Effect of long-term physical stress on collagen growth in the lung, heart, and femur of young and adult rats

Effect of treadmill exercise on tibial cortical bone in aged female rats: a histomorphometry and dual energy x-ray absorptiometry study

The aim of this study was to increase our understanding of the effect of exercise on cortical bone mass and turnover in aged female rats. Female Sprague-Dawley rats, 14 months of age, were divided into four groups: 8 controls and 10 exercised for the 9-week study, and 8 controls and 9 exercised for the 16-week study. Exercise consisted of treadmill running at 17 m/min for one h/day and 5 days/week for 9 and 16 weeks. All animals received double fluorochrome labeling of bone prior to sacrifice. Histomorphometric analysis was performed on 30-microns-thick Villanueva-stained, undecalcified cross-sections of the tibial shaft. Tibial diaphyseal mineral density of each rat in the 16-week study was measured by dual energy x-ray absorptiometry in vivo at 0, 9, and 16 weeks. The diaphyseal mineral density of the exercised group was significantly greater than that of the control group (p < 0.05 by two-way ANOVA) and the individual slopes of the density vs. time was found to be higher in the exercised than in the control animals (mean +/- SE of exercised 0.56 +/- 0.13 vs. control 0.19 +/- 0.07 mg/cm2/week, p < 0.05) by the end of the experiment. The results of the histomorphometric analysis after 9 weeks of exercise showed that the periosteal labeled surface, mineral apposition rate, and bone formation rate were profoundly increased by 192% (p < 0.001), 35%, and 206% (p < 0.01), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of treadmill exercise on vertebral and tibial bone mineral content and bone mineral density in the aged adult rat: determined by dual energy X-ray absorptiometry

Dual energy X-ray absorptiometry (DXA; Hologic QDR-1000W) in an ultrahigh-resolution mode, was used to examine the changes in tibial/fibula and vertebral L4 + L5 bone mineral content (BMC) and bone mineral density (BMD) in each 14-month-old female rat at 0, 9, and 16 weeks of study. Twenty rats were randomized by a stratified weight method into two groups, control and exercised. Exercise consisted of running on a flat-bed treadmill, 17 m/minute, 1 hour/day and 5 days/week. As compared with the control group, a significant increase in tibia/fibula BMC and vertebral BMD was apparent at 9 weeks after exercise training (P = 0.014 by 2-way analysis of variance). The slope of the gain of the tibia/fibula BMC and BMD by 16 weeks of training was ninefold and fivefold higher than that of the control group (P < 0.01 and P < 0.05, respectively, by Mann-Whitney test). The correlation coefficient (r) between the final dry weight of excised bone and the final BMC of the intact rat was 0.843 and 0.71 for tibia/fibula and vertebrae, respectively. In summary, we found that in the aged rat, by 9 weeks, exercise increases BMC and BMD in the tibia, whereas in the vertebrae, only increases in the BMD were found. This study demonstrates that this precise and accurate DXA technique is useful in a longitudinal study of in vivo bone mineral changes in the rat over time by taking into account the individual variation between animals as well as changes between groups.

Effect of swimming on prednisolone-induced osteoporosis in elderly rats

We investigated the possible ameliorating and preventive effect of swimming on prednisolone-induced osteoporosis in elderly rats. A total of 48 female Sabra strain rats were randomly assigned to the following groups and treatments: (1) control (C), (2) swimming (S), (3) prednisolone-treated (CP), and (4) swimming + prednisolone (SP). An additional 8 rats were sacrificed and examined at the onset of the study. Groups C and S were sham injected; groups CP and SP were injected with prednisolone (Ultracorten), 80 mg/kg three times per week for 10 weeks. Groups S and SP swam 1 h daily, 5 days per week for 10 weeks. SP rats swam simultaneously with prednisolone administration. At the end of the swimming period, in vivo bone mineral content (BMC) measurements were performed on rat vertebrae L4-5 by single-photon absorptiometry. Later, the humerus and femur were removed for the following measurements: morphometric, bone density (BD) by Compton scattering technique, bone ion content by atomic absorption, and hydration fraction by proton magnetic resonance (PMR). We found that the humeral BD of S rats was greater by 14% for group S over C and 3% greater for group SP over CP (P less than 0.05). Vertebral BMC was higher by 15% in group S over C and 11% higher for group SP over CP (P less than 0.05). Femoral calcium (mg/g dry bone) ion content was higher by 5% in group S over C and 8% in group SP over CP group (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of swimming on bone modeling and composition in young adult rats

The purpose of this study was to investigate the adaptability of long bones of young adult rats to the stress of chronic aquatic exercise. Twenty-eight female Sabra rats (12 weeks old) were randomly assigned to two groups and treatments: exercise (14 rats) and sedentary control (14 rats) matched for age and weight. Exercised animals were trained to swim in a water bath (35 degrees +/- 1 degree C, 1 hour daily 5 times a week) for 12 weeks loaded with lead weights on their tails (2% of their body weight) (BW). At the end of the training period following blood sampling for alkaline phosphatase, all rats were sacrificed and the humeri and tibiae bones were removed for the following measurements: bone morphometry, bone water compartmentalization, bone density (BD), bone mineral content (BMC), and bone ions content (Ca, Pi, Mg, Zn). The results indicate that exercise did not significantly affect the animals' body weight, bone volume, or length and diameters. However, bone hydration properties, BD, bone mass, and mineralization revealed significant differences between swim-trained rats and controls (P less than 0.05). Longitudinal (R1) measurement was higher by 43% for both humerus and tibia, and Transverse (R2) relaxation rates of hydrogen proton were higher by 117 and 76% for humerus and tibia, respectively; fraction of bound water was higher by 36 and 46% for humerus and tibia, respectively. BD, bone weight, and ash were higher by 13%. BMC and bone ions content were higher by 10%, and alkaline phosphatase was higher by 67%.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of swimming on bone growth and development in young rats

The effect of chronic swimming on bone modelling was studied. Forty female Sabra rats (5 weeks old) were randomly assigned to the following experimental groups: 30 rats were trained to swim (water bath 35 +/- 1 degree C, one h daily, five times a week) for 20 weeks--20 of them loaded with lead weights (1% body weight) while the rest (10 animals) swam load free. Ten sedentary rats matched for age and weight served as controls. At the end of the twenty-week swimming period, all rats were sacrificed, both humeri bones were dissected and prepared for the following examinations: morphometric, bone density (BD), bone mineral content (BMC), compression tests and cross-sectional geometrical parameters, histomorphometry and biochemical analysis of minerals (Ca, Pi, Mg, Zn). All measured parameters were found to be significantly higher (P less than 0.05) in the swimming rats irrespective of load, as compared with the controls. Bone weight was higher by 19%, bone volume by 11%, bone length by 2.8%, cortical area by 16%, BD by 7% and BMC by 15%. The compression breaking force at the distal shaft of the humerus was higher by 24% in the trained group, while the ultimate compressive stress was not significantly different. Maximal and minimal moment of inertia at the distal diaphysis were 33.4 and 40% higher, respectively, for the swimming groups than the controls. Ca, Pi, Mg and Zn levels per total humeral bone were significantly higher in the exercising rats. The histomorphometry and cross-sectional data emphasize longitudinal and transversal growth. These data indicate that swimming exercise exerts a positive effect on bone growth and development in young rats.

Interaction of stress and growth in a fibrous tissue

The influence of stress on the growth and remodeling of a soft biological tissue is considered. For this purpose, the soft tissue is idealized as a fiber network. The stress-free lengths of the fibers composing the network are not fixed as in an inert elastic solid, but are assumed to evolve as a result of growth and stress adaptation. Similarly, the topology of the fiber network may also evolve under the application of stress. A set of constitutive equations are proposed which relate the tissue stress to the deformation of the tissue as well as to its growth and microstructure. It is shown that distinctly different growth patterns which may arise during initial growth or wound healing can be modeled by the proposed mathematical analysis.

Effects of aging on hydroxyproline in human heart muscle

Hydroxyproline concentration in the NaCl-soluble, TCA-soluble, and residual fractions of heart muscle was chemically determined in 40 autopsy subjects (25 men and 15 women), to study the effects of aging. In the left ventricle, the total hydroxyproline content of the endocardium and papillary muscle increased significantly in relation to age; the increase was greatest in the TCA-soluble fraction, followed by the residual fraction. Statistical analysis revealed that hydroxyproline in the residual fraction increased from the epicardium to the endocardium and then to the papillary muscle. Significant negative correlations were found between heart weight and total hydroxyproline in the epicardium and endocardium. In the right ventricle, a significant negative correlation was noted between heart weight and total hydroxyproline content. Though no correlations were evident between age and hydroxyproline content in females, significant correlations were observed between age and the total hydroxyproline content of the endocardium and papillary muscle in males. Furthermore, soluble collagen increased in most parts of the heart in females, but insoluble collagen increased in all parts of the heart in males. It is concluded that the hydroxyproline content of heart muscle increases in proportion to age and is in inverse proportion to heart weight. The increase occurs in the TCA-soluble and residual fractions, and extends from the endocardium to the papillary muscle. More profound changes in collagen metabolism are observed in males.

Connective tissue proteins of the baboon lung: concentration, content and synthesis of collagen in the normal lung

Lung connective tissue proteins have been assayed in 12 normal juvenile baboons (Papio cynocephalus). The collagen concentration (26.8 +/- 5.1 microgram hydroxyproline per mg dry weight) is comparable to values reported for adult human lung, while the rate of collagen synthesis (0.242 +/- 0.082 nmoles hydroxyproline per mg DNA per hour) is approximately half that of human lung. Proteins other than collagen are synthesized at approximately equal rates in human and baboon lung. Elastin concentration was estimated to be 33 microgram insoluble elastin protein per mg dry weight, within the range reported for normal human lung. Values have also been calculated for the lobar contents of protein, DNA, and collagen, as well as the rates of synthesis of collagen and other proteins in the entire upper lobe of the right lung of these animals. The collagen concentrations in the lung show wide differences among various animal species. However, the baboon lung is similar to human lung. This similarity may be important in the interpretation of alterations in lung connective tissue metabolism associated with experimental diseases.

Physical training and connective tissues in young mice-heart

The effect of physical training on the chemical properties of the heart tissues was studied in male mice of NMRI-strain. The mice to be trained and their controls were about 2 weeks old at the beginning of the training, which took place on 5 degrees inclined treadmill 5 days a week for 3-22 weeks. The duration of daily exercise was progressively increased over the first 3 weeks. The final daily exercise bouts were 50 and 80 min for moderate programs and 180 min for the intensive program at a speed of 30 cm/s. The whole heart or the ventricles were used for the analyses. We found no significant changes related to training in the concentrations of nitrogen, hexosamines, and hydroxyproline both in the normal-sized and the hypertrophied hearts. The hydroxyproline concentration of the ventricles was lower than that of the whole heart tissue, but no difference was observed in the concentration of nitrogen. The hydroxyproline concentration of the heart tissue increased with age both in the trained and untrained mice (39% over 19 weeks). We conclude that collagen and non-collagen proteins in the heart tissue of young mice are stimulated in equal proportions by physical training.

[The specific gravity of the excitation formation and conduction system of the heart compared to the working myocardium as an indication of differences in structure and composition (author's transl)]

Samples of heart conducting system tissue and samples of ordinary heart muscle (left heart, right heart, and septum interventriculare) were taken from the hearts of 50 prime-conditioned bulls. The specific gravity of the heart conducting system was significantly higher than that of ordinary heart muscle. This is surprising because it cannot be explained by a difference in water content. The question arises whether or not there are differences in the composition of protein and in the content of glycogen.

Comparison of whole calvarial bones and long bones during early growth in rats. II. Turnover of calcified and uncalcified collagen masses

The increase of total collagen and its destruction were compared for whole calvaria and long bones from young growing rats prelabeled in utero with 3H-L-proline. Rats were compared from birth to 16 weeks of age. Long bones and calvaria were isolated as intact anatomical units for autoradiography or separated by collagenase into calified and uncalcified collagens. Autoradiography using 14C-L-proline demonstrated eccentric modeling of bone collagen. With growth the mass of calcified collagen (bone) increased rapidly in calvaria and long bones. A similar increase in the mass of uncalcified collagen (mainly cartilage) occured in the long bones; a very small increase occurred in the fibrous tissue of calvaria. Total and specific radioactivities of collagens at each age were compared to that present at birth. With growth remodeling an almost complete loss of pre-existing radioactive collagen occurred from uncalcified fibrous tissue of calvaria as compared to a smaller but substantial loss from the uncalcified cartilage of long bones. A marked loss of calcifed collagen occurred in long bones as compared to a smaller loss from calvarial bones. The istopic data indicate a large turnover of fibrous tissue (type I collagen) with growth remodeling as compared to a smaller turnover of bone (calcified, type I collagen) and cartilage (typc I collagen). The turnover rate of skeletal collagens depends upon whether the collagen is calcified or not, and not upon the type of collagen.

Blood circulation of long bones in trained growing rats and mice

The effect of physical training on the blood circulation of long bones was studied in growing rats and mice of NMRI-strain. The animals to be trained and their controls were about 2 weeks old at the beginning of the training. The training took place on a 5 degree inclined treadmill 5 days a week for 3 weeks in experiment I and 7 weeks in experiments II and III. The duration of the daily exercise was progressively increased over 3 weeks. The final exercise bouts were 80 min for moderate and 180 min for intensive training programs. The circulating red cell volume (ml/100 g bone) of the humeral, femoral and tibial bones of the trained animals was lower compared to the controls in all three experiments mainly due to reduced hematocrit values. The circulating blood volume (ml/100 g bone) decreased in the tibial bones of the trained animals in experiment I and showed a decreasing tendency in experiment III, but no significant differences between the groups were observed in the humeral and femoral bones. Yet, when related to the volume of the bones the circulating blood volume (ml/100 ccm bone) was significantly higher in the femoral bones of the trained animals, while the changes in the humeral bones were negligible (experiment III). The results suggest that the vascularity of long bones is affected by physical training. The varying responses in different bones are perhaps due to the amount of mechanical stress during physical activity.