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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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33 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Simulated Reentry Heating by Torching

The two first order reentry heating parameters are peak heating flux (W/square cm) and peak heat load (kJ/square cm). Peak heating flux (and deceleration, gs) is higher for a ballistic reentry and peak heat load is higher for a lifting reentry. Manned vehicle reentries are generally lifting reentries at nominal 1-5 gs so that personnel will not be crushed by high deceleration force. A few off-nominal manned reentries have experienced 8 or more gs with corresponding high heating flux (but below nominal heat load). The Shuttle Orbiter reentries provide about an order of magnitude difference in peak heating flux at mid-bottom (TPS tiles, approximately 6 W/square cm or 5 BTU/square ft - sec) and leading edge (RCC, approximately 60 W/square cm or 50 BTU/square ft- sec). Orion lunar return and Mars sample lander are of the same order of magnitude as orbiter leading edge peak heat loads. Flight temperature measurements are available for some orbiter TPS tile and RCC locations. Return-to-Flight on-orbit tile-repair-candidate-material-heating performance was evaluated by matching propane torch heating of candidate-materials temperatures at several depths to orbiter TPS tile flight-temperatures. Char and ash characteristics, heat expansion, and temperature histories at several depths of the cure-in-place ablator were some of the TPS repair material performance characteristics measured. The final char surface was above the initial surface for the primary candidate (silicone based) material, in contrast to a receded surface for the Apollo-type ablative heat shield material. Candidate TPS materials for Orion CEV (LEO and lunar return), and for Mars sample lander (MSL) are now being evaluated. Torching of a candidate ablator material, PICA, was performed to match the ablation experienced by the STARDUST PICA heat shield. Torching showed that the carbon fiberform skeleton in a sample of PICA was inhomogeneous in that sample, and allowed measurements (of the clumps and voids) of the inhomogeneity. Additional reentry heating-performance characterizations of high temperature insulation materials were performed.

Harvey, Gale A.↗
NASA NTRS1987

Histomorphometric analysis of rat skeleton following spaceflight

Male Sprague-Dawley rats were placed in orbit for 7 days aboard the space shuttle. Bone histomorphometry was performed in the long bones and lumbar vertebrae of flight rats and compared with data derived from ground-based control rats. Trabecular bone mass was not altered during the 1st wk of weightlessness. Strong trends were observed in flight rats for decreased periosteal bone formation in the tibial diaphysis, reduced osteoblast size in the proximal tibia, and decreased osteoblast surface and number in the lumbar vertebra. For the most part, histological indexes of bone resorption were normal in flight rats. The results indicate that 7 days of weightlessness are not of sufficient duration to induce histologically detectable loss of trabecular bone in rats. However, cortical and trabecular bone formation appear to be diminished during the 1st wk of spaceflight.

Non-NASA Center↗
NASA NTRS2014

ISS Squat and Deadlift Kinematics on the Advanced Resistive Exercise Device

Visual assessment of exercise form on the Advanced Resistive Exercise Device (ARED) on orbit is difficult due to the motion of the entire device on its Vibration Isolation System (VIS). The VIS allows for two degrees of device translational motion, and one degree of rotational motion. In order to minimize the forces that the VIS must damp in these planes of motion, the floor of the ARED moves as well during exercise to reduce changes in the center of mass of the system. To help trainers and other exercise personnel better assess squat and deadlift form a tool was developed that removes the VIS motion and creates a stick figure video of the exerciser. Another goal of the study was to determine whether any useful kinematic information could be obtained from just a single camera. Finally, the use of these data may aid in the interpretation of QCT hip structure data in response to ARED exercises performed in-flight. After obtaining informed consent, four International Space Station (ISS) crewmembers participated in this investigation. Exercise was videotaped using a single camera positioned to view the side of the crewmember during exercise on the ARED. One crewmember wore reflective tape on the toe, heel, ankle, knee, hip, and shoulder joints. This technique was not available for the other three crewmembers, so joint locations were assessed and digitized frame-by-frame by lab personnel. A custom Matlab program was used to assign two-dimensional coordinates to the joint locations throughout exercise. A second custom Matlab program was used to scale the data, calculate joint angles, estimate the foot center of pressure (COP), approximate normal and shear loads, and to create the VIS motion-corrected stick figure videos. Kinematics for the squat and deadlift vary considerably for the four crewmembers in this investigation. Some have very shallow knee and hip angles, and others have quite large ranges of motion at these joints. Joint angle analysis showed that crewmembers do not return to a normal upright stance during squat, but remain somewhat bent at the hips. COP excursions were quite large during these exercises covering the entire length of the base of support in most cases. Anterior-posterior shear was very pronounced at the bottom of the squat and deadlift correlating with a COP shift to the toes at this part of the exercise. The stick figure videos showing a feet fixed reference frame have made it visually much easier for exercise personnel and trainers to assess exercise kinematics. Not returning to fully upright, hips extended position during squat exercises could have implications for the amount of load that is transmitted axially along the skeleton. The estimated shear loads observed in these crewmembers, along with a concomitant reduction in normal force, may also affect bone loading. The increased shear is likely due to the surprisingly large deviations in COP. Since the footplate on ARED moves along an arced path, much of the squat and deadlift movement is occurring on a tilted foot surface. This leads to COP movements away from the heel. The combination of observed kinematics and estimated kinetics make squat and deadlift exercises on the ARED distinctly different from their ground-based counterparts. CONCLUSION This investigation showed that some useful exercise information can be obtained at low cost, using a single video camera that is readily available on ISS. Squat and deadlift kinematics on the ISS ARED differ from ground-based ARED exercise. The amount of COP shift during these exercises sometimes approaches the limit of stability leading to modifications in the kinematics. The COP movement and altered kinematics likely reduce the bone loading experienced during these exercises. Further, the stick figure videos may prove to be a useful tool in assisting trainers to identify exercise form and make suggestions for improvements

Newby, N.↗
NASA NTRS2013

The Pinnacles of Callisto

Many regions of Callisto feature an unusual landscape consisting of rolling dark plains with interspersed bright knobs (pinnacles) and ridges. In earlier work we interpreted the dark plains as dusty, mass-wasted residue from sublimation from volatile-rich bedrock and the bright knobs (often crater rims) as water ice accumulations at locations sheltered from thermal reradiation from the dusty residue. We simulated evolution of Callisto's craters as a combination of bedrock volatile sublimation, mass wasting of the dark, non-coherent residue, and redeposition of ice, and concluded that the ice pinnacles and ridges might be underlain by tens to hundreds of meters of ice. Here we report the initial work of a new study of pinnacles addressing additional questions: 1) Is there an evolutionary sequence starting, e.g., from a cratered initial surface through growth and formation of a dust mantle and pinnacles, to eventual loss of ice to sublimation resulting in just a dark, dusty surface? 2) What determines the areal density and spatial scale of pinnacles - volatile content of bedrock, crater density, surface age, broad-scale topographic setting? 3) Are pinnacles still forming? Several observations address these questions. In a few places scattered high-albedo blocks approx. 25-60 m in diameter occur in the vicinity of large icy pinnacles. We interpret these blocks to be remnants from the collapse of tall pinnacles that were undermined by mass wasting. Some high-relief icy knobs have developed a skeletonized planform due to mass wasting by avalanching, or perhaps to seeding of new sites of ice deposition on mass-wasted ice blocks. Some areas nearly lack fresh craters with well-defined ejecta and ice-free rims. This may imply rapid transformation of fresh craters by sublimation, mass wasting, and ice reprecipitation. In other areas small sharp-rimmed craters occur which lack ice pinnacles, but the craters nonetheless lack visible ejecta sheets. Our preliminary interpretation is that mass wasting is very efficient on Callisto, or alternatively the dust cover is very thick and lacks competent coarse materials.

bedrock volatile sublimation↗
NASA NTRS1998

The effects of twelve weeks of bed rest on bone histology, biochemical markers of bone turnover, and calcium homeostasis in eleven normal subjects

This study was undertaken to examine the effects of 12 weeks of skeletal unloading on parameters of calcium homeostasis, calcitropic hormones, bone histology, and biochemical markers of bone turnover in 11 normal subjects (9 men, 2 women; 34 +/- 11 years of age). Following an ambulatory control evaluation, all subjects underwent 12 weeks of bed rest. An additional metabolic evaluation was performed after 12 days of reambulation. Bone mineral density declined at the spine (-2.9%, p = 0.092) and at the hip (-3.8%, p = 0.002 for the trochanter). Bed rest prompted a rapid, sustained, significant increase in urinary calcium and phosphorus as well as a significant increase in serum calcium. Urinary calcium increased from a pre-bed rest value of 5.3 mmol/day to values as high as 73 mmol/day during bed rest. Immunoreactive parathyroid hormone and serum 1,25-dihydroxyvitamin D declined significantly during bed rest, although the mean values remained within normal limits. Significant changes in bone histology included a suppression of osteoblastic surface for cancellous bone (3.1 +/- 1.3% to 1.9 +/- 1.5%, p = 0.0142) and increased bone resorption for both cancellous and cortical bone. Cortical eroded surface increased from 3.5 +/- 1.1% to 7.3 +/- 4.0% (p = 0.018) as did active osteoclastic surface (0.2 +/- 0.3% to 0.7 +/- 0.7%, p = 0.021). Cancellous eroded surface increased from 2.1 +/- 1.1% to 4.7 +/- 2.2% (p = 0.002), while mean active osteoclastic surface doubled (0.2 +/- 0.2% to 0.4 +/- 0.3%, p = 0.020). Serum biochemical markers of bone formation (osteocalcin, bone-specific alkaline phosphatase, and type I procollagen extension peptide) did not change significantly during bed rest. Urinary biochemical markers of bone resorption (hydroxyproline, deoxypyridinoline, and N-telopeptide of type I collagen) as well as a serum marker of bone resorption (type I collagen carboxytelopeptide) all demonstrated significant increases during bed rest which declined toward normal during reambulation. Thus, under the conditions of this study, the human skeleton appears to respond to unloading by a rapid and sustained increase in bone resorption and a more subtle decrease in bone formation.

NASA Discipline Musculoskeletal↗
NASA NTRS2003

Hindlimb unloading has a greater effect on cortical compared with cancellous bone in mature female rats

This study was designed to determine the effects of 28 days of hindlimb unloading (HU) on the mature female rat skeleton. In vivo proximal tibia bone mineral density and geometry of HU and cage control (CC) rats were measured with peripheral quantitative computed tomography (pQCT) on days 0 and 28. Postmortem pQCT, histomorphometry, and mechanical testing were performed on tibiae and femora. After 28 days, HU animals had significantly higher daily food consumption (+39%) and lower serum estradiol levels (-49%, P = 0.079) compared with CC. Proximal tibia bone mineral content and cortical bone area significantly declined over 28 days in HU animals (-4.0 and 4.8%, respectively), whereas total and cancellous bone mineral densities were unchanged. HU animals had lower cortical bone formation rates and mineralizing surface at tibial midshaft, whereas differences in similar properties were not detected in cancellous bone of the distal femur. These results suggest that cortical bone, rather than cancellous bone, is more prominently affected by unloading in skeletally mature retired breeder female rats.

NASA Discipline Musculoskeletal↗
NASA NTRS2021

L’Ralph Integration and Testing

This paper describes the plans, flows, key facilities, components and equipment necessary to fully integrate, functionally test, qualify and calibrate the L’Ralph instrument on the Lucy observatory. Lucy is currently in the final design and fabrication phase (phase C) of mission development. It is scheduled to launch out of Cape Canaveral, Florida, in October 2021. Lucy will be the first space mission to study the Trojan asteroids associated with Jupiter, that are thought to be remnants of the primordial material that formed the outer planets. Lucy will fly by and carry out remote sensing on six different Trojan asteroids. The mission takes its name from the fossilized human ancestor (called “Lucy” by her discoverers) whose skeleton provided unique insight into humanity's evolution. Likewise, the Lucy mission will revolutionize our knowledge of planetary origins and the formation of the solar system. L’Ralph is one of the instruments on Lucy and it is provided by the NASA Goddard Space Flight Center (GSFC). L’Ralph is a combined multi-band visible imager (the Multi-spectral Visible Imaging Camera, MVIC, 0.4-0.85 microns) and wedge-filter infrared spectrometer (Linear Etalon Imaging Spectral Array, LEISA, 1-3.6 microns). LEISA will allow the team to look for the absorption lines that serve as the fingerprints for different silicates, ices and organics that likely will be on the surface of the Trojan asteroids. MVIC will take color images of the Trojan asteroid targets, and help determine how active they are. This paper will focus on the Integration and Test (I&T) activities for L’Ralph while it is at the NASA GSFC. L’Ralph has two assemblies, the telescope detector assembly (TDA) and main electronics box (MEB). The TDA is a single telescope feeding two focal planes, MVIC and LEISA. L’Ralph integration consists of assembly and alignment of the telescope, electronics box integration, thermal systems integration and the final assembly and testing. This I&T phase will be followed by the L’Ralph calibration and characterization, environmental tests which include electromagnetic interference (EMI)/electromagnetic compatibility (EMC), vibration with sine sweep, acoustics, shock, thermal balance, thermal vacuum, mass properties and center of gravity determination. This paper will briefly discuss L’Ralph shipment and delivery to the spacecraft vendor for observatory level I&T as well as some launch preparation activities.

Spaceflight Instruments↗
NASA NTRS2003

Disuse exaggerates the detrimental effects of alcohol on cortical bone

BACKGROUND: Alcohol abuse is associated with an increased risk for osteoporosis. However, comorbidity factors may play an important role in the pathogenesis of alcohol-related bone fractures. Suboptimal mechanical loading of the skeleton, an established risk factor for bone loss, may occur in some alcohol abusers due to reduced physical activity, muscle atrophy, or both. The effect of alcohol consumption and reduced physical activity on bone metabolism has not been well studied. The purpose of this study was to determine whether mechanical disuse alters bone metabolism in a rat model for chronic alcohol abuse. METHODS: Alcohol was administered in the diet (35% caloric intake) of 6-month-old male rats for 4 weeks. Rats were hindlimb-unloaded the final 2 weeks of the experiment to prevent dynamic weight bearing. Afterward, cortical bone histomorphometry was evaluated at the tibia-fibula synostosis. RESULTS: At the periosteal surface of the tibial diaphysis, alcohol and hindlimb unloading independently decreased the mineralizing perimeter, mineral apposition rate, and bone formation rate. In addition, alcohol, but not hindlimb unloading, increased endocortical bone resorption. The respective detrimental effects of alcohol and hindlimb unloading to inhibit bone formation were additive; there was no interaction between the two variables. CONCLUSIONS: Reduced weight bearing accentuates the detrimental effects of alcohol on cortical bone in adult male rats by further inhibiting bone formation. This finding suggests that reduced physical activity may be a comorbidity factor for osteoporosis in alcohol abusers.

NASA Discipline Cell Biology↗
NASA NTRS1999

Tensegrity and mechanoregulation: from skeleton to cytoskeleton

OBJECTIVE: To elucidate how mechanical stresses that are applied to the whole organism are transmitted to individual cells and transduced into a biochemical response. DESIGN: In this article, we describe fundamental design principles that are used to stabilize the musculoskeletal system at many different size scales and show that these design features are embodied in one particular form of architecture that is known as tensegrity. RESULTS: Tensegrity structures are characterized by use of continuous tension and local compression; architecture, prestress (internal stress prior to application of external force), and triangulation play the most critical roles in terms of determining their mechanical stability. In living organisms, use of a hierarchy of tensegrity networks both optimizes structural efficiency and provides a mechanism to mechanically couple the parts with the whole: mechanical stresses applied at the macroscale result in structural rearrangements at the cell and molecular level. CONCLUSION: Due to use of tensegrity architecture, mechanical stress is concentrated and focused on signal transducing molecules that physically associate with cell surface molecules that anchor cells to extracellular matrix, such as integrins, and with load-bearing elements within the internal cytoskeleton and nucleus. Mechanochemical transduction may then proceed through local stress-dependent changes in molecular mechanics, thermodynamics, and kinetics within the cell. In this manner, the entire cellular response to stress may be orchestrated and tuned by altering the prestress in the cell, just as changing muscular tone can alter mechanical stability and structural coordination throughout the whole musculoskeletal system.

NASA Discipline Cell Biology↗
NASA NTRS2005

Skeletal phenotype of growing transgenic mice that express a function-perturbing form of beta1 integrin in osteoblasts

Skeletal modeling entails the deposition of large amounts of extracellular matrix (ECM) to form structures tailored to withstand increasing mechanical loads during rapid growth. Specific ECM molecules bind to integrin receptors on the cell surface, thereby triggering a cascade of signaling events that affect critical cell functions. To evaluate the role of integrins during skeletal growth, transgenic mice were engineered to express a function-perturbing fragment of beta1 integrin consisting of the transmembrane domain and cytoplasmic tail under the control of the osteocalcin promoter (TG mice). Thus, transgene expression was targeted to mature cells of the osteoblast lineage, and herein we show that cultured cells resembling osteocytes from 90-day-old TG mice display impaired adhesion to collagen I, a ligand for beta1 integrin. To determine the influence of beta1 integrin on bones that are responsible for providing structural support during periods of rapid growth, we examined the phenotype of the appendicular skeleton in TG mice compared to wild type (WT) mice. According to radiographs, bones from mice of both genotypes between 14 and 90 days of age appeared similar in gross structure and density, although proximal tibiae from 35-90 days old TG mice were less curved than those of WT mice (72-92% TG/WT). Although there were only mild and transient differences in absolute bone mass and strength, once normalized to body mass, the tibial dry mass (79.1% TG/WT females), ash mass (78.5% TG/WT females), and femoral strength in torsion (71.6% TG/WT females) were reduced in TG mice compared to WT mice at 90 days of age. Similar effects of genotype on bone mass and curvature were observed in 1-year-old retired breeders, indicating that these phenotypic differences between TG and WT mice were stable well into adulthood. Effects of genotype on histomorphometric indices of cancellous bone turnover were minimal and evident only transiently during growth, but when present they demonstrated differences in osteoblast rather than osteoclast parameters. Together, these results suggest that integrin signals generated during growth enhance the acquisition of a skeletal mass, structure, and strength to withstand the mechanical loads generated by weight-bearing.

Antigens, CD29/genetics/metabolism↗
NASA NTRS2013

Analyses Made to Order: Using Transformation to Rapidly Configure a Multidisciplinary Environment

Aerospace problems are highly multidisciplinary. Four or more major disciplines are involved in analyzing any particular vehicle. Moreover, the choice of implementation technology of various subsystems can lead to a change of leading domain or reformation of the driving equations. An excellent example is the change of expertise required to consider aircraft built from composite or metallic structures, or those propelled by chemical or electrical thrusters. Another example is in the major reconfiguration of handling and stability equations with different control surface configuration (e.g., canards, t-tail v four-post tail). Combinatorial problems are also commonplace anytime that a major system is to be designed. If there are only 5 attributes of a design to consider with 4 different options, this is already 1024 options. Adding just 5 more dimensions to the study explodes the space to over one million. Even generous assumptions like the idea that only 10% of the combinations are physically feasible can only contain the problem for so long. To make matters worse, the simple number of combinations is only the beginning. Combining the issue of trade space size with the need to reformulate the design problem for many of the possibilities makes life exponentially more difficult. Advances in software modeling approaches have led to the development of model-driven architecture. This approach uses the transformation of models into inferred models (e.g. inferred execution traces from state machines) or the skeletons for code generation. When the emphasis on transformation is applied to aerospace, it becomes possible to exploit redundancy in the information specified in multiple domain models into a unified system model. F1urther, it becomes possible to overcome the combinatorial nature of specifying integrated system behavior by manually combining the equations governing a given component technology. Transformations from a system specification combined with a system-analysis mapping specification enable one-click combination of domain analyses. This is a flexibility that has been missing from many engineering codes, which often entangle design specification and physical examination much more than is required to conduct the analysis. This capability has been investigated and cultivated within the DARPA F6 program by a team of JPL and Phoenix Integration engineers building the Adapatable Systems Design and Analysis (ASDA) framework. By embracing system modeling with SysML and the Query-View-Transformation (QVT) language, the ASDA team has been able to build a flexible, easily reconfigurable framework for building up and solving large tradespaces. Examples of application and lessons learned in building the framework will be described in this paper. In addition, the motivation will be laid for various tool vendors to develop open model description standards while being able to maintain competitive advantage through proprietary algorithms and approaches. These standards will also be compared to the underpinnings of model-driven architecture and the OMG standards of the Meta-Object Facility (MOF), SysML, and QVT.

Cole, Bjorn↗
NASA NTRS2021

Coral Oxygen Isotopic Records Capture the 2015/2016 El Niño Event in the Central Equatorial Pacific

Coral oxygen isotopes (δ^(18)O) from the central equatorial Pacific provide monthly resolved records of El Niño-Southern Oscillation activity over past centuries to millennia. However, calibration studies using in situ data to assess the relative contributions of warming and freshening to coral δ^(18)O records are exceedingly rare. Furthermore, the fidelity of coral δ^(18)O records under the most severe thermal stress events is difficult to assess. Here, we present six coral δ^(18)O records and in situ temperature, salinity, and seawater δ^(18)O data from Kiritimati Island (2°N, 157°W) spanning the very strong 2015/16 El Niño event. Local sea surface temperature (SST) anomalies of +2.4 ± 0.4°C and seawater δ^(18)O anomalies of −0.19 ± 0.02‰ contribute to the observed coral δ^(18)O anomalies of −0.58 ± 0.05‰, consistent with a ∼70% contribution from SST and ∼30% from seawater δ^(18)O. Our results demonstrate that Kiritimati coral δ^(18)O records can provide reliable reconstructions even during the largest class of El Niño events.

Oxygen isotope anomalies↗
NASA NTRS1999

Expression of Novel Gene Products Upregulated by Disuse is Normalized by an Osteogenic Mechanical Stimulus: Evidence for the Molecular Basis of a Low Level Biomechanical Countermeasure for Osteoporosis?

The National Research Council's report entitled: A Strategy for Space Biology and Medical Science, highlighted several areas of fundamental scientific investigation which must be addressed to make long-term space exploration not only feasible, but safe. This "Goldberg Strategy," as well as several subsequent reports published by the NRC's Space Studies Board (e.g., Assessment of Programs in Space Biology and Medicine, Smith et. al., 1991), suggests that the principal hurdle to man's extended presence in space is the osteopenia which parallels reduced gravity. Ironically, the most significant risk to the skeleton may only be realized on return to normal gravitational fields, and full recovery of bone mass may never occur. Effective counter-measures to this microgravity induced bone loss are thus essential. Considering the similarities of space and aging induced osteopenia, an indisputable benefit of such a prophylaxis would be its potential as a treatment for the bone loss which plagues over 25 million people in the U.S. The osteogenic potential of mechanical strain is strongly frequency dependent, with sensitivity increasing up through at least 60 Hz (cycles per second). One hundred seconds per day of a 1 Hz cyclic loading will inhibit disuse osteopenia only if sufficient in magnitude to engender 1000 microstrain (mu(epsilon)) in the tissue. When loading is applied at 30 Hz, however, mechanical strains on the order of 5O mu(epsilon) (approx. 1% of the peak strains which occur in bone during vigorous functional activity), can stimulate bone formation in a duration dependent manner. In longer term animal studies, strains of less than 10 mu(epsilon), induced non-invasively via a whole body vibration, will stimulate bone formation on the surfaces of trabeculae, increase bone density, and improve strength. Finally, preliminary results from a double blind prospective clinical trial shows promise in inhibiting the bone loss which parallels the menopause. Based on these observations, we propose that these high frequency, low magnitude, mechanical strains effectively serve as a "surrogate" for musculoskeletal ground reaction forces, and thus represent an ideal countermeasure to the osteopenia which parallels microgravity conditions. The specific goal of this NASA funded work is to identify genes in bone upregulated by disuse, and to determine the efficacy of an osteogenic mechanical stimulus to downregulate their expression.

Rubin, C.↗
NASA NTRS1996

Skeletal response to corticosteroid deficiency and excess in growing male rats

The study was designed to investigate bone histomorphometric changes induced by corticosteroid deficiency and supplementation at different dose levels in the rat skeleton. Male rats were adrenalectomized (ADX) or sham-operated and divided into six groups. At 2 days after surgery, sham-operated control rats (CON + PLA) and one group of ADX rats (ADX + PLA) were implanted subcutaneously (s.c.) with placebo pellets. ADX rats in the remaining four groups (ADX + C25, ADX + C50, ADX + C100, and ADX + C300) were implanted sc with corticosterone pellets designed to release 25, 50, 100, or 300 mg of the hormone over a 60 day period. Each ADX rat was also implanted sc with an aldosterone pellet (2.5 mg) similarly designed to release its contents over the same time period. All rats were killed at 3 weeks after implantation of pellets. Terminal blood samples were collected for serum biochemistry and the proximal tibial metaphyses (PTM), tibial diaphyses, and first lumbar vertebrae (LV) were processed undecalcified for quantitative bone histomorphometry. A dose-dependent increase in serum corticosterone concentration was observed in ADX rats implanted with hormone pellets. In comparison to CON + PLA rats, ADX + PLA rats had lower cancellous bone volume associated with a stimulation in longitudinal bone growth, an increase in mineral apposition rate, and a trend for increased osteoclast and osteoblast surfaces in PTM. In contrast, cancellous bone of ADX + C25 rats was preserved at nearly the CON + PLA level. However, the higher doses of corticosterone increased cancellous bone mass, but decreased longitudinal bone growth and all indices of bone resorption and formation in a dose-dependent manner in PTM. Similar cancellous bone changes were observed in the LV of corticosterone-treated rats, with the exception of a lack of an hormonal effect on cancellous bone mass. In the tibial diaphysis, corticosterone inhibited periosteal bone formation in a dose-dependent manner, but did not affect cortical bone mass. The results indicate that corticosteroid deficiency induces cancellous osteopenia, whereas supplementation with a near physiologic dose of the hormone prevents this bone loss in ADX rats. Furthermore, corticosteroid excess inhibits bone growth and bone turnover in a dose-dependent manner, but does not induce cancellous osteopenia in growing male rats.

Non-NASA Center↗
NASA NTRS1994

Effects of Prostaglandin E2 and Risedronate Administration on Cancellous Bone in Older Female Rats

The effects of Prostaglandin E2 (PGE2) and Risedronate (Ris) both separately and in combination (PGE2 + Ris) were studied on the intact aged female rat skeleton to determine whether the combination of PGE2 with an antiresorptive agent is more effective anabolically than PGE2 alone. Nine month-old Sprague-Dawley rats were injected subcutaneously either with vehicle, 6 mg PGE2/kg per day, 1 or 5 microgram Ris/kg twice a week, or 6 mg PGE2/kg per day plus 1 or 5 microgram Ris/kg twice a week (PGE2 + 1 Ris or PGE2 + 5 Ris) for 60 days. After the treatment, we determined the longitudinal bone growth rate, the qualitative appearance of the primary spongiosa (PS), and the static and dynamic bone histomorphometry of the secondary spongiosa (SS) of the proximal tibial metaphysis (PTM) by examining undecalcified longitudinal sections after double fluorescent labeling. The relative effects of these treatments on longitudinal bone growth were ranked as follows: PGE2 + 5 Ris greater than PGE2 + 1 Ris = basal greater than PGE2 greater than 1 microgram Ris = 5 microgram Ris = aging. The density of the PS was ranked as follows: PGE2 + 5 Ris greater than PGE2 + 1 Ris = PGE2 = 5 microgram Ris = 1 microgram Ris greater than basal = aging. The increase in density of the PS was the result of stimulated longitudinal growth and the action of bisphosphonate. Bone mass in the SS was ranked as follows: PGE2 + 5 Ris = PGE2 + 1 Ris = PGE2 greater than 5 microgram Ris = 1 microgram Ris = aging = basal. However, PGE2 alone and its cotreatment with Ris accumulated bone by different tissue mechanisms. PGE2 alone created new bone by increasing activation frequency 8.3-fold and the formation to resorption ratio 1.3-fold from the controls. The combination of PGE2 and Ris depressed activation frequency (-54% to -74%), and bone formation rate (tissue-based -31%, and bone-based -42%) and eroded surface (-79% to -81%), so as to increase the formation to resorption ratio (three- to four-fold) over PGE2 alone. The increased ratio was due primarily to a greater decrease in eroded perimeter than in labeled perimeter. The major finding of this study is that the combination of PGE2 and a bisphosphonate (Ris) is more anabolic than PGE2 or Ris alone when endochondral ossification is active, but PGE2 + Ris is no more anabolic than PGE2 alone in old bone without endochondral ossification. However, the tissue mechanisms by which PGE2 alone and PGE2 + Ris treatments accumulated bone differed in that the latter allowed the same bone mass to accumulate with lower levels of cell recruitment and activity.

Lin, B. Y.↗