RESUMEN
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.
Asunto(s)
Absorciometría de Fotón/métodos , Densidad Ósea/fisiología , Fémur/diagnóstico por imagen , Animales , Femenino , Fémur/anatomía & histología , Tamaño de los Órganos , Ratas , Ratas Sprague-Dawley , Programas Informáticos , Vitamina D/administración & dosificación , Deficiencia de Vitamina D/fisiopatología , AguaRESUMEN
The relationship between energy expenditure and obesity was examined in prepubertal children. Consenting fifth graders underwent Tanner Staging, weight, height and skinfold measurements. Subjects were selected for further study to obtain equal numbers of girls and boys with a wide range of body composition. Weight, total daily energy expenditure (TDEE) by doubly labeled water (DLW), resting metabolic rate (RMR), and body composition were measured. Children were grouped into level of obesity based on tertiles of subscapular plus triceps skinfolds. The skinfold tertiles did quite well in grouping subjects by degree of obesity, as differences in percent fat in each tertile were significantly different. There were no differences in fat-free mass between the groups, while the highest tertile group weighed 14 kg more than the lowest. For DLW, energy expenditure was calculated using day 8 and day 9 urine samples as the final time point to examine precision. Mean energy expenditure using either day was nearly identical (2220 +/- 400 vs 2300 +/- 370 kcal/d), with a CV of the difference of 5.5%. No differences in RMR, energy expended in activity, or TDEE between the three groups were observed. A reduction in RMR or TDEE could not explain differences in obesity in these prepubertal children. However, the fact that the heaviest children expended the same amount of energy in activity and had the same TDEE as the leanest, while weighing 14 kg more, indicates that the obese children had a reduced activity level.
Asunto(s)
Envejecimiento/fisiología , Metabolismo Energético/fisiología , Obesidad/fisiopatología , Absorciometría de Fotón , Envejecimiento/metabolismo , Análisis de Varianza , Población Negra , Composición Corporal/fisiología , Estatura/fisiología , Peso Corporal/fisiología , Niño , Deuterio , Ingestión de Alimentos/fisiología , Femenino , Humanos , Masculino , Obesidad/metabolismo , Isótopos de Oxígeno , Reproducibilidad de los Resultados , Grosor de los Pliegues Cutáneos , Población BlancaRESUMEN
Although analysis of lactate concentrations with a Yellow Springs Instruments (YSI) automated analyzer has become very popular in Sports Medicine, the accuracy and reliability of this technique has not been carefully studied. Additionally, the influence of a common lysing agent Triton X-100 (TX) on blood lactate measurements has not been determined. Blood was collected from each of ten subjects at rest and 2, 6, 10, 14 and 20 minutes following maximal exercise (60 samples). Lactate concentration was measured by the YSI and Boehringer Mannheim (BMM) techniques. Two YSI 23L analyzers were supplied with buffer with TX (YSITX), and two without (YSINON) to permit comparisons of lysed and unlysed whole blood lactate levels over the physiological range. MANOVA analysis revealed a statistical difference (p less than .05) between duplicates only for one machine, and duplicates of that machine differed by less than 3%. Mean measurements between similarly prepared machines differed significantly for the NONTX machines, but only by less than 3%. Differences were significant between BMM and YSINON, but not between BMM and YSITX. Regression analysis indicated close agreement between BMM and YSITX (R2 = .99). There was a tendency for a large discrepancy between methods at resting concentrations.