Mechanism of calcium exchange at bone surfaces

Groer, Peter G.; Marshall, J. H.

doi:10.1007/bf02013733

Cited by 49 publications

(15 citation statements)

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“…In contrast, Ovx significantly reduced the tibial total calcium content in adult rats fed a normal calcium diet compared with sham-operated rats, i.e., 23.77 Ϯ 2.05 (sham, n ϭ 12) vs. 19.54 Ϯ 1.62 mmol/g dry wt (OvxϩN, n ϭ 13, P Ͻ 0.05), suggesting that long-term estrogen deficiency distinctly affected the cortical calcium in adult rats, but not in young rats. High-calcium diet alone or AP transplantation alone did not alter the tibial total calcium content in adult ovariectomized rats.…”

Section: High-calcium Diet Differentially Affected the Cortical Bone mentioning

confidence: 90%

“…Other pituitary hormones were not secreted due to the absence of the respective stimulatory hypothalamic hormones. In the 45 Ca kinetic study, which was a sensitive method to detect 45 Ca deposit in bone and exchangeable bone calcium pool (19,29), high plasma prolactin levels were obtained by subcutaneous injection, because an abrupt increase in prolactin level was required at the start of the experiment (day 14 in Fig. 1).…”

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confidence: 99%

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High-calcium diet modulates effects of long-term prolactin exposure on the cortical bone calcium content in ovariectomized rats

Charoenphandhu

Tudpor²,

Thongchote³

et al. 2007

American Journal of Physiology-Endocrinology and Metabolism

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High physiological prolactin induced positive calcium balance by stimulating intestinal calcium absorption, reducing renal calcium excretion, and increasing bone calcium deposition in female rats. Although prolactin-induced increase in trabecular bone calcium deposition was absent after ovariectomy, its effects on cortical bones were still controversial. The present investigation, therefore, aimed to study the effect of in vivo long-term high physiological prolactin induced by either anterior pituitary (AP) transplantation or 2.5 mg/kg prolactin injection on cortical bones in ovariectomized rats. Since the presence of prolactin receptors (PRLR) in different bones of normal adult rats has not been reported, we first determined mRNA expression of both short- and long-form PRLRs at the cortical sites (tibia and femur) and trabecular sites (calvaria and vertebrae) by using the RT-PCR. Our results showed the mRNA expression of both PRLR isoforms with predominant long form at all sites. However, high prolactin levels induced by AP transplantation in normal rats did not have any effect on the femoral bone mineral density or bone mineral content. By using 45Ca kinetic study, 2.5 mg/kg prolactin did not alter bone formation, bone resorption, calcium deposition, and total calcium content in tibia and femur of adult ovariectomized rats. AP transplantation also had no effect on the cortical total calcium content in adult ovariectomized rats. Because previous work showed that the effects of prolactin were age dependent and could be modulated by high-calcium diet, interactions between prolactin and these two parameters were investigated. The results demonstrated that 2.0% wt/wt high-calcium diet significantly increased the tibial total calcium content in 9-wk-old young AP-grafted ovariectomized rats but decreased the tibial total calcium content in 22-wk-old adult rats. As for the vertebrae, the total calcium contents in both young and adult rats were not changed by high-calcium diet. The present results thus indicated that the adult cortical bones were potentially direct targets of prolactin. Moreover, the effects of high physiological prolactin on cortical bones were age dependent and were observed only under the modulation of high-calcium diet condition.

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Section: High-calcium Diet Differentially Affected the Cortical Bone mentioning

confidence: 90%

mentioning

confidence: 99%

High-calcium diet modulates effects of long-term prolactin exposure on the cortical bone calcium content in ovariectomized rats

Charoenphandhu

Tudpor²,

Thongchote³

et al. 2007

American Journal of Physiology-Endocrinology and Metabolism

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“…Comar's calculation of OR following double tracer intake, therefore, depends to some extent on the time of calculation. * The OR (bone/diet) for new bone in Table 2 was calculated from expressions (34) and (36). OR (bone/diet), the true equilibrium value, is given by (37) or (39).…”

Section: (B) Discussionmentioning

confidence: 99%

“…For more detail in the derivation of this important expression, see expressions (32)(33)(34)(35) for the activity in body and blood under continuous intake, and the discussion elsewhere. (4) Expression (8) This postulate is, of course, a simplification of the real system.…”

Section: The Excretion Postulatementioning

confidence: 99%

“…Suppose the activity per gram calcium of the diet has been constant at the value Fo for a period of time t. Then integrating expression (7), we obtain the activity per gram calcium of the blood plasma (34) where S refers to a time t after the beginning of the continuous radioactive intake, R refers to the value of the single injection retention function at the same time t, and ~Tk is the rate of excretory plasma clearance. This expression for plasma activity under continuous intake shows the effect of dilution of the blood with nonradioactive calcium during the initial period on the radioactive diet: S is less than its steady state value by the factor (1-R).…”

Section: Observed Ratio Modelmentioning

confidence: 99%

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Alkaline earth metabolism in adult man

1973

Annals of the ICRP/ICRP Publication

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Retention of etidronate in human, dog, and rat

Kasting

Francis

1992

Journal of Bone and Mineral Research

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The retention of radioactivity in human, rat, and dog following a single injected dose of radiolabeled etidronate disodium (EHDP) is shown to follow power-law decay curves with similar slopes for times up to 4, 60, and 80 days, respectively. During this period retention declines with time according to a weak inverse power of the time since dosing, with an exponent ranging from -0.05 (dog) to -0.09 (human and rat). Direct analyses of dog bones either 90 days after a single dose or 365 days after cessation of chronic dosing indicate a more rapid bone clearance of EHDP than predicted by the initial power law. Direct skeletal analysis also shows a more rapid loss of radioactivity in the rat between 60 and 365 days, indicative of either a second power law or a terminal exponential phase in the retention function occurring after 60 days. These data are used to estimate the minimum and maximum amounts of drug that would remain in the body following long-term treatment in humans. For the intermittent cyclic EHDP treatment (ICT) regimen for osteoporosis (repeated cycles of 14 daily doses of 400 mg orally followed by 76 days drug free), the projected retention of EHDP after 3 years of treatment is 25-50 times the daily absorbed dose. Thus, for a 60 kg woman with a daily absorbed dose of 12 mg, the retained mass of EHDP would be about 300-600 mg.(ABSTRACT TRUNCATED AT 250 WORDS)

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Mechanism of calcium exchange at bone surfaces

Cited by 49 publications

References 9 publications

High-calcium diet modulates effects of long-term prolactin exposure on the cortical bone calcium content in ovariectomized rats

High-calcium diet modulates effects of long-term prolactin exposure on the cortical bone calcium content in ovariectomized rats

Alkaline earth metabolism in adult man

Retention of etidronate in human, dog, and rat

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