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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-