RESUMEN
Osteoclastic function, as estimated by the speed with which the haversian cutting cones advance through the compacta of the rib (linear erosion) was found significantly decreased (27.97-SE 0.8 mu/day versus normal 43.61-SE 0.7 mu/day) in dogs rendered chronically uremic (BUN between 36-89 mg/100 ml). The cause of the impairment of osteoclasts' function was tentatively ascribed to the chronic excess of the circulating parathyroid hormone. A decrease in the linear erosion rate, such as observed in this study, will produce predictable morphological changes. As the time necessary to erode a cavity increases, so does the lifespan of cavities, their number and consequently the bone surface area (or in the bone section the perimeter length) covered by Howship's lacunae. Thus, the increased total bone erosion perimeter in secondary hyperparathyroidism associated with moderate uremia does not necessarily reflect an accelerated tissue level erosion rate or even bone loss. As the remodeling sites in both adult man and dog have a similar standard configuration and dimensions, these observations may be extrapolated to disease in man.