibly the outcome of their pregnancy. For these low-income mothers, liver and liver products are the cheapest and the best source of vitamins A and E, haem iron, B vitamins and several other essential nutrients; hence the advice of the Department of Health may have been misplaced.

Adult↗
PubMed1994

Evaluation of staples and prostheses for use in laparoscopic inguinal hernia repair.

With the increasing popularity of laparoscopic prosthetic inguinal hernia repair, it was decided to compare the various staples and prostheses currently in use. A twofold increase in breaking or opening strength was required to disrupt the Endoscopic Multifeed Staple (31.2 Newtons vs 15.6 Newtons) compared with the Multifire Endo Hernia Staple. A linear relationship existed between the number of staples used and the maximum load tolerated. No significant difference was found between the breaking strength of the prostheses evaluated. Further research into the biomechanics of laparoscopic inguinal hernia repair is necessary to determine how important staple and prosthesis strength is for the success of the repair.

Hernia, Inguinal↗
PubMed1994

Intestinal perfusion of dietary levels of aluminium: association with the mucosa.

An aluminium (93 microM) sulphate solution freshly adjusted to pH 7.0 was perfused through the rat small bowel to mimic the reported physiological conditions that follow dietary aluminium ingestion. One third of this aluminium was taken up from the perfusate, but > 90% of this was then recovered from the intestinal mucus/mucosa and most (> 70%) from the distal third of the small bowel. The fresh perfusate was shown by ultrafiltration to contain largely particulate/colloidal aluminium-hydroxide, and this probably adhered to intestinal mucus which may be an important barrier to the gastrointestinal absorption of aluminium.

Alum Compounds↗
PubMed1993

Gastro-intestinal availability of aluminium from tea.

The in vitro speciation of aluminium (Al) in black tea infusion (pH 4.8) was assessed using 3000, 10,000 and 30,000 Da cut-off ultrafilters, and the effect of adding human gastric juice (pH 2.3) and then raising the pH to 6.5 were also studied. 78% Al in the tea infusion passed through the 3000-Da ultrafilter; this percentage increased to more than 90% with the addition of gastric juice at pH 2.3, but then reduced to approximately 5% when the incubate was adjusted to pH 6.5. The breakdown of tea-derived polyphenols to low molecular weight phenols in vivo was measured using high-resolution 1H nuclear magnetic resonance spectroscopic analysis of ileostomy effluent, but there was no evidence of low molecular weight breakdown products from the polyphenols of ingested tea in this effluent. These results suggest that only a small proportion of Al in tea is potentially available for absorption throughout the small bowel. It may be misleading to estimate systemic Al absorption from tea drinking simply from total urinary aluminium excretion as has been done previously.

Aluminum↗
PubMed1993

Automated spectrophotometric method for determining oxidized and reduced glutathione in liver.

An enzymatic recycling method has been applied to the measurement of total and oxidized glutathione with a centrifugal analyzer. When the reduced form of glutathione (GSH) was masked with 2-vinylpyridine to measure the oxidized glutathione (GSSG), the time to ensure full derivatization was three times longer than has been reported. The method is quick, simple, accurate, and precise (1.27% for GSH, 3.3% for GSSG intraassay CV; 2.15% for GSH, 5% for GSSG interassay CV), and the automation allows large numbers of samples to be conveniently assayed.

Autoanalysis↗
PubMed1992

Light and electron microscope study of GABA-immunoreactive neurones in lamina III of rat spinal cord.

In order to determine whether different morphological types of neurone in lamina III of rat spinal dorsal horn contain different neurotransmitters, a combined Golgi and immunocytochemical study was performed. Semithin sections through the cell bodies of 52 Golgi-impregnated neurones in this lamina were tested with antisera to GABA and glycine. Thirty of these cells were immunoreactive with anti-GABA antiserum and 25 of these also showed glycine-like immunoreactivity. These cells had dendrites which were oriented along the rostrocaudal axis and occupied lamina III, with some extension into lamina IV and the ventral half of lamina II. Although some of the nonimmunoreactive cells had similar morphology, many of them had dendrites which passed in a dorsal and/or ventral direction and crossed laminar boundaries. Three of the neurones which were immunoreactive with both antisera were examined with the electron microscope. These cells received a variety of synapses including some from axons which resembled low threshold myelinated mechanoreceptive primary afferents. These results indicate that there is a relationship between morphology and function for neurones in lamina III. It is suggested that the inhibitory neurones which contain both GABA and glycine selectively regulate the transmission of information from low threshold mechanoreceptive primary afferents to other dorsal horn neurones.

Animals↗
PubMed1992

Concentrations of metals in gastric juice in health and peptic ulcer disease.

The concentrations of essential metal cations in gastric juice, collected at endoscopy from 17 normal patients and 11 with peptic ulcer disease, were determined by inductively coupled plasma emission spectrometry. Mean fasting levels in normal gastric juice were as follows: sodium 47.7 mM, potassium 14.6 mM, calcium 0.8 mM, magnesium 0.36 mM, zinc 13 microM, and copper 1.2 microM: these did not differ significantly in health or disease. Because samples were contaminated with iron, the concentration of this metal was only estimated (ca 3.5 microM in normal subjects), and this secretion could represent a significant proportion of the daily loss of endogenous iron. The pH of gastric juice predicted the concentrations of magnesium and calcium, but not copper or zinc, in the juice. It is concluded that previously reported values for trace metals in gastric juice have been incorrect and that the very low amounts secreted in the gastric juice will not interfere with the absorption of other trace metals from the diet. In contrast, the concentrations of macroelements in gastric juice may be sufficient to stimulate the absorption of trace metals from the gut.

Calcium↗