Effect of transcutaneous nerve stimulation on microcirculation in intact skin and blister wounds in healthy volunteers.

Healthy non-smoking volunteers participated in two experimental studies in which the circulatory changes induced by transcutaneous nerve stimulation (TENS) were quantified by two different methods. In experimental series 1 (intact skin), nine volunteers were given TENS on the left lower leg for 60 minutes on three occasions at different frequencies each time (2 Hz, 100 Hz, and sham). Changes in blood flow were assessed by laser Doppler imaging technique every five minutes. The mean blood flow increased by 40% during low frequency TENS and by 12% during high frequency TENS. There was no change in mean blood flow during sham stimulation. In experimental series 2 (blister wound), the circulatory changes induced by TENS were studied by intravital video microscopy and computerised image analysis in standard blister wounds on the lower leg. The microcirculatory blood flow, measured as red blood cell velocity (RBC-V) in 5-14 individual capillaries in each wound, was assessed before and during 45 minutes of TENS (2 Hz and 100 Hz). Mean RBC-V increased by 23% during low frequency TENS (n = 6) and by 17% during high frequency TENS (n = 8). The results show that: laser Doppler imaging and intravital video microscopy techniques can be used to study events at the microcirculatory level; the blister wound is an interesting new standard wound for use in clinical studies; and TENS stimulates the peripheral circulation.     

EFFECT OF TRANSCUTANEOUS NERVE STIMULATION ON MICROCIRCULATION IN INTACT SKIN AND BLISTER WOUNDS IN HEALTHY VOLUNTEERS

Healthy non-smoking volunteers participated in two experimental studies in which the circulatory changes induced by transcutaneous nerve stimulation (TENS) were quantified by two different methods. In experimental series 1 (intact skin), nine volunteers were given TENS on the left lower leg for 60 minutes on three occasions at different frequencies each time (2 Hz, 100 Hz, and sham). Changes in blood flow were assessed by laser Doppler imaging technique every five minutes. The mean blood flow increased by 40% during low frequency TENS and by 12% during high frequency TENS. There was no change in mean blood flow during sham stimulation. In experimental series 2 (blister wound), the circulatory changes induced by TENS were studied by intravital video microscopy and computerised image analysis in standard blister wounds on the lower leg. The microcirculatory blood flow, measured as red blood cell velocity (RBC-V) in 5-14 individual capillaries in each wound, was assessed before and during 45 minutes of TENS (2 Hz and 100 Hz). Mean RBC-V increased by 23% during low frequency TENS (n = 6) and by 17% during high frequency TENS (n = 8). The results show that: laser Doppler imaging and intravital video microscopy techniques can be used to study events at the microcirculatory level; the blister wound is an interesting new standard wound for use in clinical studies; and TENS stimulates the peripheral cirulation.     

Bone Mass Is Preserved and Cancellous Architecture Altered Due to Cyclic Loading of the Mouse Tibia After Orchidectomy

Introduction : The study of adaptation to mechanical loading under osteopenic conditions is relevant to the development of osteoporotic fracture prevention strategies. We previously showed that loading increased cancellous bone volume fraction and trabecular thickness in normal male mice. In this study, we tested the hypothesis that cyclic mechanical loading of the mouse tibia inhibits orchidectomy (ORX)‐associated cancellous bone loss. Materials and Methods : Ten‐week‐old male C57BL/6 mice had in vivo cyclic axial compressive loads applied to one tibia every day, 5 d/wk, for 6 wk after ORX or sham operation. Adaptation of proximal cancellous and diaphyseal cortical bone was characterized by μCT and dynamic histomorphometry. Comparisons were made between loaded and nonloaded contralateral limbs and between the limbs of ORX (n = 10), sham (n = 11), and basal (n = 12) groups and tested by two‐factor ANOVA with interaction. Results : Cyclic loading inhibited bone loss after ORX, maintaining absolute bone mass at age‐matched sham levels. Relative to sham, ORX resulted in significant loss of cancellous bone volume fraction (?78%) and trabecular number (?35%), increased trabecular separation (67%), no change in trabecular thickness, and smaller loss of diaphyseal cortical properties, consistent with other studies. Proximal cancellous bone volume fraction was greater with loading (ORX: 290%, sham: 68%) than in contralateral nonloaded tibias. Furthermore, trabeculae thickened with loading (ORX: 108%, sham: 48%). Dynamic cancellous bone histomorphometry indicated that loading was associated with greater mineral apposition rates (ORX: 32%, sham: 12%) and smaller percent mineralizing surfaces (ORX: ?47%, sham: ?39%) in the final week. Loading resulted in greater BMC (ORX: 21%, sham: 15%) and maximum moment of inertia (ORX: 39%, sham: 24%) at the cortical midshaft. Conclusions : This study shows that cancellous bone mass loss can be prevented by mechanical loading after hormonal compromise and supports further exploration of nonpharmacologic measures to prevent rapid‐onset osteopenia and associated fractures.     

Low‐magnitude whole‐body vibration does not enhance the anabolic skeletal effects of intermittent PTH in adult mice

Whole‐body vibration (WBV) is a low‐magnitude mechanical stimulus that may be anabolic for bone, yet we recently found that WBV did not improve bone properties in adult mice. Because intermittent parathyroid hormone (PTH) enhances the anabolic effects of high‐magnitude skeletal loading, we sought to determine the skeletal effects of WBV in combination with PTH. Seven‐month‐old male BALB/c mice were assigned to six groups (n = 13–14/group) based on magnitude of applied acceleration (0 or 0.3 G) and PTH dose (0, 10, or 40 µg/kg/day). Mice were exposed to WBV (0.3 G, 90 Hz, sine wave) or sham loading (0 G) for 15 min/day, 5 days/week for 8 weeks. Vehicle or hPTH (1–34) was administered prior to each WBV session. Whole‐body bone mineral content increased by ～5% from 0 to 8 weeks in the 40 µg/kg PTH group only, independent of WBV loading. Similarly, PTH treatment increased tibial cortical bone volume by ～5% from 0 to 8 weeks, independent of WBV loading. Neither PTH nor WBV stimulated trabecular bone formation. Consistent with the cortical bone effect, tibias from the 40 µg/kg PTH group had significantly greater ultimate force and energy to failure than tibias in the 0 and 10 µg/kg PTH groups, independent of WBV treatment. In summary, 8 weeks of intermittent PTH treatment increased cortical bone volume and strength in adult male BALB/c mice. Daily exposure to low‐magnitude WBV by itself did not improve skeletal properties and did not enhance the PTH effect. No WBV‐PTH synergy was found in this preclinical study. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:465–472, 2011     

PTHrP‐Derived Peptides Restore Bone Mass and Strength in Diabetic Mice: Additive Effect of Mechanical Loading

There is an unmet need to understand the mechanisms underlying skeletal deterioration in diabetes mellitus (DM) and to develop therapeutic approaches to treat bone fragility in diabetic patients. We demonstrate herein that mice with type 1 DM induced by streptozotocin exhibited low bone mass, inferior mechanical and material properties, increased bone resorption, decreased bone formation, increased apoptosis of osteocytes, and increased expression of the osteocyte‐derived bone formation inhibitor Sost/sclerostin. Further, short treatment of diabetic mice with parathyroid hormone related protein (PTHrP)‐derived peptides corrected these changes to levels undistinguishable from non‐diabetic mice. In addition, diabetic mice exhibited reduced bone formation in response to mechanical stimulation, which was corrected by treatment with the PTHrP peptides, and higher prevalence of apoptotic osteocytes, which was reduced by loading or by the PTHrP peptides alone and reversed by a combination of loading and PTHrP peptide treatment. In vitro experiments demonstrated that the PTHrP peptides or mechanical stimulation by fluid flow activated the survival kinases ERKs and induced nuclear translocation of the canonical Wnt signaling mediator β‐catenin, and prevented the increase in osteocytic cell apoptosis induced by high glucose. Thus, PTHrP‐derived peptides cross‐talk with mechanical signaling pathways to reverse skeletal deterioration induced by DM in mice. These findings suggest a crucial role of osteocytes in the harmful effects of diabetes on bone and raise the possibility of targeting these cells as a novel approach to treat skeletal deterioration in diabetes. Moreover, our study suggests the potential therapeutic efficacy of combined pharmacological and mechanical stimuli to promote bone accrual and maintenance in diabetic subjects. © 2016 American Society for Bone and Mineral Research.     

Loading induces site-specific increases in mineral content assessed by microcomputed tomography of the mouse tibia

Adaptation to mechanical loading has been studied extensively in cortical, but not cancellous bone. However, corticocancellous sites are more relevant to osteoporosis and related fracture risk of the hip and spine. We tested the hypotheses that adaptation in a long bone would be greater at cancellous than cortical sites and would depend on the term of daily in vivo cyclic axial loading. We applied compressive loads to the adolescent, 10-week old, male C57BL/6 mouse tibia to examine the skeletal response immediately prior to attainment of peak bone mass. Adaptation was quantified at the completion of either 2-week (n = 8) or 6-week (n = 12) loading terms by directly comparing volumetric bone mineral content between loaded and contralateral limbs by microcomputed tomography. The increase in mineral content was site specific with a greater response found in the corticocancellous proximal metaphysis (14%) than the cortical mid-shaft (2%) after 6 weeks of loading. Furthermore, bone volume fraction and average trabecular thickness of cancellous bone in the proximal tibia increased after 6 weeks by 15% and 12% respectively. Diaphyseal response was only evident proximal to the mid-shaft as indicated by an 8% increase in maximum principal moment of inertia. Both loading terms produced similar results for mineral content, volume fraction, and moments of inertia. Our finding that non-invasive loading increases the bone volume and fraction at a corticocancellous site by as much as 15% motivates exploring the use of mechanical loading to attain greater peak bone mass and inhibit osteoporosis.     

Pulsating fluid flow modulates gene expression of proteins involved in Wnt signaling pathways in osteocytes

Strain‐derived flow of interstitial fluid activates signal transduction pathways in osteocytes that regulate bone mechanical adaptation. Wnts are involved in this process, but whether mechanical loading modulates Wnt signaling in osteocytes is unclear. We assessed whether mechanical stimulation by pulsating fluid flow (PFF) leads to functional Wnt production, and whether nitric oxide (NO) is important for activation of the canonical Wnt signaling pathway in MLO‐Y4 osteocytes. MC3T3‐E1 osteoblasts were studied as a positive control for the MLO‐Y4 osteocyte response to mechanical loading. MLO‐Y4 osteocytes and MC3T3‐E1 osteoblasts were submitted to 1‐h PFF (0.7 ± 0.3 Pa, 5 Hz), and postincubated (PI) without PFF for 0.5–3 h. Gene expression of proteins related to the Wnt canonical and noncanonical pathways were studied using real‐time polymerase chain reaction (PCR). In MLO‐Y4 osteocytes, PFF upregulated gene expression of Wnt3a, c‐jun, connexin 43, and CD44 at 1–3‐h PI. In MC3T3‐E1 osteoblasts, PFF downregulated gene expression of Wnt5a and c‐jun at 0.5–3‐h PI. In MLO‐Y4 osteocytes, gene expression of PFF‐induced Wnt target genes was suppressed by the Wnt antagonist sFRP4, suggesting that loading activates the Wnt canonical pathway through functional Wnt production. The NO inhibitor L‐NAME suppressed the effect of PFF on gene expression of Wnt target genes, suggesting that NO might play a role in PFF‐induced Wnt production. The response to PFF differed in MC3T3‐E1 osteoblasts. Because Wnt signaling is important for bone mass regulation, osteocytes might orchestrate loading‐induced bone remodeling through, among others, Wnts. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:1280–1287, 2009     

Microfluidic enhancement of intramedullary pressure increases interstitial fluid flow and inhibits bone loss in hindlimb suspended mice

Interstitial fluid flow (IFF) has been widely hypothesized to mediate skeletal adaptation to mechanical loading. Although a large body of in vitro evidence has demonstrated that fluid flow stimulates osteogenic and antiresorptive responses in bone cells, there is much less in vivo evidence that IFF mediates loading‐induced skeletal adaptation. This is due in large part to the challenges associated with decoupling IFF from matrix strain. In this study we describe a novel microfluidic system for generating dynamic intramedullary pressure (ImP) and IFF within the femurs of alert mice. By quantifying fluorescence recovery after photobleaching (FRAP) within individual lacunae, we show that microfluidic generation of dynamic ImP significantly increases IFF within the lacunocanalicular system. In addition, we demonstrate that dynamic pressure loading of the intramedullary compartment for 3 minutes per day significantly eliminates losses in trabecular and cortical bone mineral density in hindlimb suspended mice, enhances trabecular and cortical structural integrity, and increases endosteal bone formation rate. Unlike previously developed modalities for enhancing IFF in vivo, this is the first model that allows direct and dynamic modulation of ImP and skeletal IFF within mice. Given the large number of genetic tools for manipulating the mouse genome, this model is expected to serve as a powerful investigative tool in elucidating the role of IFF in skeletal adaptation to mechanical loading and molecular mechanisms mediating this process. © 2010 American Society for Bone and Mineral Research     

Androgen receptor disruption increases the osteogenic response to mechanical loading in male mice

In female mice, estrogen receptor‐alpha (ERα) mediates the anabolic response of bone to mechanical loading. Whether ERα plays a similar role in the male skeleton and to what extent androgens and androgen receptor (AR) affect this response in males remain unaddressed. Therefore, we studied the adaptive response of in vivo ulna loading in AR‐ERα knockout (KO) mice and corresponding male and female single KO and wild‐type (WT) littermates using dynamic histomorphometry and immunohistochemistry. Additionally, cultured bone cells from WT and AR KO mice were subjected to mechanical loading by pulsating fluid flow in the presence or absence of testosterone. In contrast with female mice, ERα inactivation in male mice had no effect on the response to loading. Interestingly, loading induced significantly more periosteal bone formation in AR KO (+320%) and AR‐ERα KO mice (+256%) compared with male WT mice (+114%) and had a stronger inhibitory effect on SOST/sclerostin expression in AR KO versus WT mice. In accordance, the fluid flow‐induced nitric oxide production was higher in the absence of testosterone in bone cells from WT but not AR KO mice. In conclusion, AR but not ERα activation limits the osteogenic response to loading in male mice possibly via an effect on WNT signaling. © 2010 American Society for Bone and Mineral Research     

The P2Y13 receptor regulates extracellular ATP metabolism and the osteogenic response to mechanical loading

ATP release and subsequent activation of purinergic receptors has been suggested to be one of the key transduction pathways activated by mechanical stimulation of bone. The P2Y₁₃ receptor, recently found to be expressed by osteoblasts, has been suggested to provide a negative feedback pathway for ATP release in different cell types. Therefore, we hypothesized that the P2Y₁₃ receptor may contribute to the mediation of osteogenic responses to mechanical stimulation by regulating ATP metabolism by osteoblasts. To test this hypothesis, wild‐type (WT) and P2Y₁₃ receptor knockout (P2Y₁₃R^?/?) mice were subject to non‐invasive axial mechanical loading of the left tibiae to induce an osteogenic response. Micro‐computed tomography analysis showed mechanical loading induced an osteogenic response in both strains of mice in terms of increased total bone volume and cortical bone volume, with the P2Y₁₃R^?/? mice having a significantly greater response. The extent of the increased osteogenic response was defined by dynamic histomorphometry data showing dramatically increased bone formation and mineral apposition rates in P2Y₁₃R^?/? mice compared with controls. In vitro, primary P2Y₁₃R^?/? osteoblasts had an accumulation of mechanically induced extracellular ATP and reduced levels of hydrolysis. In addition, P2Y₁₃R^?/? osteoblasts also had a reduction in their maximal alkaline phosphatase (ALP) activity, one of the main ecto‐enzymes expressed by osteoblasts, which hydrolyzes extracellular ATP. In conclusion, deletion of the P2Y₁₃ receptor leads to an enhanced osteogenic response to mechanical loading in vivo, possibly because of the reduced extracellular ATP degradation by ALP. The augmented osteogenic response to mechanical stimulation, combined with suppressed bone remodeling activities and protection from OVX‐induced bone loss after P2Y₁₃ receptor depletion as previously described, suggests a potential role for P2Y₁₃ receptor antagonist‐based therapy, possibly in combination with mechanical loading, for the treatment of osteoporosis.     

Release of nitric oxide, but not prostaglandin E2, by bone cells depends on fluid flow frequency.

Loading frequency is an important parameter for the stimulation of bone formation in vivo. It is still unclear how the information of external loading characteristics is conveyed to osteoblasts and osteoclasts. Osteocytes are thought to detect mechanical loads by sensing fluid flow through the lacuno-canalicular network within bone and to translate this information into chemical signals. The signaling molecules nitric oxide (NO) and prostaglandin E2 (PGE2) are known to play important roles in the adaptive response of bone to mechanical loads. We have investigated the effects of fluid flow frequency on the production of PGE2 and NO in bone cells in vitro. Pulsatile fluid flow with different frequencies stimulated the release of NO by MC3T3-E1 osteoblasts in a dose-dependent manner. In contrast, PGE2 production was enhanced consistently by all fluid flow regimes, independent of flow frequency. This implies that the NO response may play a role in mediating the differential effects of the various loading patterns on bone.     

Aged mice have enhanced endocortical response and normal periosteal response compared with young‐adult mice following 1 week of axial tibial compression

With aging, the skeleton may lose its ability to respond to positive mechanical stimuli. We hypothesized that aged mice are less responsive to loading than young‐adult mice. We subjected aged (22 months) and young‐adult (7 months) BALB/c male mice to daily bouts of axial tibial compression for 1 week and evaluated cortical and trabecular responses using micro–computed tomography (µCT) and dynamic histomorphometry. The right legs of 95 mice were loaded for 60 rest‐inserted cycles per day to 8, 10, or 12 N peak force (generating mid‐diaphyseal strains of 900 to 1900 µε endocortically and 1400 to 3100 µε periosteally). At the mid‐diaphysis, mice from both age groups showed a strong anabolic response on the endocortex (Ec) and periosteum (Ps) [Ec.MS/BS and Ps.MS/BS: loaded (right) versus control (left), p < .05]. Generally, bone formation increased with increasing peak force. At the endocortical surface, contrary to our hypothesis, aged mice had a significantly greater response to loading than young‐adult mice (Ec.MS/BS and Ec.BFR/BS: 22 months versus 7 months, p < .001). Responses at the periosteal surface did not differ between age groups (p > .05). The loading‐induced increase in bone formation resulted in increased cortical area in both age groups (loaded versus control, p < .05). In contrast to the strong cortical response, loading only weakly stimulated trabecular bone formation. Serial (in vivo) µCT examinations at the proximal metaphysis revealed that loading caused a loss of trabecular bone in 7‐month‐old mice, whereas it appeared to prevent bone loss in 22‐month‐old mice. In summary, 1 week of daily tibial compression stimulated a robust endocortical and periosteal bone‐formation response at the mid‐diaphysis in both young‐adult and aged male BALB/c mice. We conclude that aging does not limit the short‐term anabolic response of cortical bone to mechanical stimulation in our animal model. © 2010 American Society for Bone and Mineral Research     

Trabecular bone adaptation to loading in a rabbit model is not magnitude‐dependent

Although mechanical loading is known to influence trabecular bone adaptation, the role of specific loading parameters requires further investigation. Previous studies demonstrated that the number of loading cycles and loading duration modulate the adaptive response of trabecular bone in a rabbit model of applied loading. In the current study, we investigated the influence of load magnitude on the adaptive response of trabecular bone using the rabbit model. Cyclic compressive loads, producing peak pressures of either 0.5 or 1.0 MPa, were applied daily (5 days/week) at 1 Hz and 50 cycles/day for 4 weeks post‐operatively to the trabecular bone on the lateral side of the distal right femur, while the left side served as an nonloaded control. The adaptive response was characterized by microcomputed tomography and histomorphometry. Bone volume fraction, bone mineral content, tissue mineral density, and mineral apposition rate (MAR) increased in loaded limbs compared to the contralateral control limbs. No load magnitude dependent difference was observed, which may reflect the critical role of loading compared to the operated, nonloaded contralateral limb. The increased MAR suggests that loading stimulated new bone formation rather than just maintaining bone volume. The absence of a dose‐dependent response of trabecular bone observed in this study suggests that a range of load magnitudes should be examined for biophysical therapies aimed at augmenting current treatments to enhance long‐term fixation of orthopedic devices. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 930–934, 2013     

Postoperative TENS pain relief after knee surgery: objective evaluation

A comparison was made between the pain-relieving effect of placebo-transcutaneous electrical nerve stimulation (TENS), high frequency TENS, and epidural analgesia with dilute local anesthetics in 15 patients with open knee surgery. Assessment of pain was compared with the patients' ability to contract their quadriceps muscle; the ability was measured with integrated EMG (IEMG) before and after the different treatments. The results showed that placebo-TENS had no significant effect on either pain perception or on IEMG. High frequency TENS given for 15 min to 20 min decreased pain perception by 50% at rest and by 11% after quadriceps contraction. High frequency TENS increased muscle contraction ability by 305%, compared with the initial contraction before treatment. Epidural injection of a dilute local anesthetic decreased pain perception by 90% at rest and by 67% after contraction, and increased muscle contraction ability by 1,846%. TENS undoubtedly has a place in the postoperative pain treatment, although its effect is not as strong as that of epidural analgesia with local anesthetics. TENS, however, is easy to administer, lacks side effects, and can be administered by the patients themselves.     

Both Resistance and Agility Training Increase Cortical Bone Density in 75- to 85-Year-Old Women With Low Bone Mass: A 6-Month Randomized Controlled Trial

A randomized, controlled, single-blinded 25-wk prospective study was conducted to compare the effects of group-based resistance and agility training on bone, as measured by both dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT), in older women with low bone mass. Ninety-eight community-dwelling women aged 75-85 yr were randomized to one of three experimental groups: resistance training (n = 32), agility training (n = 34), or stretching (sham exercise) (n = 32). Total hip, femoral neck, and trochanteric bone mineral density (BMD) were measured by DXA. Peripheral QCT measurements were performed at the tibia and radius. The pQCT outcome measures at the shaft regions were cortical bone content, cortical bone cross-sectional area, cortical bone density, and density-weighted polar section modulus (SSI). The pQCT outcome measures at the distal sites were total bone content, total bone cross-sectional area, and total bone density. At trial completion, the agility training group significantly increased cortical bone density by 0.5 +/- 0.2% (SE) at the tibial shaft compared with a 0.4 +/- 0.3% loss in the stretching group. The resistance training group significantly increased cortical bone density (1.4 +/- 0.6%) at the radial shaft compared, with a 0.4 +/- 0.5% loss in the agility training group. No significant between-group differences were observed in the other bone outcome measures (by DXA or pQCT). Future research is needed to determine the mechanism(s) responsible for the observed adaptation of the cortical bone to mechanical loading.     

Combined Effects of Botulinum Toxin Injection and Hind Limb Unloading on Bone and Muscle

Bone receives mechanical stimulation from two primary sources, muscle contractions and external gravitational loading; but the relative contribution of each source to skeletal health is not fully understood. Understanding the most effective loading for maintaining bone health has important clinical implications for prescribing physical activity for the treatment or prevention of osteoporosis. Therefore, we investigated the relative effects of muscle paralysis and reduced gravitational loading on changes in muscle mass, bone mineral density, and microarchitecture. Adult female C57Bl/6J mice (n = 10/group) underwent one of the following: unilateral botulinum toxin (BTX) injection of the hind limb, hind limb unloading (HLU), both unilateral BTX injection and HLU, or no intervention. BTX and HLU each led to significant muscle and bone loss. The effect of BTX was diminished when combined with HLU, though generally the leg that received the combined intervention (HLU+BTX) had the most detrimental changes in bone and muscle. We found an indirect effect of BTX affecting the uninjected (contralateral) leg that led to significant decreases in bone mineral density and deficits in muscle mass and bone architecture relative to the untreated controls; the magnitude of this indirect BTX effect was comparable to the direct effect of BTX treatment and HLU. Thus, while it was difficult to definitively conclude whether muscle force or external gravitational loading contributes more to bone maintenance, it appears that BTX-induced muscle paralysis is more detrimental to muscle and bone than HLU.     

Effects of Increased Muscle Mass on Bone in Male Mice Overexpressing IGF-I in Skeletal Muscles

It has been hypothesized that increase in muscle mass increases the strain on bone resulting in increase in bone mass. The aim of the present study was to determine the effects of increased muscle mass on bone. A colony of transgenic mice that overexpress hIGF-I in muscle, resulting in larger muscles, was established. Six-month-old heterozygous and wild type males were used in this study. The tibial diaphysis, femoral diaphysis and distal femoral metaphysis were analyzed using pQCT densitometry. Heterozygous animals had significantly higher body weight, muscle weight and muscle area when compared with wild type animals. Tibia and femur of the heterozygous mice had significantly higher weights and lengths. The tibial and femoral diaphyses of heterozygous animals had significantly higher cortical bone area, cortical bone mineral content, cortical bone mineral density, cortical thickness and periosteal perimeter when compared with wild type animals. In the distal femoral metaphysis, the total bone area and the cancellous bone area of heterozygous mice were significantly higher than those of wild type animals. In conclusion, increased muscle mass was associated with bigger bones in animals overexpressing IGF-I. Only pure cortical bone increased in both area and mineral content in these animals; cancellous bone, however, increased only in area and not in mineral content and density.     

Bodyloading on atrophied bone and bone mineral content. An experimental study in the rabbit

The quality of a cortical bone, as reflected in the bone mineral content, has been studied in rabbit tibiae during an experimental atrophy process, and following recovery and adaptation to increased loading. Atrophy of the bone was induced by a rigid internal fixation plate applied to the tibia for 12 weeks. During the process of recovery after the plate had been removed, the bone mineral content was studied by means of an ashing procedure. The bone mineral content per unit volume cortical bone remained unchanged both at maximum atrophy and during the subsequent process of recovery.     

Mechanical Stimulation and Intermittent Parathyroid Hormone Treatment Induce Disproportional Osteogenic, Geometric, and Biomechanical Effects in Growing Mouse Bone

Mechanical loading and intermittent parathyroid (iPTH) treatment are both osteoanabolic stimuli and are regulated by partially overlapping cellular signaling pathways. iPTH has been shown clinically to be effective in increasing bone mass and reducing fracture risk. Likewise, mechanical stimulation can significantly enhance bone apposition and prevent bone loss, but its clinical effects on fracture susceptibility are less certain. Many of the osteogenic effects of iPTH are localized to biomechanically suboptimal bone surfaces, whereas mechanical loading directs new bone formation to high-stress areas and not to strain-neutral areas. These differences in localization in new tissue, resulting from load-induced versus iPTH-induced bone accumulation, should affect the relation between bone mass and bone strength, or “tissue economy.” We investigated the changes in bone mass and strength induced by 6 weeks of mechanical loading and compared them to changes induced by 6 weeks of iPTH treatment. Loading and iPTH both increased ulnar bone accrual, as measured by bone mineral density and content, and fluorochrome-derived bone formation. iPTH induced a significantly greater increase in bone mass than loading, but ulnar bone strength was increased approximately the same amount by both treatments. Mechanical loading during growth can spatially optimize new bone formation to improve structural integrity with a minimal increase in mass, thereby increasing tissue economy, i.e., the amount of strength returned per unit bone mass added. Furthermore, exercise studies in which only small changes in bone mass are detected might be more beneficial to bone health and fracture resistance than has commonly been presumed.     

Effects of teriparatide [recombinant human parathyroid hormone (1-34)] on cortical bone in postmenopausal women with osteoporosis.

Treatment with teriparatide (rDNA origin) injection [teriparatide, recombinant human parathyroid hormone (1-34) [rhPTH(1-34)]] reduces the risk of vertebral and nonvertebral fragility fractures and increases cancellous bone mineral density in postmenopausal women with osteoporosis, but its effects on cortical bone are less well established. This cross-sectional study assessed parameters of cortical bone quality by peripheral quantitative computed tomography (pQCT) in the nondominant distal radius of 101 postmenopausal women with osteoporosis who were randomly allocated to once-daily, self-administered subcutaneous injections of placebo (n = 35) or teriparatide 20 microg (n = 38) or 40 microg (n = 28). We obtained measurements of moments of inertia, bone circumferences, bone mineral content, and bone area after a median of 18 months of treatment. The results were adjusted for age, height, and weight. Compared with placebo, patients treated with teriparatide 40 microg had significantly higher total bone mineral content, total and cortical bone areas, periosteal and endocortical circumferences, and axial and polar cross-sectional moments of inertia. Total bone mineral content, total and cortical bone areas, periosteal circumference, and polar cross-sectional moment of inertia were also significantly higher in the patients treated with teriparatide 20 microg compared with placebo. There were no differences in total bone mineral density, cortical thickness, cortical bone mineral density, or cortical bone mineral content among groups. In summary, once-daily administration of teriparatide induced beneficial changes in the structural architecture of the distal radial diaphysis consistent with increased mechanical strength without adverse effects on total bone mineral density or cortical bone mineral content.