Comparison of bone density measurement techniques: DXA and Archimedes' principle.

The standard method for determination of density (g/cm3) of bones from small animals has been the application of Archimedes' principle. A recent development has been software for the determination of "density" (g/cm2) of small animal bones with dual-energy X-ray absorptiometry (DXA). We compared Archimedes' principle and DXA (Hologic QDR-2000) in the measurement of the densities of whole and hollowed femurs of 5- to 6-month-old retired female breeder rats. In an attempt to ensure detectable treatment differences, rats were used from a low-vitamin D Holtzman and a supplemental-vitamin D Sprague-Dawley colony. Whole femur densities were higher for supplemental-vitamin D colony rats than for low vitamin D rats using both techniques (Archimedes' principle, p < 0.002; DXA, p < 0.005), and the densities from the two techniques were highly correlated (r = 0.82, p < 0.0001). Actual density values were higher for Archimedes' principle than for DXA. Other variables such as femur ash weight and calcium content were also highly correlated to densities with both techniques. Hollowed femur density values were higher than whole femur values with Archimedes' principle but lower with DXA. Colony effects for hollowed femur densities were diminished with Archimedes' principle (p < 0.03) and eliminated with DXA (p < 0.53). Investigation of whole bones is more biologically relevant, and both techniques were effective in detecting differences between whole femurs from low-vitamin D and supplemental-vitamin D colony rats.

Maintenance of iron status in healthy men during an extended period of stress and physical activity.

Body weight loss and iron status of 55 male soldiers were measured during 62 d of intense physical activity and sustained stress and sleep deprivation. Body weight declined from (mean +/- SD) 75.9 +/- 9.0 to 63.8 +/- 6.7 kg (P < 0.05). Serum iron fell from 13.7 +/- 5.6 to 8.3 +/- 3.6 mumol/L by 14 d (P < 0.05), but returned to baseline values by 8 wk. Total iron-binding capacity declined from 53.4 +/- 6.8 at baseline to 47.5 +/- 6.3 mumol/L at 8 wk (P < 0.05). During the study, hematocrit, serum hemoglobin, and erythrocyte count did not change, whereas ferritin increased from 116 +/- 84 to 202 +/- 106 micrograms/L (P > 0.05). Adequate dietary iron, initiation of training with adequate body iron stores, and physical activity not in excess of pretraining workloads contributed to the maintenance of iron status during prolonged physical activity and stress. Our results suggest that some acute phase-like disturbances in iron metabolism may be a normal component of adaptation to stress and physical activity in healthy men.

Does vegetable oil attenuate the beneficial effects of fish oil in reducing risk factors for cardiovascular disease?

Contradictory reports on the protective effect of fish consumption on cardiovascular disease (CVD) risk could be due to variations in the intake of n-3 and n-6 polyunsaturated fatty acids (PUFAs). Metabolic competition between n-3 and n-6 PUFAs suggests that n-6 PUFAs in vegetable oils could attenuate the efficacy of n-3 PUFAs in fish oil to favorably alter endpoints relevant to CVD risk. We determined the effects of varying dietary amounts of fish oil on lipid and thrombotic endpoints relevant to risk factors for CVD and whether these effects were attenuated by vegetable oils. Two randomized, double-blind, placebo-controlled, parallel studies were conducted in human subjects fed varying amounts of n-3 and n-6 PUFAs; n-3 PUFA intake was varied by using fish or placebo oil capsules, and n-6 PUFA intake was modified by incorporating varying amounts of safflower oil into the diet. Endpoints included changes in membrane fatty acid composition, blood lipids, and thrombotic profile. The results indicated that absolute amounts of fish oil, and not the relative amounts of fish and vegetable oil (ratios of n-3 to n-6 PUFAs), determined the magnitude of the reduction of arachidonic acid and increase in eicosapentaenoic acid in phospholipids of plasma and platelets. The suppression of plasma triacylglycerols by fish oil was not affected by varying amounts of dietary n-6 PUFAs. Fibrinogen concentrations decreased with 15 g but not with 9 g fish oil/d fed at the same ratio of n-3 to n-6 PUFAs. The efficacy of fish oil in favorably modifying certain risk factors for CVD was not attenuated by vegetable oil.

Influence of age and normal plasma fibrinogen levels on flow-mediated dilation in healthy adults.

This study examined the effects of age-associated increases in fibrinogen on brachial artery flow-mediated dilation in 30 healthy nonsmokers. The findings demonstrate an inverse association between normal plasma fibrinogen levels and vascular function (r = -0.56, p = 0.001), suggesting elevated plasma fibrinogen may decrease the artery's responsiveness to certain vasodilatory signals, such as shear stress.

Method for the simultaneous determination of cadmium and zinc in whole blood by atomic absorption spectrophotometry and measurement in normotensive and hypertensive humans.

A method is described for the analysis of whole blood cadmium and zinc by extraction and atomic absorption spectrophotometry, in which cadmium is analyzed using a graphite furnace, and zinc using an air-acetylene flame with a single slot burner, after dilution of the extract. Recoveries for cadmium and zinc were 100% and 106%, respectively. For cadmium the day-to-day and within-run coefficients of variation were all less than 13% at low concentrations (approximately 27 nmol/1) and 6% or less at high concentrations (approximately 89 nmol/1). For zinc the coefficients of variation for day-to-day and within-run analyses were less than 6% at low (approximately 76 mumol/1) and high concentrations (approximately 138 mumol/1). The sensitivity of the procedure is 0.5 nmol/1 for cadmium and 1.2 mu mol/1 for zinc. Whole blood from 72 normotensive volunteers, 56 treated hypertensives, and 15 untreated hypertensives were analyzed using this method. Cadmium levels were elevated in smokers but not significantly affected by age or sex. Zinc levels were higher in males than in females, but not significantly affected by smoking. Levels of cadmium and zinc were increased in treated hypertensives and greater still in untreated hypertensives. Significant elevations were found for cadmium in treated hypertensive females who smoked, treated and untreated hypertensive male non-smokers, and for the cadmium to zinc ratio in these later two groups.

Comparison of a radioimmunoassay with a microparticle enzyme immunoassay of insulin for use with the minimal model method of determining whole-body insulin sensitivity.

The purpose of this study was to compare minimal model results of insulin sensitivity and glucose effectiveness using insulin levels measured by a conventional radioimmunoassay (RIA) versus an automated microparticle enzyme immunoassay (MEIA). Thirty obese subjects participated in an insulin-modified frequently sampled intravenous glucose tolerance test. The MEIA exhibited lower day-to-day variability than did the RIA. The MEIA yielded lower insulin values compared to the RIA probably because of the high cross-reactivity with proinsulin in the RIA. The MEIA yielded a good correlation with the RIA for both insulin sensitivity (r = 0.97, p = 0.0001) and for glucose effectiveness (r = 0.98, p = 0.0001). The MEIA did not significantly effect the results of the MinMod analysis and the low cross-reactivity with proinsulin makes MEIA preferable when insulin sensitivity (SI) is measured in patients with diabetes or obese individuals whose insulin:proinsulin ratio is altered.

Synergistic effects of dopamine agonists and centrally administered neurotensin on feeding.

Several lines of evidence indicate that neurotensin may modulate the activity of dopamine systems in the central nervous system. The present study investigated the possibility that intraperitoneal injections of the dopamine agonists l-dopa and bromocriptine would alter the aphagia produced by central administration of neurotensin. It was found that neurotensin suppressed feeding in food-deprived rats when injected into the lateral ventricle or the ventromedial hypothalamus. Food intake was not affected, however, when the peptide was placed in the lateral hypothalamus. A dose-dependent aphagia was also observed following peripheral injections of l-dopa and bromocriptine. Additionally, the anorectic effect of centrally administered neurotensin was potentiated by concurrent administration of doses of l-dopa or bromocriptine which, when given alone, had no effect on food intake. The data suggest that neurotensin aphagia may be mediated by the peptide's ability to increase the activity of dopamine systems in the central nervous system.

Influence of a carbohydrate drink on nutritional status, body composition and mood during desert training.

BACKGROUND: Nutritional intake by military personnel is typically inadequate during field exercises, potentially compromising health and performance. HYPOTHESIS: Drinking a supplemental carbohydrate (CHO) beverage will increase total caloric intake and maintain nutritional status during military training in the desert. METHODS: A total of 63 volunteers were randomly assigned to one of two groups to receive either a CHO or placebo beverage with military rations during an 11-d desert field exercise. Fluid intake was ad libitum and adequate rations were provided. Blood samples were collected twice to assess nutritional status, and nutrient intake was determined with consumption data. Mood state was examined by questionnaire. RESULTS: Energy intake was significantly higher in the CHO group (3050 kcal x d(-1) vs. 2631 kcal x d(-1)), with additional CHO from the beverage providing energy with some compensation by reduced fat and protein intake. Intakes of energy, folacin, calcium, magnesium, iron, and zinc in both groups were inadequate, with intakes significantly lower (p<0.05) for calcium, magnesium, and zinc in the CHO beverage group. Blood parameters of nutritional status remained within normal ranges with no differences between groups, but significant decreases were seen in pre-albumin. No changes in mood were seen during the training, nor after exposure to desert conditions. CONCLUSIONS: The operational ration supplemented with a CHO beverage significantly increases CHO and energy intakes compared with standard rations and maintains nutritional status for short exercises. Fortification with micronutrients most at risk for deficient intake from foods may be needed for longer deployments.

Flameless atomic absorption spectrophotometry of selenium in whole blood.

In this method of analysis for selenium in whole blood by flameless atomic absorption spectrophotometry, 1 mL of sample is first digested with perchloric and nitric acids. After reduction and neutralization, the sample is reacted with 2,3-diaminonaphthalene, and the product is extracted into toluene. Twenty microliters of the extract is injected into the graphite furnace of a flameless atomic absorption spectrophotometer, along with 20 microliters of a 1.0 g/L cupric nitrate solution. Blood-based standards are used to establish the standard curve. The amount of selenium required to give an absorbance of 0.0044 is 5.3 micrograms/L. Precision is good, recovery excellent. The extract is stable for 24 h.

ELISA detection of restriction site polymorphisms in the pig ryanodine receptor locus.

We compare two strategies for ELISA detection of restriction site polymorphisms (EDRSP) that are suitable for high-throughput genotyping of the pig ryanodine receptor point mutation (RYR1(hal)). In both procedures, target DNA is amplified by PCR with one primer that is 5' biotinylated and a second primer that is 5' fluoresceinylated. PCR products are captured in duplicate wells on a streptavidin-coated, 96-well plate. The duplicates may be treated in two ways. In a single restriction enzyme assay, one duplicate is exposed to a restriction enzyme that cuts one allele specifically, and the second duplicate is exposed to no restriction enzyme. In a dual restriction enzyme assay, the second replicate is exposed to a second restriction enzyme that cuts the alternate allele specifically. Thereafter, the two procedures are similar; anti-fluorescein antibodies conjugated to peroxidase are allowed to bind to the fluoresceinylated ends, the plate is washed, and a substrate is converted to a colored end product. The ratio of the absorbances in the two wells is used to classify subjects by genotype. When the dual restriction enzyme assay is run, three genotype groups are easily distinguishable. When the single restriction enzyme assay is run, heterozygotes generate values that may overlap with those of the homozygotes that are not cut by the restriction enzyme. Dual restriction enzyme assays are more accurate than single restriction enzyme assays; however, single restriction enzyme assays are sufficient for identifying pigs that carry RYR1(hal).