1. Bone and calcium metabolism in protein-deprived 5-week-old male rats who exhibited no biochemical or histological features of rickets were compared with age-and weight-matched control animals.

2. Intestinal calcium absorption was significantly lower in protein-deprived rats. This was associated with a smaller exchangeable calcium pool and lower bone formation as measured by calcium accretion and proline incorporation into hydroxyproline. However, calcium resorption from bone barely changed in this group and a disproportionately high fraction of the calcium pool continued to be excreted.

3. As a consequence, retarded bone growth occurred in the protein-deprived rat, leading to bones which were shorter and lighter than those of age-matched control animals, the epiphyseal regions appearing to bear the brunt of the growth retardation. This was not accompanied by a change in quality of bone, as the percentage ash content of extirpated bone remained normal.

4. Though alternative hypotheses are possible, the data are consistent with a primary disturbance of intestinal, and possibly renal tubular, calcium transport, perhaps associated with impaired synthesis of calcium-binding protein. An independent depression of collagen synthesis is likely.

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