+ Le ae i - t + ; : wthMie bat oa aden gttalie wacttecai ae Pee cla Ria ke eee 8 128 tion and linear bone growth. In faet, these rates were much lower than those calculated for the rachitic/ pair-fed control animals, and the bone formation indices (OAI) suggested that the osteoblasts on these surfaces were functionally lethargic. Phosphate was statistically somewhat more effective than vitamin D on these parameters and it did cure rickets histologically and histochemically, but there was no overall improvement which could be attributed to either agent per se. In contrast, the pace of endosteal lamellar bone formation was quite independent of treatment, and osteoblast activity was normal] at all times. It may be concluded, then, that thinning of the rachitic cortices is due to deficient periosteal bone formation. It is difficult to estimate the contribution of the partially or While the present studies do not necessarily contribute to our understanding of the basic biochemical lesions in cartilage and bone which produce histologic rickets, evidence has also been presented that the most mature cells in rachitic cartilage are not producing significant amounts of collagen (and presumably chondroitin sulfate) and that this basic cell defect ac- counts, at least in part, for deficient calcification of the tissue. The results from this study also suggest that the rate of bone matrix formation in rachitic bone is generally normal. SUMMARY 3H-proline was administered intraperitoneally to fully reconstituted diets to the observed stunting of young male rats with nutritional rickets produced by trition are much more severe if it occurs in young graphs of the upper tibial epiphyseal cartilages from untreated control littermates showed tracer incorpora- bones. But it is known that the effects of undernu- animals, and that if the nutritional insult is prolonged they may never attain the body weight or cell growth of animals reared on a normal diet." The osteoblast activity indices reported in this study, based in part upon the thickness of the dense lines of matrical silver grains, are at the light microscope level of resolution unlikely to be influenced by changes in the ultrastructure of bone. Poorly oriented collagen fibers in rachitic osteoid have been described in dogs5) and in rats?) by electron microscopy. It should be noted that the fine structure of the rachitic a low phosphate, vitamin De-free diet. Autoradio- tion by the cells and extracellular matrix 4 hr and 3 days post-injection, respectively, and this occurred throughout the proliferative and hypertrophic cell zones. The pattern of tracer uptake was abnormal in the thickened cartilages from rachitic rats; the oldest juxtametaphyseal chondrocytes were unable to syn- thesize significant amounts of matrical protein and this effect could not be corrected thereafter by feeding rachitic rats nutritionally adequate supplements of phosphate and/or vitamin D. The rate of bone formation was calculated from the osteoblast is not entirely normal; broad cysternae have been observed which contain a moderately dense displacement (burial) of the labeled lamellae of bone suggest is collagen which is not yet polymerized to tion, as well as by the thickness of the linear bands of following phosphorus and/or vitamin D supplementa- teum and on the articular surface of the transverse epiphyseal bone was essentially normal in rats ren- amorphous material that Robinson and Sheldon'® matrix from anatomical surfaces 3 days post-injec- fibrillar form. There is little evidence from the present study to suggest that the ultrastructural changes contribute to the sharply decreased activity of osteoblasts silver grains recorded in the photographic emulsion. Lamellar bone formation at the periosteum, endos- tion. OAI values approximating 2 were also detected dered rachitic by the deficient diet. Unexpectedly, the in the stunted bones from rats on the fully supple- mented rachitogenic diet (Group 3). Nor is it likely that the instances where the rate of lamellar bone for- mation was depressed signal a parathyroid endocrinopathy, for serum calcium concentrations in these animals were normal or slightly high (vitamin D- treated) mal.{87) explain Rohr‘!5) and the ultrastructure of the glands was norInvolvement of parathyroid activity might the very rapid osteogenesis reported by in the metaphyses of rachitic rats raised on a diet which was vitamin D-free and severely deficient in both calcium (hypocalcemic?) and phosphate. Parathyroid extract administered to rats and mice, for instance, elicits a biphasic response in bone—an initial inhibition and a secondary stimulation of bone cell amino acid transport and collagen synthesis. (2? 38) pace of appositional bone growth on the periosteum and transverse epiphyseal bone was depressed when rachitic rats were treated with phosphate and/or vitamin D, owing presumably to the functional lethargy of osteoblasts at these sites. Endosteal lamellar bone formation rates on the shaft and peripheral to the metaphysis were independentof treatment. REFERENCES 1. Sheldon, H. and Robinson, R. A. Studies on rickets. IT. The fine structure of the cellular components of bone in experimental rickets. Z. Zellforsch. 68, 685-701 (1961). 2. Sheldon, H. and Robinson, R. A. Studies in rickets. I. The fine structure of uncalcified bone matrix in experimental rickets. 7. Zellforsch. 53, 671-684 (1961). 3. Kunin, A. 8. and Krane, 5S. M. The effect of dietary phosphorus on the intermediary metabolism of epiphyseal