Bone turnover model based on a continuously expanding exchangeable calcium pool

Effect of oscillating fluid shear on solute transport in cortical bone

The consequences of an oscillatory fluid shear mechanism on nutrient transport in bone during physical activity and ultrasonic therapy are discussed. During movement, periodic stress on bone creates transient pressure gradients that circulate interstitial fluid through calcified bone. A transport model derived from oscillatory Taylor-Aris dispersion phenomena was used to predict a ratio of effective-to-molecular diffusivity, K/D, for solutes of varying sizes up to 50 nm in diameter, in pores filled with interstitial fluid and pericellular matrix. The magnitude of the estimated transport enhancement depended on the molecular size, pore dimension, applied frequency and the displacement of the fluid during pressurization. For oscillation frequencies and amplitudes corresponding to those experienced during normal human activity, transport enhancements of up to 100 fold are expected for molecules larger than 5 nm in diameter. Enhancements of up to one order of magnitude, due to ultrasound stimulations in the MHz frequency range, are also expected for 7-nm-sized solutes. No effects are anticipated for ions, whose molecular diffusion time is too fast relative to the oscillation frequency. This model is expected to be useful for understanding differences in bone growth as a function of type of movement or to develop new physical therapies.

Biochemical markers of bone resorption compared with estimates of bone resorption from radiotracer kinetic studies in osteoporosis

The pyridinium cross-links of collagen pyridinoline (Pyd) and deoxypyridinoline (Dpd) are released during bone resorption and are neither metabolized nor absorbed from the diet. The aim of this study was to validate their use in osteoporosis. We studied 19 women with osteoporosis and estimated the bone resorption rate from a combined calcium balance/kinetics technique without (R) and with partial (R(H)) and "complete" (Res) correction for long-term exchange. The strongest correlation was observed between the bone-specific marker (Dpd) and with complete correction for long-term exchange (Res) (r = 0.71, p < 0.001). The intercept was not different from zero, suggesting that bone was the major source for Dpd. The crude ratio of Dpd to Res in the 19 women was 54.5; but the regression coefficient relating Dpd as the dependent variable to Res was 31.8 (95% CI 15.6-48.0), which was higher, but not significantly, than the ratio between Dpd and calcium (16.4) in 10 bone samples (cortical and trabecular bone). The weakest correlations between a biochemical marker and a kinetic index were those between hydroxyproline (a nonspecific marker of bone resorption) and R or R(H). Treatment with hormone replacement therapy (HRT) or HRT and parathyroid hormone peptide 1-38 in seven women over 1 year resulted in similar percent changes in the biochemical markers and estimates of bone resorption. We conclude that the measurement of Dpd provides a reasonably accurate assessment of bone resorption in osteoporosis, and in the context of several repeat 24-h collections of urine offers measurement precision that is similar to that obtainable with methods depending on the use of radioisotopic tracers and the assessment of metabolic calcium balance.

The use of stable tracers to study intestinal calcium absorption. The Italian Society of Osteoporosis

This paper represents the final document released by the Italian Society of Osteoporosis (S.I.OP.), on the occasion of its fifth annual meeting held in Padova, Italy (November 30-December 3, 1993). The S.I.OP. has in fact planned to periodically organize a conference on still-debated, controversial issues. After an exhaustive discussion of the various aspects of the problem by qualified experts in the field, a solution will be proposed by the members of the Society. The problems related to the use of radioactive tracers to study intestinal calcium absorption and the possible ways to over-come them were the issues discussed last year, by four panelists (R. P. Heaney, C. Gennari, G. Mioni, and S. Minisola) coordinated by G. F. Mazzuoli.

Comparison of bone formation rates measured by radiocalcium kinetics and double-tetracycline labeling in maintenance dialysis patients

We report 23 prospective studies on 18 maintenance dialysis patients in whom we measured skeletal mineralization rate (m) using 47Ca, analyzed by the expanding pool model, and compared it with the histologic bone formation rate (bfr), volume referent, estimated on tetracycline-labeled iliac crest bone. The patients showed a spectrum of bone disease types including adynamic bone, aluminum-related osteomalacia, and various degrees of secondary hyperparathyroidism. The mean width between double labels, on which mineral apposition rate depended, was estimated using a simple formula relating area to perimeter for each feature enclosed by the labels. Values for m ranged from 0 to 155 mmol calcium per day and for bfr from 0 to 124% per year. There was close correlation between m and bfr (r = 0.976), serum alkaline phosphatase (r = 0.968), and serum immunological parathyroid hormone (iPTH) (r = 0.868). When the volumetric bfr was converted to mass units and applied to the whole skeleton, using literature values for mineral density and cortical and trabecular mass, there was close agreement between the histologic and isotopic estimates of m (r = 0.959). The results validate the two methods and suggest they are interchangeable. However, use of a rigorous method to determine bfr appears to be essential.

Assessment of bone remodeling using biochemical indicators of type I collagen synthesis and degradation: relation to calcium kinetics

In this study, we investigated the relation between calcium kinetic indices of bone remodeling (resorption rate, r; and formation rate, m, respectively) and two serum markers of type I collagen turnover: the pyridinoline cross-linked carboxyterminal telopeptide domains of type I collagen (S-ICTP a marker of bone matrix degradation) and the carboxyterminal propeptide of human type I procollagen (S-PICP, a marker of bone matrix formation). We studied three groups: (i) healthy controls (n = 19), (ii) a mixed group of high and low-turnover bone diseases without mineralization defects (myxedema, thyrotoxicosis and primary hyperparathyroidism n = 38), and (iii) osteoporosis (n = 52). In healthy controls, a significant regression of S-PICP on m was obtained (R = 0.53, SEE/Y = 0.44, P < 0.02). Significant regressions were also demonstrable in high- and low-turnover bone disease (R = 0.50, P < 0.001), SEE/Y = 61%) and osteoporosis (R = 0.49, P < 0.001, SEE/Y = 50%). In controls the regression coefficient for the regression of S-ICTP on r was 0.19 (NS), in high and low turnover bone disease 0.66, (SEE/Y = 59%, P < 0.001) and in the osteoporotic group 0.40 (SEE/Y = 61%, P < 0.01). We conclude that S-PICP and S-ICTP reflect whole skeletal bone formation and resorption rates in a variety of metabolic bone diseases including osteoporosis.

Human parathyroid peptide treatment of vertebral osteoporosis

Previous studies have shown that treatment with daily injections of human parathyroid peptide (hPTH) 1-34 increase axial cancellous bone mass partially at the expense of peripheral cortical bone. In the present work the same hPTH 1-34 regime given for 12 months has been combined with oestrogen or nandrolone therapy to control peripheral bone resorption. Spinal and iliac cancellous (but not cortical) bone increased by 40%-50% above initial values while no perceptible changes occurred in radial cortical or cancellous bone. The evidence of radiokinetic and histomorphometric studies performed before and in the last months of treatment suggested that bone remodeling had proceeded through a transient anabolic phase with increased activation, but that activation had become normal after 11-12 months in the cancellous bone of the ilium whereas it continued to be raised elsewhere in the skeleton. It is concluded that in combination with oestrogens, hPTH peptides given daily injections hold great promise for the treatment of patients with osteoporosis who have already lost substantial amounts of spinal cancellous bone.

Temporal variations in iliac trabecular bone formation in vertebral osteoporosis

The histologic heterogeneity of osteoporosis relative to normal controls has attracted great interest. There has been controversy as to whether patients with high turnover osteoporosis may convert to a normal or low turnover form, and vice versa. We have studied 44 patients over 12 years by dynamic histomorphometry and 85Sr kinetics+calcium balance performed within 60 days in 20 patients (Group 1) and 75-808 days apart in the remainder (Group 2). In the first group, the histologic tissue level bone formation rate (BFR/BV or BFR/BS) was predictive of the 85Sr measurements of bone formation (r = 0.66 P < 0.01). There was no statistically significant correlation in Group 2 and the regression coefficients were significantly different (P = 0.01). Periodic regression was used to determine if seasonal changes were responsible for this loss of correlation; none was found that was of statistical significance. No systematic changes with time in bone formation were found in Group 2 during the period of observation; nor were consistent secular changes detected when the data for both groups were examined according to procedure date. In conclusion, bone formation may change with time in postmenopausal osteoporosis. Evidence that these changes are systematic was not found and this has implications for the design of treatment studies.

Assessment of bone formation by biochemical markers in metabolic bone disease: separation between osteoblastic activity at the cell and tissue level

In this study , serum levels of classical serum markers of bone formation [carboxyterminal propeptide of procollagen type I (S-PICP), bone Gla protein (S-BGP)], and total alkaline phosphatase (S-AP)) were related to the calcium kinetic index of whole skeletal mineralization rate (m) by regression analysis in a variety of metabolic bone diseases. For each disease, the regression coefficient (r) as well as the fraction: standard error of estimate/mean dependent variable (SEE/Y) were determined. In a group of 19 normals, only the regression of S-PICP on m reached significance (r = 0.53, P < 0.02, SEE/Y = 0.44), whereas regressions of S-AP and S-BGP on m were nonsignificant. In a pooled material of high- and low-turnover bone diseases without mineralization defects or spinal fracture [myxedema, thyrotoxicosis, and primary hyperparathyroidism (n = 48)], a highly significant positive regression of S-PICP on m was demonstrable (r = 0.50, SEE/Y = 0.63, P < 0.001). The regression coefficients obtained for S-BGP and S-AP were 0.74 (P < 0.001, SEE/Y = 0.41) and 0.42 (P < 0.01, SEE/Y = 0.55), respectively. When analyzing individual diseases in this group, significant differences among the three markers were detectable. In a group of 52 osteoporotics, S-PICP correlated significantly to m (r = 0.49, P < 0.001, SEE/Y = 0.50). Corresponding r-values for S-BGP and S-AP were 0.21 (NS) and 0.48 (P < 0.001, SEE/Y = 0.61), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone remodelling does not decline after menopause in vertebral fracture osteoporosis

There is considerable current interest in whether activators of bone remodelling, such as IL-1 and other cytokines, are involved in the pathogenesis of osteoporosis. We have therefore studied indices relating to remodelling activation in 50 patients with postmenopausal vertebral osteoporosis and 12 with hip fracture osteoporosis in comparison with 25 age- and sex-matched controls. Because of uncertainty regarding the accuracy of current biochemical markers of bone formation with respect to the estimation of whole body rates of bone formation, a 85Sr-based radioisotopic method was used. This method was previously validated by comparison with data obtained after double in vivo labelling of transiliac biopsies taken nearly simultaneously. Bone resorption was estimated from urinary hydroxyproline data. Controls selected for their continued good health showed a progressive and statistically highly significant decline in indices of bone formation with time after menopause. No such decline was seen in the vertebral fracture patients (P less than 0.005). There were no hip fracture patients within 10 years of menopause so this statistical test could not be applied appropriately to them. The hydroxyproline data were consistent with the suggestion arising from the bone formation data that remodelling declines progressively after menopause in the controls but not in the vertebral fracture patients. The data also suggested that these two fracture groups were in more negative calcium balance than the controls, this being particularly marked in the hip fracture cases. Plasma osteocalcin data correlated moderately well with the kinetic measurements of bone formation. It is concluded that vertebral fracture osteoporosis is associated with prolongation of menopausal levels of bone remodelling which is inappropriate by comparison with healthy controls.

Developmental changes in calcium kinetics in children assessed using stable isotopes

Total exchangeable calcium pool size (TEP) and bone calcium accretion rate (Vo+) were measured using stable isotopes in healthy children and young adults. 42Ca or 46Ca was given intravenously to 10 children aged 10 months to 14 years and 3 women aged 23-33 years. Calcium kinetic parameters were determined using a two- or three-exponential curve of the resultant serum and urine tracer excesses. These data were compared with previously reported (radiotracer) kinetic studies of 21 children and 5 adults without known bone disease. Current results are comparable to those previously obtained, and the data from all studies were analyzed together. Total Vo+ was significantly greater in children aged 3-16 years than in adults (2.8 +/- 1.6 versus 0.7 +/- 0.2 g/day, p less than 0.01). Both TEP and Vo+ were significantly correlated to age independently of variations in body weight (p less than 0.01 for each). The ratio ko+ = Vo+/TEP was greater in children than adults (0.36 +/- 0.15 versus 0.12 +/- 0.03 day-1, p less than 0.001). These data demonstrate increased bone flow of calcium associated with increases in exchangeable calcium pools in children compared to adults. Vo+ and TEP may be maximum in early adolescence, associated with peak rates of net calcium accretion. The use of stable isotopes permits the safe evaluation of calcium kinetics in patients of all ages.

hPTH 1-34 treatment of osteoporosis with added hormone replacement therapy: biochemical, kinetic and histological responses

Twelve patients with vertebral fracture osteoporosis were recruited into a trial of treatment with hPTH 1-34 by daily injection for 1 year combined (from the 5th month) with an anti-resorptive agent (oestrogen, n = 9; nandrolone, n = 3). Treatment outcomes were monitored by biochemical and radiotracer measurements together with histomorphometry of transiliac biopsies before and at the end of treatment following double in vivo pre-labelling with demethylchlortetracycline. Indices of whole body bone formation, obtained from the analysis of 85Sr data, showed substantial increases (P less than 0.005) for all three indices measured) while biochemical (hydroxyproline) and kinetic measurements of bone resorption showed modest and equivocal changes only. As a result calcium balance improved. Gastrointestinal calcium absorption showed a tendency to improve, while urine calcium decreased; but these changes were statistically not significant except for radiocalcium absorption in the oestrogen treated subgroup. Histomorphometry revealed substantial increases in cancellous bone volume as reported previously with hPTH 1-34 given alone. However, iliac (as distinct from whole body) indices related to bone formation and resorption appeared to have returned towards pre-treatment values by the time of the second biopsy under the influence of the anti-resorptive agent given with the hPTH 1-34. It is confirmed that hPTH 1-34 therapy can increase iliac cancellous bone mass (as well as spinal cancellous bone mass as reported earlier) without a long-term increment in whole body bone resorption, providing the hPTH is combined with an anti-resorptive agent.

Calcium metabolism in postmenopausal osteoporosis: the influence of dietary calcium and net absorbed calcium

A group of 85 females aged 48-77 years with postmenopausal crush fracture osteoporosis were investigated using a 7 day combined calcium balance and calcium tracer kinetic turnover study to assess the influence of dietary calcium and net absorbed calcium on bone metabolism. During the study, patients were on their habitual diet, as determined by a prestudy registration. Dietary calcium was measured after double serving of all the meals. All urine and feces were collected and analyzed for calcium content. Bone mineralization rate and bone resorption rate were determined by applying the continuously expanding calcium pool model to the tracer kinetic data. Urine calcium excretion and net absorbed calcium were correlated (r = 0.64, p less than 0.0001) with the following equation: urinary excreted calcium (mmol/day) = 2.4 + 0.4 X net absorbed calcium (mmol/day). Dermal calcium loss was not correlated with net absorbed calcium or urinary calcium. The net amount of absorbed calcium necessary to balance urinary and dermal losses was calculated to be 4.2 mmol calcium per day. The daily calcium intake necessary for obtaining a net absorbed calcium in excess of the urinary and dermal calcium losses and thereby ensure skeletal integrity was estimated to be 34.2 mmol calcium per day compared to an average intake of 27.9 +/- 7.6 (mean +/- SD) mmol/day. Net absorbed calcium correlated negatively to bone resorption rate (r = -0.31, p less than 0.005) and positively to bone mineralization rate (r = 0.29, p less than 0.01) and to calcium balance (r = 0.66, p less than 0.0001). Dietary calcium intake and calcium balance correlated positively (r = 0.38, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Human pharmacokinetics of orally administered strontium

Pharmacokinetics of orally administered SrCl2 (2.5 mmol) were studied in six healthy male volunteers. In the overall plasma concentration time (C-t) curves, two absorption phases were observed due to two dominant intestinal absorption loci. A method was devised to obtain separately the plasma C-t curves associated with each of the two absorption loci (curve 1 and curve 2). These curves and the overall plasma C-t curve were analyzed with a nonlinear estimation program (PCNONLIN). Pharmacokinetic parameters (mean +/- SD, n = 6) calculated from the overall curve were as follows: peak plasma concentration (Cmax) 3.55 +/- 1.22 micrograms/ml and area under the plasma C-t curve (AUC affinity) 9138 +/- 1930 micrograms.min/ml. The pharmacokinetic parameters calculated from curve 1 were as follows: terminal plasma elimination half-life time 47.3 +/- 7.9 hour, the plasma elimination half-life time of the preceding phase 5.2 +/- 3.3 hour, Cmax 1 3.09 +/- 0.95 micrograms/ml, the first-order absorption rate constant for absorption locus 1 (Ka,1) 5.7 +/- 1.2 * 10(-2) minute-1 and the time lag (tlag,1) 11.7 +/- 7.9 minute. In three of the subjects the pharmacokinetic parameters of absorption locus 2 could be evaluated: Ka,2 = 4.6 +/- 0.4 * 10(-2) minute-1, tlag,2 = 77.3 +/- 4.0 minute, tmax,2 = 153 +/- 16 minute, Cmax,2 = 0.9 +/- 0.4 micrograms/ml and AUC 2 affinity = 1204 +/- 565 micrograms. minute/ml. and AUC2 affinity = 0.14, indicating that 14% of the absorbed dose was absorbed via the second locus.(ABSTRACT TRUNCATED AT 250 WORDS)

One-day test using stable isotopes to measure true fractional calcium absorption

True calcium absorption can only be measured by the time-consuming and expensive metabolic balance method and is not predicted well by measuring the fractional absorption (FA) of radiocalcium from a fixed calcium carrier. We describe here a 1 day method for measuring the actual fraction of calcium absorbed from the habitual diet (true fractional calcium absorption, TFCA) using stable isotopes of calcium. Oral and intravenous isotopes were administered with each of the three daily meals, and then the ratio of the two isotopes in the urine was measured by mass spectroscopy. In 12 subjects, TFCA determined from stable Ca correlated well with TFCA measured by the balance method (r = 0.71, P less than 0.01), and the mean values were not different (0.26 and 0.26). In contrast, no significant correlation was found between FA and TFCA. The weak relationship between FA and TFCA underscores the importance of tracing dietary calcium rather than a fixed calcium carrier in tests of calcium absorption. Using the new method, TFCA was inversely related to dietary calcium (r = -0.45, P less than 0.05), demonstrating that it could detect physiological changes in calcium absorption. Thus, this test has two important advantages: (1) it provides a simple way to measure TFCA and true fractional calcium absorption (the product of TFCA and dietary calcium), the physiologically relevant variables, and (2) because there is no radiation exposure, the test can be used in pregnant women and children, the isotopes can be prepared in advance, and several isotopes can be used simultaneously.

Modeling human calcium tracer kinetics using a minimum of assumptions

A conceptually simple model of human calcium kinetics, based on the Bauer-Carlsson-Linquist (B.C.L.) expression, is presented. The B.C.L. model assumes tracer retention in the body, occurs either in an exchangeable pool or in the skeleton, and the rate of calcium transfer from pool to bone (mineralization) is constant. As a modification, it is demonstrated that the existence of an expanding calcium pool and its rate of expansion may be directly determined from the raw data, without a priori assumptions. If data on whole body retention are unavailable, the concept of dermal tracer loss as the difference between tracer excretion and whole body retention may be used to estimate whole body retention. It has been possible to compare the modified B.C.L. expression with various multicompartmental kinetic models by analyzing raw data supplied by other workers and making comparisons with their published results. As methodologies are very different, the two sets of estimates of bone mineralization rate and exchangeable pool size have been ranked within individual groups. In five of six comparisons, the results indicate a rank correlation coefficient with a p-value better than 0.05 occurred. In all cases of data analysis from "normal" subjects, the calcium pool was found to be expanding. The existence of an expanding pool renders the model similar to a previous one, but the present one is conceptually and mathematically simpler in achieving equivalent results.

Efficacy of wheat germ lectin-precipitated alkaline phosphatase in serum as an estimator of bone mineralization rate: comparison to serum total alkaline phosphatase and serum bone Gla-protein

Serum levels of total alkaline phosphatase activity (S-T-AP), wheat germ lectin-precipitated alkaline phosphatase activity (S-L-AP), and bone Gla-protein immunoreactivity (S-BGP) were measured in 26 patients (23 females and 3 males) aged 35-73 years (mean 59 years) with primary hyperparathyroidism (n = 7), hyperthyroidism (n = 9), and hypothyroidism (n = 10) in whom the bone mineralization rate (m) was determined by 47Ca-kinetics (continuously expanding calcium pool model). A weak positive correlation (r = 0.42, P less than 0.05) was found between S-T-AP and m, which in the range from 0-18 mmol Ca/day could be estimated with a standard error of 4.6 mmol/day. A closer correlation (r = 0.65, P less than 0.001) was found between S-L-AP and m which was estimated with an error of 3.9 mmol Ca/day. The AP activity in the supernatant showed no significant correlation to m (r = 0.11, P greater than 0.50). The highest correlation coefficient (r = 0.81, P less than 0.001) was found between S-BGP and m which could be predicted with an error of 3.4 mmol Ca/day. S-BGP showed a closer correlation to S-L-AP (r = 0.71, P less than 0.001) than to S-T-AP (r = 0.58, P less than 0.01). We concluded that S-L-AP predicts bone mineralization at organ level better than S-T-AP in selected metabolic bone disorders and that the supernatant activity shows no relation to bone turnover.(ABSTRACT TRUNCATED AT 250 WORDS)

Bisphosphonate whole body retention test: relations to bone mineralization rate, renal function and bone mineral content in osteoporosis and metabolic bone disorders

The bisphosphonate whole body retention test (WBR) has been used to estimate bone mineralization rate (bone turnover). Bisphosphonates given i.v. are taken up by bone or excreted in urine. The aim of the present investigation was to test the efficacy of WBR in estimating bone mineralization rate (m) and to evaluate the influence of renal function (Clcr) and bone mass (forearm bone mineral content; BMC) on WBR. The 24-h retention of 3.7 MBq 99mTc-HMBP (1-hydroxymethylene-1,1-bisphosphonate) (Osteoscan) given i.v. was measured by a medium sensitive whole body counter in thirty-one patients with hyperparathyroidism (n = 14), hyperthyroidism (n = 8) or hypothyroidism (n = 9) (group 1) and in seventy-six females with postmenopausal spinal crush fracture osteoporosis (group 2). In the same individuals m was calculated from a 7-day 47Ca-kinetic study using the expanding calcium pool model. Multiple regression analysis of WBR vs. m and Clcr in group 1 disclosed that WBR correlated positively to m [rp = 0.49, P less than 0.01 (rp = partial correlation coefficient)] and inversely to Clcr (rp = -0.44, P less than 0.02). Inclusion of BMC in the analysis did not reveal any significant partial correlation between WBR and BMC (rp = -0.33, 0.05 less than P less than 0.10). In group 2 WBR correlated inversely to Clcr (rp = -0.48, P less than 0.001) but showed no significant relation to m (rp = 0.10, NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Bone turnover and balance evaluated by a combined calcium balance and 47calcium kinetic study and dynamic histomorphometry

Bone resorption and formation rates were evaluated at the organ level using calcium kinetic methods and at the trabecular bone tissue level using dynamic histomorphometry in 20 patients with various metabolic bone diseases (primary hyperparathyroidism (N = 9), hyperthyroidism (N = 6), and hypothyroidism (N = 5). Highly significant correlations were demonstrated between resorption and formation rates at organ level (r = .90, P less than .001) and at tissue level (volume referent) (r = .93, P less than .001), indicating a high degree of coupling between resorption and formation within the three disease states. Tissue level resorption rates (surface referent, as well as volume referent) both correlated significantly (P less than .01) to organ level resorption rate (r = .60 and r = .63, respectively). Fractional active resorption surface and cellular level resorption rate did not reveal significant correlations to calcium kinetic estimates. No correlation could be demonstrated between organ level mineralization rate and formative or labeled trabecular surfaces. However, all tetracycline based tissue level formation rates revealed highly significant correlations (P less than .01) to organ level mineralization rate (calcification rate, r = .71; surface referent bone formation rate, r = .59; volume referent bone formation rate, r = .68). Based on histomorphometric parameters for resorption and formation, actual and predicted tissue level trabecular bone balances were calculated. Both the actual and predicted bone balance correlated significantly to the organ level calcium balance (P less than .05). Correction for skeletal size based on BMC measurements did not improve any of the correlations significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of whole body bone resorption rate: a comparison of urinary total hydroxyproline excretion with two radioisotopic tracer methods in osteoporosis

In 37 female patients with primary osteoporosis, urinary hydroxyproline excretion, determined in 18 24-h consecutive complete urine collections was compared with two radioisotopic measurements of bone resorption rate measured simultaneously using 85Sr. A somewhat better fit was obtained when the kinetically determined bone resorption rate was corrected for long-term exchange processes within bone. Regression analysis showed that the intercept of the regression of hydroxyproline excretion on resorption rate, corrected or uncorrected for exchange, was significantly higher than zero at about 100 mumol/day. This is consistent with a substantial fraction of urinary hydroxyproline arising from non-bony sources. Fifteen paired studies were analysed and the results suggested that intra-individual variability in these relationships (when studies were separated by a year or more) were similar to inter-individual variability. We calculated the precision with which an estimate of bone resorption could be determined based on the calculated regressions. As a means of non-invasive quantitation of whole body bone resorption rate, the excretion rate of hydroxyproline, measured over 5 days, for example, appeared competitive with isotopic methods making no correction for exchange and relatively little worse than our exchange corrected method.

Primary hyperparathyroidism: evaluated by 47calcium kinetics, calcium balance and serum bone-Gla-protein

Combined 47Calcium kinetic and calcium balance studies with correction for dermal calcium loss were performed in thirteen patients with primary hyperparathyroidism (PHP), in whom serum bone-Gla-protein (S-BGP) was measured, and in ten matched controls. Dietary calcium was normal in PHP but both net (7.9 +/- 1.4 mmol Ca day-1 in PHP v. 3.5 +/- 0.9 mmol Ca day-1 in normals (mean +/- SE] and true (11.1 +/- 1.6 v. 6.8 +/- 0.9 mmol Ca day-1) intestinal absorbed calcium were enhanced (P less than 0.05). The renal calcium excretion (10.9 +/- 0.8 v. 5.1 +/- 0.4 mmol Ca day-1, P less than 0.001) and the dermal calcium loss (2.5 +/- 0.3 v. 1.5 +/- 0.1 mmol Ca day-1, P less than 0.02) were increased in PHP. Both patients and controls were in a negative calcium balance (P less than 0.01 and P less than 0.001, respectively) without any difference between the groups (P greater than 0.10). Mineralization (12.0 +/- 1.7 v. 4.8 +/- 0.8 mmol Ca day-1, P less than 0.02) and resorption rates (17.6 +/- 2.5 v. 7.9 +/- 0.6 mmol Ca day-1, P less than 0.02) were increased in PHP and S-BGP correlated positively to both variables (r = 0.64, P less than 0.05 and r = 0.62, P less than 0.05, respectively). Serum immunoreactive parathyroid hormone correlated positively to serum calcium (r = 0.69, P less than 0.01) but not to the calcium kinetic data.

Estimation of bone turnover evaluated by 47Ca-kinetics. Efficiency of serum bone gamma-carboxyglutamic acid-containing protein, serum alkaline phosphatase, and urinary hydroxyproline excretion

Bone gamma-carboxyglutamic acid-containing (Gla) protein (BGP, osteocalcin) is a noncollagenous protein of bone present in plasma and removed by the kidney. Plasma BGP has been shown to be elevated in patients with certain bone diseases. The present study evaluates serum BGP (S-BGP), serum alkaline phosphatase (S-AP), and urinary hydroxyproline excretion (U-OHP) in diseases with differing bone turnover rates, and compares the accuracy of these measurements for estimating bone mineralization (m) and resorption (r) rates. S-BGP, S-AP, U-OHP, and creatinine clearance (Clcr) were measured in patients with primary hyperparathyroidism (n = 13), hyperthyroidism (n = 6), and hypothyroidism (n = 6). Bone mineralization and resorption rates were calculated from a 7-d combined calcium balance and 47Ca turnover study. A highly significant correlation (r = 0.69, P less than 0.001) was found between S-BGP and m. Multiple regression analysis disclosed a partial correlation between S-BGP and m when Clcr was taken into account (r = 0.82, P less than 0.001), and between S-BGP and Clcr when m was taken into account (r = -0.62, P less than 0.005). In accordance with this, a stronger correlation (r = 0.89, P less than 0.0001) was found between S-BGP X Clcr and m than between S-BGP and m. A less significant correlation was found between S-AP and m (r = 0.45, P less than 0.05). Furthermore, U-OHP showed a highly significant positive correlation to r (r = 0.78, P less than 0.001). Thus, in the studied disorders of calcium metabolism, individual serum levels of BGP depend on both mineralization rate and renal function. Serum levels of BGP corrected for alterations in renal function are superior to uncorrected S-BGP and to S-AP levels in the estimation of bone mineralization rates.

Calcium metabolism evaluated by 47Ca kinetics. Methodologic aspects with optimization of a whole-body counter

Optimization of a four-crystal stretcher geometry whole-body (WB) counter was performed. The measured geometric characteristic did not differ significantly from the theoretically calculated characteristic (p greater than 0.05). The linearity of the WB counter was high in the range 3.7 kBq to 3.7 MBq. Longtime variability of local background was CV = 3.7 per cent. In vivo sensitivity was calculated to 18 cpm/kBq and the detection limit to about 5 kBq. The reproducibility was estimated to 0.7 per cent. The WB counter was used in 47Ca turnover and calcium balance studies of 15 normal individuals. The data were analysed according to a modification of the expanding calcium pool model using an improved Bauer-Carlsson-Lindquist formulation. Variability and method errors of main parameters for calcium metabolism were evaluated.

Calcium metabolism evaluated by 47calcium-kinetics: a physiological model with correction for faecal lag time and estimation of dermal calcium loss

Sixty-two calcium balance and 47Ca-turnover studies were performed in 51 individuals to evaluate the accuracy and the sensitivity of the methods. The data were analysed according to a modification of the expanding calcium pool model using an improved Bauer-Carlsson-Lindquist (BCL) formulation and an iterative computer procedure. A 7-day whole body retention curve (R1) combined with a retention curve constructed from excretion data alone (R2) was used to estimate dermal calcium loss (d) and to demonstrate the significance of individual corrections for delay in faecal excretion (faecal lag time = delta t). The mean d was 1.58 mmol Ca/day. The introduction of delta t improved the goodness of fit of the data to the model. delta t based on 47Ca-kinetics was superior to a fixed delta t of zero (P less than 0.01) or 2 days (P less than 0.05). The model derived renal calcium excretion rate was highly correlated (r = 0.98, P less than 0.001) to the chemical measured excretion rate. A similar highly significant correlation [RS = 0.78 (Spearman), P less than 0.001] was found between the model derived delta t and the carmine red delta t. These results indicate a high accuracy of the model. The directly measured parameters showed an excellent reproducibility with a coefficient of variation (CV) less than 4%. The reproducibility of the derived parameters was acceptable (CV = 10-20%) except for the balance (CV = 72%).

Regional measurement of bone calcium accretion rate and exchangeable pool with a whole-body counter: method and studies in subjects without bone disease

A whole-body counter was used to measure the retention and distribution of radioactivity along the longitudinal axis of the body during 10 days after the intravenous injection of 50 microCi of 47Ca. These data and the simultaneous measurements of the serum specific activity allowed us to calculate, by the Bauer-Carlsson-Lindquist (BCL) formulas generalized by Marshall, the calcium accretion rate and exchangeable pool in 7 areas: skull, thorax, pelvis, thighs, knees, legs, and ankles and feet. For the whole body, the accretion rate was 336 +/- 115 mg/24 h, and the exchangeable pool 5668 +/- 1221 mg, in 26 subjects without bone disease. Both parameters were significantly correlated with body height; the exchangeable pool was significantly higher in men than in women. The accretion rate and exchangeable pool expressed on a basis of bone content varied widely from one area to another, reflecting the ratio of spongy to compact bone: the thorax, pelvis, and arms, which contain 49% of the skeletal mass, accounted for 57% of the total accretion rate and 53% of the exchangeable pool; the skull, 18% of the skeletal mass, accounted for 14% of the accretion and 11% of the pool.

1,25-Dihydroxyvitamin D3: short- and long-term effects on bone and calcium metabolism in patients with postmenopausal osteoporosis

We evaluated the effects of therapy with a small dose (0.5 microgram/day) of 1,25-dihydroxyvitamin D3 in 12 previously untreated patients with postmenopausal osteoporosis. Combined radiocalcium kinetic and balance studies showed that at base line, net calcium absorption (mean +/- SEM) was low (7 +/- 3%), calcium balance was negative (-59 +/- 22 mg/day), and bone resorption rate (297 +/- 40 mg/day) exceeded bone formation rate (239 +/- 36 mg/day). After short-term therapy (6-8 months), calcium absorption was normal (27 +/- 3%, P less than 0.001 for difference from base line), calcium balance had improved (+2 +/- 26 mg/day, P less than 0.05), and bone resorption rate (195 +/- 35 mg/day, P less than 0.01) had decreased more than bone formation rate (197 +/- 26 mg/day, NS). Compared with base-line values, after long-term therapy (2 years) the increased level of calcium absorption was maintained (27 +/- 3%, P less than 0.001), but calcium retention declined to a level intermediate (-27 +/- 24 mg/day, NS) between base-line and short-term treatment values, and both bone resorption rate (294 +/- 33 mg/day, NS) and bone formation rate (267 +/- 34 mg/day, NS) increased. Urinary hydroxyproline excretion was lower than before treatment (26.3 +/-2.0 mg/day) after both short-term (21.1 +/- 1.6 mg/day, P less than 0.001) and long-term (22.0 +/- 1.8 mg/day, P less than 0.01) treatments. Trabecular bone volume was 11.3 +/- 1.0% at base line and increased to 16.0 +/- 1.2% (P less than 0.01) after long-term treatment. By contrast, the eight patients studied before and after 6-8 months of placebo treatment had no significant change in any variable.

Diagnostic procedures in disorders of calcium metabolism

The investigation of a patient with a suspected disorder of calcium metabolism is most rapidly and efficiently performed by observing a standard procedure, the initial stages of which are simple and mandatory, the later stages more complex and determined by the initial results and the depth of investigation required. Needless to say, the investigations are preceded by history taking and routine physical examination. The following account is a summary of available procedures, most of which have been described elsewhere in greater detail (Nordin et al., 1976a).

Effects of haemodialysis on fractional intestinal absorption of calcium in uraemia

Fractional intestinal absorption of calcium was measured in 41 haemodialysed patients 4 hours after an oral dose of 47 Ca. Fractional intestinal calcium absorption was 40.3 +/- 1.9% (SEM) when measured 10 to 12 hours after a haemodialysis session (dialysate calcium concentration: 1.75 mmol/litre). This value was significantly lower (p less than 0.001) than that in 26 healthy controls (56.8 +/- 1.8%) and higher (p less than 0.05) than that of 35 patients with chronic renal failure treated conservatively (34.5 +/- 2.1%). In 17 patients, fractional intestinal calcium absorption was measured just before and just after a dialysis session. Pre-dialysis fractional intestinal calcium absorption (33.7 +/- 3.0%) was not significantly different from fractional intestinal calcium absorption in uraemic patients treated conservatively, while after dialysis fractional intestinal calcium absorption had increased significantly to 42.0 +/- 2.6% (p less than 0.001). It is suggested that the transient increase in fractional intestinal calcium absorption observed after dialysis could be related to dialysis induced volume depletion rather than to a vitamin D-dependent mechanism.

Anabolic effect of low doses of a fragment of human parathyroid hormone on the skeleton in postmenopausal osteoporosis

Parathyroid hormone, injected daily in low dosage, exerted anabolic effects on the human skeleton, just as it does in the rat. Four postmenopausal women with primary osteoporosis were treated for six months with a synthetic fragment of human parathyroid hormone (hP.T.H. 1-34), given as a daily injection of 100 mug. This treatment caused a remarkable acceleration of bone turnover, indicated both by isotopic tracer and histological methods. At this normocalcaemic dose level, the increases in bone formation outweighed increases in resorption. Three of the four patients showed more positive calcium balances, and mean increases in calcium and phosphorus balances were statistically significant for the group as a whole, the changes being principally due to increased intestinal absorption of both elements. Many modifications of the present method of hormone administration are possible which could further increase the preponderance of anabolic effects. These results suggest that low doses of hP.T.H. 1-34, alone or in combination with other agents, may prove useful in the treatment of osteoporosis.

A new method for calculating the accretion rate of bone calcium and some observations on the suitability of strontium-85 as a tracer for bone calcium

1. A new method for calculating the accretion rate (A) of bone calcium is proposed, based on an impulse analysis of 47Ca data. The method is free of most of the assumptions inherent in previous methods of analysis and appears to give more accurate estimates. 2. In fourteen normal subjects and twelve patients with metabolic bone disease, measurements of A by the new method gave very similar results to the mineralization rate calculated by the method of Burkinshaw et al. (1969). Analysis of twelve studies performed by Neer et al. (1967) gave good agreement with their five compartment model. A close relation between A and Marshall's (1964) A5 was observed, but the latter gave systematically higher results. 3. In sixteen studies both 47Ca and 85Sr were injected simultaneously. Although there were no systematic differences between the values of A for the two tracers, the differences between individual values were greater than the known experimental errors.

The effect of age and level of dietary calcium intake on calcium metabolism in sheep

1. A combination of balance and isotope techniques has been used to study the effects of age and dietary calcium content on Ca metabolism in forty-two wether sheep.

2. The amount of Ca absorbed by young growing animals varied significantly with intake. The percentage of the dietary Ca absorbed, however, remained unchanged. In older animals the amount of Ca absorbed was not altered by changes in intake, but decreased slightly with age.

3. Retention of Ca was directly related to the amount of Ca absorbed and was independent of age or breed. Furthermore, nearly all the Ca absorbed above the minimum mean amount required for maintenance was retained.

4. Faecal endogenous loss of Ca also was related to the amount of Ca absorbed. Values for faecal endogenous Ca were much lower than those used in the calculation of dietary require-ments by the Agricultural Research Council (1965).

5. Urinary Ca excretion was variable, and was not related to age or changes in dietary Ca intake.

6. Increased absorption of Ca in young growing animals was accompanied by a decreased rate of bone resorption, but the rate of bone accretion remained unchanged. Changes in dietary Ca in older animals had no effect on either of these two processes. Results indicate that bone resorption is the main pathway governing Ca homoeostasis. Both the rates of Ca accretion into bone and resorption from bone decreased with age.

7. Neither the rapidly exchangeable Ca pool (P) nor the slowly exchangeable bone pool (E) was altered by changes in dietary intake in young or mature animals. Both, however, decreased in size with age.

8. The size of the slowly exchangeable pool (E) was directly related to the rate of Ca accretion into bone. 9. The results were used to calculate dietary Ca requirements of sheep gaining weight at different rates, and these values have been compared with values recommended by the Agricultural Research Council (1965).

Clinical significance and pathogenesis of osteoporosis

The development of osteoporosis with advancing age in man is a widespread if not a universal phenomenon. The average loss between youth and old age amounts to about 15% of the skeleton but involves a much larger proportion of trabecular than of cortical bone.THE PRINCIPAL CLINICAL MANIFESTATION OF OSTEOPOROSIS IS FRACTURE, AND THREE OSTEOPOROTIC FRACTURE SYNDROMES CAN BE DEFINED: the lower forearm fracture, which predominantly affects women between the ages of 50 and 65; the fracture of the proximal femur, which affects both sexes over the age of 70; and the relatively rare vertebral crush fracture syndrome, which may present at any age but is most common in elderly women.The lower forearm fracture rate is inversely related to the mean normal lower forearm x-ray "density" of the wrist, which falls by about 30% in the 15 years following the menopause. This process, which is associated with corresponding trabecular bone loss elsewhere in the skeleton, is associated with a corresponding rise in the fasting urinary calcium excretion. Some degree of negative calcium balance, and consequent bone resorption, probably occurs in everyone during the later part of the night because calcium absorption is completed within about three to five hours of a meal. In postmenopausal women, however, the sensitivity of the bone to parathyroid hormone appears to be increased, and their nocturnal negative calcium balance therefore comes to exceed the positive balance which can be achieved during the waking hours.Femoral neck fractures in old people reflect the further progression of osteoporosis with advancing age since the fracture rate is inversely correlated with the mean thickness of the metacarpal cortex in the normal population. This progressive osteoporosis is associated with and could well result from a steady decline in calcium absorption which is at least partially attributable to vitamin-D deficiency and reversible on vitamin-D treatment.The vertebral crush fracture syndrome represents a severe degree of spinal osteoporosis which may be associated with relatively normal peripheral bones. It probably results from an accelerated negative calcium balance which mobilizes trabecular bone preferentially. Some of the factors which may contribute to this accelerated negative balance have been identified and include a reduced rate of bone turnover, impaired calcium absorption, and low oestrogen activity as judged by vaginal smears, but there may well be others as yet unidentified.

Renal effects of calcitonin

Porcine calcitonin in a slow-release gelatin vehicle was given by intramuscular injection to 10 patients-four with primary hyperparathyroidism, four with Paget's disease, and two with carcinoma of the breast and hypercalcaemia. All cases showed a fall in serum calcium with an immediate rise in urine calcium. All except three patients with primary hyperparathyroidism showed a fall in serum phosphorus, but an immediate rise in urine phosphorus occurred in all cases. Urine hydroxyproline output fell in three patients with severe Paget's disease. Urine sodium rose in all cases, but the effects on potassium, magnesium, water, and pH were not appreciably different from results obtained in four control subjects who were given the gelatin vehicle alone.The data suggest that calcitonin caused a decrease in the tubular resorption of calcium and phosphorus. The hypocalcaemic effect appeared to be due to a decrease in bone resorption in the patients with Paget's disease but in the remaining cases could be accounted for in part or entirely by the rise in urine calcium.