Enhanced trabecular bone resorption and microstructural bone changes in rats after removal of the cecum.

The cecum, the proximal part of the large intestine, has the highest rate of calcium absorption compared with other intestinal segments. Previously, we showed that rats with the cecum surgically removed (cecectomized rats) had severe negative calcium balance, low bone mineral density (BMD), and a compensatory increase in colonic calcium absorption. Herein, we used the computer-assisted bone histomorphometric technique and microcomputed tomography (μCT) to analyze bone microstructural defects in cecectomized rats at 1 and 3 mo postsurgery compared with age-matched sham-operated control rats. Relatively low BMD as determined by dual energy X-ray absorptiometry was observed in the femora, tibiae, and lumbar vertebrae of the 3-mo cecectomized rats. μCT analysis revealed decreases in the tibial cortical thickness, periosteal and endosteal perimeters, and moment of inertia in cecectomized rats. The histomorphometric results further showed that trabecular bone volume and number were markedly decreased, whereas trabecular separation was increased in the proximal tibial metaphysis of cecectomized rats, thus leading to a decrease in trabecular volumetric BMD. Since osteoclast surface and eroded surface were increased after cecectomy, such bone loss in cecectomized rats appeared to result from an enhanced bone resorption. Moreover, decreases in bone formation rate and osteoblast surface indicated a suppression of osteoblast-mediated bone formation. In conclusion, cecectomy induced widespread osteopenia in rats presumably by enhancing the osteoclast-mediated bone resorption and suppressing bone formation. The present results underline the important role of cecum in the body calcium homeostasis.