Browsing by Subject "Bone"
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Item Density and geometry of the third metacarpal in juvenile racehorses treated with exogenous equine somatotropin(Texas A&M University, 2005-11-01) Thomson, Katherine LenoreThe effect of exogenous somatotropin (eST) on bone changes were evaluated in twenty-nine juvenile horses in race training using radiographs of the third metacarpal obtained over the course of a 128 day research project. A biodensitometer was used to measure bone density, and a micrometer was used to measure cortical bone width and medullary cavity width. Fifteen horses were given daily intramuscular injections of eST and fourteen horses were given daily intramuscular injections of sterile saline and served as the control group. By day 128, the increase in total radiographic bone aluminum equivalence (RBAE) was significantly greater in the eST horses than in the control horses. The increases in RBAE in the dorsal and the medial cortices were greater in the eST horses than in the control horses, but these differences were not significant. There was a trend for changes in the ratio of RBAE in the dorsal to palmar and in the medial to lateral cortices to be greater in the eST than in the control horses. By day 128, the increases in both the dorsal and the medial cortical bone width were significantly greater in the eST than in the control group of horses. The eST horses had a significantly greater decrease in dorsal to palmar medullary cavity width, and increase in dorsal to palmar bone diameter than the control group. A computed index of dorsal cortical bone increased significantly more in the eST than in the control group. The stresses applied to bone are greater in the dorso-medial direction in racehorses. To decrease the strain, bone must either increase in bone mineral density, cortical width, and/or bone diameter. Both the eST group and the control group did make these changes in bone over time, but the eST group more effectively remodeled and modeled bone to increase the strength of the third metacarpal than did the control group of horses. In this research project, exogenous somatotropin treatment had a positive effect on the density and geometry of the third metacarpal. These changes are believed to result in a decreased risk of bone injury to the eST treated horses.Item Ibuprofen Administered Pre- or Post- Simulated Resistance Exercise Training Does Not Diminsh Gains in Bone Formation or Bone Mass(2012-02-14) Cunningham, DavidNon-steroidal anti-inflammatory drugs (NSAIDs) have been shown to suppress bone formation when administered before, but not if administered after, an acute bout of mechanical load in rats. The NSAID ibuprofen inhibits cyclooxygenase-2 enzyme, effectively reducing loading induced prostaglandin E2. Whether this affects eventual bone mass gains after multiple sessions of a more physiological mechanical loading regimen is unclear. Therefore, the aim of this study was to test the hypothesis that gains in bone mass and size will be diminished in adult rats given ibuprofen before, but not after, each exercise bout during 20 days of simulated resistance training (SRT). Virgin female Sprague-Dawley rats (5-mo-old, n=29) completed 9 SRT sessions using stimulated muscle contractions under anesthesia at 75% peak isometric strength on alternate days; each of 20 contractions included 1 sec isometric + 1 sec eccentric contraction. Animals were blocked assigned by body weight to one of three groups: 1) ibuprofen (30mg/kg) before exercise, placebo after (I:P)(n=9), 2) placebo before, ibuprofen after (P:I)(n=10) and 3) placebo before and after (P:P)(n=10). In vivo pQCT scans measured changes in total volumetric bone mineral density (vBMD) and total bone mineral content (BMC) at the proximal tibia (cancellous), and total vBMD, total BMC and total area at midshaft tibia on days -7 and 21. Dynamic histomorphometry on both midshaft tibiae (exercised and non-exercised legs) determined mineralizing surface (MS/BS), mineral apposition rate (MAR) and bone formation rate (BFR) on the periosteal surface. There were no differences in body weights among groups at baseline or at day 21. There were significant gains due to SRT, but not ibuprofen treatment in total BMC (+10.50 ? S.D. +8.15%) and total vBMD (+5.29 ? 3.41%) at the proximal tibia. The midshaft tibia exhibited significant gains in total vBMD (6.68 ? 3.03%), total BMC (19.18 ? 5.51%) and total area (11.68 ? 5.49%) due solely to SRT. Furthermore, there were significant increases in periosteal BFR (pre 21.89 ?m3/?m2/d ?2.63; post 717.81 ?m3/?m2/d ?100.57) at the midshaft tibia in the exercised vs. non-exercised legs in all groups but no effect of ibuprofen regimen was detected on these indices of bone formation. In the context of robust increase in BFR and bone mass within this simulated resistance protocol, we were unable to detect any impact of ibuprofen administration on the response to bone loading.Item Impact of Omega-3 Polyunsaturated Fatty Acids on Bone Adaptations to Simulated Resistance Training(2013-04-30) Camp, Kaleigh AnnYoung and ovariectomized animals eating diets rich in omega-3 polyunsaturated fatty acids (n-3 PUFAs) exhibit enhanced bone formation and decrease bone loss, respectively. Eicosapentaenoic acid, an n-3 PUFA found in fish oil, competes with arachidonic acid, an n-6 PUFA, for the cyclooxygenase enzyme, modulating prostaglandin E2, a mediator of bone mechanotransduction. Whether this diet affects bone gains during exercise is not well defined. We hypothesized rats consuming a high n-3 PUFA diet would gain more bone mass with increased bone formation compared to the rats consuming a high n-6 PUFA diet in response to exercise. Virgin Sprague-Dawley rats (5-mo-old, n=18) were assigned to one of two groups: diet rich in corn oil with a n-6:n-3 dietary ratio of 23:1 (O6) or a diet rich in fish oil with an n-6:n-3 dietary ratio of 2:1 (O3). After acclimation, rats completed 9 sessions on alternate days of stimulated muscle contractions at 75% peak isometric strength. Structural and densitometric properties of proximal tibia were measured using in vivo peripheral quantitative CT. Bone formation rate was quantified on the periosteal the surface by standard bone histomorphometry after intraperitoneal injections of calcein. There was a significant main effect due to diet on total volumetric bone mineral density. The diet rich in n-3 PUFAs also allowed for increases in cancellous volumetric bone mineral density at the proximal tibia independent from exercise, as high as 28%. However, proximal tibia metaphysis bone size and shape was not modified due to changes in diet. The training protocol resulted in a robust increase in bone formation, mass, and area at the midshaft tibia. Mineral apposition rate and bone formation rate were significantly greater in the O3 group compared to the O6 group with exercise at the midshaft tibia, ~36% and ~38% respectively. However, the greater bone formation seen in the O3 groups did not translate over to significantly greater bone mass and size as noted by the pQCT results at the same bone site, because there were no detectable differences between groups. In summary, our data demonstrate that a diet high in n-3 PUFAs independently increases bone density at the proximal tibia. In addition, there was enhanced BFR due to a diet high in n-3 PUFAs with exercise, but those increases did not translate over to increased cortical bone mass or size. These data provide evidence that fish oil consumption with and without simulated resistance training exercise can be beneficial to bone outcomes.Item Investigation of Transfer Function Analysis as a Means to Predict Strain on Rat Tibiae from Ankle Torque Waveforms(2010-07-14) Bouse, ScottElectrical Muscle Stimulation (EMS) is used as a countermeasure in animal disuse studies that seek to determine which forms of exercise are most effective in mitigating the effects of disuse atrophy on bone and muscle. Although EMS has been used for many years in our lab and others, few researchers have been able to quantify the levels of strain on rat tibiae during EMS and far fewer have investigated the causal relationship between torque produced at the ankle and strain on the tibia. This thesis sought to investigate the relationship between ankle torque and tibial strain by using a combination of techniques, namely: (1) the addition of rosette strain gages, (2) improved synchronization between ankle torque and tibial strain recordings, and (3) spectral analysis between torque and strain waveforms. In previous work, few methods existed to align torque and strain recordings temporally, as those data were recorded on separate computers and synchronizing events were not captured. Attempting to create a torque-strain crossplot with unsynchronized data does not always yield valid results, so a method of reliably synchronizing those data is required. This thesis developed methods to capture simultaneous (synchronizing) events in both torque and strain recordings and then used those captured events to synchronize data between two computers. Following that synchronization, stiffness calculations were run on torque-strain crossplots to determine linear-model relationships between torque and strain for each method of synchronization. The results from those regressions were then used to determine if one or more synchronization techniques are superior to others, in terms of repeatability or precision. The results of these analyses have shown that using portions of the curves can dramatically increase computing speed while providing high levels of repeatability in synchronization measures. After synchronization techniques had been investigated, 3-element rosette data were used to calculate the principal strains on the surface of the tibiae, and the percentage of principal strains that are accounted for in the axial direction. Since the strain environment changes along the axis of the bone, the principal strain data were plotted versus the distance from proximal epiphysis to rosette gage, and statistical analysis was presented. After rosette data were analyzed, the torque and strain data pairs were fed into a signal processing suite for the purpose of transfer function calculation. Using the synchronization methods outlined above, two means of synchronization were compared in the transfer function program. Results for these analyses demonstrated that transfer functions are slightly dependent on synchronization methods, but that calculated gains do not differ between synchronization techniques. The specific shapes of the transfer functions highlight the relative attenuation/amplification of frequencies in torque and strain signals. Specifically, a range of frequencies, commonly called a band, between 24 and 32Hz is attenuated by the soft tissues and mechanical linkages in the lower leg of rats. This finding gives researchers looking to increase or decrease modeling stimulus to bone a new piece of information about the relative efficiency of EMS exercise. For example, EMS performed at 24-25Hz might produce less strain in the tibia than EMS at 22-23Hz, despite the 22-23Hz stimulation producing marginally less torque.Item Quantifying the strain response in the rat tibia during simulated resistance training used as a disuse countermeasure(2009-05-15) Jeffery, Jay MelvinDisuse of weight bearing bones has been shown to cause bone loss. This poses a health concern for people exposed to microgravity, such as astronauts. Animal studies are used to study factors related to bone loss and countermeasures to prevent bone loss. This study used a hindlimb unloaded (HU) rat model to simulate microgravity and a muscle stimulation countermeasure to simulate resistive exercise. Uniaxial strain gages were implanted on the antero-medial aspect of the proximal tibia to measure the mechanical strain during a typical exercise session. In a separate but parallel study, the exercise was shown to be an effective countermeasure to disuse related bone loss. The current study sought to understand the loading of the bone during the exercise. To determine if the strain response changes during a protocol using this countermeasure, strains were measured on a group of weight bearing animals and a group that were hind limb unloaded and received the countermeasure for 21 days. Strain magnitudes and rates were considered and related to torques at the ankle joint. No significant differences in strain magnitudes were noted between the baseline control group and the hindlimb unloaded group that received the countermeasure. The two kinds of contractions used in an exercise session are isometric and eccentric. The isometric contractions are used to adjust the stimulation equipment for the eccentric contractions, which constitute the exercise. Peak strain levels during the isometric contractions ranged from 900 to 2200 microstrain while the eccentric were 38% lower and ranged from 600 to 1400. Eccentric strain rates were 62% lower than the isometric contractions strain rates. These results indicate that the strain environment during the isometric contractions may be causing more of the osteogenic response than the eccentric contractions, which have previously been thought to be the primary part of the countermeasure.Item Roles for zebrafish trpm7 in growth, skeletogenesis, kidney function and physiological ion homeostasis(2009-12) Elizondo, Michael Reuben; Parichy, David M.; Wallingford, John B.; Fischer, Janice A.; Paull, Tanya T.; Shankland, MartyDevelopment of the adult form requires coordinated growth and patterning of multiple traits in response to local gene activity as well as global endocrine and physiological effectors. In recent years the zebrafish has been utilized as a favorable animal model as a step towards dissecting and better understanding these postembryonic developmental processes. One of the more powerful methods utilized in zebrafish has been the identification of new gene functions through the use of mutant screens. The nutria mutant was recovered from one such screen to identify postembryonic defects in pigment pattern, growth and metamorphosis. These mutants exhibited a pigment cell defect, touch unresponsiveness and severe growth retardation. Here I will discuss my work towards dissecting the underlying developmental processes governing the phenotypic changes in nutria mutants. I characterize gross alterations in skeletal development in nutria mutants that lead to accelerated endochondral ossification but delayed intramembranous ossification. I show that the nutria phenotype results from mutations in trpm7, which encodes a transient receptor potential (TRP) family member that functions as both a cation channel and a kinase. I find trpm7 expression in the fish-specific, ion homeostasis-regulating gland known as the corpuscles of Stannius (CS), and in the mesonephric kidney. I show that mutants also develop kidney stones. Together these results suggest a role for trpm7 activity in regulation of physiological ion homeostasis. Next I confirm that role by identifying late-embryonic and early larval defects in the CS and the kidney, two organs that regulate physiological ion homeostasis. I demonstrate the early larval detection of kidney stones in trpm7 mutants and show that their appearance is presaged by decreased levels of total calcium and magnesium. Furthermore I establish a link between trpm7 function in the CS and stanniocalcin1 (stc1), a potent molecular regulator of calcium homeostasis. Finally, using transgenic overexpression and morpholino-oligonucleotide knockdown, I demonstrate that stc1 modulates calcium and magnesium levels in trpm7 mutant and wild-type backgrounds. Together these analyses establish postembryonic roles for trpm7 function in growth, skeletogenesis, kidney function, and physiological ion homeostasis.Item Volume effect of bone utilizing the staircase test method(2010-12) Jones, Jesse L.; Ekwaro-Osire, Stephen; Maxwell, Timothy T.; Hashemi, JavadThe focus of this research was to determine if the Staircase Test Method could indeed be utilized in order to quantify the fatigue strength of bovine cortical bone and if by utilizing the Staircase Test Method, the volume effect of cortical bone could be determined based on the Weibull fatigue model in addition to the multiplication factors extracted by literature. The experimental research methods used in this study included a fully-reversible tensile compression loading applied to three volumes of 109, 383 and 1158 cubic millimeters using the Staircase Test Method implementing a constant steep size of 5.5 MPa and various starting stress values. Finally, the mean values were obtained for the posterior section of bovine femur for volumes 109 and 383 cubic millimeters. The fatigue strengths for the initial posterior section utilizing the Staircase Test Method resulted in values of 81.58 and 66.0 MPa for volumes one and two, respectively. These values fell within range of previous studies using similar conditions. The results of the mean values obtained utilizing the Staircase Test Method for the anterior section of bovine femur of volumes one, two and three were calculated as 83.42, 74.25 and 68.75 MPa. These values were then plotted and the average relative error for all three volumes was reported to be 12%. This falls within previous experimental error done by a previous study. Conclusively, the Staircase Test Method was proven valid based on the results of the posterior value for the fatigue strength when compared to previous studies. In regards to the volume effect, the posterior fatigue strength was significantly lower than the predictive values for both volumes groups one and two. A corrected Weibull modulus of (m=5.3) for the posterior section used in order to account for the difference in the fatigue strength (~20%) based on the modified Weibull prediction equation. A corrected Weibull modulus was not needed for the anterior section (m=8.0) based on the results obtained when compared to the predicted values using the modified Weibull equation. Thus, the volume effect was clearly represented for both anterior and posterior portions of the femur for bovine cortical bone with the posterior section resulting in a significantly lower Weibull modulus.