Concentric and eccentric isokinetic resistance training similarly increases muscular strength, fat-free soft tissue mass, and specific bone mineral measurements in young women

Women participated in 5 months of unilateral concentric (n = 37) or eccentric (n = 33) isokinetic resistance training of the legs and arms. Limb muscular strength increased as did total body, leg, and arm fat-free soft tissue mass, total body BMC, hip BMD, and forearm BMC and BMD. Isokinetic training benefits bone mineral acquisition.

INTRODUCTION AND HYPOTHESIS

Isokinetic resistance training (IRT) is osteogenic; however, it is not known if concentric or eccentric modalities of IRT produce differential effects on bone. We tested our hypothesis that high-load eccentric versus concentric mode of IRT would produce greater increases in muscular strength, fat-free soft tissue mass (FFSTM), bone mineral density (BMD) and content (BMC) in trained legs and arms.

METHODS

Participants were randomized to 5 months of concentric (n = 37) or eccentric (n = 33) training. The non-dominant leg and arm were used during training; dominant limbs served as controls. Muscular strength was measured with an isokinetic dynamometer; body composition was measured by dual-energy X-ray absorptiometry.

RESULTS

Muscular strength of the concentrically and eccentrically trained leg (18.6%; 28.9%) and arm (12.5%; 24.6%) significantly increased with training. Gains in total body (TB) BMC (p < 0.05) and, in the trained limbs, total proximal femur BMD (p < 0.05) and total forearm BMD (p < 0.05) and BMC (p < 0.05) occurred in both groups. FFSTM increased for the TB and trained leg and arm (all p < 0.001) in both modes.

CONCLUSION

Regardless of the mode, high-intensity, slow-velocity IRT increases muscular strength and FFSTM of trained limbs and imparts benefits to TB BMC and site-specific BMD and BMC in young women.

Relationships among bone mineral density, body composition, and isokinetic strength in young women

The purpose of this study was to examine the relationships among bone mineral density (BMD), body composition, and isokinetic strength in young women. Subjects were 76 women (age: 20 +/- 2 yr, height: 164 +/- 6 cm, weight: 57 +/- 6 kg, body fat: 27 +/- 4%) with a normal body mass index (18-25 kg/m(2)). Total body, nondominant proximal femur, and nondominant distal forearm BMD were measured with dual-energy x-ray absorptiometry. Isokinetic concentric (CON) and eccentric (ECC) strength of the nondominant thigh and upper arm were measured at 60 deg/sec. Fat-free mass (FFM) correlated (P < 0.001) with BMD of the total body (r = 0.56) and femoral neck (r = 0.52), whereas fat mass (FM) did not relate to BMD at any site. Leg FFM, but not FM, correlated with BMD in all regions of interest at the proximal femur. Weak associations were observed between arm FFM and forearm BMD. Isokinetic strength did not relate to BMD at any site after correcting for regional FFM. In conclusion, strong, independent associations exist between BMD and FFM, but not FM or isokinetic strength, in young women.

The influence of patient strength, aerobic capacity and body composition upon outcomes after coronary artery bypass grafting

BACKGROUND

Physical activity, physical fitness and body habitus of patients may be important predictors of outcomes after cardiac surgery. This study sought to quantify physical fitness and determine whether components of fitness enhance the prediction of outcomes in a group of patients undergoing coronary artery bypass grafting.

METHODS

A group of 200 patients were evaluated prior to coronary artery bypass surgery. A Veterans Specific Activity Questionnaire (VSAQ) measured aerobic capacity. A grip dynamometer assessed strength. Skin-fold thickness was used to calculate percent body fat and lean body mass index. Patients were divided into low risk (0-2.5%) and high risk (>2.5%) groups based on the STS National Cardiac Surgery Database prediction of operative mortality.

RESULTS

Patients with both a high percent body fat and a low VSAQ were at higher risk for at least one serious complication (p<0.05) and a longer postoperative length of stay (p<0.05).

CONCLUSION

This study suggests: 1) An index of physical fitness can be obtained preoperatively in cardiac surgical patients; 2) This information aids in the prediction of operative risk.

Effects of combined aerobic and resistance training versus aerobic training alone in cardiac rehabilitation

PURPOSE

This study examined the effects of performing combined resistance and aerobic training, versus aerobic training alone, in patients with coronary artery disease.

METHODS

Thirty-six patients with coronary artery disease were randomized to either an aerobic-only training group (AE) or a combined aerobic and resistance training group (AE + R). Both groups performed 30 minutes of aerobic exercise 3 days/week for 6 months. In addition, AE + R group performed two sets of resistance exercise on seven different Nautilus machines after completion of aerobic training each day. Twenty patients (AE: n = 10; AE + R: n = 10) completed the training protocol with > 70% attendance.

RESULTS

Strength gains for AE + R group were greater than for AE group on six of seven resistance machines (P < 0.05). VO2peak increased after training for both AE and AE + R (P < 0.01) with no difference in improvement between the groups. Resting and submaximal exercise heart rates and rate-pressure product were lower after training in the AE + R group (P < 0.01), but not in the AE group. AE + R increased lean mass in arm, trunk, and total body regions (P < 0.01), while AE increased lean mass in trunk region only (P < 0.01). Percent body fat was reduced for AE + R after training (P < 0.05) with a between group trend toward reduced body fat (P = 0.09). Lean mass gain significantly correlated with strength increase in five of seven resistance exercises for AE + R.

CONCLUSIONS

Resistance training adds to the effects of aerobic training in cardiac rehabilitation patients by improving muscular strength, increasing lean body mass, and reducing body fat.

In vivo internalization of Staphylococcus aureus by embryonic chick osteoblasts

Staphlylococcus aureus is the primary pathogen associated with osteomyelitis, an acute and recurrent bone disease. Internalization of S. aureus by cultured embryonic chick calvarial osteoblasts has been observed. The purpose of this study was to demonstrate that internalization of bacteria by embryonic chick calvarial and tibial osteoblasts occurs in vivo. In initial experiments, 10(8) colony forming units (cfu) of S. aureus, strain UAMS-1 or Cowan 1, were injected subcutaneously under the scalp skin of 17 day chick embryos. After 45 min, calvariae were harvested and processed for transmission electron microscopy (TEM). In subsequent experiments, 10(9) cfu of UAMS-1 were injected into the allantoic sac of 17 day chick embryos via a small opening in the egg shell. After 48 h, calvariae and tibiae were harvested for TEM. S. aureus cells were found in approximately 14% of the calvarial osteoblasts after subcutaneous injection and in 11% of calvarial and tibial osteoblasts following intraallantoic injection. Endosomes were observed in some cells, but most bacteria internalized appeared to be free in the cytoplasm. Osteoblasts with as few as five bacteria had a greater loss of cytoplasmic integrity and a more heterochromatic nucleus than osteoblasts with fewer bacteria or than uninfected osteoblasts. S. aureus cells in calvariae and tibiae were also observed in the cytoplasm of approximately 4% of the osteocytes in mineralized bone matrix. Thus, internalization of S. aureus by osteoblasts in vivo augments the previous observation in vitro. This study has also shown that osteoblasts with few bacteria continue differentiating into osteocytes. Results of these experiments support the hypothesis that internalization of S. aureus by osteoblasts may play a role in the etiology of osteomyelitis.

Staphylococcus aureus infection of mouse or human osteoblasts induces high levels of interleukin-6 and interleukin-12 production

Staphylococcus aureus is the principal causative agent of the inflammatory bone disease osteomyelitis. Unfortunately, the pathogenesis of this often chronic infection is poorly understood and is complicated by the recent observation that bone-forming osteoblasts can harbor S. aureus. Such an infection presents a significant challenge for the host immune response, because osteoblasts are not known to initiate protective cell-mediated immune responses. Cultured mouse and human osteoblasts infected with S. aureus were found to express high levels of interleukin (IL)-6 and IL-12p75, on the basis of complementary investigations demonstrating both S. aureus-induced up-regulation of expression of IL-6 and IL-12p40 mRNA and secretion of IL-6 and IL-12p75 by these cells. Additionally, a quantitative bioassay demonstrated that IL-12p75 secreted after infection was biologically active. These studies are the first to demonstrate induced IL-12p75 expression by osteoblasts and suggest a previously unrecognized role for osteoblasts in initiating immune responses after S. aureus infection.

Mechanisms of Staphylococcus aureus invasion of cultured osteoblasts

Staphylococcus aureus is a bacterial pathogen causing approximately 80% of all cases of human osteomyelitis. This bacterium can adhere to and become internalized by osteoblasts and previous studies indicate that osteoblasts are active in the internalization process. In the current study, we examined the roles of microfilaments, microtubules and clathrin-dependent receptor-mediated endocytosis in the internalization of S. aureus by MC3T3-E1 mouse osteoblast cells. Microfilament and microtubule polymerization was inhibited with cytochalasin D and colchicine. Clathrin-coated pit formation was examined by using the transaminase inhibitor, monodanslycadaverine. The results of this study indicate that mouse osteoblasts utilize actin microfilaments, microtubules and clathrin-coated pits in the internalization of S. aureus; however, microfilaments seem to play the most significant role in the invasion process.

Staphylococcus aureus adhesion to bone matrix and bone-associated biomaterials

Staphylococcus aureus is a frequent cause of orthopedic infections in humans. The bacterium expresses several adhesins that facilitate bacterial binding to the bone matrix and to bone implant biomaterials coated with host plasma constituents. The relevant S. aureus adhesins are termed microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) and specific MSCRAMMs are involved in bone and joint infections.

Comparison of growth and metabolism of avian osteoblasts on polished disks versus thin films of titanium alloy

The purpose of this study was to evaluate the efficacy of using high vacuum, thermal evaporation to deposit thin films of Ti-6Al-4V onto plates for subsequent cell culture investigations. Osteoblastic response to thin-film coated plates was compared to that of cells grown on Ti alloy disk inserts and uncoated culture plates. The Ti alloy disks were polished, cleaned, and passivated following a commercial protocol for orthopedic implants. Mean surface roughness was 262 nm for the Ti alloy disks and 4.756 nm for the coated culture plates. Osteoblasts isolated from 16-day chick embryo calvariae were cultured on polystyrene, thin films, and disks. At confluence, the cells were cultured an additional 48 h and were evaluated for cell number (DNA content), rate of glycolysis (lactate production), alkaline phosphatase activity (ALPase), and collagenous (3H-proline hydroxylation) and noncollagenous protein synthesis. Cell morphology was similar for the controls, disks, and thin-film groups. DNA, lactate, cell layer ALPase, 3H-hydroxyproline, and noncollagenous protein were not different (p > 0.05) among the control, thin-film, and disk groups. Medium ALPase was lower (p < 0.05) in the thin-film group compared to the control group. Although aluminum and vanadium percentages varied from nominal in the thin-film groups (11Al-2V as opposed to 6Al-4V), avian osteoblasts responded similarly to the Ti alloy thin films, disks, and uncoated culture plates for the smooth surfaces tested. The thin-film cell culture system used for elemental material studies appears to offer a promising method for the investigation of cellular response to alloyed biomaterials as well. Proper adjustments in alloy percentages before deposition, however, need to be made if thermal evaporation is utilized.

Extracellular pH modulates the activity of cultured human osteoblasts

The effect of medium pH on the activity of cultured human osteoblasts was investigated in this study. Osteoblasts derived from explants of human trabecular bone were grown to confluence and subcultured. The first-pass cells were incubated in Hepes-buffered media at initial pHs adjusted from 7.0 to 7.8. Osteoblast function was evaluated by measuring lactate production, alkaline phosphatase activity, proline hydroxylation, DNA content, and thymidine incorporation. Changes in medium pH were determined from media pHs recorded at the beginning and end of the final 48 h incubation period. As medium pH increased through pH 7.6, collagen synthesis, alkaline phosphatase activity, and thymidine incorporation increased. DNA content increased from pH 7.0 to 7.2, plateaued from pH 7.2 to 7.6, and increased again from pH 7.6 to 7.8. The changes in the medium pH were greatest at pHs 7.0 and 7.8, modest at pHs 7.4 and 7.6, and did not change at 7.2, suggesting that the pHs are migrating towards pH 7.2. Lactate production increased at pH 7.0 but remained constant from 7.2 to 7.8. These results suggest that in the pH range from 7.0-7.6 the activity of human osteoblasts increases with increasing pH, that this increase in activity does not require an increase in glycolytic activity, and that pH 7.2 may be the optimal pH for these cells.

Extracellular pH modulates the activity of cultured human osteoblasts

The effect of medium pH on the activity of cultured human osteoblasts was investigated in this study. Osteoblasts derived from explants of human trabecular bone were grown to confluence and subcultured. The first-pass cells were incubated in Hepes-buffered media at initial pHs adjusted from 7.0 to 7.8. Osteoblast function was evaluated by measuring lactate production, alkaline phosphatase activity, proline hydroxylation, DNA content, and thymidine incorporation. Changes in medium pH were determined from media pHs recorded at the beginning and end of the final 48 h incubation period. As medium pH increased through pH 7.6, collagen synthesis, alkaline phosphatase activity, and thymidine incorporation increased. DNA content increased from pH 7.0 to 7.2, plateaued from pH 7.2 to 7.6, and increased again from pH 7.6 to 7.8. The changes in the medium pH were greatest at pHs 7.0 and 7.8, modest at pHs 7.4 and 7.6, and did not change at 7.2, suggesting that the pHs are migrating towards pH 7.2. Lactate production increased at pH 7.0 but remained constant from 7.2 to 7.8. These results suggest that in the pH range from 7.0-7.6 the activity of human osteoblasts increases with increasing pH, that this increase in activity does not require an increase in glycolytic activity, and that pH 7.2 may be the optimal pH for these cells.

Calcium hydroxide ameliorates tobramycin toxicity in cultured chick tibiae

Results from this laboratory have shown that bone metabolism is directly related to extracellular pH and that high concentrations of tobramycin released from impregnated polymethylmethacryrate (PMMA) beads has pH-dependent toxic effects on bone. In the present study, beneficial effects of calcium hydroxide-impregnated PMMA were investigated regarding tobramycin toxicity and bone metabolism in chick embryo tibiae in vitro. Also using Ca(OH)2 as a pH regulator, the antibiotic efficacy of tobramycin-impregnated PMMA was evaluated with respect to inhibition of Staphylococcus aureus growth. When Ca(OH)2 was added to PMMA beads containing tobramycin, the beads released hydroxyl and calcium ions into the culture medium and released more antibiotic than beads containing only tobramycin. Bone metabolism (glycolysis, total protein synthesis, and collagen synthesis) was enhanced by Ca(OH)2-impregnated beads with or without tobramycin. Additionally, bacterial growth was inhibited more strongly when S. aureus was incubated with tobramycin- and Ca(OH)2-impregnated PMMA disks than with disks containing only tobramycin. This study demonstrates the feasibility of adding Ca(OH)2 to tobramycin-impregnated PMMA beads as a regulator of local pH and a promoter of bone metabolism for protection of bone when high concentrations of tobramycin are used to treat osteomyelitis. It also suggests that lower concentrations of antibiotic may be effective if Ca(OH)2 and tobramycin are administered simultaneously.

Comparison of human osteoblasts and osteogenic cells from heterotopic bone

Heterotopic ossification is a common complication in which bone develops in soft tissues. Although frequently benign, in some patients the condition becomes painful, restricts motion, and requires surgical intervention. This condition and the cells responsible for it are poorly characterized. Using cell culture techniques, this study compares the performance of osteogenic cells obtained from heterotopic ossification with trabecular osteoblasts isolated from the same patient. Cells isolated from trabecular bone samples and heterotopic ossification sites from six patients were evaluated for osteocalcin production after exposure to 1,25-dihydroxycholecalciferol, alkaline phosphatase activity, typing and synthesis of collagen, cell proliferation, and total protein content. Samples of heterotopic ossification and trabecular bone from three of the patients were examined histologically. Heterotopic ossification derived cells were shown to produce osteocalcin, Type 1 collagen, and alkaline phosphatase activity. They also had increased rates of collagen synthesis, alkaline phosphatase activity, and cell proliferation compared with the normal osteoblasts. Initial tissue from the heterotopic ossification sites showed increased numbers of osteocytes/mm2 compared with normal trabecular bone. Although heterotopic ossification derived cells functioned qualitatively like osteoblasts, they exhibited elevated levels of activities traditionally ascribed to osteoblasts, such as collagen synthesis and alkaline phosphatase activity.

Cigarette smoking and its orthopedic consequences

Cigarette smoking and its ramifications are coming under increasing scrutiny in the field of orthopedic surgery. Smoking has been implicated in impeding bone metabolism and fracture repair, and increasing the rate of postoperative infection and the incidence of nonunion. This article reviews the current body of knowledge on these topics, as well as the potential adverse effects of smoking on wound healing and microsurgical procedures. An in-depth discussion on the pathophysiologic mechanisms of nicotine is also included.

Interaction of tobramycin and pH in cultured chick tibiae

The toxicity of tobramycin at concentrations released from antibiotic-impregnated polymethylmethacrylate beads was determined using cultured embryonic chick tibiae. Because previous results from this laboratory have shown that osteoblast metabolism is inhibited at low pH and because of the potential for a low local pH in infected bone, the antibiotic was tested in medium with pH values from 6.8 to 7.4. Bone metabolism was evaluated by measuring the rates of glycolysis (lactate production), protein synthesis ([3H]proline uptake), and collagen synthesis ([3H]proline hydroxylation). Tobramycin at the concentrations released from the beads (1.0-1.5 mg/ml) contributed to lowering the pH of the medium. At pH 7.4, the antibiotic produced as much as a 30, 39, and 48% decrease in glycolysis, protein synthesis, and collagen synthesis, respectively. Tibiae exposed to tobramycin for 3 days, followed by 2 days without the antibiotic, showed only a partial recovery from its toxic effects. Although tobramycin was relatively less toxic in an acidic environment, the overall metabolic activity of the bones was poorest when the tobramycin concentration was high (2.0 mg/ml) and pH was low (6.8). The results of this study support the following conclusions: (a) tobramycin at high concentrations is toxic to bone, (b) a combination of high tobramycin concentration and low pH in the bone microenvironment may greatly inhibit bone metabolism, and (c) treatment and prevention of osteomyelitis by means of tobramycin-impregnated beads may be augmented by preventing the pH from decreasing in traumatized areas.

Internalization of Staphylococcus aureus by cultured osteoblasts

Staphylococcus aureus is the most common cause of both acute and chronic osteomyelitis; however, the pathogenesis of osteomyelitis is poorly understood. We investigated the ability of S. aureus to associate with chick osteoblasts in culture and have demonstrated internalization of bacteria by the osteoblasts. Two strains of S. aureus were examined that were ingested by osteoblasts to different extents, suggesting strain differences in uptake. Initial association of S. aureus strains with osteoblasts was independent of the presence of matrix collagen produced by the osteoblasts. Internalization of bacteria required live osteoblasts, but not live S. aureus, indicating osteoblasts are active in ingesting the organisms. The bacteria were not killed by the osteoblasts, since viable bacteria were cultured several hours after ingestion.

Toxic effects of wound irrigation solutions on cultured tibiae and osteoblasts

Irrigating wounds with solutions of antiseptic or antibiotic agents is routinely performed in orthopaedic surgery to reduce the incidence of microbial infection. The effects of these agents on healthy bone tissue is unknown. Three commonly employed antiseptic agents (hydrogen peroxide, Betadine solution, Betadine scrub) and one antibiotic solution (bacitracin) were tested on tibiae and osteoblasts isolated from embryonic chicks. Osteoblast function was evaluated by glycolytic energy metabolism (lactate production), cell number (DNA content), and collagen synthesis ([3H]proline hydroxylation). Two series of experiments were performed. To study concentration-related effects, tibiae or cells were exposed to a range of concentrations of the agents (diluted in saline, 0.9% NaCl) for 2 min, rinsed with saline, and incubated for 24 h in medium containing [3H]proline. For the recovery study, the cells were exposed to an effective, but nonlethal, concentration of the antiseptic agents for 2 min, rinsed with saline, and the incubation was continued in complete culture medium for 6, 12, 24, 48, or 72 h with [3H]proline added for the final 6 h. Solutions containing the antiseptic agents were cytotoxic to both bones and cells at concentrations well below those used clinically in irrigation solutions. In contrast, bacitracin at the concentrations tested was safe for osteoblasts and tibiae. These results suggest that the use of irrigation solutions containing H2O2, Betadine solution, or Betadine scrub on exposed bone tissue should be considered with caution.

Lumbar intervertebral disc transfer. A canine study

STUDY DESIGN

Degenerative lumbar disc disease has been implicated as a cause of low back pain. Current treatment options for low back pain involve nonphysiologic fusion of the involved segments and have variable success rates. This is an experimental study of lumbar intervertebral disc transplantation using a canine surgical model.

OBJECTIVES

This study evaluated the feasibility of lumbar disc transplantation and its effects on disc metabolism and morphology.

METHOD

Eight mature mongrel dogs underwent disc transfer surgeries, in which the L2-L3 and L4-L5 intervertebral discs, with a small segment of adjacent superior and inferior vertebral body, were removed and transposed. The transplanted disc were stabilized by plates or by a flexible cable wire construct using Songer cables (DANEK, Inc., Memphis, TN). Unrestricted activity was allowed postoperatively. At 4 months, the spines were harvested, and the transplanted discs were evaluated biochemically and histologically. Intervening nontransplanted discs served as viable controls and thrice-frozen discs served as nonviable controls. Cell viability was assessed by measuring proteoglycan synthesis and DNA content.

RESULTS

Proteoglycan synthesis (35S uptake normalized to DNA content) was maintained in transplanted anulus fibrosus tissue, but was decreased in nucleus pulposus samples (P < 0.05). DNA content was not altered significantly in the transplanted discs. Histologic analysis of the transplanted discs showed revascularization and remodeling of the bone adjacent to the disc and preservation of the lamellar architecture of the anulus fibrosus. The transplanted nucleus pulposus samples had chondrocyte-like cells present, but the staining characteristics of the nucleus material was variable. The contour of the transplanted disc endplates was irregular in all specimens.

CONCLUSIONS

The structure and function of autograft intervertebral discs were maintained after disc transfer surgery; the transplant discs, however, were not completely normal in either their morphology or their metabolic functioning.

Medium pH modulates matrix, mineral, and energy metabolism in cultured chick bones and osteoblast-like cells

The effects of medium pH were tested on calvariae, tibiae, and osteoblast-like cells from chick embryos. Bones and isolated cells were incubated for 5 h or 2 days in Hepes-buffered medium at pH values ranging from 6.8 to 8.2. Osteoblast function was evaluated by lactate production, oxygen consumption, alkaline phosphatase activity (AlPase), Ca and inorganic phosphate (Pi) flux, proline hydroxylation, DNA content, and thymidine incorporation. As medium pH was increased, glycolysis, collagen synthesis, and AlPase increased, while Ca efflux decreased. No effect of pH was seen on mitochondrial activity, Pi efflux, or cell number or proliferation. The importance of glycolysis as an endogenous pH regulator was demonstrated by inhibition with iodoacetic acid or glucose restriction and by adding lactate to the medium. The results suggest that the pH of bone interstitial fluid may be regulated by glycolysis and that changes in pH of this compartment may have marked effects on osteoblast function.

Smokeless tobacco contains an inhibitor of prolyl hydroxylase activity

The effects of smokeless tobacco extract (STE) and various constituents of STE on prolyl hydroxylase activity were determined using enzyme extracted from chick embryos. STE inhibited prolyl hydroxylase activity in a concentration-dependent manner, but nicotine and anabasine had essentially no effect. Enzymatic activity was inhibited by zinc, but not by the other inorganic elements in STE; however, the zinc concentration in STE was not high enough to produce the observed inhibition. The inhibition by STE was diminished by increasing concentrations of 2-oxoglutarate, but not by increasing concentrations of other cofactors. Thus, STE contains an inhibitor of prolyl hydroxylase which may be competitive with 2-oxoglutarate.

Inhibition of cell metabolism by a smokeless tobacco extract: tissue and species specificity

Smokeless tobacco contains a nonnicotine inhibitor of posttranslational modification of collagen (hydroxylation of [3H]proline) by cultured chick embryo tibias and osteoblasts. This study was undertaken to determine whether a methanol extract of smokeless tobacco (STE) containing the inhibitor has similar effects on collagen-producing cells and tissues other than bone. Its effects on DNA synthesis and cell proliferation (incorporation of [3H]thymidine) were also determined. Frontal bone, aorta, and cartilage were incubated for 2 days in medium containing STE. Glycolysis (lactate production) was stimulated by 80% in cartilage, but was not affected in the other tissues; medium alkaline phosphatase activity was unaffected. In frontal bone and cartilage, [3H] hydroxyproline content was decreased 88% and 57%, respectively, and [3H]proline content was decreased 68% and 37%, respectively; neither was affected in the aorta. Confluent cultures of collagen-producing mouse fibroblasts or primary osteoblasts obtained from chick embryo calvarias were incubated for 2 days in medium containing increasing concentrations of STE. Glycolysis and DNA synthesis were not affected. Cell proliferation was unaffected in fibroblasts, but was inhibited (34%) at the highest STE concentration in osteoblasts. AIPase activity was not detectable in fibroblast medium, but was decreased up to 72% in osteoblast medium. Inhibition of collagen synthesis by STE was concentration related in both cell types. At the highest concentration, [3H] hydroxyproline and [3H]proline contents in the cell layers were decreased to the following respective values: fibroblasts 56% and 45% and osteoblasts 50% and 29%, respectively. When incubation with STE was discontinued for 1 day, recovery did not occur. These findings suggest that inhibition of collagen synthesis by STE is not specific for bone, that collagen-producing cells are directly affected, and that recovery is not immediate. This inhibitor could contribute to the periodontal disease often seen in users of smokeless tobacco. Its identification and removal would produce a safer product.

A serum substitute promotes osteoblast-like phenotypic expression in cultured cells from chick calvariae

The effects of medium supplements were tested on embryonic chick calvarial cells in culture. Isolates were divided among four treatment groups: Nu-Serum, chicken serum, fetal bovine serum, or calf serum. Expression of the osteoblastic phenotype was assessed by cell morphology, DNA content, [3H]thymidine incorporation, lactate production, cellular and medium alkaline phosphatase activities, and collagen synthesis. Cells grown in Nu-Serum demonstrated increased alkaline phosphatase activity and a six-fold higher rate of collagen synthesis compared to chicken serum. These cells displayed a polygonal profile, abundant rough endoplasmic reticulum, Golgi apparati, and elaborated an extensive matrix of banded collagen which was well mineralized by day 10 of culture. Although highly mitogenic, chicken serum promoted a more fibroblastoid morphology. Compared to the sera tested, Nu-Serum preferentially promoted the osteoblast-like phenotype in chick calvarial cells in culture.

Nicotine inhibits collagen synthesis and alkaline phosphatase activity, but stimulates DNA synthesis in osteoblast-like cells

Use of smokeless tobacco is associated with various oral lesions including periodontal damage and alveolar bone loss. This study was performed to test the effects of nicotine on bone-forming cells at concentrations that occur in the saliva of smokeless tobacco users. Confluent cultures of osteoblast-like cells isolated from chick embryo calvariae were incubated for 2 days with nicotine added to the culture medium (25-600 micrograms/ml). Nicotine inhibited alkaline phosphatase in the cell layer and released to the medium, whereas glycolysis (as indexed by lactate production) was unaffected or slightly elevated. The effects on medium and cell layer alkaline phosphatase were concentration dependent with maximal inhibition occurring at 600 micrograms nicotine/ml. Nicotine essentially did not affect the noncollagenous protein content of the cell layer, but did inhibit collagen synthesis (hydroxylation of [3H]proline and collagenase-digestible protein) at 100, 300, and 600 micrograms/ml. Release of [3H]hydroxyproline to the medium was also decreased in a dose-dependent manner, as was the collagenase-digestible protein for both the medium and cell layer. In contrast, DNA synthesis (incorporation of [3H]thymidine) was more than doubled by the alkaloid, whereas total DNA content was slightly inhibited at 600 micrograms/ml, suggesting stimulated cell turnover. Morphologic changes occurred in nicotine-treated cells including rounding up, detachment, and the occurrence of numerous large vacuoles. These results suggest that steps to reduce the salivary concentration of nicotine in smokeless tobacco users might diminish damaging effects of this product on alveolar bone.

Comparison of the effects of smokeless tobacco extract with the effects of prolyl hydroxylase inhibitors on collagenous and noncollagenous protein synthesis by osteoblasts

The effects of smokeless tobacco extract (STE) and prolyl hydroxylase inhibitors on protein synthesis by isolated osteoblast-like cells were compared. STE and 2,2'dipyridyl markedly inhibited alkaline phosphatase (Alpase) and [3H]proline hydroxylation without affecting glycolysis (lactate production). However, pyridine 2,5-dicarboxylate (2,5-PDC) did not inhibit [3H] proline hydroxylation, Alpase activity, or glycolysis at moderate concentrations. The [3H]hydroxyproline to [3H]proline ratio in the cell layers demonstrated a concentration-dependent decrease with increasing STE and inhibitor concentrations. In the cell layers, the collagenous protein (CP) content was decreased after exposure to STE, 2,2'dipyridyl, and 2,5-PDC and the noncollagenous protein (NCP) content was decreased after exposure to STE and 2,5-PDC. However, the effects on CP were at least twofold greater than on NCP. Similar results were observed regarding protein released to the culture medium. These data demonstrate that STE, like 2,2'dipyridyl, inhibits the hydroxylation of proline and the synthesis of collagenase-digestible protein.

Interrelationships of vitamin D, bone metabolism and blood calcium concentration in the chick

It is not known if the effects of vitamin D deficiency on chick bone are due to direct actions of the vitamin or if they are secondary to other changes, such as hypocalcemia. Day-old cockerels were fed either a rachitogenic diet containing no Ca (-D-Ca), 1.4% Ca (-D), or 3% Ca (-DHiCa) and given corn oil (-D groups) or vitamin D3 in corn oil (+D and +D-Ca) p.o. for up to 21 days. Radii were harvested and incubated for 6-8 h in a defined medium. Medium samples were taken every 2 h and analysed for Ca, Pi and lactate. Some bones were incubated in a respirometer to measure O2 consumption. Compared to +D, -D birds showed evidence of D deficiency by decreased plasma Ca concentration (35%), bone and body weight (43%) and Ca release from bone (70%) and by histological changes in bone characteristic of rickets. Increases were seen in total and bone alkaline phosphatase activity in plasma (270 and 706%, respectively), Pi release (23%), O2 consumption (23%) and lactate production (52%) by the -D radii. The marked hypocalcemia seen in the -D chicks did not occur in -DHiCa birds. Nevertheless, bone and body weights were decreased in this group and bone lactate production, O2 consumption and total and bone alkaline phosphatase in plasma were increased. Rachitic bone lesions were only partially corrected by the high-Ca diet. Release of Ca and Pi from the -DHiCa bone was not different than from +D radii. Comparing +D-Ca and -D-Ca groups with +D chicks, both were hypocalcemic with decreased bone weight, body weight and bone Ca release, while showing elevated lactate production and Pi release. The only difference between the +D-Ca and -D-Ca groups was a 50% decrease in Ca release by -D-Ca bone. The results suggest that in chicks: (1) some, but not all, of the effects of vitamin D deficiency on bone can be corrected by normalizing plasma Ca and (2) evaluation of the effects of vitamin D deficiency on bone may require hypocalcemia, since some responses are masked by normocalcemia.

Short-term storage of freshly harvested bone

An in vitro study was designed to test effects of various graft storage media on glucose metabolism and collagen synthesis of embryonic chick tibiae, using these variables as indices of bone cell viability. Normal saline solution, distilled water, and 5% dextrose in lactated Ringer's solution were evaluated after a 5-hour incubation and again after a 3-day recovery period in a complete culture medium. The study suggests that bone grafts may be stored in normal saline solution or 5% dextrose in lactated Ringer's solution for up to 5 hours. Normal saline solution is recommended because of fewer deleterious effects. Distilled water should not be used as a storage medium for bone grafts.

Smokeless tobacco contains a nonnicotine inhibitor of bone metabolism

The effects of smokeless tobacco on bone were investigated using tibiae from chick embryos. The bones were cultured in nicotine (15-1500 micrograms/ml) or in smokeless tobacco extract (STE, 15 mg tobacco/ml culture medium) and the effects on bone glucose metabolism (oxygen consumption and lactate production) and collagen synthesis ([3H]proline hydroxylation) were tested in vitro. Only the highest concentration of nicotine tested produced substantial effects as demonstrated by decreased oxygen consumption and [3H]hydroxyproline content (82 and 90%, respectively) and by a 15% increase in lactate production. Results with STE, which contained nicotine concentrations ranging from 104 to 125 micrograms/ml, showed similarly reduced [3H]hydroxyproline content (90%), but oxygen consumption was only reduced 36%, while lactate production was elevated 60%. The ability of the bones to recover from treatment with STE was demonstrated by increased oxygen consumption and [3H]hydroxyproline content (18 and 78%, respectively) and decreased lactate production (47%) compared to the STE-treated bones. These findings suggest the following conclusions: (1) both nicotine and STE at concentrations found in the saliva of smokeless tobacco users stimulate glycolysis and markedly inhibit bone collagen synthesis and mitochondrial activity; (2) effects of STE on bone are not due to nicotine; and (3) under the conditions studied, bone partially recovers from the effects of STE.

Hydrogen peroxide inhibits glucose metabolism and collagen synthesis in bone

Effects of H2O2 on bone were evaluated in an organ culture system. Tibiae from chick embryos were incubated for up to 3 days in culture medium containing 0.07 to 20 mM H2O2. Glucose metabolism was monitored by measuring lactate production and oxygen consumption, and collagen synthesis was determined by hydroxylation of proline. In addition to markedly inhibiting these parameters, H2O2 also decreased bone weight and alkaline phosphatase activity. Multiple exposures to H2O2 were somewhat more effective than a single exposure. Since H2O2 inhibits bone at low concentrations in vitro, the results suggest that the potential for harmful effects of H2O2 in the oral cavity should be investigated.

1,25-Dihydroxyvitamin D3 decreases alkaline phosphatase activity in cultures of embryonic chick tibiae

The influence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on the alkaline phosphatase (AlPase) activity in cultures of chick embryo tibiae was determined. A dose-related, decreased release (30-47%) of AlPase from the bones was seen with the metabolite at 0.05-0.5 ng/ml of medium with a similar effect on the bone content of enzyme. The highest dose (1 ng/ml) decreased the bone content by 38% without further effect on AlPase release. Combining a low level of 1,25(OH)2D3 (0.05 ng/ml) with parathyroid hormone (PTH, 1 U/ml) reduced release of enzyme additively, but caused no greater decrease in bone content of activity than PTH alone. No effects of 24,25-dihydroxyvitamin D3 [24,25(OH)2D3, 0.5 ng/ml] on release or bone content of AlPase were found when this metabolite was added alone or in combination with PTH; however, 24,25(OH)2D3 did prevent the inhibition of release of AlPase when added with 1,25(OH)2D3. After a 1-day exposure to 1,25(OH)2D3, continued incubation in metabolite-free medium resulted in an 89% increase in bone content of AlPase. The results suggest that 1,25(OH)2D3, as well as PTH, may have regulatory roles in bone growth through their effects on AlPase.

Inhibition of net calcium efflux from bone by ethanol in vitro

Ethanol administered to animals is known to cause hypocalcemia. This investigation was undertaken to evaluate direct early effects of ethanol on the net fluxes of Ca2+ and inorganic phosphate (Pi) into or out of bone using tibiae from 13-day-old chick embryos and 8-day-old suckling rats in vitro. When chick bones were incubated with ethanol in the medium (10 microliters/ml), net Ca2+ efflux was decreased 19, 22, 27, and 31% at 2, 4, 6, and 8 h, respectively. Metabolically inhibited bones showed a net influx rather than efflux of Ca2+ and were not further affected by ethanol. The ethanol had no consistent effect on net Pi efflux and slightly reduced lactate production. At three doses of ethanol (3, 10, and 30 microliters/ml of medium) the reduction of Ca2+ efflux was dose related in both chick and rat bones. Ethanol completely inhibited parathyroid hormone-stimulated, net Ca2+ efflux from chick bones, even at ethanol levels that by themselves did not affect Ca2+ efflux. These findings are consistent with the hypothesis that the hypocalcemia in ethanol-treated animals may be due in part to inhibition of net Ca2+ efflux from bone.

Magnesium promotes both parathyroid hormone secretion and adenosine 3',5'-monophosphate production in rat parathyroid tissues and reverses the inhibitory effects of calcium on adenylate cyclase

Reduced extracellular Ca2+ is known to promote PTH secretion, while severe Mg2+ depletion has the opposite effect. We have correlated the effects of Mg2+ and Ca2+ on parathyroid hormone (PTH) secretion and cAMP accumulation by rat parathyroid tissues in vitro with the effects of these two metals on adenylate cyclase activity in broken membrane preparations. PTH secretion was maximal at 0.5 mM Ca2+, falling to low levels as the Ca2+ concentration was increased to 2.5 mM. Deletion of Mg2+ from the medium resulted in a marked decrease in PTH secretion at any given Ca2+ concentration. At a constant Ca2+ concentration of 1 mM, both PTH secretion and cAMP production rose to maximal rates as the Mg2+ concentration was increased from 0 to 2 mM. The adenylate cyclase of rat parathyroid membranes was stimulated by both GTP and guanyl-5'-yl-imidodiphosphate [Gpp(NH)p]. EDTA-treated membranes could not be stimulated by Gpp(NH)p. Repletion with Mg2+ was more effective than repletion with Ca2+ in restoring responsiveness to the guanine nucleotide. When membranes were maximally preactivated by Gpp(NH)p and then assayed in the presence of variable concentrations of metal ions, enzyme activity was directly inhibited by Ca2+ and stimulated by Mg2+. Adenylate cyclase sensitivity to Ca2+ inhibition was dependent upon the Mg2+ concentration; in the presence of 0.6 mM Mg2+ a 50% inhibition was produced by 0.05 mM Ca2+, while in the presence of 8 mM Mg2+ a 10-fold higher Ca2+ concentration was required for a similar inhibitory effect. The results suggest that Ca2+ may decrease PTH secretion at least in part by a direct inhibition of adenylate cyclase. Mg2+ may promote PTH secretion either by enhancing the activation of adenylate cyclase by endogenous guanine nucleotides or by competing with Ca2+ for binding to a distinct regulatory site on the enzyme.

Hypocalcemic, hypophosphatemic rickets in rat pups suckling vitamin D-deprived mothers

The effects of maternal vitamin D deprivation on rat pups were examined in terms of serum levels of Ca, phosphorus (P), and 25-hydroxyvitamin D (250HD), ash content, and histological appearance of long bones. In each of 10 experiments, litters of 8--10 young were examined at 2 or 3 different ages within the range of 5--57 days. Pregnant mothers were fed a diet containing 0.4% Ca, and 0.4% P and either no vitamin D(--D) or 5 IU D3/g diet (+D). Mothers fed the --D diet developed marked hypocalcemia (4--5 mg/dl) during lactation, but no change in milk Ca or P. The earliest changes in pups suckled by mothers on --D diets compared to pups suckled by mothers on +D diets were significant reductions at 8 days in serum P (6--12% in 3 of 5 experiments) and in serum 250HD3. By the 15th day, serum 250HD3 was undetectable, body weight was reduced by 26%, serum Ca was reduced by 9%, and serum P was reduced by 15%. During the following 10 days, when gradual weaning took place, serum Ca decreased progressively, serum P returned to normal, serum Mg became elevated, bone ash (as percent of dry weight of tibia) was decreased, and decalcified sections of the proximal end of the tibia revealed irregularity and widening (1.5- to 3-fold) of the hypertrophic cartilage layer and the metaphyseal trabeculae. All of these changes were also prominent in 8-week-old --D rats. The results indicate that rat pups suckling vitamin D-deprived mothers can develop biochemical evidence (including hypophosphatemia) as well as histological evidence of vitamin D deficiency similar to that of human vitamin D deficiency rickets. This is in contrast to rats deprived of vitamin D after weaning, who do not develop hypophosphatemia or characteristic histological evidence of rickets unless deprived of P as well as vitamin D.

Effects of calcium and cyclic nucleotides on rat calcitonin and parathyroid hormone secretion

Recently we developed a system for studying concurrent secretion of calcitonin (CT)and parathyroid hormone(PTH)in vitro from single rat thyroparathyroid gland complexes. In the present study, mechanisms involved in secretion of CT and PTH were explored by altering the medium [Ca ] and by using the Ca antagonist, verapamil. We also re-examined the idea that cyclic nucleotides may help regulate secretion of these hormones and attempted to determine if effects of cyclic nucleotides might be altered by changes in medium [Ca]. Thyroparathyroid glands from 8-day-old rats were incubated in serum-free medium for 8h, and CT and PTH levels in the medium were measured by radioimmunoassays. We show for the first time that: (1) although low [Ca] is well known to promote PTH release, some extracellular Ca is needed for PTH secretion to occur at a maximal rate; (2) inhibition of Ca entry into cells with verapamil mimics the effects of low medium Ca on both CT and PTH release; and (3) cyclic nucleotides may exert their effects on secretion of CT and PTH at least in part via effects on Ca entry into cells.

Magnesium and the mineral metabolism of chick embryo tibiae in organ culture

Using bone organ culture techniques, three concentrations of magnesium were evaluated for their effects on the mineral mass of embryonic chick tibiae incubated for 3 days with or without a metabolic inhibitor (1 mM iodoacetic acid) added to the media. Varying the medium Mg level from 0.3 to 3.0 mM had little effect on the net increase in mineral in live bones (without the inhibitor), but in dead tibiae (with the inhibitor) there was a marked net decrease in mineral deposition with increasing Mg concentration. Bone Mg mass varied directly with the level of Mg in the medium regardless of whether or not the tibiae were inhibited. Responsiveness to parathyroid hormone (PTH) with regard to mineral loss and increased lactate production was not affected by Mg even in tibiae incubated in Mg-free media. However, PTH-treated bones cultured in Mg-free media had a significantly elevated Mg mass, suggesting that the hormone may have a Mg-conserving effect on bone during severe Mg deficiency. The findings of this study support the hypothesis that bone cells regulate the level of Mg to which newly forming mineral is exposed and that PTH-responsiveness in embryonic chick tibiae is not dependent on the ambient Mg concentration.

Influence of dietary vitamin D3 on the circulating concentration of its active metabolites in the chick and rat

Plasma concentrations of 25-hydroxyvitamin D3 (25-OHD3) and 1 alpha,25-dihydroxyvitamin D3 (1 alpha, 25-(OH)2D3) in growing chicks and weanling rats were measured by a new radioreceptor assay to determine the effects of varying dietary levels of vitamin D3. The plasma concentration of 25-OHD3 fell from 14.1 ng/ml in 1-day-old chicks to undetectable levels after 3 weeks on a rachitogenic diet. Circulating 1 alpha,25-(OH)2D3 hormone also decreased from 8.9 ng/100 ml to undetectable levels at 3 weeks in these chicks. Chicks receiving an optimal supplement of vitamin D3 (1.4 IU/g diet) for three to four weeks had plasma 25-OHD3 and 1 alpha,25-(OH)2D3 levels of 21-35 ng/ml and 5.1-7.5 ng/100 ml, respectively. Nutritional supplementation with a 50-fold excess of vitamin D3 (70 IU/g diet) elicited a substantial increase in plasma 25-OHD3 to 87-130 ng/ml, while plasma 1 alpha,25-(OH)2D3 was not increased. Increasing dietary calcium from 1.4 to 2.8% did not alter the circulating level of vitamin D3 metabolites in chicks fed 1.4 IU of vitamin D3/g diet. Direct measurement of the renal 25-OHD3-1 alpha-hydroxylase in vitro, showed that lowering dietary calcium or exclusion of vitamin D3 stimulated the biosynthesis of 1 alpha,25-(OH)2D3, but raising calcium did not alter the enzyme activity. It is concluded that the circulating concentration of the 1 alpha,25-(OH)2D3 hormone in the chick is unaffected by abnormally high intakes of vitamin D3 or calcium, but the renal production of the hormone increases during vitamin D3 or calcium deprivation. Additional studies in rats fed a diet supplemented with either 2 or 1000 IU of vitamin D3/g verify that the circulating concentration of 25-OHD3 is markedly increased when the dietary intake of vitamin D3 is elevated. Moreover, 1 alpha,25(OH)2D3 is not increased under these conditions, but actually falls significantly when the dietary level of vitamin D3 is raised from 2 to 1000 IU/g. These studies in both the chick and rat indicate that dietary vitamin D3 excess enhances circulating 25-OHD3, probably because the vitamin D3-25-hydroxylase enzyme is not strigently controlled. The fact that the circulating 1 alpha,25-(OH)2D3 is not concomitantly increased may reflect either decreased synthesis or increased utilization of the 1 alpha,25-(OH)2D3 sterol.

Electron microscopic localization of lactate dehydrogenase in osteoclasts of chick embryo tibia

Lactate dehydrogenase (LDH) was localized in osteoclasts of fixed and unfixed 19-day chick embryo tibias using a copper ferrocyanide capture reaction and osmiophilic polymer generation. This study revealed that: (I) LDH activity in fixed, briefly rinsed osteoclasts was associated principally with limiting membranes of cytoplasmic vacuoles and vesicles and with the plasma membrane; (2) LDH activity in unfixed osteoclasts was associated only with mitochondria; and (3) some mitochondria were stained in fixed tissue given a long rinse. These results indicate that: cytoplasmic LDH diffused out of unfixed tissue; mitochondrial LDH was inactivated by formaldehyde in fixed tissue; and formaldehyde-inhibited mitochondrial LDH can be reactivated by a long rinse. Although the vesicles that stained for LDH activity were found in all parts of the cell, they were concentrated near the ruffled border, and there is evidence that they contained material from the bone surface. These results suggest that the LDH associated with cytoplasmic vesicles of the osteoclasts may be important in processing of material resorbed from the bone surface and that osteoclasts mitochondria may utilize lactate from the bone fluid for energy production.

Effects of dietary vitamin D and calcium on lysyl oxidase activity in chick bone metaphyses

Activity of lysyl oxidase, an enzyme responsible for production of aldehydic precursors for lysine-derived collagen crosslinks, was measured in tibial metaphyses from chicks receiving different dietary levels of vitamin D and Ca for 2 weeks after hatching. Enzyme activities were increased twofold in D-deficient chicks compared to activities from chicks receiving control levels of vitamin D. Addition of Ca to the D-deficient diet had no effect on lysyl oxidase activity. It is suggested that vitamin D may play a role in the age-related decrease in lysyl oxidase activity that normally occurs in chick bone.

The effect of vitamin D on the structural crosslinks and maturation of chick bone collagen

The quantitative relationships were determined between the structural crosslinks, dihydroxylysinonorleucine (Lys(OH)2-Nle) and hydroxylysinonorleucine (Lys (OH) -Nle) in NaB 3H4-reduced diaphyseal bone collagen from 1-, 2-, 3- and 4-week-old chicks fed either a vitamin D-deficient diet, a normal-vitamin D diet or a high-, but non toxic, vitamin D diet from time of hatching. Chicks fed the normal diet showed a progressive decrease in the ratio of Lys(OH)2-Nle/Lys(OH)-Nle with age. This decrease was accelerated in chicks receiving the High-vitamin D diet. In the vitamin D-deficient group, the ratio was higher than controls at 1 and 2 weeks and increased further at 3 and 4 weeks. Similar changes in Lys(OH)2-Nle/Lys(OH)-Nle ratio did not occur in skin collagen. Compared to Control-vitamin D animals, the increased crosslink ratios in the vitamin D-deficient bone collagen occurred prior to changes in growth rate and could not be correlated with lysine hydroxylation or the hypocalcemia seen in this group. These results suggest that the type of crosslink analysis used in this study provides one of the earliest and most sensitive indications of a bone disturbance due to vitamin D deficiency and that vitamin D specifically acts to increase the rate of maturation of bone collagen.

Effects of ethanol on chicks in vivo and on chick embryo tibiae in organ culture

Hypocalcemia previously reported in rats and dogs following oral administration of ethanol may have been caused by a movement of calcium from blood to bone. This present study was undertaken to determine whether ethanol also causes hypocalcemia in chicks and to investigate the direct effects of ethanol on mineral accretion, glucose metabolism and growth of embryonic chick tibiae in an organ culture system. A high dose of ethanol (6 g/kg body wt) produced hypocalcemia, hypermagnesemia and an elevated hematocrit in chicks. Results in vitro were as follows: 1) 5 to 30 mul ethanol/ml medium produced dose-related increases in bone mineral from 58-440%; 2) lactate production was inhibited at all ethanol levels; 3) increased mineral accretion did not occur in ethanol-treated tibiae when iodoacetate was in the medium, but did occur in mechanically disrupted bones exposed to ethanol; and 4) the ethanol response in bone was directly related to the medium phosphate concentration. The results lead to the following conclusions: 1) ethanol has a direct stimulatory effect on bone mineral accretion and an inhibitory effect on bone glucose metabolism in vitro; 2) viable bone cells and an adequate phosphate supply are necessary for the ethanol response, but tissue integrity is not; and 3) the hypocalcemic effect of ethanol in vivo may at least partially result from ethanol-stimulated bone mineral deposition.

The effects of fluoride on the mineralization of embryonic chick tibiae in organ culture

The effects of various concentrations of fluoride on the mineralization of embryonic chich tibiae were studied in vitro. After 4 days incubation in medium with a physiological Ca x PO4 product (1.8 mM2), fluoride promoted a highly significant dose-related enhancement of bone mineralization. In experiments where the medium Ca x PO4 product was varied by changing either Ca or PO4 while keeping the other constant at 1.8 mM, fluoried at 7.5 muM or at 100 muM affected bone mineralization differbntly at low and high products. At medium Ca x PO4 products below 3 mM2, fluoride significantly enhanced bone mineral deposition compared to paired control bones, while at products above 5 mM2, fluoride significantly inhibited bone mineralization. This dual effect of fluoride was observed in both live bones and bones metabolically inhibited by 1 mM iodoacetic acid. Comparison of the effects of fluoride on the mineralization of live and dead bones suggested that the effects are dependent on the cellular control of Ca x PO4 product in the bone extracellular fluid. These findings support the hypothesis that fluoride may play an important role in governing the rate of mineralization in growing bones.

Vitamin D, dietary calcium and parathyroid hormone interactions in chicks

The effect of dietary vitamin D levels on the response to iv injected parathyroid hormone (PTH) was studies in chicks fed one of three diets: D-deficient, Control-D (1.4IU cholecalciferol/g diet), or High-D (70 IU cholecalciferol/g diet) during the first 4 weeks post-hatching. Compared to chicks on Control-D diet, chicks on the D-deficient diet had significantly decreased plasma Ca levels at 2 and 4 weeks and increased plasma P levels at 17 and 21 days. The plasma Ca response to a low dose of PTH (15 USP U/100 g body wt) 1 hr postinjection was normal at 1 week, reduced at 2 weeks and absent at 4 weeks in D-deficient chicks. However, a 4-16-fold higher dose of PTH did elicit a significant, though subnormal, response in this group at 3 and 4 weeks. Chicks fed the D-deficient diet with 2.8% Ca, compared to 1.4% Ca, showed a near normal plasma Ca level and bone ash content and only a small increase in plasma P at 17 and 21 days. However, the plasma Ca response to 15 U PTH/100 g body wt in this group was significantly increased only at 17 days and not at 21 days. In contrast, the hyperphosphatemic response to PTH was not markedly diminished in the D-deficient group, and it was restored to Control-D levels in the D-deficienyt High Ca group. These data suggest that different mechanisms may be involved in the Ca and P responses.

Cellular control of calcium movements in bone. Interrelationships of the bone membrane, parathyroid hormone and alkaline phosphatase

Bone ECF is separated from the general ECF by a functional membrane which has been shown to limit the mineralization of embryonic tibiae and to selectively pump Ca out of the bone ECF. Energy to run this pump may be derived from ATP hydrolyzed by Ca-2+-stimulated ATPase, an enzyme activity which bone alkaline phosphatase may possess. The data suggest that PTH rapidly and selectively increases Ca pumping possibly by increasing ATPase activity in the bone cell cytosol through increased Ca influx and by increasing the intracellular ATPase level through inhibited secretion or excretion of the enzyme.