OSTEOPENIA FOLLOWING TOTAL GASTRECTOMY IN THE RAT - STATE OF MINERAL METABOLISM AND BONE HISTOMORPHOMETRY

Total gastrectomy (GX) in humans is frequently followed by osteopenia, but the details are unclear. The present investigations in the rat we re aimed at elucidating its pathogenesis. Seventeen weeks after GX, we evaluated Ca, Mg and P metabolism as well as bone parameters, includi ng fluorochrome-based bone histomorphometry. In GX rats, fecal Mg was increased, but intestinal absorption of P, Ca, and Mg was within norma l limits, as was the urinary excretion of Ca, Mg, hydroxyproline and t he pyridinium cross-links. In contrast, urinary P as well as cyclic AM P were significantly increased. In serum of GX rats, gastrin and 25-hy droxyvitamin D (25-OHD) were decreased, and Ca, Mg, P, parathyroid hor mone (PTH), calcitonin, and the bone marker osteocalcin were normal, w hereas 1,25-dihydroxyvitamin D [1,25(OH)(2)D] was significantly increa sed. GX rats had significantly reduced bone density and mineral conten t, severe high-turnover osteopenia, characterized by normal width but significantly decreased maturation time of osteoid, increased bone for mation rate, and increased numbers of osteoclasts. We concluded that a fter GX (1) there is high-turnover osteopenia with normal mineralizati on and other histomorphometric features resembling those seen in state s with hyperphosphaturia and subsequent hypervitaminosis D; (2) normal serum PTH levels and several indirect indicators of parathyroid gland function argue against the presence of(secondary) hyperparathyroidism , whereas increased bone mobilization due to elevated 1,25(OH)(2)D exp lains the maintenance of homeostasis of serum minerals, especially Ca, at the expense of bone mineral; (3) a complex interplay of mineral-me tabolic effecters exists, among which low 25-OHD-PTH-independent renal phosphate losses, and high 1,25(OH)(2)D are prominent features. The p resented animal model is recommended for future research in this area.