Effects of prostaglandins on regional remodeling changes during tibial healing in beagles: a histomorphometric study

The growing role of eicosanoids in tissue regeneration, repair, and wound healing

Tissue repair and regeneration are essential processes in maintaining tissue homeostasis, especially in response to injury or stress. Eicosanoids are ubiquitous mediators of cell proliferation, differentiation, and angiogenesis, all of which are important for tissue growth. Eicosanoids regulate the induction and resolution of inflammation that accompany the tissue response to injury. In this review, we describe how this diverse group of molecules is a key regulator of tissue repair and regeneration in multiple organ systems and biologic contexts.

Effects of long-term administration of carprofen on healing of a tibial osteotomy in dogs

OBJECTIVE

To evaluate effects of long-term administration of carprofen on healing of a tibial osteotomy in dogs.

ANIMALS

12 healthy female Beagles.

PROCEDURES

A mid-diaphyseal transverse osteotomy (stabilized with an intramedullary pin) of the right tibia was performed in each dog. The carprofen group (n = 6 dogs) received carprofen (2.2 mg/kg, PO, q 12 h) for 120 days; the control group (6) received no treatment. Bone healing and change in callus area were assessed radiographically over time. Dogs were euthanized 120 days after surgery, and tibiae were evaluated biomechanically and histologically.

RESULTS

The osteotomy line was not evident in the control group on radiographs obtained 120 days after surgery. In contrast, the osteotomy line was still evident in the carprofen group. Callus area was significantly less in the carprofen group, compared with the area in the control group, at 20, 30, and 60 days after surgery. At 120 days after surgery, stiffness, elastic modulus, and flexural rigidity in the carprofen group were significantly lower than corresponding values in the control group. Furthermore, histologic evaluation revealed that the cartilage area within the callus in the carprofen group was significantly greater than that in the control group.

CONCLUSIONS AND CLINICAL RELEVANCE

Long-term administration of carprofen appeared to inhibit bone healing in dogs that underwent tibial osteotomy. We recommend caution for carprofen administration when treating fractures that have delays in healing associated with a reduction in osteogenesis as well as fractures associated with diseases that predispose animals to delays of osseous repair.

Cytokine Release from Osteoblasts in Response to Different Intensities of Pulsed Electromagnetic Field Stimulation

We use an in-vitro osteoblast cell culture model to investigate the effects of low-frequency (7.5 Hz) pulsed electromagnetic field (PEMF) stimulation on osteoblast population, cytokines (prostaglandin E(2) (PGE(2)), transforming growth factor beta1(TGFbeta1), and alkaline phosphatase (ALP) activity to find the optimal intensity of PEMF for osteoblast growth. The results demonstrate that PEMF can stimulate osteoblast growth, release of TGFbeta1, and, in addition, an increase of ALP activity. The synthesis and release of PGE(2) in the culture medium are reduced with increasing numbers of cells. Higher intensity does not necessarily mean increased osteoblast growth, and the most efficient intensity is about 2 mV/cm in this case. Although the lower intensities of the PEMF are yet to be determined, the results of this study can shed light on the mechanisms of PEMF stimulation on non union fracture therapy and osteoporosis prevention in the future.

Optimum intensities of ultrasound for PGE(2) secretion and growth of osteoblasts

This study compared the effects of different intensity ultrasound (US) on osteoblasts in the far-field model with effects of the near-field model from the literature, to understand the relations between prostaglandin E(2) (PGE(2)) and osteoblast growth. We used an in vitro model to investigate the effects of 1-MHz, pulsed 1:4, and five different spatial-average temporal-peak intensity (150, 300, 600, 1200 and 2400 mW/cm(2)) US stimulations in far-field exposure (240 mm) on osteoblasts for 15 min. Optimum intensity in this study was 600 mW/cm(2), and cell density and PGE(2) secretion could be significantly stimulated at this intensity. This research may indicate that the growth of osteoblasts by US stimulation was, at least partly, due to increases in the synthesis and secretion of PGE(2). This well-controlled model can lead to further research on the biologic mechanisms for US.

In vitro effects of low-intensity ultrasound stimulation on the bone cells

Mechanical perturbations serve as extracellular signals to a variety of cells, including bone cells. Low-intensity pulsed ultrasound produces significant multifunctional effects that are directly relevant to bone formation and resorption. Ultrasound stimulation has been shown to accelerate bone-defect healing and trabecular bone regeneration. In this study, we use an in vitro bone cell culture model to investigate the effect of low-intensity pulsed ultrasound. The rat alveolar mononuclear cell-calvaria osteoblast coculture system was used in this study. Before treatment, the bone cells were cultured for 3 days to facilitate their attachment and differentiation. Then, ultrasound exposure (frequency = 1 MHz, intensity = 0.068 W/cm(2)) or sham exposure for 20 min per day was applied until the end of the experiment. Half of the culture media were obtained on the 4th, 5th, 6th, 7th, 8th, 9th, and 10th days for the analysis of cytokines and biochemical parameters. At the end of the experiment, cells were fixed and stained for identification and quantification of the osteoblast and osteoclast cells. After low-intensity pulse ultrasound stimulation, the osteoblast cell counts were significantly increased, whereas the osteoclast cell counts were significantly decreased. The total alkaline phosphatase amount in the culture medium was increased after 7 days of ultrasound stimulation, and tumor necrosis factor-alpha in ultrasound-stimulated bone cells was significantly increased after the 7th day of culture and reached 474.77% of the control medium on the 10th day of culture. The results of this study suggest that low-intensity ultrasound treatment may have a stimulatory effect on bone-healing processes.

Bone defect healing enhanced by ultrasound stimulation: an in vitro tissue culture model

Ultrasound has many medical applications. Previous animal and clinical studies have clearly shown a positive effect of ultrasound on the rate of osseous repair. The present in vitro study was designed to elucidate the specific response of bony tissue to ultrasound treatment. Bilateral femora were obtained from 36 mature male Wistar rats. A bone defect was created at the center of each distal metaphysis. The femora were maintained for either 7 or 14 days in in vitro tissue culture and received 15 min of ultrasound stimulation or a sham exposure. The ultrasound intensity used was either 320 or 770 mW/cm2. Healing of the bone defect was evaluated by histomorphological examination and by analysis for the synthesis and secretion of prostaglandin E2. The results showed that ultrasound stimulation can accelerate both defect healing and trabecular bone regeneration. All experimental femoral defects treated with ultrasound healed faster than the untreated cortical defects, but only the defects receiving 770 mW/cm2 reached a level that was significantly different. The healing rate for the 320-mW/cm2 stimulated defects was intermediate between that of the 770-mW/cm2 and sham-exposed defects. With ultrasound stimulation, prostaglandin E2 secretion by the experimental femora decreased significantly. Changes in the prostaglandin synthesis and concentration were found to correspond to changes in the amount of trabecular regeneration and to acceleration of bone healing. This highly controlled and well-studied model of ultrasound stimulation of bone healing in vitro can be used to further examine the biological mechanisms involved.

Prostaglandin E2 (PGE2) and risedronate was superior to PGE2 alone in maintaining newly added bone in the cortical bone site after withdrawal in older intact rats

The objects of this study were (1) to determine the effects of risedronate (Ris) and prostaglandin E2 (PGE2) alone and in combination, on tibial diaphyses of older intact female rats; and (2) to observe the fate of any extra bone if formed after withdrawal of the treatment. Nine-month-old female Sprague-Dawley rats were treated with 6 mg of PGE2/kg/day, 1 or 5 micrograms of Ris/kg twice a week, or 6 mg of PGE2/kg/day plus 1 or 5 micrograms of Ris/kg twice a week for the first 60 days and followed by vehicle injections for another 60 days. Cross-sections of double fluorescent labeled, undecalcified tibial diaphyses proximal to the tibiofibular junction were processed for histomorphometry. We found that: (1) neither the 1 microgram nor the 5 micrograms of Ris treatment in the 60-day on/60-day off group showed any histomorphometric differences from age-related controls; (2) while the 60 days of PGE2 treatment added extra cortical bone (6%) on the tibial shaft (due to stimulation of periosteal, endocortical, and marrow trabecular bone formation), the new endocortical and most of the new marrow trabecular bone were lost when treatment was withdrawn; however, the new periosteal bone remained; (3) PGE2 with Ris added the same amount of new bone to tibial diaphysis as did PGE2 alone and upon withdrawal, new marrow trabecular bone was lost but new periosteal and endocortical bones were preserved in PGE2 + 1 microgram of Ris on/off group. In contrast, all the new bone was maintained in the PGE2 + 5 micrograms of Ris on/off group; (4) PGE2 + Ris cotreatment failed to block the increase in cortical bone porosity induced by PGE2; and (5) in the PGE2 alone and PGE2 + 1 microgram of Ris on/off groups bone turnover was higher than that in the PGE2 + 5 micrograms of Ris on/off group. These results indicate that on/off treatment with PGE2 and Ris is superior to PGE2 alone in that it forms the same amount of new bone during treatment, but preserves more cortical bone during withdrawal. Depression of bone resorption and turnover were the tissue mechanisms responsible for this protection.

The biochemical pathway mediating the proliferative response of bone cells to a mechanical stimulus

Calvarial bone cells of rats were subjected to either a cyclic biaxial strain of 0.17 per cent (1700 microstrain) or a hydrostatic pressure of 2.5, five, or ten pounds per square inch (17.2, 34.5, or sixty-nine kilopascals). The frequency was held constant at one hertz for both types of mechanical stimulation. When cultured bone cells that had been subjected to a cyclic biaxial strain for two hours were harvested twenty-two hours later, it was found that the level of prostaglandin E2 had increased significantly (p < 0.01) as had cellular proliferation (p < 0.01), as indicated by the incorporation of [3H]-thymidine. The addition to the medium of indomethacin, an inhibitor of prostaglandin synthesis, at a ten-micromolar concentration significantly inhibited (p < 0.01) the increase in prostaglandin E2 synthesis but had no effect on the strain-induced increase in cellular proliferation, as indicated by the incorporation of [3H]-thymidine. Twenty-four hours after exposure to the same cyclic biaxial strain for thirty seconds, other cultured bone cells showed a significant increase in the level of cytoskeletal calmodulin (p < 0.05) and in the DNA content (p < 0.05). N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide (W-7), a calmodulin antagonist, was added to the medium at a one-micromolar concentration, which had been shown to have no effect on the increase in the DNA content of control cells; W-7 completely blocked the increase in the level of cytoskeletal calmodulin and in the DNA content in the cells that were subjected to a cyclic biaxial strain. The bone cells subjected to a hydrostatic pressure showed a dose-dependent increase in the concentration of cytosolic Ca2+, as measured with Fura 2-AM, a fluorescent indicator of intracellular calcium. With a pressure of ten pounds per square inch (sixty-nine kilopascals), the increase in the concentration of cytosolic Ca2+ was nearly eight times greater than that at 2.5 pounds per square inch (17.2 kilopascals) (126 +/- 15.2 compared with 16 +/- 8.0 nanomolar, mean and standard deviation). The addition to the medium of neomycin, an inhibitor of the inositol phosphate cascade, at a ten-millimolar concentration completely blocked the increase in the concentration of cytosolic Ca2+ in these cells; this concentration of neomycin had been shown to have no effect on proliferation in control bone cells. There was also a dose-dependent relationship between the duration of the stimulus and the cellular proliferation. Remarkably, one cycle of pressure at ten pounds per square inch (sixty-nine kilopascals) and a frequency of approximately one hertz produced a 57 per cent increase in the incorporation of [3H]-thymidine at twenty-four hours (p < 0.001). From these findings, we hypothesized that the inositol phosphate cascade-cytosolic Ca(2+)-cytoskeletal calmodulin system plays a dominant role in the signal transduction of a mechanical stimulus into increased proliferation of bone cells, at least under the conditions reported here.

Exogenous prostacyclin, but not prostaglandin E2, produces similar responses in both G6PD activity and RNA production as mechanical loading, and increases IGF-II release, in adult cancellous bone in culture

Cyclic mechanical loading in vivo that leads to new bone formation is also associated in osteocytes and surface bone cells with almost immediate increases in G6PD activity, and later increases in RNA production. Both these early, loading-related, responses can be reproduced in organ culture of adult cancellous bone, and both are abolished by the presence of indomethacin in the culture medium at the time of loading. The implication that prostaglandins (PGs) are involved in the control of loading-related osteogenesis is supported by increases in prostacyclin (PGI2) and PGE2 release from cores of cancellous bone during loading. In the experiments reported here, PGE2 and PGI2 were added exogenously (10(-6) M) to perfusable cores of adult canine cancellous bone to determine whether they would simulate the loading-related responses in G6PD activity and RNA synthesis. PGE2 increased G6PD activity in surface cells and osteocytes within 8 minutes but had no effect on [3H]-uridine incorporation at 6 hours. PGI2 stimulated both G6PD activity and [3H]-uridine incorporation equally in osteocytes and surface cells. Neither PG produced any significant change in medium concentrations of IGF-I, and PGE2 had no effect on IGF-II. In contrast PGI2 elevated the medium concentration of IGF-II threefold. IGF-I and IGF-II were localized immunocytochemically to osteocytes and surface cells in both treated and untreated cores. Prostacyclin, but not PGE2, appears to imitate the early loading-related increases in G6PD activity and RNA synthesis in bone cells in situ. Prostacyclin, but not PGE2, also stimulates the early release of IGF-II.

Healing of cancellous bone osteotomy in rabbits--Part I: Regulation of bone volume and the regional acceleratory phenomenon in normal bone

We performed a simple, undisplaced, incomplete osteotomy of the distal medial condyle of mature New Zealand White rabbits and permitted healing without fixation for 4 weeks. During the recovery period, the rabbits received the bone label calcein in their drinking water. From ground stained and unstained sections, we determined histomorphometric parameters in five zones: osteotomy gap, juxtaosteotomy, lateral condyle, metaphysis, and diaphysis. At 4 weeks, newly formed cancellous bone had obliterated the osteotomy gap. Osteotomy also stimulated new bone formation in cancellous bone of the medial condyle around the osteotomy. At that site, we found a fivefold increase in new bone without a change in bone volume (BV). Stimulation of bone formation was not observed in cancellous bone of the lateral condyle that had not been operated on or in cortical bone of the metaphysis or diaphysis. The maintenance of BV, despite increased new bone formation in the osteotomized medial femoral condyle, was probably due to a local acceleration of bone remodeling.

Intraosseous infusion of prostaglandin E2 in the caprine tibia

We evaluated the effects of intraosseously administered prostaglandin E2 (PGE2) within the proximal metaphysis of the goat (caprine) tibia under intraosseous normotensive and hypertensive conditions. PGE2 was administered at 0.5 or 1.0 mg (1 ml vol) twice daily for 10 days via an Osteoport which had been surgically implanted within the proximal tibial metaphysis. Intraosseous hypertension was produced when venous outflow obstruction (VOO) was created by ligation of the popliteal vein, which drained the proximal tibia, and occlusion of the diaphyseal medullary space distally with bone cement. After VOO, the intraosseous pressure measured at the metaphysis increased significantly (p < 0.05) from a baseline mean of 14.9 +/- 4.2 mm Hg to 28.6 +/- 5.3 mm Hg. Serum radioimmunoassays indicated that VOO prolonged the venous drainage of PGE2 from the tibia after an infusion. Static histomorphometric analysis indicated a marked dose-dependent increase in new bone formation in all PGE2 groups at 30 days after the PGE2 infusion. Significant (p < 0.05) formation of new bone occurred, primarily at the subperiosteal and endocortical surfaces, and moderately increased the marrow cavity of cancellous new bone as compared with the VOO-only group and the controls. Bone remodeling indices were also increased by PGE2. The PGE2 infusion, combined with VOO, produced significantly more new bone formation than the PGE2 infusion alone. Intensive marrow fibrosis was associated with the active bone remodeling.

Increased bone growth by local prostaglandin E2 in rats

The effects of prostaglandin E2 (PGE2) on bone growth were investigated in rats. Daily injection of PGE2 (1, 10, and 100 pmol) was given via local intraosseous route into the metaphysis of the left tibia for 14 days. The contralateral right tibia injected with vehicle and saline was for the control. The rats receiving no injection provided as normal control. The results obtained indicated that PGE2 slightly but significantly decreased the body weight increment without effect on tibial length. The most prominent effect of PGE2 was the increase of metaphyseal bone trabeculae by 45-81% in a dose-dependent manner. The microscopic examination revealed that PGE2 unequivocally increased the new woven bone formation. The bone cell population study showed no difference between the number of osteoblasts and osteoclasts in primary spongiosa of the PGE2-injected limbs and those of contralateral limbs. However, the numbers of osteoblasts and osteoclasts were markedly increased in secondary spongiosa in the PGE2-injected limbs. This finding confirmed a stimulatory role of PGE2 in the bone formation. The local intraosseous injection of PGE2 was proven to be a good model for the study of local growth factors on bone metabolism with a lower effective dose which eliminates the systemic side effects.

Effect of local prostaglandin E2 on periosteum and muscle in rabbits

We assessed the target tissue for the stimulatory effect of prostaglandin E2 (PGE2) on bone formation previously observed during fracture healing. PGE2 was infused into tibial periosteal tissue in the right leg of 7 rabbits and into the anterior tibial muscle in the right leg of 7 other rabbits for 6 weeks. Solvent solution was infused into the left leg. PGE2 infusion at the periosteum caused the formation of primitive woven bone with large amounts of connective tissue; solvent infusion caused small amounts of normal periosteal bone formation. In the neighboring cortical bone, remodeling was increased after PGE2 infusion compared to solvent infusion. In the muscle, PGE2 infusion caused the formation of connective tissue with small amounts of woven bone. Thus, the major effects of PGE2 infusion at the site of the periosteum was the formation of primitive woven bone and in muscles the formation of connective tissue.

Loading-related increases in prostaglandin production in cores of adult canine cancellous bone in vitro: a role for prostacyclin in adaptive bone remodeling?

Cyclic mechanical loading sufficient to engender strains of physiologic magnitude applied to recently excised canine cancellous bone cores in vitro increased the release of prostaglandin E (PGE) and prostacyclin (PGI2, measured as its breakdown product 6-keto-PGF1 alpha), during a 15 minute loading period in which PG levels were measured in perfusing medium at 5 minute intervals. Peak production occurred in the 0-5 minute sample. Mean levels preload compared to during load were PGE, 2.66 and 3.67 ng/ml (p less than 0.002); and 6-keto-PGF1 alpha, 543 and 868 pg/ml (p less than 0.007). The elevated levels then declined to preload levels during the loading period. However, the 5-10 minute but not the 10-15 minute samples still contained levels greater than preload values. A second 15 minute period of load, 1 h following the end of the first, produced smaller increases in the levels of release that were statistically significant only for the first 0-5 minute sample during load (preload compared to load mean values, PGE, 1.09-1.66 ng/ml, p less than 0.02; 6-keto-PGF1 alpha, 401-558 pg/ml, p less than 0.04). Immunolocalization revealed PGE and 6-keto-PGF1 alpha in lining cells and 6-keto-PGF1 alpha but not PGE in osteocytes. Addition to the medium of 1 microM PGE2, approximating the concentration produced by loading, had no significant effect on the specific activity of the extractable RNA fraction labeled with [3H]uridine, whereas 1 microM PGI2 produced an increase similar to that seen previously with loading.(ABSTRACT TRUNCATED AT 250 WORDS)

Early hemodynamic response to tibial osteotomy in rabbits: influence of indomethacin and prostaglandin E2

The hemodynamic role of prostaglandins in the inflammatory phase of bone healing was studied on day 4 after creation of a nailed midtibial osteotomy in 40 rabbits, divided into groups of 10, treated with either indomethacin (oral dosage 10 mg/kg), subcutaneous (s.c.) prostaglandin E2 (PGE2) (dosage 1 mg/kg), or PGE2 infusion into the abdominal aorta (rate 20 ng/kg/min) for a 20-min period immediately before the animals were killed. The last group served as controls. Regional blood flow was measured by means of radioactive microspheres, and plasma volume was assessed by distribution of circulating [125I]fibrinogen. Neither indomethacin nor s.c. PGE2 treatment had any hemodynamic effects in the osteotomy area. PGE2 infusion caused increased blood flow in bone, bone marrow, and muscle of the lower limbs except in the osteotomy area. Thus, the influence of prostaglandins and indomethacin on bone healing of a rabbit midtibial osteotomy does not appear to be a direct vascular effect in the early healing phase.

Immobilization increases bone prostaglandin E. Effect of acetylsalicylic acid on disuse osteoporosis studied in dogs

The effect of acetylsalicylic acid (aspirin) on bone mass and bone prostaglandin E (PGE) in immobilization osteoporosis was studied in 12 growing dogs using a unilateral hind limb cast-fixation model. Osteoporosis was induced by fiberglass-cast immobilization of the right hind limb for 4 weeks, with the left hind limb as a control. Six dogs received buffered aspirin at 25 mg/kg body weight per os every 8 hours; 6 dogs received no treatment. All the dogs were killed after 4 weeks, and bone samples were collected. Bone mineral content of the distal tibial metaphysis was measured by single-photon absorptiometry. In vitro release of PGE from the calcaneus, tibial cortical bone, tibial cancellous bone, and ilium were measured using a specific radioimmunoassay for PGE. Compared with the controls, the casted limb of untreated dogs had half the bone mass and a twofold increase in bone PGE. Aspirin treatment was associated with a 65 percent reduction in bone PGE and a 13 percent bone mass sparing effect. These results provide indirect evidence that PGE plays a role in immobilization osteoporosis.

A systemic acceleratory phenomenon (SAP) accompanies the regional acceleratory phenomenon (RAP) during healing of a bone defect in the rat

The rate of remodeling in the region of a bone defect exceeds normal tissue activity. It was Frost who described this reaction as a regional acceleratory phenomenon (RAP). We investigated the local healing process with rats with a burr hole defect (1.2 mm in diameter) in the left tibia. We differentiated an initial phase of bone formation followed by a phase of predominant resorption. To determine whether this regional enhancement of bone formation would result in a systemic impact on bone metabolism, we analyzed both tibiae and femora and the fourth lumbar vertebra. On day 7 both femora of rats with the tibial defect showed a significant increase in computerized x-ray density, dry weight, ash weight, and Ca2+ content. Both tibiae and the fourth lumbar vertebra showed a significant increase in mineralizing surface, mineral apposition rate, and bone formation rate. Because of these results we conclude that a systemic acceleratory phenomenon (SAP) accompanies the RAP. SAP affects only the cancellous, but not the cortical bone compartment. SAP is associated closely with the occurrence of woven bone during the formation phase of the healing process. Thus we assume that woven bone formation plays a pivotal role in the mediation of SAP.

The role of prostaglandins in bone in vivo

Prostaglandins of the E series, primarily E2 and E1, have the greatest activity in bone. Following discovery of their potent ability to stimulate bone resorption in vitro, clinical investigations have placed prostaglandins at sites of localized bone resorption associated with inflammatory or space occupying lesions in vivo. These studies have shown that prostaglandin production at such sites may be increased by cytokines such as interleukin-1 but the mechanisms by which prostaglandins stimulate bone resorption are not yet known. Observation of periosteal bone formation in patients given, pharmacological doses of prostaglandin has led to investigation of its bone forming activity. Young, growing rats have increased metaphyseal bone formation and this is accompanied by increased periosteal and endocortical bone formation in older animals. In the mature animals there is a generalized activation of remodelling with increased formation in the remodeling cycle. This is also seen in oophorectomized rats and results in repletion of the lost bone in this model of osteoporosis. In animal models of localized disuse osteopenia, prostaglandins are found to be elevated at the site of bone loss and prostaglandin inhibitors at least partially protect against the exaggerated resorption that occurs. This is also seen in models of orthodontic tooth movement, periodontitis and osteomyelitis. Prostaglandin synthesis inhibitors have been shown to delay healing of bone and this has led to limitations on their use clinically in some situations. Exogenously administered prostaglandins have been found to enhance periosteal callus formation, but healing is not uniformly enhanced. Prostaglandins have also been associated with hypercalcemia in certain animal tumors that model human hypercalcemia of malignancy but are probably most important in this condition as mediators in the localized resorption of bone at tumor sites. These in vivo studies have shown that prostaglandins are involved with increases in both bone formation and bone resorption. In vitro studies have shown that prostaglandins stimulate osteoblasts as well as osteoclastic bone resorption but understanding these effects under in vivo conditions will require further investigation.

The effect of strain on bone cell prostaglandin E2 release: a new experimental method

A new method of investigating the mechanisms of strain-induced bone remodeling has been developed. Bone cells were subjected to cyclical strains in vitro by computer-controlled stretching of the plastic substrate on which they were cultured, enabling both physiological and pathological strains to be investigated. Physiological strains have not previously been investigated in vitro. The prostaglandin E2 (PGE2) released by the cells was found to depend on the strain magnitude. It was independent of cycle time, and 5 hours after straining had ceased, it had returned to control levels. These results are similar to the in vivo findings that bone remodeling is dependent on strain magnitude and not strain frequency, indicating that PGE2 may play an important role in strain-induced bone remodeling. The relationship between PGE2 release and strain magnitude was biphasic, with particularly high levels being released at strains that would be associated with either abnormally strenuous activity or microstructural bone damage. It is therefore possible that PGE2 stimulates the osteogenesis caused by increased functional demands, and initiates the remodeling caused by bone damage. This new method of investigating strain-induced remodeling is useful, as any cell type, any mediator, and any strain pattern or parameter can be individually studied.

Eicosanoic fatty acid reduction in the tibiotarsus of biotin-deficient chicks

Day-old male broiler chicks (Hubbard x Hubbard) were fed a purified diet containing biotin at 0 microgram/kg of diet (biotin-deficient) or 500 micrograms/kg of diet (biotin-adequate). Biotin-deficient (BD) chicks had decreased growth and feed efficiency and greater twisted leg and dermatitis symptoms than biotin-adequate (BA) chicks. Lipids in cortical bone of the tibiotarsi in BD chicks contained higher levels of linoleate, gamma-linolenate, and alpha-linolenate. Prostaglandin precursors, dihomo-gamma-linolenate (20:3 omega 6), arachidonate (20:4 omega 6), and eicosapentaenoate (20:5 omega 3) were all lower in BD chicks compared with BA chicks. Periosteal bone appositional and bone formation rates, and percent new bone formation were reduced in the tibiotarsi of BD chicks. Anatomically there were two different bone modeling patters at the mid-diaphysis. The cortex was thickest laterally in chicks fed the BA diet and thickest medially in chicks fed the BD diet. The quantitative differences in bone growth and the distinct bone modeling patterns, coupled with corresponding decreases in PG precursors, suggest that biotin deficiency may alter bone growth and modeling via a PG-dependent mechanism.

Indomethacin and bone remodeling. Effect on cortical bone after osteotomy in rabbits

Remodeling in cortical bone close to a plated tibial midshaft osteotomy was histomorphometrically evaluated in 32 rabbits. The animals were divided into two groups, one being treated with indomethacin (10 mg/kg per day) and the other receiving placebo. In the placebo-treated group, the remodeling activity was higher in the osteotomized leg compared with the intact leg. Two and 6 weeks after osteotomy, the number of resorptive and formative foci was reduced in the indomethacin-treated group compared with the placebo group. Porosity did not differ between the groups after 2 weeks; but after 6 weeks, it was reduced in the indomethacin-treated animals. Throughout the study, the bone formation rate did not differ between the two groups. This study demonstrates that indomethacin inhibits the remodeling of traumatized bone.

Bone formation induced in an infant by systemic prostaglandin-E2 administration

We report a case of long-term systemic administration of prostaglandin E2 (PGE2) to a newborn infant with ductus-dependent congenital heart disease. After 46 days of treatment, radiography showed cortical hyperostosis of the long bones. The child died 62 days after discontinuation of prostaglandin treatment. Histologic examination of tubular bones showed hyperostosis presumably due to prostaglandin-induced rapid formation of primitive bone. The additional finding of extensive resorption of the outer cortical surface and bone formation at the inner surface suggested a reversible phase after discontinuation of treatment.

Systemic effects of prostaglandin E2 on vertebral trabecular remodeling in beagles used in a healing study

Prostaglandin E2 (PGE2) at a dose of 10 mg/kg was administered orally to beagles used in a study of rib fracture and drill hole defect healing. Double fluochrome labels were given prior to surgical manipulation and before necropsy at 30 days. Bone remodeling was evaluated in trabecular bone of the fourth lumbar vertebra. There was a decrease in the number and extent of posttreatment labels (P less than 0.05) in the controls, with decreased mineral apposition rate (P less than 0.05) and decreased active bone formation rate (P less than 0.01). In dogs given PGE2 for 30 days following surgery, the extent of posttreatment labels (P less than 0.05) and bone formation rate (P less than 0.01) were increased. There was no difference found, however, in static morphometric parameters, including osteoid and osteoblast-covered surface, indicating that the stimulation of bone formation may have been transitory and matrix synthesis had declined. In another group of dogs given PGE2 for 5 days prior to surgical manipulation and between the first and second pretreatment labels, the extent of the double-labeled surface was increased (P less than 0.05) indicating an acute PG effect to sustain formation at remodeling sites. These studies show that PGE2 given orally has a systemic effect on bone remodeling in vertebral trabeculae that involves the stimulation of formation activity.

The role of bone cells in increasing metaphyseal hard tissue in rapidly growing rats treated with prostaglandin E2

The skeletal effects of graded doses of prostaglandin E2 (PGE2) given to weanling Sprague-Dawley rats for 3 weeks were investigated to elucidate the role of bone cells in increasing hard tissue mass. Decalcified (3 micron) sections were quantified in the light microscope by point hit and intersect counting using a Merz grid. Hard tissue mass (bone and calcified cartilage) and osteoblast, osteoclast and osteoprogenitor cell numbers were counted in metaphyseal tissue bands 0.24, 0.48, 0.72, 1.20, 1.68, 2.16, 2.64, 3.12, 3.60 and 4.08 mm from the growth plate metaphyseal junction. Changes were different and more marked in the secondary spongiosa than the primary spongiosa of the proximal tibial metaphysis of treated rats. In the primary spongiosa of rats treated with 3 or 6 mg PGE2/kg/d (1) an increase in bone and hard tissue masses and (2) a decrease in osteoclasts, osteoprogenitor cell numbers and surface to volume ratio was observed. In the secondary spongiosa (lower metaphysis) of rats treated with 2 same dose levels (1) an increase in bone mass, calcified cartilage cores, and hard tissue mass and perimeter, an elevation of osteoprogenitor cell and osteoblast numbers, a depression of osteoclast, osteoclast nuclei numbers and surface to volume ratio and new sites of intramembranous ossification (woven bone formation) originating from the cortico-endosteal envelope was observed. In this growing rat skeletal model, we showed that PGE2 increases metaphyseal calcified tissue mass by depressing hard tissue resorption and stimulating the replication and differentiation of osteoblast precursors to form new foci of woven bone.(ABSTRACT TRUNCATED AT 250 WORDS)