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Previous studies have shown that low-density, rod-like trabecular structures develop in regions of low stress, whereas high-density, plate-like trabecular structures are found in regions of high stress. This phenomenon suggests that there may be a close relationship between the type of trabecular structure and mechanical properties.In this study, 160 cancellous bone specimens were produced from 40 normal human tibiae aged from 16 to 85 years at post-mortem. The specimens underwent micro-CT and the microstructural properties were calculated using unbiased three-dimensional methods. The specimens were tested to determine the mechanical properties and the physical/compositional properties were evaluated.The type of structure together with anisotropy correlated well with Young’s modulus of human tibial cancellous bone. The plate-like structure reflected high mechanical stress and the rod-like structure low mechanical stress. There was a strong correlation between the type of trabecular structure and the bone-volume fraction. The most effective microstructural properties for predicting the mechanical properties of cancellous bone seem to differ with age.

Our aim was to determine the relationship between age and the mechanical and physical properties of trabecular bone, to describe the patterns in which the variations in these properties take place, and to investigate the influence of the physical properties on the mechanical characteristics of trabecular bone during growth. We used 30 lambs in three age groups and 20 sheep in two age groups. Cubes of subchondral bone were cut from the proximal tibia according to a standardised protocol. We performed non-destructive compression tests of the specimens in three orthogonal directions and compression tests to failure in the axial direction. The physical properties of the specimens were also determined. The data were correlated with age and compared in skeletally immature and mature animals. Multiple regression analyses were performed between the mechanical and the physical properties.Age correlated positively with elastic modulus, bone strength, energy absorption to failure, elastic energy, mechanical anisotropy ratio, tissue density, apparent density, apparent ash density, and bone mineral content, and inversely with ultimate strain, viscoelastic energy absorption, relative energy loss, the collagen content of bone and the percentage porosity. The values of all variables were significantly different in the skeletally mature and immature groups. The apparent density of trabecular bone tissue was found to be the major predictor of its compressive mechanical properties. Together with the content of bone muscle and bone collagen, the apparent density could explain 84% of the variation in the elastic modulus, whereas only a small portion of the variation in ultimate strain could be explained by the variation in apparent density.

The interaction between a small dermatan sulphate proteoglycan isolated from human uterine cervix and collagen type I from human and rat skin was investigated by collagen-fibrillogenesis experiments. Collagen fibrillogenesis was initiated by elevation of temperature and pH after addition of proteoglycan, chondroitinase-digested proteoglycan or isolated side chains, and monitored by turbidimetry. Collagen-associated and unbound proteoglycan was determined by enzyme-linked immunosorbent assay after aggregation was complete. (1) The binding of proteoglycan to collagen could be explained by the presence of two mutually non-interacting binding sites, with Ka1 = 1.3 x 10(8) M-1 and Ka2 = 1.3 x 10(6) M-1. The number of binding sites per tropocollagen molecule was n1 = 0.11 and n2 = 1.1. The 0.1 high-affinity binding site per tropocollagen molecule indicates that the strong interaction between proteoglycan and collagen results from a concerted action of tropocollagen molecules in fibrils. Digestion of the proteoglycan with chondroitinase ABC did not affect these binding characteristics. (2) Proteoglycan did not affect the rate of fibrillogenesis, but increased the steady-state A400 by up to 90%. This increase was directly proportional to the saturation of the high-affinity type of binding sites. Neither isolated core protein nor isolated side chains induced a similar high increase in steady-state A400. (3) Electron micrographs showed that the fibril diameter was affected only to a minor extent, if at all, by the proteoglycan, whereas bundles of laterally aligned fibrils were common in the presence of proteoglycan. (4) Results obtained with human and rat collagen were similar.

We have previously established an uremic rat model which is suitable for investigating the effect of various treatment modalities on the progression of renal osteodystrophy [1]. Four months subsequent to 5/6 nephrectomy, animals were treated three times a week for 3 months with either vehicle, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], 1,25(OH)2D3+24,25-dihydroxyvitamin D3 [24,25(OH)2D3], 1,25(OH)2D3+calcitonin (CT), or 1,25(OH)2D3+ 24,25(OH)2D3+CT. At termination of the study, clinical chemistry, chemical composition, and mechanical properties of femurs, calvarial parathyroid hormone (PTH)-elicited adenylate cyclase (AC), and phospholipase C (PL-C) activities, femoral cross-sectional area, and bone histomorphometry were analyzed. The main findings were that 1,25(OH)2D3±24,25(OH)2D3 treatment enhanced elasticity as well as time to fracture at the femoral metaphysis. CT potentiated the increase in elasticity obtained by 1,25(OH)2D3±24,25(OH)2D3 treatment. Only 24,25(OH)2D3 administration rectified the supernormal PTH-stimulated uremic bone AC, and only 1,25(OH)2D3 medication normalized the diminished CT-elicited AC. The obliterated uremic bone PTH-sensitive PL-C was fully normalized by all drug regimens. Femoral shaft inner zone diameter was enhanced by uremia, however, all drug treatments normalized it. Ditto effect was registered with either drug treatment on the subnormal outer and inner zone widths. Histomorphometrical analyses showed that 1,25(OH)2D3 administration reduced both eroded and osteoid surfaces. Most prominently, adjuvant 24,25(OH)2D3 or CT administration potentiated the beneficial effect of 1,25(OH)2D3 on fibrosis and osteomalacia. We assert that vitamin D3 treatment markedly reverses the development of renal osteodystrophy, and CT potentiates the effect of vitamin D3.

We studied the bladders of 24-month-old intact rats, rats that had been ovariectomized at the age of 6 months, and intact and ovariectomized rats treated by estrogen from the age of 16 months. The study thus comprized four groups: group I: bilaterally ovariectomized rats; group II: intact rats; group III: ovariectomized rats treated with estrogen; group IV: intact rats treated with estrogen. The weight and collagen concentration of the bladders were determined. The ovariectomized bladders weighed significantly less and had a higher collagen concentration than the intact bladders. Estrogen substitution for ovariectomized rats reversed these parameters. Detrusor strips were also used for organ bath studies. All bladders were similar in regard to the nervemediated frequency-response relationship. The atropine-resistant response was studied by adding scopolamine to the organ bath. Strips from ovariectomized rats had a significantly diminished atropine-resistant response, which was abolished by estrogen substitution. The present study suggests that micturition problems in menopause might have a structural as well as a pharmacological explanation.

A quantitative histologic analysis of the striated anal sphincter of virgin female rats aged 2 months and 24 months was performed to evaluate age-related changes. A 27% (8% to 46%, 95% confidence limits) increase in the cross-sectional area of the muscle in the older rats was observed compared with the young. This was due to an increase in both muscle and connective tissue. There was hypertrophy of both the small and large muscle fibres without change in the number with age. No evidence of age-related degenerative changes in this muscle in the virgin female rat was found.

A quantitative histologic analysis of the striated anal sphincter of 24-month-old virgin female rats was performed to evaluate the effect of oophorectomy and estrogen substitution. The oophorectomized rats had a 21% (11-31%, 95% confidence limits) reduction in the cross-sectional area of the striated muscle tissue compared with controls. This was due to a reduction in the mean cross-sectional area of the muscle fiber, whereas the number of fibers was unchanged. Although the relative amount of stromal tissue was increased in the oophorectomized rats, the total stromal tissue was unchanged. No difference in the cross-sectional area of muscle tissue was found between the estrogen-substituted, oophorectomized rats and controls. This indicates that the estrogen depletion in the oophorectomized rats has induced the reduction in muscle tissue in the striated anal sphincter.

During the maturation in vitro of reconstituted collagen fibrils prepared from rat skin, the mechanical and thermal stability of collagen increased and the pepsin-solubility decreased. At the same time a larger fraction of the pepsin-soluble collagen attained a lower molecular thermal stability that resulted in a biphasic thermal transition of the soluble collagen. Type-I collagen, with a similar biphasic thermal transition, was isolated from acid-insoluble rat skin collagen.

Predicting the course of parathormone (PTH)-elicited bone turnover in both humans and experimental rat models with moderate chronic uremia, using only standard clinical chemistry analyses, is often difficult. Consequently, rat bone from 1+2/3 nephrectomized animals, after 230 days of progressive renal failure, was examined for PTH-stimulated adenylate cyclase (AC) and phospholipase C (PLC) activities. Correlations to biological parameters related to the function of bone and kidney were made. Reduced renal function was demonstrated by increased serum creatinine; circulating 1,25 dihydroxyvitamin D3 below detection level; diminished renal PTH-elicited AC activity; and decreased urinary cAMP excretion. PTH-activated renal PL-C was also reduced. However, no significant differences were seen in urine creatinine, calcium, phosphate, and hydroxyproline, nor in serum PTH, alkaline phosphatase, calcium, and phosphate. Notwithstanding, renal osteodystrophy developed as estimated by increased plasticity of the long bones, as well as reduction of the diaphyseal (Dd) and inner femoral midshaft (Di) diameters. Femoral cancellous bone exhibited a substantial elevation of both eroded surface (ES) and osteoid surface (OS) as well as a marked reduction in trabecular bone volume (TBV). Calvarial PTH-activated AC was enhanced, whereas corresponding PL-C was markedly reduced. PTH-enhanced AC correlated positively with ES and negatively with Di, respectively. PTH-enhanced PL-C, however, correlated positively with bone calcium content and negatively with ES. Our results indicate that bone modeling and remodeling are to a large extent related to PTH-elicited signaling systems, and cannot easily be predicted by standard clinical chemistry analyses.

The shrinkage temperature (Ts) and the pepsin-solubilizability of collagen fibrils in bone matrix obtained from decalcified femur diaphysis from 2-, 5-, 15- and 25-month-old rats were found to decrease with age. Digestion with human fibroblast collagenase dissolved less than half of the collagen, whereas sequential treatment by pepsin followed by collagenase resulted in its complete dissolution. This result shows that collagenase and a telopeptide-cleaving enzyme, when acting in an appropriate sequence, have a great potential for the degradation of bone collagen. The ‘melting’ profile of the pepsin-solubilized collagen showed a biphasic transition with transition peak at 35.9 degrees C and 40.8 degrees C. With increasing age an increasing proportion of the collagen ‘melted’ in the transition peak at 35.9 degrees C (pre-transition), and the ‘melting’ temperature (Tm) of the collagen decreased in parallel with Ts in relation to age. Both Ts and Tm decreased by 3 degrees C in the age span investigated. The age-related change in Ts could therefore be accounted for by the decrease in molecular stability. The collagenase-cleavage products of the bone collagen obtained by the sequential treatment with pepsin and collagenase showed only one peak transition (at 35.1 degrees C), and the Tm for the products was independent of age. The results indicate that the pre-transition for the pepsin-solubilized collagen is due to an age-related decrease in thermal stability may have implications for the mechanical strength and turnover of the bone collagen. In contrast with bone collagen, soft-tissue collagen showed neither the age-dependency of thermal stability nor the characteristic biphasic ‘melting’ profile.

Rat skin type-I and type-III collagens were degraded by human fibroblast collagenase at a temperature below the ‘melting’ temperature for the two resulting fragments, namely the N-terminal three-fourths, TCA, and the C-terminal one-fourth, TCB. The specific cleavage of the collagen was confirmed by electrophoresis and determination of molecular length by electron microscopy. The two fragments were separated by gel filtration and the thermal stabilities of the isolated fragments were determined. For type-I collagen, the ‘melting’ temperatures of the two fragments were found to differ by only 0.5 degrees C and were 4.5-5.0 degrees C below that of the uncleaved molecule. The ‘melting’ temperatures of the uncleaved molecule and the N-terminal fragment were independent of the extent of N-terminal intramolecular cross-linking. For type-III collagen, the ‘melting’ temperatures of the fragments were found to differ by 1.3 degrees C. The small fragments of the two types of collagen ‘melted’ at the same temperature, whereas the large type-III fragment ‘melted’ at a slightly higher temperature than did the large type-I fragment. Reduction of the disulphide bonds located in the C-terminal type-III fragment did not affect the thermal stability of this fragment. The thermal stability of uncleaved type-III collagen was found to be variable, but the reason for this is not known at present.

We tested in compression specimens of human proximal tibial trabecular bone from 31 normal donors aged from 16 to 83 years and determined the mechanical properties, density and mineral and collagen content.Young’s modulus and ultimate stress were highest between 40 and 50 years, whereas ultimate strain and failure energy showed maxima at younger ages. These age-related variations (except for failure energy) were non-linear.Tissue density and mineral concentration were constant throughout life, whereas apparent density (the amount of bone) varied with ultimate stress. Collagen density (the amount of collagen) varied with failure energy. Collagen concentration was maximal at younger ages but varied little with age.Our results suggest that the decrease in mechanical properties of trabecular bone such as Young’s modulus and ultimate stress is mainly a consequence of the loss of trabecular bone substance, rather than a decrease in the quality of the substance itself. Linear regression analysis showed that collagen density was consistently the single best predictor of failure energy, and collagen concentration was the only predictor of ultimate strain.