[Contamination of the food chain with caesium-137 and strontium-90 in Switzerland]. / Kontamination der Nahrungskette mit Cäsium-137 und Strontium-90 in der Schweiz.

One task of the field physiology of nutrition is the monitoring of the quality of feedstuffs. Rations may consequently be prepared with unadulterated components. This review uses the example of contamination with the radionuclides caesium-137 und strontium-90 and shows how these two unwanted substances reach the end host via the food chain and how their untoward effects are expressed in animals and humans. The extent of the contamination with artificial radioactivity is followed with periodical measurements according to the program of the Division for Radiological Protection of the Swiss Federal Office of Public Health. The interpretation of the measurements and the directives of this division are designed to protect primarily human health, but also that of animals.

Nutrition studies on protein and energy in domestic cats.

The effects of three diets varying in their protein, fat and carbohydrate contents and of physical activity on energy and protein metabolism were investigated in eight domestic cats. The diets were based on canned food with addition either of minced cattle heart, melted swine fat or polenta. The activity-induced heat production was measured in a respiration chamber using the Doppler effect of radio-waves reflected from moving bodies. In the group receiving the high-protein diet, urinary nitrogen concentration was higher which was reflected in higher urinary loss of energy without affecting the amount of energy retained. Nitrogen utilization was not significantly influenced by nitrogen intake. Mean daily total heat production ranged between 163 and 187 kJ/kg BW/day or 215 and 270 kJ/kg BW(0.75)/day. The daily crude protein requirement of adult cats was determined to be 2.7 g/kg BW/day. The daily requirement of metabolizable energy for maintenance was estimated to be 153 kJ/kg BW/day or 226 kJ/kg BW(0.75)/day. The activity-induced heat production was 25.1 kJ/kg BW/day which corresponded to 13.5% of the total daily heat production. The daily requirement for metabolizable energy was thus reduced by 20.9 kJ/kg BW/day or 13.7%. The activity pattern of the cats was not characterized by a circadian rhythm.

[Copper and zinc in animal feed for the adult horses in Switzerland]. / Le cuivre et le zinc dans les aliments du cheval adulte en Suisse.

The copper and zinc contents of 25 rations for adult horses were evaluated. The total amount of copper and zinc daily ingested was obtained by adding the amount of each element contained and added of the commercial feed to the amount contained in ingested hay and oats. The total amount of copper and zinc ingested daily was compared with the official recommendations for the maintenance of an adult horse of 550 kg. The results show that a traditional ration oats/hay does not contain a sufficient amount of copper and zinc in order to cover their respective requirements. Furthermore, many rations which include commercial feed also do not cover the requirements of these two elements. The importance of these observations is discussed in the light of the eventual need to complete the rations.

Influence of dietary phosphorus deficiency with or without addition of fumaric acid to a diet in pigs on bone parameters.

The purpose of this study was to examine if substantial bone loss occurs in weaned pigs by feeding a phosphorus-deficient diet with or without fumaric acid. Eighteen weaned pigs were used. The animals were assigned to three groups: group C (control; 0.65% P on DM basis), group LP (low phosphorus; 0.37% P on DM basis) and group LPF (low phosphorus plus fumaric acid; 0.35% P on DM basis plus 2% fumaric acid). These three diets were fed to the groups for a period of four weeks after a two-week adaptation period. Blood samples were collected once a week. Carboxyterminal telopeptide of type I collagen (ICTP) in serum was used as a bone resorption marker. Osteocalcin (OC) and bone-specific alkaline phosphatase (bAP) were used as bone formation markers. Bone mineral density (BMD) and content (BMC) were determined by peripheral quantitative computer tomography. BAP activities significantly increased (24%) in group LPF, and at the last sampling day group LPF had significantly increased activities in comparison to group C. In contrast, ICTP concentrations significantly increased with time in group LP and LPF, and at the last sampling day group LPF had significantly increased activities in comparison to group C. BMD and BMC in femur and tibia significantly decreased in group LP and LPF. The results show that P-deficient diets induce a bone loss. Fumaric acid did not influence the degree of bone loss. With a better understanding of its effect on bone, dietary phosphorus requirements in pigs could be more precisely defined.

Influence of a low calcium and phosphorus diet on the anabolic effect of human parathyroid hormone (1-38) in female rats.

Parathyroid hormone (PTH) or synthetic N-terminal PTH fragments administered intermittently have been established as anabolic agents in animal and human bones. In the present study, the influence of a low calcium diet on the anabolic effect of human PTH(1-38) [hPTH(1-38)] was investigated. Forty-eight 10-week-old female Sprague-Dawley rats were randomly assigned to a diet with a low calcium content (LCa) or a diet with the recommended amount of calcium (RCa). After an adaptation period of 15 days, the rats were randomly assigned to hPTH(1-38) treatment (+LCa/+RCa) or vehicle only (-LCa/-RCa) for an additional 14 days. Total bone mineral density (BMD) values of several bones were determined using quantitative computed tomography and from ratios of ash weight to volume. Biomechanical competence of the fourth lumbar vertebrae and of the right femora was assessed. An anabolic effect could be detected in both PTH-treated groups. However, the bones of the +LCa group showed significantly lower BMD and also a diminished increase in maximal breaking force compared with those of the +RCa group. The study demonstrates that the anabolic effect of hPTH(1-38) is blunted by the LCa diet. This suggests that, during PTH treatment, dietary calcium intake is critical.

Pathophysiological effects of low dietary phosphorus in pigs.

SUMMARY: The homeostasis of inorganic phosphate (P(i)) is regulated by parathyroid hormone (PTH), 1,25-dihydroxyvitamin D (1,25(OH)(2)D), and P(i)itself in the intestine, kidney, and bone in all the mammalian species studied. Determinations of the serum concentrations of PTH, 1,25(OH)(2)D and osteocalcin were done in 82 southern Romanian Landrace pigs originating from three herds with dietary P(i)deficiency. Serum P(i)concentrations were negatively correlated with those of 1,25(OH)(2)D. In lactating animals and sucklings, the linear relationships between P(i)and 1,25(OH)(2)D were not present. Serum P(i)concentrations were positively correlated with those of PTH. In lactating animals and young pigs, the linear relationships between P(i)and PTH were not evident. PTH and 1,25(OH)(2)D concentrations were negatively correlated. The serum concentrations of 1,25(OH)(2)D and osteocalcin were positively correlated. Milk P(i)concentrations ranging from 3.10 to 7.49 mmol/L were correlated positively with urinary P(i)concentrations ranging from 0.26 to 11.37 mmol/L. In conclusion, similarly to other species, P(i)homeostasis is achieved in pigs by feedback mechanisms between P(i), PTH and 1,25(OH)(2)D and osteocalcin production is induced by 1,25(OH)(2)D. The effect of lactation on P(i)homeostasis remains to be explored.

Animal nutrition and acid-base balance.

In domestic animals, acid-base balance may be influenced by nutrition. The major research effort in this area has been made on the prevention of hypocalcemic postparturient paresis in dairy cows. This disorder is caused by the sudden increase of calcium secretion into the colostrum. The manipulation of the dietary cation-anion difference makes it possible to maintain the cows in metabolic acidosis during the critical period that precedes calving, presumably via a mechanism that involves the strong ion difference in the extracellular fluid. As a consequence the mobilization of calcium is enhanced and the incidence of the disorder is decreased. Conversely, a dietary induced metabolic alkalosis leads to a more severe degree of hypocalcemia and the incidence of the disease is increased. The underlying mechanisms of the prevention are only partially understood. Nevertheless, this preventive method is already widely applied in practice. Nutrition effects on acid-base balance also influence growth and food intake in higher vertebrates and fish. As a consequence, the incidence of developmental orthopedic diseases in fast-growing domestic animal species may be affected. Also, the bone mineral content of athletic horses may be influenced by dietary induced modification of the acid-base status. The mineral loss due to metabolic acidosis may lead to an increase in the incidence of stress fractures. This overview should give insight into relevant aspects of nutrition and acid-base balance in domestic animal species.

The course of selected bone resorption marker concentrations in response to short-term hypocalcemia experimentally induced with disodium EDTA infusions in dairy cows.

The collagen metabolites hydroxyproline (HYP), deoxypyridinoline (DPD), and the carboxyterminal telopeptide of type I collagen (ICTP) are suitable markers for bone resorption in humans and several animal species. The purpose of this study was to describe the course of bone resorption markers during short-term hypocalcemia induced with disodium ethylenediaminetetraacetic acid (Na2EDTA) and to investigate whether bone resorption is increased in dairy cows under these conditions. EDTA infusions have been used as a model for periparturient paresis in dairy cows and to estimate the calcium mobilization rate from body reserves in ruminants. 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). Two experiments were conducted: (1) Six 4-11 years-old Brown Swiss cows were infused intravenously with EDTA for 5 h. Blood and urine samples were taken repeatedly from 1 day before until 10 days after infusion. (2) Towards the end of the lactation, the experiment was repeated with the same animals after a 14-day-period of feeding a low calcium diet (26 g/animal per day). The EDTA-infusion induced hypocalcemia and hypophosphatemia. The HYP-, DPD- and ICTP-concentration remained mainly unaffected during both infusions. Only DPD showed an increase during infusion and HYP an increase 2 days after the infusion. In conclusion, the EDTA infusion had little effect on the concentrations of the measured bone markers, which may be due to the fact that the serum calcium pool was refilled by increased absorption of Ca via the gastrointestinal tract. From these results, it can be concluded that bone resorption was not influenced by EDTA infusion.

[Comparative study of three feeding methods for draught horses of the Swiss army]. / Etude comparative de trois modes de rationnement pour les chevaux du train de l'armée suisse.

Three feeding methods were compared in 36 4- to 6-year-old Franche-Montagne horses during the military school of St-Luzisteig (GR) of Spring 1992. The horses were separated into 3 groups: a group with the traditional oats-hay ration (OH), a group with a pelleted feed and hay ration (PFH), and a group with the complete diet (CD). Feed analyses were performed and food consumption, eating behavior and digestibility were studied. The horses received their daily amount of feed in 3 portions covering the requirements for a medium work: OH = 8 kg hay and 3 kg oats, PFH = 8 kg hay and 3 kg pelleted feed and CD = 10 kg of the complete diet. For the 3 rations, the amount of digestible crude protein for horses was higher than the reference value for the requirement of a 600 kg horse with a medium work. In the 3 diets, the calcium content was higher than the required 32 g per day (g/d). Not enough sodium (OH: 1.2 g/d; PFH: 7.3 g/d; CD: 9.6 g/d) and too much potassium (OH: 140.3 g/d; PFH 153.0 g/d; CD: 167.5 g/d) were present in the diets, both without consequences for the blood parameters. In 3 meals of 60 minutes, the horses of the group OH, PFH and CD ingested 82%, 89% and 92%, respectively, of the daily ration. The complete diet was ingested more quickly than the hay. The number of mastications per minute was smaller for the complete diet than for the hay. Ingestion times were similar for oats and pelleted feed. However, the number of mastications per minute was smaller for the pelleted feed. The digestibility of nutrients was not influenced by the method of feeding. In conclusion, these results demonstrate that the 3 types of ration studied here are adequate for the swiss army horses if sodium is added to the diet. However, despite the fact that both PFH and CD correct excessive supply or deficiencies of nutrients and despite the fact that these two feeding methods offer nutrients in amounts that are closer to the requirements of the horse, the method PFH was introduced in 1994.

Biochemical markers of bone formation and resorption around parturition and during lactation in dairy cows with high and low standard milk yields.

Substantial changes occur in skeletal metabolism during lactation. These dynamic changes are monitored with biochemical bone markers. The goal of the present study was to follow these changes in lactating cows and to investigate whether cows with a higher milk yield have a higher mobilization rate of calcium from bone. Hydroxyproline, deoxypyridinoline, pyridinoline, and the carboxyterminal telopeptide of type I collagen (ICTP) were chosen as markers for bone resorption, whereas osteocalcin was used as a bone formation marker. Urine and blood samples were collected from cows with a mean standard milk yield of 4900 and 6500 kg, respectively, 14 d before, and 14 d, 1 mo, 1.5 mo, and monthly after parturition. Urinary hydroxyproline, deoxypyridinoline, and pyridinoline concentrations increased with time, but no differences between the two groups were evident. Concentrations of 1,25-dihydroxy vitamin D and ICTP of the two groups showed an increase 14 d after parturition. Furthermore, using multivariate regression models with age and milk yield as covariates, ICTP concentrations were higher in the group with a higher milk yield. In contrast, osteocalcin concentrations decreased 14 d after parturition and returned to prepartum values 1 mo after parturition. The increase of ICTP concentrations in both groups indicates that bone was substantially resorbed. At the same time, probably less Ca was embedded in bone, as indicated by the decrease of the osteocalcin concentrations. In conclusion, cows showed increased bone resorption around parturition, and cows with higher milk yield mobilize calcium more actively from bone than cows with lower milk yield.

Long-term excessive magnesium supplementation is deleterious whereas suboptimal supply is beneficial for bones in rats.

The long-term effects of a suboptimal magnesium supply inducing a marginal or moderate deficiency or of an excessive magnesium supplementation corresponding to a basal diet with a high pharmacological intake were investigated in 36 growing Sprague-Dawley female rats. The rats were randomly divided in three groups and received a purified diet with 7 g calcium, 5 g phosphorus and either 0.2, 0.5 or 2 g magnesium per kg diet for 7 months. At the end of the trial, plasma and erythrocyte total magnesium concentrations were significantly lower in the magnesium-deficient group than in the respective control group. Serum concentrations of 1,25-dihydroxyvitamin D, PTH and IGF-I and the length of the right humeri were not affected by the dietary treatment. The volumes corrected for body weight, the medio-lateral diameters and the ratios dry weight/length of the right humeri, and the dry weight corrected for body weight of the left tibiae and of the right humeri were significantly smaller in the magnesium-supplemented group than in the two other groups. The magnesium contents of the left tibiae and of the first lumbar vertebrae were significantly lower in the magnesium-deficient group than in the two other groups. In the right femora, dual energy X-ray absorptiometry revealed significantly smaller areas in the proximal part and significantly smaller mineral contents in the second proximal quarter in the magnesium-supplemented group compared with the two other groups. Peripheral quantitative computer tomography of the right humeri revealed in the cortex significantly larger values for the relative area, mineral content, mineral density and thickness in the magnesium-deficient group compared with the control group. The maximum point of the load-deformation curve was significantly reduced in the fifth lumbar vertebrae and in the proximal femoral metaphyses of the magnesium-supplemented group. These results indicate that the long-term suboptimal magnesium supply improved some of the parameters indicators of bone health whereas the long-term supplementation was deleterious.

Effects of EDTA-induced hypocalcaemia and stress on plasma TNF-alpha, IL-1-ra, G-CSF, GM-CSF and S-100 in dairy cows.

The pathophysiology of postparturient paresis is still not completely understood. Knowledge recently acquired in immunology, endocrinology and cell physiology has still to be integrated in order to elucidate the aetiopathogenesis of the disease. For that purpose, the effect of the EDTA infusion model on the plasma concentrations of selected cytokines and growth factors, and of a calcium binding protein was examined in dairy cows. Six 6- to 11-year-old Brown Swiss cows in mid lactation were infused with a 5% solution of Na2EDTA in one jugular vein over a period of 5 h. Blood samples were collected from the contralateral side daily two days before, and then hourly for five hours during the infusion, hourly for five hours after the end of the infusion, and once daily for 10 days thereafter. The plasma concentrations of cortisol, tumour necrosis factor-alpha, interleukin-1 receptor antagonist, granulocyte colony-stimulating factor, granulocyte and macrophage colony-stimulating factor, and the calcium binding protein S-100 were determined. Before the EDTA infusion, during the infusion and for two days thereafter, the mean plasma concentrations of cortisol were significantly higher than those from days 4 to 10 after the infusion. The plasma concentrations of tumour necrosis factor-alpha and interleukin-1 receptor antagonist followed a similar profile. At the end of EDTA infusion, low concentrations of granulocyte colony-stimulating factor were detected in one cow only. On days 3 and 4, the mean plasma concentrations of granulocyte colony-stimulating factor were significantly higher than the pre-infusion values, but this was followed by a significant decrease on post-infusion day 5. From day 4 to 7, the plasma concentrations of S-100 were significantly lower than the pre-infusion values. The importance of these findings in the pathophysiology of postparturient paresis remains to be established.

Diurnal variation in concentrations of various markers of bone metabolism in dogs.

OBJECTIVE: To evaluate diurnal variation in concentrations of selected markers of bone metabolism in dogs. ANIMALS: Ten 3- to 4-year-old ovariectomized Beagles. PROCEDURE: Blood and urine samples were obtained in the morning before dogs were fed (8 AM) and then at 2-hour intervals for 24 hours. This procedure was repeated 2 weeks later. Concentrations of osteocalcin (OC) and carboxy terminal telopeptide of type-I collagen (ICTP) were measured in serum, using a radioimmunoassay; concentrations of hydroxyproline (HYP), pyridinoline (PYD), and deoxypyridinoline (DPD) were analyzed in urine. Hydroxyproline concentration was measured by means of a colorimetric test, whereas PYD and DPD concentrations were quantified by use of high-performance liquid chromatography. RESULTS: In both parts of the study, HYP concentrations increased significantly, compared with values before feeding, until 8 hours after feeding; HYP concentrations then returned to prefeeding values. Concentrations of DPD and PYD decreased from before feeding until 2 PM and then increased until 8 PM. The ICTP concentrations slowly decreased until 4 PM but returned to prefeeding values thereafter. In both parts of the study, concentrations of OC decreased during the day and then increased to reach values similar to those obtained before feeding. CONCLUSIONS: Changes in the concentrations of bone markers were detected throughout the day in the dogs of this study. Increase in HYP concentration most likely was related to feeding. As documented for bone resorption and formation in other species, circadian rhythms were evident for concentrations of DPD, PYD, and OC. Investigators should consider the time of sample collection when measuring these markers.

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.

Comparison of bone resorption markers during hypocalcemia in dairy cows.

This study investigated whether hydroxyproline, deoxypyridinoline, or the carboxyterminal telopeptide of type I collagen could be used as markers to provide evidence of bone resorption during hypocalcemia of dairy cows. Serum concentrations of the amino-terminal propeptide of type III procollagen were also analyzed to study the effect of parturition on type III collagen, which is a component of soft connective tissues. Urine and blood samples were collected on d 1 to 5, on d 9, and d 14 after parturition from 18 cows with symptoms of periparturient paresis (group 1) and 19 healthy control cows without symptoms (group 2). Urine concentrations of hydroxyproline and deoxypyridinoline were measured with a colorimetric assay and an enzyme immunoassay, respectively. Serum concentrations of the amino-terminal propeptide of type III procollagen were measured using a commercially available radioimmunoassay. A radioimmunoassay was developed to analyze serum concentrations of the carboxyterminal telopeptide of bovine type I collagen. The mean corrected urinary hydroxyproline concentrations in group 1 increased from parturition to d 14; concentrations in group 1 were significantly higher for group 2 after d 5. Mean corrected deoxypyridinoline concentrations in urine increased after parturition to reach a peak at d 9, and serum concentrations of the carboxyterminal telopeptide of type I collagen peaked at d 5. However, mean concentrations of deoxypyridinoline and the carboxyterminal telopeptide of type I collagen did not differ significantly between groups. The variation in the behavior of the three markers is likely a reflection of the different phases and aspects of the bone collagen degradation. In conclusion, assays for urinary deoxypyridinoline and serum carboxyterminal telopeptide of type I collagen determinations are useful tools to follow the course of degradation of bone collagen in dairy cows.

[Determination of bone markers in dairy cows with parturient paresis]. / Bestimmung von Knochenmarkern bei Milchkühen mit Gebärparese.

The collagen metabolites hydroxyproline (HYP), deoxypyridinoline (DPD) and pyridinoline (PYD) are suitable markers for bone resorption in humans and several animal species. In a field trial cows with symptoms of periparturient paresis (group A) and healthy control cows without symptoms (group B) were compared and urine and blood samples were collected on day 1, 2, 3, 4, 5, 9 and 14 after parturition. In group A the mean +/- SE serum Ca concentration on day 1 was 1.4 +/- 0.1 mmol/l whereas those of group B were 2.0 +/- 0.1 mmol/l. A significant increase of the corrected urinary HYP concentration was observed from parturition to day 14 (from 2.8 to 8.8 mumol/mmol creatinine) and the concentrations at the different times were higher in group A than in group B. The mean corrected total and free DPD and total PYD concentration in urine increased after parturition to reach a peak at day 9. For DPD and PYD the mean concentrations between the two groups did not differ significantly. The DPD and PYD are useful tools to follow bone resorption in dairy cows, although in our study no difference between the two groups could be found which means that both groups were able to mobilize Ca from bone.

Influence of the dosing frequency of parathyroid hormone-(1-38) on its anabolic effect in bone and on the balance of calcium, phosphorus and magnesium.

The effect of the frequency of administration of synthetic human parathyroid hormone fragment 1-38 [hPTH-(1-38)] on bone formation and on the balance of calcium, phosphorus, and magnesium was investigated in 32 9-week-old female Sprague-Dawley rats, using a randomly complete block design. Rats received subcutaneously during 14 days either the vehicle solution once a day or 50 micrograms hPTH-(1-38)/kg BW once a day at 8:00 a.m., twice a day at 8:00 a.m. and 5:00 p.m. or three times a day at 8:00 a.m., 0:30 p.m., and 5:00 p.m. The balance study was performed during the last 48 h of the hPTH-(1-38) treatment schedule after which femora, tibiae, and lumbar vertebrae were removed for the determination of the dry weight, volume, and contents of Ca, P, Mg, hydroxyproline, and DNA. PTH treatment was associated with a significant increase of the apparent intestinal absorption of Ca, P, and Mg. Mean urinary Ca excretion augmented with the increase of the frequency of dosing. Urinary Ca excretion correlated negatively with the Ca apparent intestinal absorption and with the Ca content of the tibiae in the 2 groups with the highest frequency of dosing. The mean Ca, P, and Mg balances, the mean contents of bone Ca, P, and Mg and the mean bone dry weights were significantly increased with PTH treatment. In contrast to the mean volume of tibiae which was not affected by the PTH administration, the mean volume of the fifth lumbar vertebrae increased with the treatment. With the 2 times and 3 times daily treatments, mean hydroxyproline concentrations in the femora were significantly higher than the control values. An increase of the mean hydroxyproline content of the third lumbar vertebrae was evidenced with the 1 time and 2 times daily treatment, but the mean of the highest frequency of dosing was not different from that of the control group. The DNA content of femoral and of the fourth lumbar vertebrae significantly decreased with the frequency of dosing.

Early effects of short-term parathyroid hormone administration on bone mass, mineral content, and strength in female rats.

The present study was designed to examine the metabolic changes and early effects of short-term parathyroid hormone (PTH) treatment on bone mass, mineral content, and strength. Forty-eight 10-week-old intact female rats were randomized into six groups. The three PTH-treated groups were subcutaneously given PTH 50 microg/kg body weight daily for 5 (PTH5), 10 (PTH10), or 15 (PTH15) days. The three respective time control groups (C5, C10, and C15) were injected with saline solution. In serum, total calcium, alkaline phosphatase, and insulin-like growth factor-I (IGF-I) were analyzed. Bone mass was estimated with wet and dry weights of the femora and hydroxyproline content of the tibiae. Ash weight and calcium, magnesium, and phosphorus contents (determined by AAS) were used to measure femoral mineral content. Bone mineral density (BMD) of the femora was measured using dual-energy X-ray absorptiometry (DXA) and the biomechanical properties of the femoral neck were tested. After 5 days of PTH treatment, some trends of the anabolic actions of PTH could be observed, but there was no significant effect on relevant parameters of bone formation. After 10 days, bone mass, mineral content (assessed by ash weight), and BMD of the PTH-treated rats were significantly increased compared with those of controls. The relative femoral magnesium content of the PTH-treated animals was significantly higher than that of controls. After 15 days, the length of the femora, bone mass, mineral content, BMD, and the width of the femoral neck were increased, and its biomechanical properties were significantly improved in PTH-treated rats compared with the respective time control group. PTH treatment significantly increased circulating alkaline phosphatase and decreased systemic IGF-I concentrations throughout the study. In conclusion, intermittent PTH administration to still growing female rats is anabolic in bone with significant effects already taking place after 10 days of treatment. The effects of PTH consisted of: (1) an increase in bone mass and mineral content with a transient augmentation of relative magnesium content; and (2) improved width and mechanical properties of the femoral neck after 15 days of treatment. These effects are accompanied by an increase in longitudinal bone growth. They are unlikely related to any changes in systemic IGF-I concentrations.

Parathyroid hormone increases bone formation and improves mineral balance in vitamin D-deficient female rats.

The present study was designed to investigate whether enhanced bone formation due to intermittent PTH administration is dependent on vitamin D metabolites. Forty-eight female Sprague-Dawley rats were randomized into four groups: 1) vitamin D-sufficient, saline-injected (+D Sal); 2) vitamin D-sufficient, human (h) PTH-(1-38)-treated (+D PTH); 3) vitamin D-deficient, saline-injected (-D Sal); and 4) vitamin D-deficient, hPTH-(1-38)-treated (-D PTH) animals. The -D diet contained 2% calcium (Ca), 1.25% phosphorus (P), and 20% lactose to maintain normocalcemia and normophosphatemia despite vitamin D deficiency. The +D diet contained 0.8% Ca, 0.5% P, 20% lactose, and 1000 IU/kg vitamin D. After 45 days of either diet, the rats were injected with 50 microg/kg BW PTH or saline, s.c., daily for 2 weeks. Serum Ca, Mg, P, albumin, and creatinine were similar in all groups. PTH administration decreased endogenous PTH concentrations in the -D PTH compared with those in the - D Sal group. Serum alkaline phosphatase activity, bone mass measurements, dual energy x-ray absortiometric analysis of mineral density, and mechanical testing values in vertebrae and femora of the -D Sal animals did not significantly differ from those in +D Sal animals. Moreover, in both diet groups, PTH improved bone biochemical activity (as assessed by serum alkaline phosphatase), bone mass, mineral density, and biomechanical properties. These results indicate that mineral supply, more than vitamin D itself, may be important for normal bone mineralization and to enable PTH to enhance bone formation. A balance study performed during the last 3 days of the experiment revealed that PTH increased apparent intestinal magnesium absorption in the +D group only. Ca and P retention, however, were augmented in both diet groups after PTH treatment. In conclusion, in normocalcemic and normophosphatemic -D rats, PTH treatment reduced the increased endogenous hormone concentration and improved Ca and P retention. Furthermore, PTH may have a vitamin D-dependent influence on intestinal magnesium absorption. Finally, short term PTH treatment is anabolic in bone of vitamin D-deficient rats when adequate mineral amounts are provided in the diet.