Biomedical subjects

K O O'Brien

Publications and source records attributed to K O O'Brien.

24 records · Page 2Linked to original sources

PubMed1996

Changes in calcium kinetics associated with menarche.

To evaluate the consequences of puberty on calcium (Ca) metabolism, we measured Ca kinetic parameters in 43 healthy girls 1-60 months post menarche. There was a close relationship between the logarithmic transform of the number of months post menarche and the bone Ca deposition rate (Vo +) (r = -0.90, P < 0.001). Using multiple regression analysis with the logarithmic transforms of chronological age and months post menarche as independent parameters, we found that the number of months post menarche was more significantly correlated with Vo + (t = -7.4, P < 0.0001) than with chronological age (t = -3.1, P = 0.003). A longitudinal study of 17 girls demonstrated a peak Vo + approximately 8 months before menarche, with a decrease in Vo + after menarche. These studies indicate that the peak time for bone Ca deposition is in the premenarcheal and perimenarcheal time period. The close correlation between Vo + and months post menarche demonstrates the importance of puberty in consideration of bone Ca metabolism in girls.

Adolescent↗

PubMed1994

Effects of development on techniques for calcium stable isotope studies in children.

We evaluated the effects of age and pubertal status on the tracer excess measured in urine samples collected during the 120 h after the oral and intravenous administration of calcium stable isotopes to 90 children (16 preterm infants and 74 females aged 4.9-16.8 years). Analysis of subjects shows differences in distribution volume and fractional absorption of calcium based on developmental status, with four separate groups being identified. These are: (i) premature infants; (ii) prepubertal girls (Tanner stage 1); (iii) early pubertal girls (Tanner states 2-3); and (iv) late pubertal girls (Tanner stages 4-5). Identification of groups in this fashion allows for adequate dosing in calcium stable isotope studies, with the minimum dose being given to achieve an increase in urinary isotopic content consistent with the precision of the analytical equipment.

Adolescent↗

PubMed1994

Application of magnetic sector thermal ionization mass spectrometry to studies of erythrocyte iron incorporation in small children.

The optimal evaluation of iron metabolism requires the administration of two isotopes of iron. However, high-precision measurement of isotopic ratios from blood samples obtained after administration of two stable isotopes of iron to human subjects has not previously been reported. Using a cation-exchange system to isolate iron from blood samples, we found that high-precision (< 0.2%) measurements of 58Fe/56Fe and 57Fe/56Fe could be performed using magnetic sector thermal ionization mass spectrometry. Clinical studies in four 1-year-old infants showed that this technique could be used to demonstrate a lower rate of iron absorption in small children given an iron supplement (57Fe) with milk compared to those given iron (58Fe and ferrous sulfate) with ascorbic acid. This technique will enable the evaluation of iron metabolism in populations in whom the use of radioactive iron tracers is not appropriate.

Adolescent↗

PubMed1994

Calcium kinetics in lactating women with low and high calcium intakes.

Absorption of calcium and its mobilization from bone during lactation are important for delivery of calcium to breast-feeding infants; whether calcium intake offsets bone resorption is not known. We hypothesized that calcium absorption is increased in lactation and greater in women on low calcium diets, resulting in similar rates of bone resorption and accretion. Calcium absorption and kinetic indexes were calculated by using two stable isotopic tracers in 8 women; 6 were studied both during lactation and nonlactation. Women consumed low calcium diets, with half receiving supplemental calcium. Intestinal absorption was related to serum 1,25-dihydroxyvitamin D and did not increase during lactation. Despite decreased urinary calcium excretion during lactation, especially in women with low calcium intake, net balance tended to be lower during lactation. Mean residence time decreased and bone resorption exceeded accretion in almost all lactating women. Calcium need for milk production appears to be met by decreased urinary excretion and increased bone resorption, and not by increased intestinal absorption.

Adult↗

PubMed1994

Mineral metabolism in children with dermatomyositis.

OBJECTIVE: To measure calcium metabolism in 12 children with juvenile dermatomyositis (JDM). METHODS: We used dual-tracer stable isotope studies to measure calcium metabolism in 12 children with JDM and a group of 43 healthy children (Group HC) of similar ages. Five of the JDM subjects were receiving steroids (Group JDM-ST) and 7 were not (Group JDM-NS). RESULTS: The rate of calcium absorption in Group JDM-ST was lower than that in Group HC (19 +/- 10% vs 30 +/- 11%, p < 0.05). The lower rate of absorption was associated with a net loss of calcium each day (calculated calcium retention, Vbal, of -35 +/- 14 mg/day compared to +140 +/- 97 mg/day in Group HC, p < 0.01). Group JDM-NS showed slightly lower calcium absorption than Group HC and significantly lower Vbal (+33 +/- 70 mg/day, p < 0.01 vs Group HC) than Group HC. Group JDM-ST subjects also had decreased bone calcium deposition rates. CONCLUSION: Patients with JDM may be at risk for significant loss of bone mineral associated with decreased calcium absorption, especially in the acute phase of their disease when they are receiving steroid therapy.

Absorption↗

PubMed1993

High fiber diets slow bone turnover in young men but have no effect on efficiency of intestinal calcium absorption.

Dietary fiber reduces the absorption of dietary calcium from a meal, but its impact on calcium kinetics is unknown. We therefore evaluated the effects of a high fiber diet on calcium balance and kinetics and on calcium-regulating hormones. Seven young men each participated in two 23-d experiments. In the low fiber period the controlled diet provided 6.5 g fiber/d and 530 mg calcium/d. In the high fiber period fiber was increased to 31.3 g/d and calcium to 586 mg/d by substituting high fiber cereal. Measured between d 7 and 12 of each period, the high fiber diet significantly lowered the apparent absorption of calcium (from 60.6 +/- 23.8% to 37.1 +/- 26.5%) and reduced calcium balance, although balance remained positive overall. Fiber had no effect on serum total or ultrafiltrable calcium, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D or parathyroid hormone concentrations measured on d 1, 7, 12 and 20. Calcium kinetics was studied between d 17 and 23 by administering oral 44Ca and intravenous 42Ca to fasting subjects. Fractional absorption of calcium in the fasting state was unaffected by fiber. However, during the high fiber period, subjects had significantly lower bone accretion, resorption and turnover rates, and calcium flow to bone from the exchangeable pool than during the low fiber period. We conclude that the fiber-induced reduction in calcium absorption slowed down bone calcium turnover but did not increase the efficiency of intestinal absorption.

Adult↗