The effect of protein-energy malnutrition on the development of bones in newborn rats.

Collagen synthesis, 45Ca uptake, and the half-life of 45Ca in mandibles and long bones of rat pups suckled on dams fed 25 or 6% protein diets were determined. Collagen synthesis in both mandibles and long bones was impaired in the malnourished group at an early age. Protein-energy malnutrition appears to affect different developmental processes in these two bones. The principal interference with collagen synthesis in the mandible occurs when bone proline is converted into hydroxyproline. In contrast, proline uptake from the blood for deposit in bone matrix is the step of collagen synthesis mainly affected in long bone. In addition, the critical growth period of mandible was different from that of long bone. The calcium complex fraction (calcium bound to protein plus that in inorganic salts) was the main compartment affected in the malnourished group. However, the efficiency of calcification per milligram of matrix in the calcium complex fraction of the mandible and long bone was approximately the same in the control and malnourished groups, thus suggesting that accumulation of calcium occurs in parallel with the formation of bone matrix regardless of the nutritional conditions. The half-life of 45Ca in the various calcium fractions of both types of bone was 72 hours in both the control and malnourished groups except the calcium complex portion of the long bone of the control group, which was about 100 hours.