The Influence of Short‐Term Anion Salt Exposure on Urine pH and on Resistance to Experimentally Induced Hypocalcaemia in Cows

The objective of this experiment was to induce acidification by anion salt supplementation for 2 days or 10 days and to study the prophylactic effects of such supplementation in preventing hypocalcaemia in cows. It was further attempted to monitor the extent to which any effect on the calcium‐regulating mechanisms would persist following a 10‐day period of acidification with anion salts. Study animals were three untreated control cows and three cows supplemented with ammonium chloride and ammonium sulphate in their ration for 2 days or 10 days through the rumen cannula. The basic ration of hay was dominated by Urochloa spp. The pH of the urine of the control cows was around 8.00 throughout the experiment and was considered normal. Anion‐supplemented cows produced urine with a daily mean pH between 5.5 and 7.0, possibly due to anion salt exposure. The ability to withstand hypocalcaemic challenges was tested by a standardized intravenous infusion of disodium ethylenediaminetetraacetate (Na₂EDTA). The calcium regaining time (CRT), expressed as time spent to reach 1.00 mmol/l of ionized calcium during recovery from the EDTA‐induced hypocalcaemia, was used to compare cow responses. In the control cows the unexpectedly short CRT, especially during the weekly EDTA tests, could be a result of the repeated induced episodes of hypocalcaemia caused by the EDTA infusions. The improved CRT in the anion‐supplemented cows may thus be interpreted as the combined effect of the repeated hypocalcaemic episodes due to EDTA infusions and probably the effect of anion‐induced metabolic acidosis on endocrine‐regulated calcium homeostatic mechanisms. The effect of anion salt exposure for 10 days on the improvement of calcium‐regulating mechanisms was not clear due to the unexpected improvement of CRT that was exhibited by the untreated control cows as well. An on‐farm trial of the effect of a 2‐day or 10‐day anion exposure of dry cows on calcium‐regulating mechanisms is suggested.     

Unexpected Outcome after Two Consecutive Infusions of Disodium EDTA. in Dairy Cows

Disodium ethylenediaminetetraacetic acid (Na₂EDTA) is a cation chelator which is used as an anticoagulant in blood samples and as a therapeutic agent in lead poisoning. Several experiments have been carried out with EDTA to induce hypocalcemia in cows and other animals, and toxic effects have rarely been reported. In this study, hypocalcemia was induced by means of a 5 % Na₂EDTA infusion (0.55 mg/kg/min Na₂EDTA for 5 h = total dose of 100.6 g). Accidental acute toxicity and fatalities occurred after a consecutive second infusion in several cows. Researchers designing new experiments should be aware of a potential EDTA toxicity at a routinely used dose and rate of administration.     

Induced Hypocalcaemia by Na2EDTA Infusion. A Review

Disodium ethylenediaminetetraacetate (Na₂EDTA) has been used in infusion studies in cows and other species for more than 35 years, primarily for the induction of hypocalcemia as a model for milk fever. This paper reviews such studies and discusses blood calcium kinetics, toxicology, changes in various blood parameters and the effect on blood circulation, cardiac function and smooth muscle motility in the gastro-intestinal tract and in the pregnant uterus. It is concluded that Na₂EDTA infusion may serve as a valid model for spontaneous hypocalcemia. However, experimental results may vary with factors such as the choice of method for blood total calcium analysis, and the rate of EDTA infusion. Standardization of these and certain other experimental conditions may greatly improve the comparability of results obtained in EDTA infusion studies. For cows, an infusion rate of 1.2 ml/kg/h of a 5 % (w/v) solution, corresponding to 0.25 mmol/kg/min, has been suggested as a standard infusion.     

Change of cross-linked telopeptide of type I collagen (ICTP) and other bone resorption markers in patients with bone fragility fractures

Background The serum concentration of cross-linked telopeptide of type I collagen (ICTP) has been reported to be a useful marker and for both diagnosis and monitoring of bone metastasis. This study was performed to clarify the changes in various bone turnover markers, including ICTP, after bone fragility fracture. Methods Seventy-six bone fragility fracture patients (14 men and 62 postmenopausal women; mean age, 77.0 years) were evaluated for bone resorption markers, including serum ICTP. We measured urinary N-terminal telopeptides of type I collagen (NTX) several times after fracture. Furthermore, serum ICTP, serum NTX, urinary deoxypyridinoline (DPD), and urinary C-telopeptide-cross-linked type I collagen (CTX) were measured at the times of both minimum and maximum urinary NTX. Results Urinary NTX was increased significantly from 86.4 ± 57.9 to 214.3 ± 137.2 nmol BCE/mmol Cr following fracture. Serum ICTP showed a similar significant increase from 7.6 ± 4.7 to 10.4 ± 5.5 ng/ml in bone fragility fracture patients. Furthermore, other markers also showed similar increases. The level of increase in urinary NTX (148.0%) was especially high compared with other bone resorption markers. On the other hand, the level of increase in serum ICTP (36.8%) was similar to that in serum NTX (39.8%). Serum ICTP levels were significantly correlated with other bone resorption markers, with an especially strong correlation between serum ICTP and serum NTX (r = 0.647, P < 0.001). The percentage of cases in which ICTP exceeded the cutoff value for suspected bone metastasis in postmenopausal women was 73.6%. Conclusions The value of ICTP increases with bone fragility fracture and is correlated with other bone resorption markers, and ICTP obviously exceeded the reference value as compared with other bone resorption markers.     

A 7‐day continuous infusion of PTH or PTHrP suppresses bone formation and uncouples bone turnover

Human in vivo models of primary hyperparathyroidism (HPT), humoral hypercalcemia of malignancy (HHM), or lactational bone mobilization for more than 48 hours have not been described previously. We therefore developed 7‐day continuous‐infusion models using human parathyroid hormone(1–34) [hPTH(1–34)] and human parathyroid hormone–related protein(1–36) [hPTHrP(1–36)] in healthy human adult volunteers. Study subjects developed sustained mild increases in serum calcium (10.0 mg/dL), with marked suppression of endogenous PTH(1–84). The maximal tolerated infused doses over a 7‐day period (2 and 4 pmol/kg/h for PTH and PTHrP, respectively) were far lower than in prior, briefer human studies (8 to 28 pmol/kg/h). In contrast to prior reports using higher PTH and PTHrP doses, both 1,25‐dihydroxyvitamin D₃ [1,25(OH)₂D₃] and tubular maximum for phosphorus (TmP/GFR) remained unaltered with these low doses despite achievement of hypercalcemia and hypercalciuria. As expected, bone resorption increased rapidly and reversed promptly with cessation of the infusion. However, in contrast to events in primary HPT, bone formation was suppressed by 30% to 40% for the 7 days of the infusions. With cessation of PTH and PTHrP infusion, bone‐formation markers abruptly rebounded upward, confirming that bone formation is suppressed by continuous PTH or PTHrP infusion. These studies demonstrate that continuous exposure of the human skeleton to PTH or PTHrP in vivo recruits and activates the bone‐resorption program but causes sustained arrest in the osteoblast maturation program. These events would most closely mimic and model events in HHM. Although not a perfect model for lactation, the increase in resorption and the rebound increase in formation with cessation of the infusions are reminiscent of the maternal skeletal calcium mobilization and reversal that occur following lactation. The findings also highlight similarities and differences between the model and HPT. © 2011 American Society for Bone and Mineral Research     

Correlations of new markers of bone formation and resorption in kidney transplant recipients

Renal osteodystrophy is a common complication of chronic renal failure and renal replacement therapy. Successful kidney transplantation reverses many of these abnormalities, but the improvement is often incomplete. The evaluation of renal osteodystrophy in everyday practice is based on noninvasive measurements. Taking this into consideration the aim of the present study was to assess new markers of bone metabolism: serum CrossLaps degradation products of C-terminal telopeptides of type I collagen tartrate-resistant acid phosphatase (TRAP) and bone-specific alkaline phosphatase (bALP), as well as their correlations with bone mineral disease (BMD) in kidney transplant recipients. Twenty-six patients (aged 26 to 54 years) receiving a triple immunosuppressive regimen with stable graft function were enrolled in the study. Serum parathormone (PTH) osteocalcin type collagen C-terminal peptides (ICTP), and procollagen type I carboxyterminal extension peptide (PICP) concentrations were measured by radioimmunoassay (RIA), Serum CrossLaps, bALP, beta2-microglobulin, TRAP 5b by enzyme-linked immunoassay (ELISA), and deoxypyridinoline (DPD) in urine immunochemiluminescence. BMD, as measured by dual-energy X-ray absorptiometry (DEXA), correlated negatively with markers of bone formation (bALP, osteoclacin, and PICP) and resorption (TRAP, ICTP, and beta2-microglobulin). The only positive correlation was between urine DPD and BMD at the femoral neck. Interestingly, BMD correlated negatively with CsA concentration. TRAP 5b correlated positively with serum creatinine, ALP, bALP, osteocalcin, iPTH, ICTP, and serum beta2-microglobulin, and negatively with CsA concentration, and azathioprine and prednisone dose. DPD did not correlate with any parameters. Serum CrossLaps correlated with markers of both bone formation and resorption. Because TRAP and serum CrossLaps correlated with markers of both bone formation and or resorption, additional studies are needed to establish the value of these markers of bone resorption to assess renal osteodystrophy.     

The Effect of Modifying Dietary Calcium Intake Pattern on the Circadian Rhythm of Bone Resorption

In order to assess day-to-day variations of the circadian rhythm of biochemical bone resorption markers, urinary morning (6–8 a.m.) and evening (7–10 p.m.) samples from 35 individuals were monitored during 3 subsequent days. The bone-specific deoxypyridinoline (DPD) crosslinks of type I collagen followed a circadian rhythm in all individuals. In contrast, no such pattern was observed in the urinary hydroxyproline/creatinine and calcium/creatinine measurements. The DPD crosslink measurements showed a much larger difference between the morning and evening samples collected within 1 day compared with the variation between the samples collected in the morning or evening on subsequent days, indicating the importance of adequate timing of urine sampling for clinical trials aiming to monitor effects on bone resorption. The analysis of DPD crosslinks was then used to evaluate the effects of different patterns of dietary calcium intake on the circadian rhythm of bone resorption in osteoporotic patients. No significant effect on the circadian rhythm of the DPD crosslinks was found after concentrating the normal daily calcium intake to the evening (6–10 p.m.) during 8 days (n = 7). Ingestion of a dietary calcium supplement (600 mg) at 10 p.m. during 8 days (n = 7) resulted in an increased urinary calcium excretion in the morning, and a flattening of the circadian peak and nadir concentrations of urinary DPD/creatinine. The absolute levels of DPD/creatinine in the morning and evening urine samples, respectively, were not significantly altered compared with the control day. We conclude that dietary calcium supplementation in the evening only marginally affects the circadian rhythm of urinary DPD crosslinks in established osteoporosis patients. Received: 23 December 1996 / Accepted: 1 November 1998     

Specificity of urinary excretion of cross-linked N-telopeptides of type I collagen as a marker of bone turnover

Urinary excretion of cross-linked N-telopeptide of type I collagen (NTX) has been reported to be a specific indicator of bone resorption. We studied the utility of a new immunoassay for NTX as an indicator of changes in bone resorption caused by treatment with pamidronate (APD) followed by T₃. Twenty-two male subjects received either placebo (Group 1) or APD on study days 1–2 (Group 2). One week later all subjects received T₃ 100 g/day (days 8–15). Urinary NTX, pyridinoline (PYD), hydroxyproline (HYP), and creatinine (cr) were measured on 2-hour fasting urine samples at baseline (day 1), after APD/placebo (day 8), after T₃ (day 16), and at days 30 and 58. NTX/cr excretion fell 85% after treatment with APD (P<0.001 versus baseline), but not after placebo. The fall in mean urinary NTX after receiving APD was greater than the fall in PYD (25%) or HYP (31%) (P<0.001 NTX versus PYD and HYP). After treatment with APD, NTX excretion remained suppressed below baseline until day 58, whereas PYD and HYP excretion returned to baseline by study day 16. Persistence of APD's effect on bone until day 58 was suggested by the fact that serum calcium and parathyroid hormone levels had not returned to baseline by day 58. On day 16, after all subjects were treated with T₃, urinary NTX/cr rose significantly (P<0.01) in Group 1 (-bisphosphonate) but not in Group 2 (+bisphosphonate). We conclude that urinary NTX is responsive to acute thyroid hormone-induced increases and bisphosphonate-induced decreases in bone resorption, and may reflect these changes more accurately than PYD or HYP.Portions of the data presented here were presented at the Fifteenth Annual Meeting of the American Society for Bone and Mineral Research, Tampa, Florida, September 18–22, 1993.     

Changes in Bone and Calcium Metabolism Following Hip Fracture in Elderly Patients

Although hip fracture is one of the most common causes of acute immobilization in elderly patients, little is known about the influence of immobilization on changes in bone and calcium metabolism following this event. We therefore compared serum biochemical indices of bone and calcium metabolism in 20 elderly subjects with hip fracture with those measured in 20 healthy age-matched controls. Rankin scores, a measure of functional dependence with 0 representing independence and 5 representing total dependence, were assigned. We also examined serial changes in these biochemical indices from shortly following the fracture to the early recovery period. Ionized calcium, intact parathyroid hormone (PTH), intact bone Gla protein (BGP), pyridinoline cross-linked carboxyterminal telopeptide of type I collagen (ICTP), 25-hydroxyvitamin D (25-OHD), and 1,25-dihydroxyvitamin D (1,25-[OH]₂D) were measured. One week after the fracture, mean serum concentrations of calcium and ICTP were elevated in correspondence to degree of immobilization (mean Rankin score; 4.4), while serum concentrations of BGP, PTH, 25-OHD, and 1,25-[OH]₂D were depressed. Rankin score (mean: 4.4) correlated positively with ICTP and negatively with BGP at this time. At 2 months, calcium and ICTP elevation decreased and BGP, PTH and 1,25-[OH]₂D were less depressed, coinciding with a decline in Rankin score from 4.2 to 2.2. Indices were further improved at 3 months (mean Rankin score, 1.3), with calcium and BGP returning to normal. We concluded that increased bone resorption, and decreased bone formation, and hypercalcemia are present by 1 week following the hip fracture, and some resorption increase persists for at least 3 months. These changes could explain in part the high risk of another hip fracture. Received: 3 April 2000 / Accepted: 15 December 2000     

Low‐Grade Metabolic Acidosis May Be the Cause of Sodium Chloride–Induced Exaggerated Bone Resorption

Stepwise increase in NaCl intake in healthy male test subjects led to a low‐grade metabolic acidosis. This was most likely the cause for increased bone resorption during high sodium chloride intake, as determined by analyzing bone resorption markers. Introduction : We examined the effect of increased dietary sodium chloride (NaCl) on bone metabolism and acid‐base balance. Materials and Methods : Subjects were nine healthy men (mean age, 25.7 ± 3.1 yr; mean body weight [BW], 71.5 ± 4.0 kg). During the first period (6 days), subjects received 0.7 mEq NaCl/kg BW per day (phase 1), during the second period (6 days) 2.8 mEq NaCl/kg BW per day (phase 2), during the third period (10 days) 7.7 mEq NaCl/kg BW per day (phase 3), and during the fourth period (6 days) 0.7 mEq NaCl/kg BW per day (phase 4). Results : Twenty‐four‐hour urinary excretion of calcium and sodium rose significantly with increasing NaCl intake (p < 0.001 for both). Urinary excretion of bone resorption markers C‐ and N‐terminal telopeptide of type I collagen (CTX, NTX) increased from phase 2 to phase 3 (CTX, p = 0.013; NTX, p < 0.001) and decreased from phase 3 to phase 4 (CTX, p < 0.001; NTX, p = 0.002). Bone formation markers N‐terminal propeptide of type I procollagen, bone‐specific alkaline phosphatase, and osteocalcin remained unchanged from low to high NaCl intake. Blood pH levels decreased (p = 0.04) between phases 1 and 3. Blood bicarbonate (HCO₃^?) and base excess (BE) decreased from phases 1 to 3 (p < 0.001 for both) and from phases 2–3 (HCO₃^?, p = 0.003; BE, p = 0.015). Nearly all bone resorption markers and acid‐base variables reached their baseline levels in phase 4. Conclusions : We conclude that low‐grade metabolic acidosis may be the cause of NaCl‐induced exaggerated bone resorption.     

Markers of bone metabolism in hemodialyses and hemodiafiltration

Renal osteodystrophy is a common complication of chronic renal failure and renal replacement therapy. The purpose of the study was to assess whether hemodialysis (HD) or hemodiafiltration (HDF) affects bone turnover. In all, 45 HD and 17 HDF patients were evaluated with respect to bone metabolism markers. We assessed PTH; markers of bone formation-alkaline phosphatase and its bone isoform, osteocalcin; markers of bone resorption- PICP, ICTP; Ctx; beta2-microglobulin; and urinary DPD. BMD were determined for femoral neck and lumbar spine (L2-L4) using DEXA. Hemodialyzed patients had lower calcidiol, calcitriol, and BMD in the femur neck, and higher phosphate, Kt/V, residual renal function, venous pH, osteocalcin, ALP, bALP, DPD, beta2-microglobulin, ICTP, Ctx, osteoprotegerin, and RANKL than patients on HDF. HDF seems to ameliorate bone metabolism in comparison with HD. Bone turnover in end-stage renal failure might be affected to some extent by the choice of renal replacement therapy.     

Comparison of serum levels of pyridinoline and pyridinoline cross-linked carboxy-terminal telopeptide of type I collagen as markers of bone resorption in patients receiving maintenance hemodialysis

Background Serum levels of pyridinoline, measured by high-performance liquid chromatography, and pyridinoline cross-linked carboxy-terminal telopeptide of type I collagen (ICTP), measured by a newly developed radioimmunoassay kit, were compared and analyzed to determine whether ICTP can replace pyridinoline as a marker of bone resorption in hemodialysis patients. Methods Thirty-five patients receiving maintenance hemodialysis were studied. Ten of the 35 patients were selected for an investigation of the kinetics of ICTP during hemodialysis treatment to compare with that of pyridinoline. Pyridinoline, ICTP, and other known bone metabolic markers were measured in all 35 patients immediately before hemodialysis. The correlation between pyridinoline and ICTP was analyzed by using relative amounts of these markers and the findings of bone resorption on a plain roentgenogram of the hands. Results The mean removal and recovery rates of ICTP were 25.3% and 103.4%, respectively. The correlation coefficient between pyridinoline and ICTP was 0.756 (P<0.001). Pyridinoline, but not ICTP, positively correlated with intact parathryroid hormone (iPTH) and osteocalcin. A higher correlation was shown between iPTH and pyridinoline than between iPTH and ICTP. ICTP was better correlated with lower levels of pyridinoline (r=0.651,P<0.005) than higher ones (r=0.230, not significant). A positive correlation was observed between pyridinoline and ICTP in patients without subperiosteal resorption. Conclusion ICTP is not superior to pyridinoline as a marker of bone resorption in hemodialysis patients, especially in those with a progressed state of bone resorption.     

Urinary deoxypyridinoline excretion for the evaluation of bone turnover in chronic renal failure

BACKGROUND: The urinary excretion of deoxypyridinoline (DPD) was evaluated in predialysis chronic renal failure (CRF), together with intact PTH and several classic markers of bone turnover in order to assess whether urine free and total DPD excretion are equivalent parameters of bone turnover in CRF, and to evaluate the relationship between urine DPD excretion, PTH and the other bone markers. METHODS: The study was carried out in 94 patients with different degrees of renal failure due to various kidney diseases. Besides urinary DPD expressed as free DPD, total DPD, free/total DPD, free DPD/Cr and total DPD/Cr, the following determinations were made: intact PTH, bone alkaline phosphatase (BALP), total alkaline phosphatase (AP), osteocalcin (BGP), serum C-terminal telopeptide of collagen type I (ICTP) and hydroxyproline (OHpro). The patients were divided into 3 groups according to the increasing severity of renal failure (Ccr >40, 40-20, <20 ml/min). RESULTS: The ratio free/total DPD decreased (NS) with advancing renal failure, and was inversely correlated with total DPD excretion. While PTH increased progressively to about four times the values observed in the Ccr >40 group, there was a parallel increase only in BGP and ICTP, parameters retained in the serum with decreasing renal function, while AP, BALP, total DPD and OHpro did not change. However, significant correlations between total DPD/Cr and PTH, BALP, BGP and ICTP were also found. CONCLUSIONS: In CRF free DPD is an unreliable index of bone turnover due to a probable interference in its production from the peptide-bound DPD. Total DPD or total DPD/Cr are better used. In spite of the significant correlations observed in advanced renal failure between PTH and most of the parameters examined, a resistance of bone tissue to PTH action in CRF must be considered.     

The effect of thionapthene-2-carboxylic acid-lysine on the hypercalcemia of malignancy in the rat

Summary Thionapthene-2-carboxylic acid (TNCA) was previously shown to lower serum calcium concentrations in hypercalcemic rats; however, oral administration of TNCA may cause gastric irritation. We have assessed thionapthene-2-carboxylic acid lysine salt (TNLY) for its effects on serum calcium concentration and survival in rats bearing the hypercalcemic Leydig cell tumor. TNLY (0.6–1.8 mmol/kg/day) produced a marked and prolonged dose-related decrease in serum calcium concentration. At the highest dose of 1.8 mmol/kg/day, hypocalcemia occurred. Effects were sustained for 96 hours or longer. In tumor-bearing rats that were not yet hypercalcemic, pretreatment with TNLY (0.9 mmol/kg/day) did not induce hypocalcemia and the onset of hypercalcemia was prevented. Neither TNLY nor dichloromethylene diphosphonate (CL₂MDP), a potent inhibitor of bone resorption, significantly prolonged overall survival. We concluded that TNLY is a potent antihypercalcemic agent that warrants further testing for use in the treatment of hypercalcemic disorders.     

Effect of ONO‐5334 on Bone Mineral Density and Biochemical Markers of Bone Turnover in Postmenopausal Osteoporosis: 2‐Year Results From the OCEAN Study

Cathepsin K inhibitors, such as ONO‐5334, are being developed for the treatment of postmenopausal osteoporosis. However, their relative effects on bone resorption and formation, and how quickly the effects resolve after treatment cessation, are uncertain. The aim of this study was to examine the efficacy and safety of 24‐month treatment with ONO‐5334 and to assess the effect of treatment cessation over 2 months. We studied 197 postmenopausal women with osteoporosis or osteopenia with one fragility fracture. Patients were randomized to ONO‐5334 50 mg twice daily, 100 mg or 300 mg once daily, alendronate 70 mg once weekly (positive control), or placebo for 24 months. After 24 months, all ONO‐5334 doses were associated with increased bone mineral density (BMD) for lumbar spine, total hip, and femoral neck (p < 0.001). ONO‐5334 300 mg significantly suppressed the bone‐resorption markers urinary (u) NTX and serum and uCTX‐I throughout 24 months of treatment and to a similar extent as alendronate; other resorption marker levels remained similar to placebo (fDPD for ONO‐5334 300 mg qd) or were increased (ICTP, TRAP5b, all ONO‐5334 doses). Levels of B‐ALP and PINP were suppressed in all groups (including placebo) for approximately 6 months but then increased for ONO‐5334 to close to baseline levels by 12 to 24 months. On treatment cessation, there were increases above baseline in uCTX‐I, uNTX, and TRAP5b, and decreases in ICTP and fDPD. There were no clinically relevant safety concerns. Cathepsin K inhibition with ONO‐5334 resulted in decreases in most resorption markers over 2 years but did not decrease most bone formation markers. This was associated with an increase in BMD; the effect on biochemical markers was rapidly reversible on treatment cessation. © 2014 American Society for Bone and Mineral Research.     

Effects of continuous and intermittent administration and inhibition of resorption on the anabolic response of bone to parathyroid hormone.

The role of resorption in the anabolic response of bone to parathyroid hormone (PTH) is not well understood. In contrast to the increase in bone mass induced by intermittent PTH in intact rats, continuous infusion of PTH into thyroparathyroidectomized (TPTX) rats failed to increase bone volume. The objective of this study were to determine if continuous infusions of low doses of PTH were anabolic in intact rats and if inhibition of resorption would enhance or block an anabolic action of PTH. Young male rats were treated with either continuous infusion or intermittent injections of hPTH-(1-34) for 12 days. In experiment 1, PTH, infused daily at 4 micrograms per 100 g, increased femur calcium and dry weight. Unlike infusion of 8 micrograms PTH, which did not alter bone mass, intermittent PTH at 8 micrograms was anabolic and increased bone mass by increasing trabecular thickness and number. Infusion of 16 micrograms induced hypercalcemia and death. In experiment 2, lower dose daily infusions of 0.25-4 micrograms PTH per 100 g did not increase bone mass. In experiment 3, in rats pretreated with dichloromethylene diphosphonate (Cl2MDP) to inhibit resorption and subsequently exhibiting decreased bone formation, PTH, irrespective of the method of administration, reversed the inhibitory effects of Cl2MDP on bone formation. Thus, intermittent and continuous PTH increase bone formation independently of effects on bone resorption, but only intermittent PTH increases bone mass consistently.     

Suppression of Bone Resorption in Early Postmenopausal Women by Intranasal Salmon Calcitonin in Relation to Dosage and Basal Bone Turnover

In the present study, we assessed the ability of increasing doses of intranasal calcitonin to suppress urinary deoxypyridinoline cross-link (DPD), a specific biochemical marker of bone resorption, in early postmenopausal women. Subjects consisted of 30 healthy Thai women within 5 years of postmenopause, randomly assigned to 50, 100, or 200 IU of intranasal calcitonin 5 days/week for 3 months. Calcium supplementation by calcium carbonate capsules at 750 mg of elemental calcium per day was given to all subjects. Twenty four-hour urine for DPD and creatinine assays was collected at baseline, 1 month, and 3 months after treatment. All DPD values were corrected with urinary creatinine before analyses. Data were expressed as mean ± SEM. DPD decreased significantly 1 month after intranasal calcitonin treatment (P < 0.01). However, at 3 months, DPD increased when compared with the values at 1 month (P < 0.01), suggesting that there may be a reduction in the suppression of bone resorption after prolonged calcitonin therapy. Using a stepwise multiple regression model to address whether dosage and DPD at baseline influence the response to intranasal calcitonin, it was found that DPD suppression after intranasal calcitonin was not related to dosage but was strongly associated with baseline DPD (P < 0.0001). Suppression of bone resorption in early postmenopausal women by intranasal calcitonin is determined more by the state of bone turnover at baseline than the dosage of calcitonin. Received: 10 March 1997 / Accepted: 14 November 1997     

Effects of Short-Term Treatment with Clodronate on Parameters of Bone Metabolism and Their Diurnal Variation

The goal of the present study was to answer the question whether the diurnal variation of markers of bone turnover is abolished by inhibition of osteoclasts by bisphosphonates and to assess the effects of short-term treatment with clodronate on parameters of calcium and bone metabolism. Nine healthy, postmenopausal women, all aged 68 years, were studied before and after oral administration of clodronate, first 800 mg daily for 2 weeks and then 1600 mg daily for 2 weeks. During the two-study sessions of 24 hours, the subjects received exactly similar meals and were recumbent from 10:00 p.m. to 6:00 a.m. Blood was sampled every 2 hours and urine was collected in 4-hour aliquots. On each study occasion, three markers of bone resorption (ICTP, serum type-I collagen carboxyterminal telopeptide; F-Pyr, urinary-free pyridinoline; and NT_x, crosslinked N-telopeptide of type I collagen) and one marker of bone formation (PICP, serum type I procollagen carboxyterminal propeptide) showed a diurnal variation; only that of NT_x was lessened by treatment with clodronate. Mean area under curve (AUC) values for the 24-hour study periods decreased by 41% (P= 0.0002) and 4.7% (P= 0.016) for urinary NT_x and F-Pyr, but remained unchanged for serum ICTP (P= 0.41) and PICP (P= 0.99). Treatment with clodronate decreased mean AUC for the serum concentration of total calcium by 1.4% (P= 0.030) and that for the urinary excretion of calcium by 33% (P= 0.021). Mean AUC for serum-intact PTH increased by 19% (P= 0.004). We conclude that short-term treatment with clodronate lowers serum and urine calcium levels and causes compensatory hyperparathyroidism. Treatment also clearly decreases the urinary excretion of NT_x and lessens its diurnal variation. As assessed by sensitive markers such as NT_x, the nocturnal rise in bone resorption is greatly blunted by inhibition of osteoclasts with bisphosphonates. Received: 13 October 1995 / Accepted: 3 May 1996     

Evaluation of the usefulness of serum phosphatases and osteocalcin as serum markers in a calcium depletion-repletion rat model

Summary The present study examined the usefulness of the serum alkaline phosphatase (ALP) activity, osteocalcin, and tartrate-resistant acid phosphatase (TrACP) activity as bone turnover markers in a calcium depletion/repletion rat model. Weanling rats were fed calcium-deficient diet for 4 weeks, followed by 2 weeks of dietary calcium repletion. Serum phosphatases and osteocalcin were determined and compared with those of corresponding age-matched, pair-weighted controls. Rats were sacrificed at the end of each phase of the study, and bone phosphatase activities in tibiae and vertebrae were measured. During calcium depletion, rats developed hypocalcemia and lost significant bone calcium, which were reversed with dietary calcium repletion. During depletion when previously published histologic studies indicated a suppressed bone formation and stimulated bone resorption, serum ALP activity and osteocalcin levels were significantly elevated and serum TrACP activity reduced; at the same time, the bone ALP and TrACP activities were increased. Because the serum level of 1,25 dihydroxyvitamin D₃ (1,25(OH)₂D₃) which has been shown to stimulate the synthesis of skeletal ALP and of osteocalcin, was also significantly increased during depletion, the increased serum ALP and osteocalcin level could be indirect consequences of the hypocalcemia-mediated elevation in 1,25(OH)₂D₃ level. These effects were reversed upon calcium repletion, during which previously published histologic studies demonstrated a stimulated bone formation and a suppressed resorption in these rats. In conclusion, although there is increasing evidence for the usefulness of these serum proteins as markers of bone metabolism in humans, a great deal more work is required before we can understand the significance of these assays. Until such is accomplished, these assays should not be assumed to be validated.     

Nocturnal rise in markers of bone resorption is not abolished by bedtime calcium or calcitonin

As assessed by urine pyridinium cross-links, bone resorption increases at night. This has been ascribed to either the nocturnal rise of serum parathyroid hormone (PTH) or immobilization. ICTP is the carboxyterminal telopeptide region of type I collagen in bone, cross-linked via pyridinium cross-links and liberated during the degradation of type I collagen. To study whether the nocturnal rise in bone resorption is seen also in serum type I collagen carboxyterminal telopeptide (ICTP) and whether this rise is abolished by bedtime calcium or calcitonin, nine healthy postmenopausal women participated in three 24 hour sessions. At 2200 hours, either 1 g of oral calcium or 200 IU of intranasal calcitonin or no treatment (control session) were given. The participants were recumbent from 2200 hours to 0600 hours. Like urinary pyridinolines, serum ICTP showed a clearcut nocturnal rise during the control session, increasing from 3.7±0.3 g/liter (mean±SE) at 2000 hours to 4.9±0.4 g/liter at 0600 hours (P<0.001). Administration of calcium did not affect either serum ICTP or urinary pyridinolines, although it decreased serum intact PTH by 18% (P<0.001) as assessed by areas under curve (AUC) after 2200 hours. Serum ICTP and urinary pyridinolines remained unchanged also after administration of calcitonin which increased the AUC for serum intact PTH by 9% (P<0.05). In conclusion, serum ICTP follows a circadian rhythm in healthy postmenopausal women. The nocturnal rise in markers of bone resorption is not due to PTH, and its dependency on the function of osteoclasts is open to question.