Eroded Surface Research Articles

KIAA1199 is a secreted molecule that enhances osteoblastic stem cell migration and recruitment

Factors mediating mobilization of osteoblastic stem and progenitor cells from their bone marrow niche to be recruited to bone formation sites during bone remodeling are poorly known. We have studied secreted factors present in the bone marrow microenvironment and identified KIAA1199 (also known as CEMIP, cell migration inducing hyaluronan binding protein) in human bone biopsies as highly expressed in osteoprogenitor reversal cells (Rv.C) recruited to the eroded surfaces (ES), which are the future bone formation sites. In vitro, KIAA1199 did not affect the proliferation of human osteoblastic stem cells (also known as human bone marrow skeletal or stromal stem cells, hMSCs); but it enhanced cell migration as determined by scratch assay and trans-well migration assay. KIAA1199 deficient hMSCs (KIAA1199down) exhibited significant changes in cell size, cell length, ratio of cell width to length and cell roundness, together with reduction of polymerization actin (F-actin) and changes in phos-CFL1 (cofflin1), phos-LIMK1 (LIM domain kinase 1) and DSTN (destrin), key factors regulating actin cytoskeletal dynamics and cell motility. Moreover, KIAA1199down hMSC exhibited impaired Wnt signaling in TCF-reporter assay and decreased expression of Wnt target genes and these effects were rescued by KIAA1199 treatment. Finally, KIAA1199 regulated the activation of P38 kinase and its associated changes in Wnt-signaling. Thus, KIAA1199 is a mobilizing factor that interacts with P38 and Wnt signaling, and induces changes in actin cytoskeleton, as a mechanism mediating recruitment of hMSC to bone formation sites.

A novel device to prevent osteoporosis by promoting bone metabolism using a newly developed double-loading stimulation with vibration and shaking.

In Japan, 13 million people have osteoporosis, including approximately 9 hundred thousand people who are bedridden owing to bone fractures from falls. Preventing osteoporosis is considered to be an important and effective way of preventing fall-related fractures. Thus, we developed a novel method of locomotor stimulation and analyzed its effectiveness in mice. Specifically, we created a double-loading device that combines vibration and shaking stimulation. The device was used to continuously stimulate ovariectomy-induced decreased bone density mouse models 30 minutes daily for 10 weeks. We then collected femur samples, created undecalcified tissue slices, calculated parameters using bone histomorphomtry, and conducted comparative testing. BS/TV (bone surface/tissue volume), N.Oc/ES (osteoclast number/eroded surface), Oc.S/ES (osteoclast osteoid surface/eroded surface), Omt (osteoid maturation time), Tb.N (trabecular number), Mlt (mineralization lag time) < (p < 0.01), N.Ob (osteoblast number), N.Ob/TV (osteoblast number/tissue volume), sLS (single labeled suface), N.Mu.Oc/ES (multinucle osteoclast number/eroded surface), and N.Mo.Oc/ES (mononucle osteoclast number/eroded surface) (p < 0.05) were significantly higher in the stimulation group than in the non-stimulation group. In addition, BS/BV (bone surface/bone volume), Tb.Sp (trabecular separation), MAR (mineral apposition rate), Aj.Ar (adjusted apposition rate) (p < 0.01), ES (eroded surface ), ES/BS (eroded surface/bone surface), and BRs.R (bone resorption rate) (p < 0.05) were significantly lower in the stimulation group than in the non-stimulation group. These results suggest that stimulation activated osteoblasts and osteoclasts, thereby leading to highly active bone remodeling. We anticipate that bone mineralization will subsequently occur, suggesting that this stimulation technique is effective in preventing osteoporosis by alleviating sudden bone density loss.

Study of Erosion–Corrosion and Corrosion Behavior of Commercially Pure-Ti During Slurry Erosion

The erosion–corrosion (EC) and pure erosion of commercially pure titanium have been investigated in a 3.5% sodium chloride solution containing 10, 30, and 60 g/l SiO2 particles with an average size of 318 μm. The tests were performed at impact velocities of 4, 6, and 9 m/s under two impact angles of 40 deg and 90 deg. Polarization technique was used to study corrosion behavior of the material during erosion–corrosion. The eroded surfaces were examined by a scanning electron microscope (SEM) and a surface profilometer. The pure erosion, corrosion, and erosion–corrosion rates increased as impact velocity and sand concentration increased. The corrosion rates of the eroding surfaces under a normal impact were lower than those at an impact angle of 40 deg. The S/T ratio, i.e., the ratio of synergy to erosion–corrosion rates was about 80% at an impact velocity of 4 m/s, which indicated the high effect of the electrochemical corrosion on the degradation of CP-Ti at low velocity. The S/T ratio decreased to 30% and 15% at the impact velocities of 6 and 9 m/s, respectively. The S/T ratio was also decreased with increasing sand concentration indicating a greater role of mechanical degradation upon the erosion–corrosion rate in the concentrated slurries.

Study of the Effects of Sand Blasting on Soda Lime Glass Erosion

In Saharian regions, the erosion of glass by sand particles during sandstorms is a regular phenomenon. The progressive loss of matter on surface affects both the optical transmission and the mechanical strength. In the present work, we examine the effects of sand blasting on the erosion of soda lime glass intended for vehicles windshields manufacture. We used a sand coming from Algerian Sahara (Ouargla) which is characterized by a mostly rounded shape. All sand blasting erosion tests were simulated in laboratory. The erosive wear of soda lime glass is evaluated at different impingement angles (30, 45, 60 and 90°, with sand masses varying from 10 to 300 g and three different velocities (16, 20 and 24 m/s). The results obtained show that the erosion rate (Er), the mean roughness (Ra) and the mass loss (∆m) reach their maximum at 90° (flow normal to the surface). After exposure to a sand mass of 300 g at normal incidence, the glass surface becomes totally blurred. The ∆m of the glass is 54 mg and the Ra reaches about 3.57µm and the optical transmission (To) is affected proportionally to the sand mass used (mP). It decreases from 91.5% down to 12 % when the mass reaches 300 g. The morphologies of eroded surface were examined by the scanning electronic microscopy. From these observations, we noticed that the erosion mechanism is often of a brittle kind characterized by the formation of radial and lateral cracks that develop into chippings.

SAT0442 Subchondral Bone Remodeling, but not Bone Mass, is Increased in Local Early Stage Lesions of the Osteoarthritic Human Hip Joint as Studied by Stereological Histology

BackgroundOsteoarthritis (OA) is a common joint disease, but the pathology is not fully understood. It has been suggested that bone changes are important for the pathogenesis of OA. However, only...

AB0170 Bone formation and resorption in arthritis – a histological study using 3D stereological estimators in SKG mice

BackgroundBone destruction in the joints of patients with rheumatoid arthritis (RA) is the result of a combined bone resorption by osteoclasts and bone formation by osteoblasts. However, most knowledge about...

In vivo micro-computed tomography allows direct three-dimensional quantification of both bone formation and bone resorption parameters using time-lapsed imaging

Bone is a living tissue able to adapt its structure to external influences such as altered mechanical loading. This adaptation process is governed by two distinct cell types: bone-forming cells called osteoblasts and bone-resorbing cells called osteoclasts. It is therefore of particular interest to have quantitative access to the outcomes of bone formation and resorption separately. This article presents a non-invasive three-dimensional technique to directly extract bone formation and resorption parameters from time-lapsed in vivo micro-computed tomography scans. This includes parameters such as Mineralizing Surface (MS), Mineral Apposition Rate (MAR), and Bone Formation Rate (BFR), which were defined in accordance to the current nomenclature of dynamic histomorphometry. Due to the time-lapsed and non-destructive nature of in vivo micro-computed tomography, not only formation but also resorption can now be assessed quantitatively and time-dependent parameters Eroded Surface (ES) as well as newly defined indices Mineral Resorption Rate (MRR) and Bone Resorption Rate (BRR) are introduced. For validation purposes, dynamic formation parameters were compared to the traditional quantitative measures of dynamic histomorphometry, where MAR correlated with R = 0.68 and MS with R = 0.78 ( p < 0.05). Reproducibility was assessed in 8 samples that were scanned 5 times and errors ranged from 0.9% (MRR) to 6.6% (BRR). Furthermore, the new parameters were applied to a murine in vivo loading model. A comparison of directly extracted parameters between formation and resorption within each animal revealed that in the control group, i.e., during normal remodeling, MAR was significantly lower than MRR ( p < 0.01), whereas MS compared to ES was significantly higher ( p < 0.0001). This implies that normal remodeling seems to take place by many small formation packets and few but large resorption volumes. After 4 weeks of mechanical loading, newly extracted trabecular BFR and MS were significantly higher ( p < 0.01) in the loading compared to the control group. At the same time, ES was significantly decreased ( p < 0.01). This indicates that modeling induced by mechanical loading takes place primarily by increased area, not width of formation packets. With these results, we conclude that the non-invasive direct technique is well suited to extract dynamic bone morphometry parameters and eventually gain more insight into the processes of bone adaptation not only for formation but also resorption.

Vitamin K2 Promotes Bone Healing in a Rat Femoral Osteotomy Model with or without Glucocorticoid Treatment

The purpose of the present preclinical study was to determine whether vitamin K(2) would promote bone healing in a rat femoral osteotomy model with or without glucocorticoid (GC) treatment. Thirty-eight 6 week-old female Sprague-Dawley rats underwent a unilateral osteotomy of the femoral diaphysis followed by intramedullary wire fixation and then were randomized into four groups that received the following treatment schedules: vehicle, vitamin K(2), GC + vehicle, and GC + vitamin K(2). GC (prednisolone, 2.5 mg/kg) was administered subcutaneously twice a week. Vitamin K(2) (menatetrenone, 30 mg/kg) was administered orally five times a week. After 8 weeks of treatment, the wires were removed and a bone histomorphometric analysis was performed on the bone tissue inside the callus. Vitamin K(2) administration to GC-untreated rats decreased the osteoclast surface/bone surface (OcS/BS), osteoblast surface (ObS)/BS, eroded surface (ES)/BS, and bone formation rate (BFR)/BS and increased the lamellar area/bone area. Although GC treatment increased the ES/BS and decreased the ObS/BS, BFR/BS, and lamellar area/bone area, vitamin K(2) administration to GC-treated rats decreased the OcS/BS and prevented an increase in the ES/BS and a decrease in the lamellar area/bone area. These results suggested that vitamin K(2) downregulated bone turnover and stimulated lamellar bone formation in GC-untreated rats and prevented an increase in bone resorption while maintaining bone formation and prevented a decrease in lamellar bone formation in GC-treated rats. Thus, vitamin K(2) appears to be effective for promoting bone healing in a rat femoral osteotomy model with or without GC treatment.

Fractal Characterization of Slurry Eroded Surfaces at Different Impact Angles

In the present work, the topographical images of slurry erosion surfaces at different impact angles were quantified using fractal analysis. The study showed that the variation of fractal value of slope of linearized power spectral density with the impact angle is largely similar to the relationship between the erosion rate and the impact angle. Both the fractal value and erosion rate were maximum at 45 deg and 90 deg for ductile and brittle materials, respectively. It was found also that the variation of fractal values versus the impact angle has a general trend that does not depend on magnification factor. The fractal features to the eroded surfaces along different directions showed high directionality at oblique impact angle and were symmetrical at normal impact.

Influence of heat treatment on slurry erosive wear resistance of Al6061 alloy

Material loss due to slurry erosion is a serious problem in many industrial applications like hydraulic turbines, slurry pumps, pipe lines, etc. where the ideal choice of engineering materials is a real challenge. Light weight aluminum alloys are finding wide applications in the field of aerospace, automobile, defence, etc. due to improved physical, mechanical and tribological properties. Among all available alloys Al6061 is extensively used owing to its reasonable strength and ease of processing. Currently these alloys are also explored as candidate materials for propeller blade of torpedoes where major failure occurs due to slurry erosive wear. In the light of the above present investigation is aimed to study the slurry erosive wear behavior of heat treated Al6061 alloy in 3.5%NaCl solution with sand particles slurry. The studies were carried out at different sand concentration (10–40%), varying rotational speed (500–1500 rpm), at different time duration (5–25 h) and varied impinging particle size (100–600 μm). The effect of heat treatment on erosive wear behavior of Al6061 alloy were studied by subjecting to solutionising at temperature of 530 °C for a duration of 2 h, followed by quenching in air, water and ice media. Both natural and artificial aging at 175 °C was performed on quenched samples from 4 to 10 h duration in steps of 2 h. The rate of material loss is found to be higher with increased sand concentration due to increased impinging action of sand particles. Increased speed of slurry rotation increases the velocity of impingement of sand particles on the surface of erodent and resulted in higher weight loss. Increased time duration up to 20 h, the wear rate increases. However, beyond this test duration, the wear rate attains a steady state with further increase in test duration. It is found that heat treatment has profound effect on slurry erosive wear resistance of Al6061 alloy. It is also observed that with increase in aging duration for all quenching medias studied there is a reduction in slurry erosive wear rate. However, ice as quenching media offers higher erosive wear resistance compared to water, air and unheat treated alloy. SEM studies were carried out on eroded surface to observe the mechanism of metal removal. The eroded surface also indicates that increased sand concentration, higher rotational speed and increased particle size resulted in severe damage on tested surfaces.

Histomorphometric Study of Alveolar Bone Healing in Rats Fed a Boron‐Deficient Diet

Bone healing after tooth extraction in rats is a suitable experimental model to study bone formation. Thus, we performed a study to determine the effects of boron (B) deficiency on bone healing by using this model. The first lower right molar of weanling Wistar rats was extracted under anesthesia. The animals were divided into two groups: +B (adequate; 3 mg B/kg diet), and -B (boron-deficient; 0.07 mg/kg diet). The animals in both groups were killed in groups of 10 at 7 and 14 days after surgery. The guidelines of the NIH for the care and use of laboratory animals were observed. The mandibles were resected, fixed, decalcified, and embedded in paraffin. Buccolingually oriented sections were obtained at the level of the mesial alveolus and used for histometric evaluations. Total alveolar volume (TAV) and trabecular bone volume per total volume (BV/TV) in the apical third of the alveolus were determined. Percentages of osteoblast surface (ObS), eroded surface (ES), and quiescent surface (QS) were determined. No statistical significant differences in food intake and body weight were observed. Histomorphometric evaluation found -B rats had 36% and 63% reductions in BV/TV at 7 and 14 days, respectively. When compared with +B rats, -B rats had significant reductions (57% and 87%) in ObS concomitantly with increases (120% and 126%) in QS at 7 and 14 days, respectively. The findings show that boron deficiency results in altered bone healing because of a marked reduction in osteogenesis.

A histomorphometric study of alveolar bone modelling and remodelling in mice fed a boron-deficient diet

Objective Emerging evidence indicates that boron (B) plays a role in bone formation and maintenance. Thus, a study was performed to determine whether dietary B-deficiency affects periodontal alveolar bone modelling and remodelling. Design Weanling Swiss mice ( n = 30) were divided into three groups: control diet (GI, 3 mg B/kg); B-deficient diet (GII, 0.07 mg B/kg); and pair-fed with GII (GIII). The animals were maintained on their respective diets for 9 weeks and then sacrificed. The guidelines of the NIH for the care and use of laboratory animals were observed. The mandibles were resected, fixed, decalcified in 10% EDTA and embedded in paraffin. Buccolingually oriented sections were obtained at the level of the mesial root of the first lower molar and stained with H–E. Histomorphometric studies were performed separately on the buccal and lingual sides of the periodontal alveolar bone. Percentages of osteoblast surfaces (ObSs), eroded surfaces (ESs), and quiescent surfaces (QSs) were determined. Results No statistically significant differences in food intake and body weight were observed between the groups. When compared with GI and GIII mice, GII mice (B-deficient) had 63% and 48% reductions in ObS and 58% and 73% increases in QS in buccal and lingual plates, respectively. ES were not affected by B nutriture. Conclusion The results are evidence that dietary boron deprivation in mice alters periodontal alveolar bone modelling and remodelling by inhibiting bone formation.

Synergistic Effect of Vitamin K2 and Prostaglandin E2 on Cancellous Bone Mass in Hypophysectomized Young Rats

Hypophysectomy (HX) results in cessation of bone growth and cancellous osteopenia in rats. It has been reported that prostaglandin E2 (PGE2) improves cortical and cancellous bone mass in HX rats. The purpose of the present study was to examine whether combined administration of vitamin K2 and PGE2 would have a more beneficial effect on bone than single administration of either alone in HX rats. Forty-three female Sprague-Dawley rats, 6 weeks of age, were randomized by the stratified weight method into five groups: intact controls, HX, HX + vitamin K2 (30 mg/kg, p.o., daily), HX + PGE2 (0.83 mg/kg, i.m., 5 days a week), and HX + vitamin K2 + PGE2. The duration of the experiment was 4 weeks. There was a reduction in cancellous bone volume/total tissue volume (BV/TV) of the proximal tibial metaphysis and a reduction in total tissue area and cortical area (Ct.Ar) of the tibial diaphysis. Vitamin K2 did not affect cancellous BV/TV or Ct.Ar. On the other hand, PGE2 attenuated the loss of cancellous BV/TV in association with higher bone formation rate/bone surface (BFR/BS) and eroded surface (ES)/BS compared with intact controls. PGE2 also increased percent Ct.Ar compared with nontreated HX rats as a result of attenuation of a decrease in periosteal BFR/BS. Vitamin K2 had a synergistic effect with PGE2 on cancellous BV/TV as a result of the suppression of an increase in ES/BS observed by PGE2 treatment. These results suggested that PGE2 had an anabolic action on cancellous and cortical bone and that despite no apparent effect of vitamin K2 on bone, it had a synergistic effect with PGE2 on cancellous bone mass in young HX rats.

A histomorphometric study of alveolar bone modeling and remodeling in mice fed a boron‐deficient diet

Emerging evidence indicates that boron (B) plays a role in bone formation and maintenance. Thus, a study was performed to determine whether B-deficiency affects alveolar bone modeling and remodeling. Weanling Swiss mice (n=30) were divided into 3 groups: control diet (GI, 3 mg B/kg); B-deficient diet (GII, 0.07 mg B/kg); and pair-fed with GII (GIII). The animals were maintained on their respective diets for 9 wk and then sacrificed. The guidelines of the NIH for the care and use of laboratory animals were observed. The mandibles were resected, fixed, decalcified in 10% EDTA and embedded in paraffin. Buccolingually oriented sections were obtained at the level of the mesial root of the first lower molar and stained with H-E. Histomorphometric studies were performed separately on the buccal and lingual sides of the periodontal alveolar bone. Percentages of osteoblast surfaces (ObS), eroded surfaces (ES), and quiescent surfaces (QS) were determined. No statistically differences in food intake and body weight were observed between the groups. When compared to GI and GIII mice, GII mice (B-deficient) had 63% and 48% reductions in ObS and 58% and 73% increases in QS in buccal and lingual plates, respectively. The results are evidence that boron deprivation alters periodontal alveolar bone modeling and remodeling by inhibiting bone formation. Grants: CONICET PIP 6042, Extramural Agreement USDA, ARS 58-5450-4N-F038.

FACIES CONTROL ON THE COMPOSITION OF SERPUKHOVIAN AND EARLY BASHKIRIAN FORAMINIFERAL ASSEMBLAGES IN THE MIDDLETIEN-SHAN MOUNTAINS, CENTRAL ASIA

Serpukhovian-lower Bashkirian deposits are widely developed in the Middle Tien-Shan Mountains of Uzbekistan and adjacent countries of Central Asia. These deposits formed in a sedimentary basin exhibiting four distinctive facies that differ in foraminiferal diversity and population density. The facies types, named for mountain ranges containing representative sections, are called 1) Talassic, for inner shelf, shallow- water marine carbonates; 2) Ugamic, for carbonaceous deposits accumulating on an open, shallow-water, outer carbonate shelf platform; 3) Karzhantauic, for interbedded volcaniclastics and shallow-water marine carbonates deposited on a eroded surface; and 4) Paltauic, for basinal beds containing thin-bedded, graded and laminated organic limestones and interbedded turbidites. A statistical program (Sorenson's Coefficients of Species Similarity) was used to compare assemblages in eight foraminiferal zones from coeval fades across the basin. Highest similarity coefficients occur in the early Serpukhovian and are probably related to a marine transgression that flooded the basin. Regression and volcaniclastic sedimentation account for lower coefficients in the remainder of the Serpukhovian. Increased foraminiferal diversity and abundance in the earliest Bashkirian were probably caused by the opening of new connections to adjacent Paleotethyan basins only to be followed by more restricted environmental conditions and lower similarity coefficients later in the early Bashkirian.

Concentration of bisphosphonate (incadronate) in callus area and its effects on fracture healing in rats.

The aim of the present study was to investigate effects of incadronate on early stages of fracture healing and to detect its concentration in callus area (Ca.Ar). Rats were injected three times per week with either two doses of incadronate (10 microg/kg and 100 microg/kg) or vehicle for 2 weeks. Femora were then fractured and fixed and animals were divided into pretreatment (P-10 and P-100) and continuous treatment (C-10 and C-100) groups. Incadronate treatment was stopped in P-10 and P-100 groups but continued in C-10 and C-100 groups. Animals were killed at 2 weeks and 4 weeks after fracture. Results showed significantly large callus, compared with the control, only in C-100 group at 4 weeks but not at 2 weeks. Both linear labeled surface (LS) and eroded surface (ES) decreased significantly in C-10 and C-100 groups at 2 weeks and 4 weeks. Osteoclast number (N.Oc) decreased significantly in C-10 and C-100 groups at 2 weeks but increased slightly at 4 weeks. However, there was no significant difference in the above parameters in P-10 and P-100 groups at 4 weeks. Apoptotic osteoclasts were observed only in the C-100 group at 4 weeks. A time-course decrease in incadronate concentration was detected in P-10 and P-100 groups whereas an increase was observed in C-10 and C-100 groups. These findings suggest that larger callus under incadronate treatment may result from the inhibition of bone resorption, histological characteristics of callus may be correlated with incadronate concentration, and metabolism of incadronate in bone may be related to the rate of bone turnover.

A mechanics model of erosion of ductile materials by backward extrusion

Examination of eroded surfaces of ductile materials under a scanning electron microscope typically shows thin slivers or platelets; these subsequently break off to provide wear debris. Cousens and Hutchings [A.K. Cousens, I.M. Hutchings, Wear 88 (1983) 335–348] have studied this phenomenon in careful experiments, in which commercially pure aluminium and aluminium alloys were eroded by using glass beads and iron shot in an air blast erosion tester. It was observed that a thin surface layer hardened both due to embedding of the fragments of erodent and due to work hardening. The repeated impacts by erodents, then, caused the softer material to extrude out backwards, from discontinuities in the hardened layer. It is proposed that this `backward extrusion' is due to `plastic ratchetting' of the material below the hardened layer, which is progressively compressed and extruded out. The proposed mechanism has been modelled by using kinematical shakedown theorem of the theory of plasticity and the impact pressure which needs to be exceeded for the process to continue has been evaluated. By expressing the impact pressure in terms of impact velocity and material properties of the shot and the eroding surface a non-dimensional velocity is defined and related to the shakedown behaviour of the eroding system. It is shown that for the backward extrusion process to continue the non-dimensional impact velocity must be above a critical value.

Trabecular remodeling processes in the ovariectomized rat: modified node-strut analysis

The purpose of this study was to evaluate the trabecular bone remodeling processes in ovariectomized rats, focusing on diminishing trabecular connectivity. We used modified node-strut analysis defining three areas in the trabecular surfaces for the three-dimensional understanding of trabecular resorption derived from two-dimensional conventional sections, in addition to conventional bone histomorphometry and node-strut analysis. Seven-month-old female Wistar rats were used and treated with bilateral ovariectomy (ovx) and sham operation. Six rats in each group were examined at 4 and 8 weeks. We prepared undecalcified sections from the left tibiae with Villanueva bone and Goldner stains. We divided the trabecular bone surfaces (BS) into three areas: node (Nd), terminus (Tm), and strut (St), and measured the bone resorption and formation parameters, including eroded surface (ES), osteoclast surface (Oc.S), osteoid surface (OS), and double-labeled surface (dLS) in each defined area. In conventional bone histomorphometry, the ovx group showed high turnover osteopenia compared with the sham operation group. In node-strut analysis, the ovx group showed significantly lower values for node-related parameters than did the sham operation group. In the modified node-strut analysis, bone resorption parameters in the ovx group showed significantly higher values, particularly for strut and terminus-eroded surfaces (StES/BS, TmES/BS), and for each area of osteoclast surface (NdOc.S/BS, TmOc.S/BS, and StOc.S/BS) compared with the sham operation group. Bone formation parameters in the ovx group also showed significantly higher values, particularly for strut and terminus osteoid surfaces (TmOS/BS, StOS/BS), and for each area of double-labeled surface (NddLS/BS, TmdLS/BS, and StdLS/BS) compared with the sham operation group at 4 weeks. At 8 weeks, each area of bone formation parameter in the ovx group showed significantly higher values than that in the sham operation group. These results suggest that in the ovx group, the trabecular plates became perforated and the perforative cavities progressively enlarged, and/or the edges of plates were eroded regardless of elevated bone formation, resulting in diminished trabecular connectivity, and the node area might not be influenced relatively by bone remodeling in the early resorption.

Surgically induced uremia in rats. II: Osseous PTH-susceptible signaling systems as predictors of bone resorption.

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 (PL-C) 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 mid-shaft (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.

Particle collisions in the vicinity of an eroding surface

In the vicinity of a surface which is being eroded there is a region where particles arriving at and departing from the surface can collide. The frequency of collisions and the resulting motion of spherical particles have been investigated theoretically and experimentally. An expression is derived for the flux of spheres necessary for a high frequency of collisions. The directions and velocities of particles after collision have also been calculated, assuming elastic collisions. In the low-flux limit collisions do not reduce the number of particles reaching the surface. Long-exposure (ca. 1 s) and high-speed (5000 frames s-1) photography confirms these findings for the case of 0.6+or-0.1 mm diameter glass spheres travelling at 13+or-1 m s-1. These conclusions conflict with the ideas of many authors who suggest that collisions help protect the eroded surface. The present paper shows that collisions degrade the incident beam of particles by increasing the angular divergence of the beam and creating a spectrum of velocities. Stray particles have also been observed entering the region of interest, increasing the frequency of collisions. Stray particles and changes in the incident beam are probably the causes of the observed reduction in erosion rate at high levels of flux.