Ca&Bone

[Mechanotransduction, or the impact of physical activity on bone architecture]

MONDUK Péter, SZEKERES László

JUNE 20, 2005

Ca&Bone - 2005;8(02)

[It has long been known that, along with bone mineral content, bone strength is also fundamentally determined by its architecture.This architecture is shaped primarily by the forces that act on the bone, i.e., gravity and muscle traction conveyed by the tendons.Thus the bone acts as a kind of a mechanostat. The authors provide an overview of the literature on the systems that regulate mechanotransduction turning mechanical strain into bone texture. Regularly performed movements that provide a frequently changing axial load induce an extracellular fluid flow in the lacunar system of the bones.This flow induces prostaglandin synthesis in the osteocytes, which in turn inhibits the Receptor Activator of Nuclear factor κB (RANK) - RANK-Ligand (RANKL) mechanism through the secretion of osteoprotegerin by osteoblasts.This leads to osteoclast inhibition. Furthermore, leptin secretion by osteoblasts increases, which enhances osteoblast activation and inhibits the apoptosis of osteocytes and osteoblasts by both an autocrine and paracrine route. All these together act in the direction of bone formation. Based on the available evidence, the authors conclude that regular exercise results in an increased bone mass, better muscle strength and firmer balance, which leads to a decreased fracture risk.Thus, physical activity, through its beneficial effects on cardiac and bone health described above, contribute to the improvement of the quality of life.]

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[Disturbance of bone development in experimental hepatic cirrhosis in growing rats]

FERENCZ VIKTÓRIA, HORVÁTH CSABA, FOLHOFFER Anikó, KÁRI Béla, GAÁL János, MÉSZÁROS SZILVIA, WOLF Zsuzsanna, MESTER Ádám, HEGEDÛS Dalma, HORVÁTH Andrea, SZALAY Ferenc

[INTRODUCTION -The pathomechanism of hepatic osteopathy is not fully understood.We investigated how bone parameters change in growing rats with experimentally induced fatty liver, liver cirrhosis and hepatocellular carcinoma. METHODS - Liver disease was induced by administration of CCl4 and phenobarbital (PB) following a single injection of diethylnitrosamine (DEN) in 55 Fischer 344 rats.Animals were sacrificed and their femur removed at week 8 or 16. Bone mineral content (BMC), femoral length, cortical index (ratio of cortical thickness and total diameter at the diaphysis) and ultimate bending load (Fmax) of femora were determined. Results of animals treated with DEN+PB+CCl4 (group DPC, n=21) were compared to untreated animals (n=14) and to a second control group treated only with DEN+PB (group DP, n=20). RESULTS - Fatty liver and cirrhosis developed in each animal in the DPC group (n=21) at week 8 and in a subgroup of these animals (n=11) hepatocellular carcinoma also appeared by week 16. No changes in bone parameters were observed in this group at week 8, but lower BMD, femoral length, cortical index and Fmax values were found at week 16 compared to the untreated controls or to the DP group (p<0.05 for both). In the DP group no fatty liver or cirrhosis was observed at any time. Femoral length and Fmax values were higher in the DP group at week 8 compared to the untreated controls (p<0.05 for both).At week 16, however, no difference could be detected. CONCLUSION - Experimentally induced liver cirrhosis and hepatocellular carcinoma are associated with growth inhibition and reduced bone mineral content, cortical index and mechanical resistance in growing rats.]

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