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Biomedical subjects

E J Underwood

Publications and source records attributed to E J Underwood.

7 recordsLinked to original sources
PubMed1979

Trace elements and health: an overview.

Trace element deficiencies, toxicities and imbalances in man are more difficult to relate to geochemical factors than they are in farm animals. The reasons for this are discussed and examples of such differences between man and grazing animals presented. The most convincing evidence of a geochemical causal link with human disease comes from the incidence and distribution of endemic goitre. The influence of technological developments upon this relation is discussed. Other associations between the physical environment, including the air and drinking water, and to health are given and critically examined in relation to the criteria necessary to distinguish between association and causation. The nature and extent of man-made modifications of the natural geochemical environment through technological change are discussed in relation to intakes of Fe, I, Zn, Pb and Se and their relation, in turn, to human health and disease. The currently proposed permissible limits or maximum tolerances of potentially toxic elements are presented, and the importance to these tolerances of the chemical and physical forms of the element and their metabolic interactions with other elements is emphasized.

Agriculture↗
PubMed1979

The effect of sulphur on 75Se absorption and retention in sheep.

Four Border-Leicester X Merino wethers were used in a 4 X 4 Latin square experiment to study the effects of dietary sulphur on selenium absorption and retention. The basal diet contained 0.05% S and sodium sulphate was added to give additional treatment levels of 0.11, 0.17 and 0.24% total sulphur. Sodium selenate was added to all diets to bring the dietary selenium level to a constant 0.25 mg/kg. One hundred muCi 75Se as sodium selenate (specific activity 50 muCi/mg Se) was administered to the rumen per fistulam after a 10-day period of adjustment on each diet. Radioactivity in blood, urine, faeces and rumen digesta was measured at intervals over the succeeding 7 days. Twenty percent of the total activity in the rumen fluid was in the TCA supernatant fraction after 3 hours, and this proportion tended to increase slightly as sulphur intake increased. Fecal excretion of selenium accounted for between 44 and 51% of the dose after 7 days, the high levels being associated with increasing sulphur intake. However, these differences were not significant. Urinary excretion of selenium accounted for between 12% (0.05% S) and 22% (0.24% S) of the dose after 7 days, with treatment differences being significant. Levels of radioactivity in blood were significantly higher in sheep fed the 0.05% S diet compared with those fed the higher levels. The results show that sulphur affects apparent selenium excretion and suggest that the metabolism of these two elements is intimately related.

Absorption↗
PubMed1979

Changes in activity of the Cu-Zn superoxide dismutase enzyme in tissues of the rat with changes in dietary copper.

The effects of dietary copper level on tissue activities of the copper containing superoxide dismutase (CuSOD) were investigated, and these activities related to those of other copper containing enzymes particularly cytochrome oxidase. Male weaning rats were fed a basal diet (containing 0.8 mg Cu/kg) or this diet supplemented with 4 or 24 mg Cu/kg. After 6 weeks, rats fed the basal diet were then repleted using the high copper diet. In the two copper supplemented groups, no differences were observed in any of the parameters measured. In these groups, tissue activities of CuSOD were in the order of liver greater than kidney greater than RBC greater than testis greater than heart greater than brain greater than lung greater than muscle. In the basal group, CuSOD activity decreased in liver; RBC and heart to 14, 25, and 61%, respectively, of control activities after 6 weeks' depletion; tissues other than brain or muscle showed smaller but significant changes. Conversely, heart and muscle cytochrome oxidase activities decreased to 30 and 45% of control activity and liver to 70%. With repletion, CuSOD activities in liver and heart increased more rapidly than did cytochrome oxidase activities. It is concluded that liver CuSOD activity, which is normally high, is greatly reduced with little change in cytochrome oxidase activity; the reverse is found for heart and muscle tissue. The relevance of these changes to the maintenance of tissue integrity is discussed.

Animals↗
PubMed1976

Mineral imbalances in farm animals and their study and diagnosis with isotopic tracers.

Twenty-two mineral elements are known to be essential for animal life. These are calcium, phosphorus, sulphur, potassium, sodium, chlorine, magnesium, iron, iodine, copper, manganese, zinc, cobalt, molybdenum, selenium, chromium, tin, vanadium, fluorine, silicon, nickel and arsenic. Naturally occurring and man-made dietary imbalances of many of these elements and their interactions with other minerals are described and their functions and requirements by farm animals are outlined. The nature and importance of metabolic interactions among the mineral elements are discussed and the important concept stressed that there is no single minimum requirement or safe tolerance of a particular mineral, but a series of such minimum requirements and safe tolerances depending on the extent to which other minerals with which it interacts is present or absent from the diet. Radioactive tracer elements are shown to be of great value in the determination of mineral nutrient availability to the animal and for following mineral metabolic movements in the body. They are also shown to have considerable potential for the diagnosis of mineral imbalances. Various in vivo and in vitro techniques, involving both radioactive and stable tracers developed for the early diagnosis of mineral deficiencies are described and the strengths and weaknesses of such techniques in comparison with standard biochemical tests, are discussed. The need for further critical studies with isotopic tracers in the detection and diagnosis of mineral imbalances is emphasized. The main types of biochemical criteria used in the diagnosis of mineral deficiencies and excesses are given, with appropriate examples of their use.

Animals↗
PubMed1975

Cobalt.

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Adult↗