Properties of growing trabecular ovine bone. Part I: mechanical and physical properties.

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.

Thermal and mechanical stability of the lens capsule.

PURPOSE: Several procedures in cataract surgery carry the risk of high temperature increases in the capsular bag. The present study was undertaken to determine the shrinkage temperature of the human lens capsule and to investigate the effect of temperature on the mechanical behavior of the lens capsule. METHOD: Thermal-shrinkage characteristics of the lens capsule were determined during gradual heating of circular specimens (2 mm in diameter) prepared from anterior lens capsules from 25 human donors, ranging in age from 20 to 98 years. Uniaxial mechanical testing was carried out at 22 degrees C, 36 degrees C and 61 degrees C on ring-shaped test specimens prepared from anterior lens capsules from 5- to 6-month-old pigs. RESULTS: The mean shrinkage temperature (Ts) for the human lens capsule was 51.5 degrees C (range 49.3-54.3) and the mean shrinkage area in percent of the original area (AST) was 49% (36-66). Ts was significantly associated with the age of the donors and decreased 0.1 degree C per year until age 65 after which Ts was found to increase. AST showed no association with age. The mechanical effect of temperatures below the shrinkage temperature was modest. The capsule became slightly more extensible with increasing temperature. The effect of temperatures above the shrinkage temperature was an increased ultimate strain, a reduced ultimate stiffness and a slightly reduced ultimate stress. CONCLUSION: Thermal stability of the human lens capsule (type IV collagen) seems to be considerably lower than that of fibrous connective tissue (type I collagen). A potential risk of capsular shrinking has to be taken into account when the capsule is exposed to thermal stress during cataract surgery.

Age variations in the properties of human tibial trabecular bone.

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.

Ischemia and reperfusion of the porcine myocardium: effect on collagen.

We studied the effect of acute myocardial infarction and late reperfusion on myocardial collagen in a closed chest porcine model, to investigate if any collagen degradation could be detected in blood samples and myocardium. Sixteen 60-80 kg pigs were used with six animals serving as controls and 10 submitted to ischemia-reperfusion. In the ischemia-reperfusion group the left anterior descending coronary artery was occluded for 6 h by inflation of a percutaneous transluminal coronary angioplasty balloon followed by reperfusion for 3 h. Blood samples were taken from the aorta and the coronary sinus and analyzed for creatine kinase and collagen degradation products, i.e. the N-terminal propeptide of procollagen type III (PIIINP) and C-terminal pyridinoline cross-linked telopeptide of collagen type I (ICTP). Myocardial tissue samples were analyzed for content of hydroxyproline, collagen volume fraction and amount of extractable PIIINP/dry weight. Transmission electron microscopy of biopsies was performed to evaluate myocytes and collagen structure outside and within the infarct zone. Creatine kinase showed a statistically significant increase during ischemia and reperfusion but we found no evidence of release of collagen degradation products either during ischemia or reperfusion compared with control. Myocardial content of hydroxyproline, collagen volume fraction and extractable PIIINP/dry weight did not differ between groups. Transmission electron microscopy of biopsies from the infarct zone showed myocyte damage but no visible evidence of collagen degradation when photos were evaluated blindly. In this porcine model of acute myocardial infarction and late reperfusion no release of collagen degradation products from the myocardium or any decrease in or damage to myocardial collagen was detected.

Aluminium-induced bone disease in uremic rats: effect of deferoxamine.

We have previously established a rat model of chronic uremia, which is suitable to investigate the effect of various treatment modalities on renal osteodystrophy [1]. After four months subsequent to 5/6 nephrectomy, some animals were treated by gavage for 9 weeks with tap water (controls), or with aluminium (Al-citrate) 3 x 25 mg/week/kg b.wt +/- subsequent deferoxamine (DFO) 3 x 50 mg/week/kg b.wt. for 4 weeks. At termination of the study, serum clinical chemistry, femoral chemical composition and mechanical properties, calvarial parathyroid hormone (PTH)-elicited adenylate cyclase (AC) and phospholipase C (PLC) activities, cross-sectional femoral area, as well as bone histomorphometry, were analyzed. Animals given Al displayed moderately enhanced serum Al and bone Al accumulation, however, DFO-treatment did not fully alleviate bone Al retainment. A small increase in serum PTH was seen in all animals rendered uremic. Furthermore, a marked fall in serum alkaline phosphatase (ALP) below normal controls was observed in Al +/- DFO-treated animals compared with uremic controls. The uremic condition led to reduced femoral ratios of hydroxyproline (HYP) over Ca(2+) and phosphate (P(i)), while Al-intoxication alone enhanced femoral Hyp contents above values seen for normal controls. The protracted ureamia caused a deterioration of long bone resilience and brittleness, however, Al +/- DFO-treatment seemed to normalize the latter. Contrastingly, Al +/- DFO-gavage enhanced time to fracture. Uremic rats intoxicated with Al showed a complete loss of calvarial PTH-sensitive AC and PLC activities. DFO-treatment normalized PTH-elicited PLC, while PTH-susceptible AC remained super-normal. Al apparently exerts a long term down-regulation of both PTH-sensitive signaling systems as evidenced by studies of rat UMR 106 osteosarcoma cells in culture. The uremic condition enhanced endosteal bone resorption as shown by femoral shaft dimension analysis, while Al +/- DFO-treatment insignificantly reversed the condition. Finally, histomorphometrical analyses showed that DFO-administration tended to normalize aberrant trabecular bone volume, while rectifying both bone resorption and degree of mineralization. In conclusion, we assert that Al-intoxication hampers both processes (i.e. formation and resorption) of bone turnover, and that DFO-treatment to a certain extent prevents the uremia- and Al-induced bone disease in rats.

Vitamin D3 analogs and salmon calcitonin partially reverse the development of renal osteodystrophy in rats.

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.

The anabolic effects of parathyroid hormone on cortical bone mass, dimensions and strength--assessed in a sexually mature, ovariectomized rat model.

The aim of the study was to determine the effect of parathyroid hormone (PTH), the antiresorptive agents estrogen and bisphosphonate (risedronate), and also the combination of PTH with these antiresorptive drugs on femoral cortical bone mass, dimensions and strength in a sexually mature, ovariectomized rat model. A total of 138, 3-month-old Sprague-Dawley rats were randomized into seven groups: 1--sham operated (control); 2--ovariectomized (OVX); 3--OVX plus estrogen; 4--OVX plus bisphosphonate (risedronate [NE]; 5--OVX plus hPTH (1-34); 6--OVX plus hPTH (1-34) and estrogen; 7--OVX plus hPTH (1-34) and risedronate. Treatment regimens were initiated 4 weeks after OVX and were continued for 5 and 15 weeks for each treatment group. Changes in bone mass (ash content), cross-sectional area, cortical thickness and dimensions and bone strength were assessed in middiaphyseal, femoral specimens. The results revealed that ovariectomy had no effect on cortical bone mass and biomechanical competence. OVX rats treated with estrogen and also OVX rats treated with risedronate showed no significant difference from either OVX or control groups. After only 5 weeks of treatment, hPTH monotherapy increased ash content, cross-sectional area, cortical thickness and compressive bone strength (load) significantly. After 15 weeks of treatment, OVX rats treated with PTH monotherapy or PTH in combination with risedronate showed identical load-values. These values were significantly higher than those seen in both control and OVX rats. However, PTH in combination with estrogen failed to augment cortical bone strength over control or OVX levels after therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect on vertebral bone mass and strength of long term treatment with antiresorptive agents (estrogen and calcitonin), human parathyroid hormone-(1-38), and combination therapy, assessed in aged ovariectomized rats.

The aim of the study was to assess the long term effect of the antiresorptive agents estrogen and salmon calcitonin, the anabolic drug PTH, and combination therapy on vertebral bone mass and bone biomechanical competence in aged osteopenic ovariectomized (OVX) rats. Seventy-nine 1-yr-old retired breeder Wistar rats were randomized into seven groups: 1) sham-operated, 2) OVX, 3) OVX plus estrogen, 4) OVX plus salmon calcitonin, 5) OVX plus human (h) PTH-(1-38), 6) OVX plus hPTH-(1-38) and estrogen, and finally, 7) OVX plus hPTH-(1-38) and calcitonin. Treatment regimens were initiated 8 weeks after ovariectomy and continued for 24 weeks. Whole body bone mass was measured by dual photon absorptiometry at intervals of 4 weeks and at death. Changes in spinal bone mass (BMC), biomechanical competence, and structure were assessed from the lumbar vertebral bodies. The results revealed a protective effect of both estrogen and calcitonin on ovariectomy-induced loss of whole body bone mass, but only estrogen had a significant effect on spinal BMC. hPTH-(1-38) monotherapy increased vertebral bone mass (BMC and ash content), size, and biomechanical parameters 20-80% over OVX levels. A more rapid effect on vertebral bone mass was seen when hPTH-(1-38) was combined with estrogen or salmon calcitonin. The study has shown that in aged OVX osteopenic rats, hPTH-(1-38) therapy increases vertebral bone mass and bone quality and also maintains trabecular connectivity. Both estrogen and calcitonin reduce the ovariectomy-induced bone loss, but cannot restore bone mass to sham-operated levels. On the basis of this study, it is concluded that PTH therapy seems to hold promise in the management of postmenopausal and age-related osteoporosis.

Biomechanical analysis of cervix uteri in nonpregnant, pregnant and antigestagen (ZK 98 299) treated pregnant rats.

The biomechanical properties of the cervix uteri of the rat were studied under different pharmacological conditions. Four groups of rats were enrolled: A. non-pregnant (N = 12), B. 18 days pregnant treated with vehicle (N = 14), C. 18 days pregnant treated with the antigestagen ZK 98 299 (Onapristone) for 19 hours (N = 15), D. 22 days pregnant during spontaneous labor (N = 12). Load-dimension curves of two 2 mm ring-preparations from each cervix were obtained by a material testing machine. The results showed that the sampling position, the cervical ripening process, and the influence of antigestagen treatment were reflected in the biomechanical and compositional parameters. In conclusion the methodology in the present study constitute a model in which the effect of pharmaca on cervical ripening can be tested. The study demonstrated that antigestagen treatment induced biomechanical changes in the cervix comparable to those occurring during physiological cervical ripening at term.

Evaluation of the skeletal effects of combined mild dietary calcium restriction and ovariectomy in Sinclair S-1 minipigs: a pilot study.

A pilot study was conducted to investigate the combined effects of ovariectomy (OVX) with preceding and concomitant mild dietary calcium restriction on the minipig skeleton. Minipigs 4 months old were fed diets containing 0.9, 0.75, or 0.5% calcium (Ca). At 10 months, the 0.75 and 0.5% pigs were OVX and the 0.9% were either sham operated or OVX. All pigs were maintained on their respective diets for an additional 6 months. Excised lumbar vertebrae and long bones were evaluated by densitometry and histomorphometry, and vertebral cancellous bone samples were tested biomechanically. In pigs fed the 0.9% Ca diet, OVX alone effected decreases of 6% in vertebral bone mineral density (BMD), 15% in trabecular bone volume (BV/TV), and 13% in trabecular number (Tb.N), an increase of 15% in trabecular separation (Tb.Sp), and a nonsignificant increase (p < 0.056) in vertebral cancellous final erosion depth (F.E.De) compared with the 0.9% Ca sham-operated group. Decreasing dietary Ca to 0.5% in combination with OVX effected an 8% reduction in vertebral BMD that was not associated with any significant alterations in parameters of vertebral cancellous bone microstructure or remodeling compared with the 0.9% Ca sham-operated pigs. Increases in serum PTH noted in the 0.5% Ca OVX group were generally paralleled by increases in calcitriol. In OVX pigs fed a diet containing 0.75% Ca, a 10% reduction in vertebral BMD was observed. This was associated with significant increases in F.E.De and vertebral marrow star volume (Ma.St.V) compared with the 0.9% Ca sham-operated pigs and the other OVX groups. In addition, Tb.Sp was increased and Tb.N decreased compared with the 0.9% Ca sham-operated pigs. Increases in serum PTH in this group were not accompanied by increases in calcitriol. Midradial and midfemoral BMD values were reduced in the 0.75 and 0.5% Ca OVX groups compared with the 0.9% Ca sham-operated pigs. Histomorphometric analyses of cortical bone suggested the reduction in cortical bone mass in the 0.75% Ca OVX group may have been largely due to net loss on the endocortical surface versus possible failure to accrue bone in the 0.5% Ca OVX group. Ash density and biomechanical parameters for vertebral cancellous bone decreased progressively in the 0.9% sham-operated, 0.9% Ca OVX, and 0.75% Ca OVX groups and then increased in the 0.5% Ca OVX group. After normalization for bone mass (ash), mechanical changes were still apparent, particularly for the 0.75% Ca OVX group compared with other OVX groups, reflecting that structural changes had taken place in the trabecular network.(ABSTRACT TRUNCATED AT 400 WORDS)

Cortical bone mass, composition, and mechanical properties in female rats in relation to age, long-term ovariectomy, and estrogen substitution.

The study comprised 12 groups of female rats: 6 groups of intact rats killed at 2, 6, 9, 12, 15, and 24 months of age, 4 groups of rats ovariectomized at 6 months and killed together with the intact rats at 9, 12, 15, and 24 months of age, and 2 groups of rats (one intact and one ovariectomized) treated with estrogen (2 micrograms estradiol valerate/rat/week s.c.) for 8 months before they were killed at 24 months of age. The composition, dimensions, and mechanical strength of intact bone and bone collagen from femoral diaphyses were investigated in relation to age, ovariectomy, and estrogen administration. Up to 6-9 months of age, the axial length, percentage ash, density, and compressive mechanical stress increased, whereas percentage collagen decreased. An age-related increase in bone mass, cross-sectional area, and wall thickness and a decrease in mechanical quality of bone collagen were apparent from 2 to 24 months of age. An age-related periosteal bone formation and the absence of endosteal bone resorption were demonstrated in intact rats. Compared with intact rats, ovariectomy was followed by an increase in body weight, a tendency to reduced percentage ash and a depressed bone mass, cross-sectional area, and wall thickness of femoral diaphyses. The compressive mechanical stress of intact bone and the mechanical quality of bone collagen were unaffected by ovariectomy. Ovariectomy did not influence the periosteal bone formation but induced an endosteal bone resorption not present in the intact rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term observation of the detrusor smooth muscle in rats. Its relationship to ovariectomy and estrogen treatment.

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 nerve-mediated 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.