OSTEOSCLEROSIS AFTER INTERMITFENT ADMINISTRATION OF LARGE DOSES OF VITAMIN D IN THE RAT A Note on the Pathogenesis of Osteopetrosis

The rate and amount of growth of any tissue are dependent on a number of stimuli, of which some are known but others are not so well understood. Differences in the rate of growth are demonstrated more easily in bone than in most other tissues, and it is clear that when the stimuli are sustained the growth and remodelling of bone are continuous, but when the stimuli are interrupted or discontinuous, growth and remodelling are intermittent. This is well shown in some animals by bone changes which recur naturally at regular intervals; that is, they are cyclical in nature and appear to be under hormonal control. These cycles may be seasonalfor example, egg laying of pigeons (Bloom, Bloom and McLean 1941), moult in birds (Meister 1951), growth of antlers in deer ; or daily, as in laying hens (Bloom, Domm, Nalbandov and Bloom 1958). Similar cyclical changes may be induced artificially in the rabbit by intermittent administration ofhormone (Storey 1958). The osseous structure in some bone diseases also suggests that the condition is essentially a cyclical disturbance of the normal growth and remodelling of bone. Some of the osteodystrophies, such as osteitis deformans and osteopetrosis, may be explained in this way,