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Biomedical subjects

C D Thomson

Publications and source records attributed to C D Thomson.

At least 37 records · Page 2Linked to original sources
PubMed1990

Selenium content of foods consumed in Otago, New Zealand.

Selenium (Se) concentrations were determined in over 600 foods sampled in Dunedin, New Zealand. Foods included those produced in the region, foods which were expected to contribute significantly to the total Se intake, breads and other wheat products which might be affected by the importation of Australian wheat, and imported vegetarian foods. Foods with the highest Se concentrations were brazil nuts, sunflower seeds and all varieties of fish and kidneys. Somewhat lower concentrations were found in liver, pork, chicken, eggs, cashew nuts, soybeans and mushrooms. Vegetables, fruits, cereals and milk products were generally low in Se with the exceptions of mushrooms, imported legumes, rice and bananas. Those foods showing the greatest difference in Se content from those of other countries were cereal products and meat foods. The effect of a number of cooking methods on Se concentrations indicated that in general, little Se was lost during cooking. The importation of a shipment of high-Se wheat from Australia in 1984 raised Se concentrations in breads and other wheat products two to four fold.

Animal Feed↗
PubMed1990

Reduced selenium in asthmatic subjects in New Zealand.

Selenium is an essential component of glutathione peroxidase, an enzyme that helps protect cells against oxidation damage and modulates the lipoxygenase pathway of arachidonic acid metabolism. Low selenium concentrations might therefore influence the inflammatory process in asthma by reducing the activity of glutathione peroxidase. Whole blood and plasma selenium concentrations and glutathione peroxidase activity have been measured in 56 asthmatic patients and 59 non-asthmatic control subjects in New Zealand, a country with a low dietary selenium intake and a high prevalence of asthma. When compared with control subjects the asthmatic patients had lower values for whole blood selenium concentrations (-4.9, 95% confidence interval -10.2 to 0.4 ng/ml) and glutathione peroxidase activity (-3.3, 95% CI -5.8 to -0.8 units/g Hb). There was a 1.9 and 5.8 fold increased risk of asthma in subjects with the lowest range of whole blood selenium concentration and glutathione peroxidase activity respectively (95% CI 0.6 to 5.6 and 1.6 to 21.2). Levels were lower in patients and control subjects without an atopic predisposition, but were not affected by prednisone use. Similar differences between the asthmatic and control subjects were not observed for selenium concentration or glutathione peroxidase activity measured in plasma, which reflects short term rather than long term selenium content. These findings are consistent with the hypothesis that low selenium concentrations may have a role in the pathogenesis of asthma in New Zealand.

Adolescent↗
PubMed1989

Physician supply and distribution in Georgia.

Physician supply in Georgia must be considered an urgent issue. Several important points must be recognized and addressed. The lowest physicians rates are in the more rural county population groupings. The only county population grouping with a surplus of physicians is in the over 150,000 population. The majority of physicians are concentrated in the metropolitan counties. Sixteen percent of all physicians practice in the 134 counties having less than 50,000 population. The majority of physicians are in primary care specialties. Family practice is the most dominant specialty in rural areas. By the year 2000, Georgia can expect to add 5,600 physicians due to growth. By the year 2000, Georgia can expect to lose 2,600 physicians due to retirement. Family practitioners are the most uniformly distributed of the specialties examined. They are also the specialty most needed. The average age of Georgia physicians is 46. General surgeons are in the oldest average age group (50), whereas internists are in the youngest (44). Older physicians are concentrated in the more rural areas. A significant number of all physicians are over age 55. The majority of these will be retired by the year 2000. Physicians over age 65 represent 9.2% of all physicians from the survey. In Georgia, 13.6% of all physicians were Foreign Medical School Graduates. They tend to locate their practices in medically underserved areas. The specialty choices most frequently favored by FMGs are: pediatrics, internal medicine, family practice, and obstetrics/gynecology. A total of 71.2% of all physicians accept Medicare patients; 83.8% accept Medicare patients. Ninety-two percent of all obstetricians accept obstetric patients, but this participation is threatened by problems with malpractice insurance.

Adult↗
PubMed1988

Selenium and vitamin E supplementation: activities of glutathione peroxidase in human tissues.

Twenty-seven New Zealand women received daily for 4 wk, 200 micrograms selenium as sodium selenite, 170 mg alpha-tocopherol acetate, or a placebo. Se supplementation raised platelet selenoglutathione peroxidase (Se-GSHPx, p less than 0.001) and also Se and Se-GSHPx in whole blood and plasma. Se concentrations and Se-GSHPx activities in liver biopsies taken after supplementation were greater (p less than 0.05) for the Se group and a good correlation was found between Se and Se-GSHPx in liver and muscle for all subjects. Platelet Se-GSHPx correlated well with Se and Se-GSHPx in liver, indicating its suitability for assessing Se bioavailability. This is the first reported study of relationships between Se and Se-GSHPx in human liver and muscle tissue and platelet Se-GSHPx after Se supplementation. These observations verify in man relationships observe in animal studies, giving support to assumptions made in methods for assessing Se status and bioavailability in man, in particular the use of platelet GSHPx.

Adaptation, Physiological↗
PubMed1988

Blood selenium and glutathione peroxidase activity of populations in New Zealand, Oregon, and South Dakota.

The relationship of whole blood selenium (Se) to glutathione peroxidase (GPX) activity was examined for individuals in New Zealand, Oregon, and South Dakota who represented, respectively, populations with exposure to low, medium, and high amounts of Se. The mean (respective) blood Se levels were 60, 200, and 400 ng/ml. Intergroup differences in blood Se levels were highly significant (P less than 0.001). GPX assays were performed using two variations of an enzyme-coupled procedure to assess the equivalence of the two methods. Despite a fourfold difference in absolute activities measured by these methods, the GPX activities were highly correlated (r = .86) between procedures. Average blood GPX activity was significantly lower (P less than 0.001) for the New Zealand group compared with the other two groups, but there was no difference in GPX activities between the Oregon and South Dakota groups. Linear regression of GPX vs. Se values within each group indicated a significant correlation of these parameters only in the New Zealand group (r = .46, P less than 0.01). Comparison of these parameters for combined data from all three groups also showed a significant positive correlation (r = .60, P less than 0.001). A saturation model (In GPX = k1 + k2 (Se)-1)) fits the combined data better (r = .80, P less than 0.01) than does direct comparison of the two parameters. These results suggest that GPX activity is an appropriate indicator of human Se status only in populations with below normal exposure to Se, as activity of this enzyme is saturated at relatively low levels.

Glutathione Peroxidase↗
PubMed1988

The absence of adaptive changes in tissue activities of glutathione-S-transferase, superoxide dismutase and catalase following selenium and vitamin E supplementation in subjects with low selenium status.

Three groups of New Zealand women were given daily in a double blind randomised study, 200 micrograms Se as sodium selenite, 170 mg alpha-tocopherol or a placebo for 4 wk. Activities of glutathione-S-transferase, superoxide dismutase and catalase were assayed in erythrocytes, plasma and platelets and in liver and muscle biopsy tissues. No changes in activities of any of these tissue enzymes were observed in any of the three groups. There were also no changes in non-selenium dependent glutathione peroxidase activities in liver or plasma. The lack of changes in any of these enzymes following selenium supplementation suggests that adaptive changes to the low selenium status of these subjects had not occurred through these lipid peroxidation defense mechanisms.

Adult↗
PubMed1986

Urinary and fecal excretions and absorption of a large supplement of selenium: superiority of selenate over selenite.

A correction needs to be made to the form of selenium used in earlier studies; what was believed to be selenite-Se in solution is now known to have been selenate-Se. In the present study, excretion of Se was followed in 13 women after ingestion of 1 mg Se as selenite or selenate in solution. Fecal excretion of selenate-Se was less than for selenite-Se reflecting a higher apparent absorption [94 +/- 4% (SD), 62 +/- 14%, respectively]. Peak excretion of Se occurred 3 h earlier for selenate-Se than for selenite-Se and was 6 times higher. Total urinary excretion of selenate-Se was 3 times that of selenite-Se and still 2 times as high when expressed as % absorbed dose. Total recovery of Se in urine and feces was similar for both forms. There was remarkable agreement between these results and those reported earlier for selenate-Se (Selovet-1) and selenite-Se.

Adult↗
PubMed1985

Effect of a megadose of ascorbic acid, a meal and orange juice on the absorption of selenium as sodium selenite.

Urinary and faecal excretions of selenium were measured for five days following a dose of 1 mg Se as sodium selenite in ten young women after an overnight fast. The selenite was taken two hours before a meal or mixed with 1 g ascorbic acid; or with a continental type breakfast providing 4.5-5.6 micrograms Se and 0.6-0.8 mg Cu, with or without 200 ml orange juice (60 mg ascorbic acid). The light meal appeared to have little effect on selenite-Se absorption, and orange juice appeared even to assist it. But the availability of Se was reduced almost to zero when selenite and 1 g ascorbic acid were taken together well before the meal.

Adult↗
PubMed1985

Selenium absorption by canine jejunum.

Deficiency of the trace element selenium causes disease in domestic animals and may also be implicated in the pathogenesis of some human illness. In this study, the triple-lumen perfusion method was used to measure the rate of absorption of trace quantities of selenium (50 micrograms/liter in a physiological electrolyte solution) from the jejunum when given as D,L-selenomethione, D,L-selenocystine, or sodium selenite to healthy dogs in vivo. Selenium absorption from the test segment (expressed as percent administered dose per centimeter +/- SEM) was 1.97 +/- 0.04 from D,L-selenomethionine, 1.15 +/- 0.06 from D,L-selenocystine, and 0.51 +/- 0.07 from sodium selenite (P less than 0.01, N = 5). In separate studies in four anesthetized dogs, the jejunum was perfused with L-[75Se] selenomethionine while concentrations of 75Se were measured in the portal venous blood; these studies established that [75Se]selenomethionine disappearing from the gut lumen corresponded quantitatively to 75Se appearing in the portal venous effluent (74 +/- 6%) and incorporated into intestinal tissue (24 +/- 5%). These results are consistent with the hypothesis that the absorption of amino acid-bound selenium is accelerated by the specific amino acid active transport mechanisms in the gut mucosa. Sodium selenite is absorbed more slowly, possibly by simple diffusion through the intestinal mucosa, than the amino acid-bound selenium compounds.

Animals↗
PubMed1985

Effects of supplementation with high-selenium wheat bread on selenium, glutathione peroxidase and related enzymes in blood components of New Zealand residents.

The effects of supplementation with high-Se wheat bread on selenium (Se) concentrations, glutathione peroxidase (EC 1.11.1.9, GSHPx) activities and related enzymes in the prevention of lipid peroxidation were studied. Four New Zealand women were supplemented with 200 micrograms Se daily for 8-13 weeks followed by a post-dosing period of 9-12 weeks. GSHPx activities increased in whole blood, erythrocytes, plasma and platelets of all subjects but increases were considerably less than those of Se concentrations in whole blood, plasma and erythrocytes. During the post-dosing period Se concentrations and GSHPx activities fell to levels which were in most cases somewhat higher than baseline values. Glutathione-S-transferase activities in erythrocytes, plasma and platelets did not change during the study, nor did superoxide dismutase in erythrocytes and platelets, erythrocyte catalase or plasma alpha-tocopherol. Thus Se supplementation of healthy New Zealand subjects increased GSHPx activities but did not produce any adaptive changes in other components of the lipid peroxidation defense mechanisms.

Adult↗
PubMed1985

Urinary excretion of selenium by New Zealand and North American human subjects on differing intakes.

Lower renal plasma clearances of selenium (CSe 0.1-0.2 ml min-1), indicating excretion of a smaller proportion of Se presented to the kidneys, were found in New Zealand (NZ) residents with low plasma Se ((Se)p 50-70 ng ml-1) on customary intakes below 30 micrograms d-1 Se. North American subjects consuming 80 micrograms d-1 with (Se)p 120-140 ng ml-1 had CSe between 0.2 and 0.3 ml min-1. Several weeks' supplementation with high-Se bread increased NZ subjects' (Se)p to 120-175 ng ml-1 and CSe to 0.4-0.7 ml min-1. (Se)p remained elevated when supplementation ceased, but CSe returned to the basal range within a few days. Americans' clearances showed no such abrupt decrease when their dietary intake was similarly reduced. The NZ residents thus appeared to excrete selenium more sparingly than others. Rapid alterations in clearance after supplements and single doses were probably due to changes in the proportions of different forms of selenium in the plasma.

Adaptation, Physiological↗
PubMed1985

Selenium-dependent and non-selenium-dependent glutathione peroxidase in human tissues of New Zealand residents.

Glutathione peroxidase was assayed in human tissues of New Zealand residents by the coupled assay method. Total glutathione peroxidase was assayed using cumene hydroperoxide. The non-selenium-dependent activity was not detected with t-butyl hydroperoxide and thus was determined from the difference between total activity and the selenium-dependent activity using hydrogen peroxide or t-butyl hydroperoxide. Only selenium-dependent activity was found in whole blood, erythrocytes, platelets and biopsy skeletal muscle. A small non-selenium dependent activity was measured in plasma and a larger activity in biopsy liver supernatant and homogenate. Glutathione-S-transferase was detected in all tissues.

Benzene Derivatives↗
PubMed1982

Effect of prolonged supplementation with daily supplements of selenomethionine and sodium selenite on glutathione peroxidase activity in blood of New Zealand residents.

Glutathione peroxidase (EC 1.11.1.9, GSH-Px) activities and selenium (Se) concentrations in blood of 12 New Zealand residents were followed during prolonged supplementation with physiological doses (100 microgram Se) of sodium selenite (selenite-Se) or selenomethionine (Semet-Se). GSH-Px activities increased in all subjects but at 17 wk the mean increase was not significantly greater for Semet-Se (6.2 +/- SD 3.2 units/g Hb) than for selenite-Se (3.7 +/- 1.8 units/g Hb). After dosing ceased, GSH-Px activities for most subjects returned to predosing values in 17 to 40 wk, but in some subjects activities remained high. Increases in Se concentrations in whole blood, erythrocytes, and plasma were greater after Semet-Se than after selenite-se. Se concentrations tended to plateau after selenite-Se while after Semet-Se they continued to rise as long as dosing continued. Enzyme activity of one of four subjects supplemented daily with 500 microgram selenite-Se was unchanged, despite a great increase in plasma Se. Blood Se and GSH-Px of 23 New Zealand residents who ingest regular large doses (0.5 to 3 mg Se) mainly of selenite-Se showed that those who dosed weekly had greater values than the less frequent dosers. Three subjects showed extremely high values. It is suggested that each individual might have an optimal level of GSH-Px activity, so that the level reached is a balance between Se intake and other factors, including possible stressor effect of selenite.

Adult↗
PubMed1981

Effect of daily supplements of selenium on patients with muscular complaints in Otago and Canterbury.

The alleged beneficial effect of selenium (Se) on fibromuscular rheumatism in residents of low soil-Se areas of New Zealand has been explored. Three dosing trials, two of them double blind trials, using physiological daily supplements (100 micrograms Se) of sodium selenite or selenomethionine and a placebo have been carried out. Blood Se and glutathione peroxidase (EC 1.11.1.9; GSHPX) activities were monitored and clinical assessment of the efficacy of the treatment was made during the trials. Blood Se and GSHPX activities rose in all patients who received Se whereas those in control groups remained more or less constant throughout the study. Clinical assessment of muscular symptoms showed that approximately half of the patients in both trial groups and placebo groups responded to treatment. Thus we have been unable to give conclusive evidence of a response to Se supplementation for relief of muscular complaints.

Adolescent↗
PubMed1980

Selenium in human health and disease with emphasis on those aspects peculiar to New Zealand.

Evidence is accumulating to suggest that selenium (Se) is an essential trace element for man and is reviewed with emphasis on those aspects peculiar to New Zealand. The extremely low Se levels in New Zealand soils results in a low Se content of foods, low dietary intakes, low urinary excretions, and low blood Se concentrations and glutathione peroxidase activities. Of these, plasma Se gives a short-term index of nutritional status while erythrocyte Se and glutathione peroxidase activities give a long-term index. The consequences of the low Se status of New Zealanders are not immediately apparent as a deficiency disease has not been detected in residents consuming a normal diet. However a Se-responsive muscular syndrome has been described in a surgical patient on total parenteral nutrition. Similar groups that might be vulnerable to a Se deficiency are children with metabolic disorders consuming synthetic protein diets, premature babies and infants during the first few months of life, and patients with cancer whose lowered dietary intake is coupled with the traumatic nature of their disease. Other groups that have been studied in relation to a possible role for Se in specific illnesses are patients with cardiovascular disease and hypertension, rheumatoid arthritis and other muscular syndromes and surgical patients with or without cancer. It is not yet possible to predict a minimum Se requirement for health but it appears that the intake of New Zealanders might be on the borderline. At present supplementation by the general population is not justified, but may be necessary for certain vulnerable groups such as patients on restricted diets. The most effective means of supplementation for increasing the Se status of New Zealanders is under study.

Adolescent↗
PubMed1979

Relation between erythrocyte selenium concentrations and glutathione peroxidase (EC 1.11.1.9) activities of New Zealand residents and visitors to New Zealand.

1. Erythrocyte, plasma and whole blood selenium concentrations and glutathione peroxidase (EC 1.11.1.9; GSHPx) activities were measured (1) in 104 healthy New Zealand residents living in Otago, a low-soil-Se area (2) in sixty-four surgical patients, including nineteen patients on total parenteral nutrition and twenty-three cancer patients (3) in fifty-two 'overseas subjects' (twenty-five visitors to Otago from outside New Zealand and twenty-seven Otago residents on return from overseas travel). 2. Blood Se concentrations reflected dietary Se intake; means for Otago patients, healthy subjects and overseas subjects were different 0.043, 0.059, 0.136 micrograms Se/ml blood respectively) and mean for overseas residents was greater than for New Zealand overseas travellers. 3. Erythrocyte Se concentration was always greater than plasma Se, and plasma Se was a smaller proportion of erythrocyte Se for patients compared with the controls. 4. GSHPx activities were different in the three groups, and varied directly with erythrocyte Se until a plateau was reached at approximately 0.14 micrograms Se/ml erythrocytes. 5. Overseas subjects showed no relationship between erythrocyte Se and GSHPx activity. This agrees with some overseas studies and the significance of this finding is discussed. 6. Plasma Se concentration remained the most sensitivie index of short-term changes in Se status, and erythrocyte Se and GSHPx activities for long-term changes in New Zealand subjects. Use of these measurements for overseas subjects with higher blood levels is discussed.

Erythrocytes↗
PubMed1979

Blood selenium and glutathione peroxidase activity in normal subjects and in surgical patients with and without cancer in New Zealand.

This study was carried out in Otago, South Island, where most arable land has a low soil selenium content (less than 0.5 microgram/g) and where selenium (Se) responsive diseases in livestock are common. Se concentration in whole blood, erythrocytes and plasma, and activity of glutathione peroxidase (EC 1.11.1.9) were measured in blood from 104 healthy Otago residents, 80 patients with cancer and 66 noncancer surgical patients. The older residents over 60 years had lower blood Se levels (0.047 +/- 0.010 microgram Se/ml blood) than the young and middle-aged (0.060 +/- 0.012 microgram Se/ml). Blood Se levels of cancer patients were no lower than those of elderly subjects and patients without cancer, and were less than half comparable United States values. Blood Se levels were decreasing in two cancer patients, and the lowest values (less than 0.03 microgram Se/ml blood) were obtained for five cancer patients, and two noncancer patients after a long period of inanition; these were similar to values for patients on parenteral nutrition with negligible intakes. Lower blood Se levels were associated with lower serum albumin and enzyme activities. It is suggested that low Se status of cancer patients was more likely a consequence of their illness than the cause of the cancer.

Adult↗