. Lae ‘ ry . SR . rd ge bed chien ssa ded badbeaa ae o tene apaceint Beesdt 127 who have employed this diet“*) and the Steenbock_ Black rachitogenie diet®® as well, and it remains unresolved. However, in view of data indicating that the fully supplemented rachitogenic ration is utilized as effectively for growth as is Purina Laboratory Chow, disparate results from these control groups most probably reflect differences in daily food intake. In point of fact, since those rats fed the phosphate and vitamin D-supplemented ration for 3 weeks ate much less than the pair-fed controls, we do not believe that they are an adequate group against which to compare the effects of deficient dicts. Parameters such as linear and appositional bone growth in this study, and epiphyseal cartilage thickness and cell ities in enzyme activity’? #7 5) did not extend fully to the chondromucoprotein moiety of the cartilage matrix. An inability of the juxtametaphyseal cells in rachitic animals raised on the Steenboch-Black diet to incorporate radiosulfur was also reported by Hjert- quist,{°) and this abnormality was not reversed by vitamin D and a return of these animals to a normal diet. On the other hand, the rate of 35S uptake by cells in the cartilage is normally dependent upon vitamin D©@5.*8) which appears to be essential for the preduction of a calcifiable matrix. Thus these observations seem to suggest that the most maturecells in rachitie rat cartilage are not producing significant amounts of chondroitin sulfate and collagen, and that DNA synthetic indices in the growth plate in a previous study, seemed to be most sensitive to the ef- this basic cell deficit may account at least in part for the deficient calcification long observed in rachitic tis- tion, (8) structure of the chondromucoproteins and other components of rachitic cartilage is too immature or ab- fects of what must be considered voluntary starva- In most animals, irrespective of dietary treatment, the distribution of radioproline in chondrocytes, cartilage matrix, and bone 4 hr and 3 days after injec- tion, was similar to that reported by Tonna, et al.” and corresponded with the pattern for radioglycine described by others.@° 1%. *1.23) Early, grains in the emulsion were found over the nucleus and cytoplasm of chondrocytes, osteoblasts, and undifferentiated mesenchymal cells, newly formed osteocytes, cartilage matrix, bone surfaces, and in the cytoplasm of osteoclasts. Three days after injection, radioproline was less heavily invested in the cells and was detected principally in the matrical proteins of bone and cartilage, suggesting that the builk of radioactivity was destined for the synthesis and export of collagen by these cells. Most of the cells labeled initially retained a nuclear label after three days, presumably due to utilization of some tracer for structural nuclear protein synthesis as suggested by Carneiro and Leblond’ and Revel and Hay." Thus, the progressive loss of label from the cytoplasm of cells and its burial deep within matrix provides direct evidence for the functional capacity of osteoblasts and chondrocytes. However, distributional changes in the initial tracer load and in the rate of bone matrix synthesis were ob- served in the treated rats. Whereas, for instance, all the chondrocytes (upper, middle, and lower layers of the cartilage plates) in control tissues seemed able to synthesize and form collagen—albeit with less vigor as they matured— only a shght autoradiographic image was recorded over the mature juxtametaphyseal cells in either the rachitic cartilages or those from rachitic rats ostensibly healed by phosphorus and vitamin D. Thus, the efficacy of phosphate, in particular, and vitamin D to heal rickets histologically and correct the abnormal- sue. Implicit, also, is the possibility that the state or normal for mineralization to proceed.{?7-2 These experiments, of course, do not contribute to the con- troversy about the dependent®® or independent»3) cellular control for the secretion of protocollagen and mucopolysaccharides in cartilage. The findings in this study tend not to support the autoradiographie and biochemical evidence from other laboratories that the rate of bone formation in rachitic rats is excessive. Rohr ™*) reported that the rachitic rat metaphyses contained more osteoblasts than normal and that the export of radioglycine from these cells and matrix formation occurred more rapidly than normal. Parsons and Self“ reported a higher specific activity of labeled proline/hydroxyproline in rachitic rat metaphyses 48 hr after injection. But their data relative to bone turnover, 1e., normal urinary hydroxyproline specific activity and a fall in the specific activity of tibial bone 2-3 days post-injection compared to a significant rise in control tissue, suggest rather that the overall rate of bone formation in nckets is normal or slow. We observed regional differences in the rates of lamellar bone formation. But with the sole exception of a lowrate of endosteal apposition along the margins of the metaphyseal cortex (Table 57), the pace of periosteal and endosteal osteogenesis in the compacta was within normal limits (= pair-fed controls). Frost‘) noted that the osteo- blast birth rate in haversian bone of osteomalacic patients (adult rickets) was increased; however, while there were more cells, they showed decreased vigor, and bone formation rates were low. Dietary supplements of phosphorus or vitamin D administered for at least. 7 days to rachitic rats ap- peared to be without any great ameliorating influence on the rates of periosteal and epiphyseal bone apposi-