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  • 1
    Electronic Resource
    Electronic Resource
    Influence of age on effects of endogenous 1,25-dihydroxyvitamin D on calcium absorption in normal women (1994)
    Springer
    Calcified tissue international 55 (1994), S. 330-334 
    Details
    ISSN: 1432-0827
    Keywords: Age ; Vitamin D ; Calcium absorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Recent reports of increases in serum 1,25-dihydroxyvitamin D [1,25(OH2)D] concentration with aging despite no changes or decreases in calcium absorption suggest that elderly women have intestinal resistance to vitamin D action. Thus, in 15 young adult (30±1 year) and 15 elderly (74±1 year) women (mean±SE), we assessed the responsiveness of intestinal calcium absorption to increases in circulating 1,25(OH)2D induced by 4 days of an experimental diet (150 mg calcium and 1600 mg phosphorus daily). True fractional calcium absorption (FCA) (44Ca mixed with food and 42Ca given intravenously, then their ratio in urine measured by mass spectrometry) was determined. Baseline serum intact parathyroid hormone (PTH) concentration was higher in the older women (P=0.01) whereas serum 1,25(OH)2D concentration and true FCA were similar. In both groups, serum 1,25(OH)2D concentrations increased (P〈0.002) on the experimental diet. After 4 days on the diet, serum 1,25(OH)2D increased over baseline by 30.5 and 35.6% and, despite these increases, true FCA was 40±3 versus 40±4%/24 hours (NS between groups) in the young and elderly women, respectively. These data suggest that either elderly women have normal intestinal responsiveness to vitamin D or that the resistance to it is too mild to be detected by these methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00299309
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  • 2
    Electronic Resource
    Electronic Resource
    Calcium kinetics in glycogen storage disease type 1a (1996)
    Springer
    Calcified tissue international 59 (1996), S. 449-453 
    Details
    ISSN: 1432-0827
    Keywords: Glycogen storage disease 1a ; Von Gierke's disease ; Calcium metabolism ; Calcium kinetics ; Calcium stable isotopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Glycogen storage disease type 1a (Von Gierke's disease) is one of the more common glycogen storage diseases (GSD). GSD 1a patients can have severe idiopathic osteopenia, often beginning at a young age. Since calcium tracer studies offer a sensitive probe of the bone microenvironment and of calcium deposition, kinetics might be disturbed in patients with GSD 1a. Plasma dilution kinetics obtained using the stable isotope 42Ca are shown in this paper to be quite different between GSD 1a patients and age-matched controls. Comparison of kinetic parameters in these two populations is made using a new binding site model for describing calcium dynamics at the plasma-bone interface. This model describes reversible binding of calcium ions to postulated short-term and long-term sites by a retention probability density function ψ (t). Using this analysis, adult GSD subjects exhibited a significant decrease (P=0.023) in the apparent half-life of a calcium ion on the longer-term site compared with controls. The general theory of calcium tracer dilution kinetics is then discussed in terms of a new model of short-term calcium homeostasis recently proposed by Bronner and Stein [5].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00369209
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  • 3
    Electronic Resource
    Electronic Resource
    Calcium Kinetics in Glycogen Storage Disease Type 1a (1996)
    Springer
    Calcified tissue international 59 (1996), S. 449-453 
    Details
    ISSN: 1432-0827
    Keywords: Key words: Glycogen storage disease 1a — Von Gierke's disease — Calcium metabolism — Calcium kinetics — Calcium stable isotopes.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Glycogen storage disease type 1a (Von Gierke's disease) is one of the more common glycogen storage diseases (GSD). GSD 1a patients can have severe idiopathic osteopenia, often beginning at a young age. Since calcium tracer studies offer a sensitive probe of the bone microenvironment and of calcium deposition, kinetics might be disturbed in patients with GSD 1a. Plasma dilution kinetics obtained using the stable isotope 42Ca are shown in this paper to be quite different between GSD 1a patients and age-matched controls. Comparison of kinetic parameters in these two populations is made using a new binding site model for describing calcium dynamics at the plasma-bone interface. This model describes reversible binding of calcium ions to postulated short-term and long-term sites by a retention probability density function ψ (t). Using this analysis, adult GSD subjects exhibited a significant decrease (P= 0.023) in the apparent half-life of a calcium ion on the longer-term site compared with controls. The general theory of calcium tracer dilution kinetics is then discussed in terms of a new model of short-term calcium homeostasis recently proposed by Bronner and Stein [5].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00369209
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  • 4
    Electronic Resource
    Electronic Resource
    Calcium Kinetics in Children with Osteogenesis Imperfecta Type III and IV: Pre- and Post-Growth Hormone Therapy (2000)
    Springer
    Calcified tissue international 67 (2000), S. 97-100 
    Details
    ISSN: 1432-0827
    Keywords: Key words: Stable isotopes — Bone-metabolism — Children.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Children with osteogenesis imperfecta (OI) type III and type IV were studied using a 42Ca stable isotope technique. Serum dilution kinetics of 42Ca were studied pre- and post-growth hormone (GH) treatment in 9 OI III (age range 5–9 years) and 8 OI IV patients (age range 5–12 years). Each subject was studied twice: at baseline and following GH therapy (range 1–1.5 years). Isotopic enrichments of 42Ca were followed over 7 days using thermal ionization mass spectrometry. A binding site model, which describes reversible and irreversible binding of calcium (Ca) ions to postulated short- and long-term binding sites in bone, was used to analyze the kinetic data. In type III patients, GH treatment (1) increased the fraction of short-term binding sites, θ (0.777 ± 0.112 versus 0.877 ± 0.05, respectively; P= 0.034); (2) increased the apparent half-life of a Ca ion attached to the long-term binding site by 76% (P= 0.009); (3) although not statistically significant (P= 0.098), a trend toward an increased growth rate was observed with increasing change in θ (Δθ); (4) patients experienced a 75% increase in growth rate during the first 6 months of treatment. In type IV patients, GH treatment increased the apparent half-life of a Ca ion attached to the long-term binding site by 83% (P= 0.048), however, no trend toward an increased growth rate was observed with increasing Δθ in these patients. These significant changes in Ca binding to bone may influence growth in type III patients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00223001110
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