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Biomedical subjects

A C Vailas

Publications and source records attributed to A C Vailas.

At least 37 records · Page 2Linked to original sources
PubMed1991

Cortical bone maturation in young hypophysectomized rats.

Cortical bone growth and maturation were studied in young growing rats (62 days) that were hypophysectomized. After 10 days, femur bones were obtained for morphological and biochemical analysis of the middiaphysis. Hypophysectomy significantly decreased (42%) normal body growth demonstrated by reductions in body weight. Bone morphology data indicate that hypophysectomy significantly inhibits the circumferential growth of the middiaphysis as well as region-specific thickness compared with the control group. The effects of hypophysectomy on cortical bone mineral composition and density were significantly greater in the hypophysectomized rats. Bone density and total mineral density were significantly greater, 17% and 24%, respectively, in the hypophysectomized group compared with control animals. Bone collagen maturation, measured by the amount of the mature collagen cross-link hydroxylysylpyridinoline, in the hypophysectomized animals was significantly greater (130%). Also, collagen concentration and content per unit volume were significantly greater, 24% and 70%, respectively, in the hypophysectomized group. Our findings suggest that "normal" growth and maturation of cortical bone in rapidly growing animals is dependent upon the modulation of pituitary hormones. These data also suggest that an increased rate of mature collagen cross-link formation may be modified by the turnover rate of collagen and other matrix constituents. In addition, hormonal mechanisms associated with a suppression of bone growth may enhance the probability of mature collagen cross-link formation.

Animals↗
PubMed1990

Effects of spaceflight on rat humerus geometry, biomechanics, and biochemistry.

The effects of a 12.5-day spaceflight (Cosmos 1887 biosatellite) on the geometric, biomechanical, and biochemical characteristics of humeri of male specific pathogen-free rats were examined. Humeri of age-matched basal control, synchronous control, and vivarium control rats were contrasted with the flight bones to examine the influence of growth and space environment on bone development. Lack of humerus longitudinal growth occurred during the 12.5 days in spaceflight. In addition, the normal mid-diaphysial periosteal appositional growth was affected; compared with their controls, the spaceflight humeri had less cortical cross-sectional area, smaller periosteal circumferences, smaller anterior-posterior periosteal diameters, and smaller second moments of area with respect to the bending and nonbending axes. The flexural rigidity of the flight humeri was comparable to that of the younger basal control rats and significantly less than that of the synchronous and vivarium controls; the elastic moduli of all four groups, nonetheless, were not significantly different. Generally, the matrix biochemistry of the mid-diaphysial cross sections showed no differences among groups. Thus, the spaceflight differences in humeral mechanical strength and flexural rigidity were probably a result of the differences in humeral geometry rather than material properties.

Animals↗
PubMed1990

Acute modification of biomechanical properties of the bone-ligament insertion to rat limb unweighting.

We investigated the acute adaptation of the rat femur-medial collateral ligament-tibia (FMT) complex to 7 days of limb unweighting by means of a hind-limb suspension protocol. Male, young adult, Harlan Sprague-Dawley rats were randomly assigned to either control or suspended groups. Rats deprived of hind limb-to-ground contact forces had a 42% decrease in soleus muscle mass compared with the control group. Medial collateral ligament (MCL) length and cross-sectional area were measured, and each FMT complex was tension tested to failure. All failed at their tibia-MCL insertion. The ultimate load in the FMT and the peak Kirchhoff stress in the MCL (occurring immediately before insertion site failure) were significantly reduced in the suspended group. The suspended MCLs were 9.7% larger in area and 5.7% shorter in length than the controls under the same preload (0.25 N). We found no significant differences between the control and suspended MCLs in Green strain, stretch, or deformation immediately before insertion site failure, nor did we find a significant difference in the MCL tangent modulus. This study indicates that even acute periods of limb unweighting can structurally compromise bone-ligament insertions. Further, this study implies that the adaptations responsible for this structural compromise must involve acute changes in the intrinsic zone (or zones) of the bone-ligament insertion.

Animals↗
PubMed1990

Suspension effects on rat femur-medial collateral ligament-tibia unit.

To study the influence of a 2-wk absence of normal weight-bearing forces on dense fibrous connective tissues of growing animals, the geometrical and biomechanical characteristics were examined of femur-medial collateral ligament (MCL)-tibia units (FMT unit) of age-matched controls and tail-suspended young male rats. During the 2-wk suspension, the rate of longitudinal growth of MCL decreased significantly, but no differences were found in the cross-sectional area of the MCL of the two groups. The tensile stiffness of suspension FMT units was significantly less than control, and the proportional, maximum, and failure loads of FMT units were also significantly less for the suspended animals. The stresses in the suspension MCL at the proportional limit were significantly less than control values. These results indicated that a 2-wk absence of normal weight-bearing forces adversely affected the rate of longitudinal growth of MCL and the mechanical properties of the rat FMT unit.

Animals↗
PubMed1990

Spaceflight effects on biomechanical and biochemical properties of rat vertebrae.

The biomechanical and biochemical responses of lumbar vertebral bodies during a 12.5-day spaceflight (Cosmos 1887 biosatellite) were determined for rapidly growing rats (90-day-old, Czechoslovakian-Wistar). By use of age-matched vivarium controls (normal cage environment) and synchronous controls (simulated flight conditions), as well as a basal control group (killed before lift-off on the 1st day of flight), the combined influences of growth and space-flight could be examined. Centra of the sixth lumbar vertebrae (L6) were compressed to 50% strain at a fast strain rate while immersed in physiological buffer (37 degrees C). The body masses of vivarium and synchronous controls were significantly heavier than either the flight or basal controls. The flight group had an L6 vertebral body compressional stiffness that was 39% less than the vivarium controls, 47% less than the synchronous control, and 16% less than the basal controls. In addition, the average initial maximum load of the flight L6 was 22% less than vivarium controls and 18% less than the synchronous controls, whereas the linear compressional load of the flight group averaged 34% less than the vivarium and 25% less than the synchronous groups. The structural properties of the vertebrae from the 12.5-day-younger basal group closely resembled the flight vertebrae. Calcium, phosphorous, and hydroxyproline concentrations were not significantly different among the groups. Nevertheless, the lack of strength and stiffness development in spaceflight, coupled with a smaller proportion of mature hydroxypyridinoline cross-links, suggested that the 12.5 days of spaceflight slowed the maturation of trabecular bone in the vertebral bodies of rapidly growing rats.

Animals↗
PubMed1990

Incomplete normalization of dog gracilis muscle grafts with neurovascular repair despite long-term recovery.

Skeletal muscle grafts performed with neurovascular repair are used extensively in clinical situations. However, most controlled experimental studies on the efficacy of such grafts have been conducted on muscles with a relatively small mass and over a limited recovery period. Therefore, selected cellular and matrix component properties of the comparatively large dog gracilis muscle (75 g) were studied 9-12 mo after orthotopic neurovascular grafting. The grafted muscle wet weights were 71% of the contralateral control (sham-operated) muscles. In addition, the concentrations of noncollagenous protein (13%), DNA (28%), and RNA (34%) were significantly reduced in the grafts. However, the concentration of collagen was significantly higher (41%) in the grafts. In this regard, the type III collagen phenotype showed the greatest relative increase. There was no difference between the grafted and control proteoglycan concentration. The metabolic profiles of the grafted muscles were significantly different from control. The activities of myofibrillar adenosinetriphosphatase (34%) and alpha-glycerophosphate dehydrogenase (25%) were reduced, whereas citrate synthase remained unchanged. These data suggest that recovery of up to 1 yr was insufficient for the normalization of several connective tissue matrix components and biochemical properties of the grafts.

Adenosine Triphosphatases↗
PubMed1990

Changes in geometrical and biomechanical properties of immature male and female rat tibia.

Tibial geometry and mechanical properties in male and female rapidly growing rats were measured to provide comparative data for spaceflight, exercise, or disease experiments that use immature rats as an animal model. A total of 68 immature Sprague-Dawley rats (43-58 d of age) were divided into 8 groups according to age and sex. Tibial length and middiaphysial cross-sectional data were analyzed, and tibial mechanical properties were obtained via three-point bending tests to failure. Results indicated that tibial geometry and mechanical properties were changed significantly during this 15-d period of rapid growth, with male rats having greater increases than female rats. Both male and female tibial lengths nevertheless increased significantly during this growth period, as did middiaphysical cross-sectional area. Tibial flexural rigidity increased significantly for both sexes during this growth period. The male tibiae changed primarily in structural characteristics, but some material properties also changed with age. In the female rats, however, the major changes in mechanical properties of the tibia were attributable only to structural changes in the bone.

Age Factors↗
PubMed1990

Interactive effects of nutrition, environment, and rat-strain on cortical and vertebral bone geometry and biomechanics.

Because of differences between rodent experiments on USSR and USA spaceflights, the present experiment was designed to generate comparative data about the sensitivity of cortical (humerus) and vertebral (T7) bones to cage environment, diet, and rat-strain differences. For 2 weeks (48-62 d), male Taconic-Sprague-Dawley and Czechoslovakian-Wistar rats were maintained in flight-simulation cages (1 rat/cage = USA, 10 rats/cage = USSR) and fed either USSR or USA diets. All rats increased (greater than 60%) their body mass during the two weeks, and there were no differences among humeral lengths for the different groups. Rats in USSR cages had significantly larger total and medullary cross-sectional areas for the humerus, and the cross-sectional areas of T7 of Taconic rats were greater than the Czech rats. USSR caging resulted in significantly enhanced structural and material properties in rat humeri, while the USA diet produced significantly greater humeral maximum and failure loads. The flexural rigidity of the Czech-rat humeri was significantly greater than the Taconic rats. Humeri from Czech rats on the USA diet had significantly greater material properties in the elastic-loading region than did Taconic rats on the USSR diet. Further, the humeral failure loads of Taconic rats on the USSR diet were more adversely affected by USA cages than were the Czech rats on the USSR diet. In T7 vertebrae, no significant structural differences were found among the groups, but material properties were influenced by all three factors; generally, the combination of factors that produced the significantly greater T7 material properties was: USSR caging, USSR diet, and the Czech strain of rat.

Animal Nutritional Physiological Phenomena↗
PubMed1989

Biomechanical and biochemical changes in lumbar vertebrae of rapidly growing rats.

Although growth-related biochemical, morphological, and biomechanical properties of rat cortical bone have been investigated, similar properties of immature rat vertebral bone have not been well characterized. Information about these properties is necessary, however, for comparative analyses of rat vertebral bone adaptation. Thus a method was developed to characterize growth-related differences in immature rat vertebral bone. The centra of sixth lumbar vertebrae (L6) of 44-day-old and 54-day-old male Sprague-Dawley rats were compressed to 50% of their initial height at a 50%/s strain rate while immersed in a potassium phosphate buffer solution (pH 7.4, 37 degrees C). Structural and material properties for the 54-day-old group that were significantly greater than those for the 44-day-old group included load, stress, and energy at the proportional limit; initial maximum load and stress; and load and energy at 50% strain. The structural stiffness of L6, as well as its elastic modulus, was significantly greater in the older animals. The calcium concentrations and calcium-to-collagen ratios in 54-day-old vertebrae were significantly greater than in younger animals. These results indicated that the specimen preparation and testing protocol developed for rat vertebrae produced reliable biomechanical results, even with the relatively small size of rat vertebrae bodies, and that the quantity and quality of the matrix of immature rat vertebral bone changed significantly during this period of rapid growth. Our test protocol will be useful for investigating the responses of rat vertebral bone to exercise, disease, and spaceflight.

Animals↗
PubMed1989

Effects of short-term immobilization versus continuous passive motion on the biomechanical and biochemical properties of the rabbit tendon.

Little work has been done on the effect that continuous passive motion (CPM) may have on maintaining the mechanical and biochemical characteristics of tendons deprived of normal load-bearing stimuli. This study compared changes in mechanical properties and collagen concentrations of the tibialis anterior tendon between two groups of rabbits: control animals that received no treatment and experimental animals that received CPM to one ankle and immobilization to the other. Treatment duration was three weeks. Mechanical testing yielded values for elastic modulus, stiffness, stress, strain, and strain energy density at linear and maximum loads. Hydroxyproline concentrations were measured to determine tendon collagen content. Findings indicated that cyclic tensile loading of tendons by CPM lessened the harmful effects of immobilization. Linear load and stress for CPM and control tendons were similar, while the same measures for immobilized tendons were 16% and 25% less than control tendons. Ultimate strength of the control tendons, however, exceeded CPM tendons by 16% and immobilized tendons by 20%. Hydroxyproline levels were comparable for the CPM, control, and immobilized tissues. For a short duration (three weeks), CPM reduced the detrimental effects of immobilization in the tendon, primarily in the linear-load region.

Animals↗
PubMed1988

Response of immature chicken meniscus to strenuous exercise: biochemical studies of proteoglycan and collagen.

Male white Leghorn chickens were exercised on a treadmill at 70-80% of their maximal oxygen consumption starting at 4 weeks and continuing up to 20 weeks of age. The effect of the strenuous exercise regime on the extracellular matrix of menisci was followed through studies of proteoglycans and collagen. Avian menisci contain type I collagen, chondroitin sulfate proteoglycans, which increase with age in amount and degree of aggregation, and dermatan sulfate proteoglycans, which decrease with age. Five weeks of exercise cause a premature decrease of dermatan sulfate proteoglycans, while the chondroitin sulfate-containing molecules become significantly more aggregated than those of the tissue of age-matched controls. Strenuous exercise also causes a significant decrease in the number of pyridinoline crosslinks per mole of collagen in the menisci of young runners. The exercise-induced changes of proteoglycan and collagen occur only during the period of active growth, and all parameters return to normal when the animals reach skeletal maturity. The early proteoglycan aggregation and dermatan sulfate decrease induced by exercise are probably an adaptation to the increased loading. Although the mechanism by which strenuous exercise reduces or delays the formation of collagen pyridinoline crosslinks in menisci of skeletally immature animals is unknown, their decrease could negatively affect the mechanical properties of the tissue during the period of active growth.

Adaptation, Physiological↗
PubMed1988

Effects of a 1-wk spaceflight on morphological and mechanical properties of growing bone.

The morphological and mechanical responses of tibia and humerus were assessed in growing male rats after a 1-wk spaceflight aboard NASA Spacelab 3. In contrast to flights of longer duration, changes in middiaphysial cross-sectional morphology were minimal. Inhibition of longitudinal growth was not found in the tibia but was apparent in the humerus. The normal age-related increase in tibial middiaphysial density was not observed in the flight animals. Three-point bending tests indicated that a 1-wk spaceflight impeded the maturation of bone strength and stiffness, with the effects more pronounced in the tibia than in the humerus. Material property alterations in bone thus overshadowed morphological factors in determining the bone's mechanical response. It is likely that deprivation of normal weight-bearing loads was a major factor contributing to the observed changes, but endocrine and other local factors must also be considered.

Animals↗
PubMed1988

Adaptation of bone and tendon to prolonged hindlimb suspension in rats.

The rat hindlimb suspension model was used to ascertain the importance of ground reaction forces in maintaining bone and tendon homeostasis. Young female Sprague-Dawley rats were randomly assigned to either a suspended or a nonsuspended group. After 28 days, femur bones and patellar tendons were obtained for morphological and biochemical analyses. Prolonged suspension induced a significant change in the geometric configuration of the femur middiaphysis by increasing the minimum diameter (12%) without any significant alterations in cortical area, density, mineral, and collagen concentrations. Femur wet weight, length, DNA, and uronic acid concentrations of suspended animals were not significantly different from bones of nonsuspended rats. However, the collagen and proteoglycan concentrations in patellar tendons of suspended rats were 28% lower than the concentrations of matrix proteins in tissues obtained from nonsuspended animals. These data suggest that elimination of ground reaction forces induces alterations in tendon composition and femur diaphyseal shape by changing regional rates in bone remodeling and localized tendon strain. Therefore it appears that ground reaction forces are an important factor in the maintenance of cortical bone and patellar tendon homeostasis during weight-bearing conditions.

Adaptation, Physiological↗
PubMed1988

Immature tendon adaptation to strenuous exercise.

White Leghorn roosters (3 wk old) were randomly assigned to runner or control groups. Runners were subjected to a progressive treadmill running program for 8 wk, 5 days/wk at 70-80% maximal O2 consumption (VO2 max). After 8 wk, runners showed a significant elevation in gastrocnemius fumarase activity (51%) and a 21% increase in VO2max compared with controls. The exercise program induced a significant increase in tendon collagen deposition (46%) without any changes in DNA, proteoglycan, and collagen concentrations or tendon dry weight. Also, tendon collagen from runners contained fewer (50%) pyridinoline cross-links. These results suggest that high-intensity exercise causes greater matrix-collagen turnover in growing chickens, resulting in reduced maturation of tendon collagen.

Adaptation, Physiological↗
PubMed1987

Mechanical, morphological and biochemical adaptations of bone and muscle to hindlimb suspension and exercise.

The influences of weightbearing forces on the structural remodeling, matrix biochemistry, and mechanical characteristics of the rat tibia and femur and surrounding musculature were examined by means of a hindlimb suspension protocol and highly intensive treadmill running. Female, young adult, Sprague-Dawley rats were designated as either normal control, sedentary suspended, or exercise suspended rats. For 4 weeks, sedentary suspended rats were deprived of hindlimb-to-ground contact forces, while the exercise suspended rats experienced hindlimb ground reaction forces only during daily intensive treadmill training sessions. The suspension produced generalized atrophy of hindlimb skeletal muscles, with greater atrophy occurring in predominantly slow-twitch extensors and adductors, as compared with the mixed fiber-type extensors and flexors. Region-specific cortical thinning and endosteal resorption in tibial and femoral diaphyses occurred in conjunction with decrements in bone mechanical properties. Tibial and femoral regional remodeling was related to both the absence of cyclic bending strains due to normal weightbearing forces and the decrease in forces applied to bone by antigravity muscles. To a moderate extent, the superimposed strenuous running counteracted muscular atrophy during the suspension, particularly in the predominantly slow-twitch extensor and adductor muscles. The exercise did not, however, mitigate changes in bone mechanical properties and cross-sectional morphologies, and in some cases exacerbated the changes. Suspension with or without exercise did not alter the normal concentrations of collagen, phosphorus, and calcium in either tibia or femur.

Animals↗
PubMed1986

Experimental studies on the influences of physical activity on ligaments, tendons and joints: a brief review.

The clinical practices of the future depend upon the experimental findings of today. Because of the uniqueness of connective tissue, animal experimentation will be essential for advances in this field. During the last decade, the improvements in technology and the increased interest of basic scientists and research clinicians on the effects of physical activity has markedly enhanced the amount of information available to practicing physicians. Studies spanning the appearances of structure to the changes in the crosslinks of collagen, clearly demonstrate that limb immobilization (inactivity) is deleterious to all structures involved whether evaluated anatomically, physiologically, or biomechanically. Furthermore, when surgical repair is included, there are stages when the deleterious processes become accelerated with or without immobilization. Hence, clinical immobilization must be utilized in a prudent and careful manner. There is sufficient experimental evidence for clinicians to utilize motion and mechanical stimuli as a means to improve the structure and function of tendons, ligaments, and joints. However, the unresolved issues are the mode, time of initiation, or the intensity of application. Even when used with repair, recovery of normal structures and function is protracted. The primary or secondary mechanisms associated with these effects of physical activity are unknown and virtually uninvestigated at the present time.

Animals↗
PubMed1986

Heterogeneous mechanical response of rat knee menisci to thermomechanical stress.

Thermodilatometric, dynamic thermomechanical, and light-microscopic analyses were done on the anterior and posterior regions of the rat knee menisci to correlate regional differences in morphology and extracellular matrix composition with regional mechanical behavior. Following the administration of a general anesthetic, menisci were excised from 12 young female Sprague-Dawley rats. During thermodilatometric and thermomechanical testing, tissue temperature was increased at a constant rate of 3.5 degrees C/min from 30 to 100 degrees C. Light microscopy revealed regional differences in cell density and proteoglycan content. The anterior horn was significantly heavier (greater than 87%) and thicker (greater than 60%) than the posterior region. During thermal analyses, both the anterior and posterior horns decreased in tissue thickness as the temperature increased from 30 to 73 degrees C. After 73 degrees C, however, the posterior horn expanded significantly, whereas the anterior remained in a comparatively contracted state. The rates of linear contraction and expansion of the posterior horn were seven times those of the anterior horn, and the stiffness of the anterior horn was significantly greater than the posterior horn.

Analysis of Variance↗