16. A C T I O N S OF H O R M O N E S
647
of P T H showed a narrowing of the zone of hypertrophic cartilage and
a slight widening of the epiphyseal ends. The narrowing was due to a
breakdown of the cartilage matrix combined with the formation of
nests of fibroblasts from dividing mature cartilage cells and to a flattening and reorientation of the less mature cells. The abrupt change from
intense azurophilia to complete azurophobia in the region of hypertrophic cells seen in the controls was absent in the treated explants;
instead the azurophilia decreased gradually from the centre of the cartilage towards the connective tissue inside the shaft. The widening of the
epiphysis caused by increased proliferation of cartilage cells was only
temporary, and was followed by a considerable shrinkage caused by
a loss of matrix. The bone matrix completely disappeared; osteoblasts
were absent and in their place giant vacuolated osteoclasts like those
observed in the parietal bone could be seen, and there was no formation
of new bone. A comparison of the effects obtained with different doses
showed a linear relationship between the extent of the changes and the
concentration of hormone used.
The observation that lacunar resorption in hormone-treated parietal
bone occurred always in the older central part, and never in the recently
formed peripheral region, suggested that the developmental stage of
the bone was of importance for the effectiveness of the hormone.
Gaillard (1959) tested this theory by comparing the effect of parathormone on the central, middle and peripheral zone of mouse parietal
bone. After 3 days exposure the fragments from the central zone
displayed an intensive resorption of bone, while the peripheral parts
were unchanged. In the intermediate region there was less resorption
than in the central zone, but the process continued and, after a further
3 days in culture, the changes were similar in extent to those seen in
explants from the central region after 3 days treatment. At this time
there was still no lysis of bone in cultures obtained from the periphery
but many of them showed a marked fragility of the intercellular matrix.
This difference in effect could be correlated with the number of
osteoclasts present in the three different areas before explantation.
Using Barnicot's neutral red method (1947) Gaillard (1959) determined
the number of pre-existing osteoclasts and found that the central part
contained a large number, the middle layer a small number and the
peripheral bone none at all. During cultivation in the presence of
PTH, their number rose slightly in the central part and considerably
so in the middle region, which corresponds well with the increased
resorption seen in this area between the third and sixth days; in the
peripheral parts no osteoclasts were formed. In bone explants grown
without the hormone the number of pre-existing osteoclasts declined
rapidly and they disappeared completely between the fourth and sixth
647
of P T H showed a narrowing of the zone of hypertrophic cartilage and
a slight widening of the epiphyseal ends. The narrowing was due to a
breakdown of the cartilage matrix combined with the formation of
nests of fibroblasts from dividing mature cartilage cells and to a flattening and reorientation of the less mature cells. The abrupt change from
intense azurophilia to complete azurophobia in the region of hypertrophic cells seen in the controls was absent in the treated explants;
instead the azurophilia decreased gradually from the centre of the cartilage towards the connective tissue inside the shaft. The widening of the
epiphysis caused by increased proliferation of cartilage cells was only
temporary, and was followed by a considerable shrinkage caused by
a loss of matrix. The bone matrix completely disappeared; osteoblasts
were absent and in their place giant vacuolated osteoclasts like those
observed in the parietal bone could be seen, and there was no formation
of new bone. A comparison of the effects obtained with different doses
showed a linear relationship between the extent of the changes and the
concentration of hormone used.
The observation that lacunar resorption in hormone-treated parietal
bone occurred always in the older central part, and never in the recently
formed peripheral region, suggested that the developmental stage of
the bone was of importance for the effectiveness of the hormone.
Gaillard (1959) tested this theory by comparing the effect of parathormone on the central, middle and peripheral zone of mouse parietal
bone. After 3 days exposure the fragments from the central zone
displayed an intensive resorption of bone, while the peripheral parts
were unchanged. In the intermediate region there was less resorption
than in the central zone, but the process continued and, after a further
3 days in culture, the changes were similar in extent to those seen in
explants from the central region after 3 days treatment. At this time
there was still no lysis of bone in cultures obtained from the periphery
but many of them showed a marked fragility of the intercellular matrix.
This difference in effect could be correlated with the number of
osteoclasts present in the three different areas before explantation.
Using Barnicot's neutral red method (1947) Gaillard (1959) determined
the number of pre-existing osteoclasts and found that the central part
contained a large number, the middle layer a small number and the
peripheral bone none at all. During cultivation in the presence of
PTH, their number rose slightly in the central part and considerably
so in the middle region, which corresponds well with the increased
resorption seen in this area between the third and sixth days; in the
peripheral parts no osteoclasts were formed. In bone explants grown
without the hormone the number of pre-existing osteoclasts declined
rapidly and they disappeared completely between the fourth and sixth