676
H O N O R
B .
F E L L
A N D
L .
M .
R I N A L D I N I
reason, a very high toxic dose of vitamin A is less effective than a lower
concentration.
The reversibility of the effects of vitamin A on the explanted limbbone rudiments of 6-7-day embryonic chicks was investigated by
Herbertson (1955). The explants were grown for periods of up to 9 days
in medium containing vitamin A, and were then transferred to normal
medium for not more than 7 days. In the shaft, the changes in the
hypertrophic cartilage were arrested, but lost matrix was not replaced;
there was increased periosteal ossification, however. The epiphyses
partially recovered and began to enlarge. Sections showed that the
increase in size was due to profuse mitosis, and not to the formation of
new matrix; during the period of the experiment metachromatic
material did not reappear in the cartilage.
(b) Effect of vitamin A on incorporation of inorganic sulphate by cartilage.
Fell, Mellanby and Pelc (1956) studied the effect of vitamin A on the
uptake of radioactive inorganic sulphate (
3 5
S 0 4 ) by the cartilaginous
limb-bone rudiments of 7-day chick embryos in culture.
The first effect of the vitamin was to prevent sulphate from being
incorporated in the matrix; this was followed by loss of sulphate
that had already been incorporated. The loss of sulphate was closely
correlated with the disappearance of metachromasia in preparations
stained with toluidine blue. This result first led us to suspect that in
hypervitaminosis A, cartilage matrix was broken down under the
influence of enzymes, but how this was accomplished was not known.
(c) Comparison of effects of papain protease and vitamin A on cartilage in
culture. Thomas (1956) found that when papain protease was injected
into rabbits, in a few hours the animals' ears collapsed and hung down
like those of a spaniel. The cartilage of these drooping ears had lost
most of its metachromasia and the intercellular partitions had become
very narrow. This effect closely resembled that of vitamin A on cartilage
in culture. A comparative study was therefore made of the effects of
papain and of vitamin A on cartilage in culture (Fell and Thomas, 1960)
and in rabbits (Thomas, McCluskey, Potter and Weissmann, 1960).
In rabbits, the effects on the cartilage of a small dose of papain and
a large dose of vitamin A were found to be indistinguishable, and the
vitamin even caused a partial collapse of the ears. In the cultures also
there was a close similarity between the effects of the two agents on the
cartilage. The main difference was that the enzyme, which acted
directly on the matrix, had a much more evenly distributed effect
than the vitamin which acted via the cells and produced greater
changes in some parts of the rudiment than in others. When both
compounds were added to the medium simultaneously, they had a
dramatic additive effect on the cartilage.
H O N O R
B .
F E L L
A N D
L .
M .
R I N A L D I N I
reason, a very high toxic dose of vitamin A is less effective than a lower
concentration.
The reversibility of the effects of vitamin A on the explanted limbbone rudiments of 6-7-day embryonic chicks was investigated by
Herbertson (1955). The explants were grown for periods of up to 9 days
in medium containing vitamin A, and were then transferred to normal
medium for not more than 7 days. In the shaft, the changes in the
hypertrophic cartilage were arrested, but lost matrix was not replaced;
there was increased periosteal ossification, however. The epiphyses
partially recovered and began to enlarge. Sections showed that the
increase in size was due to profuse mitosis, and not to the formation of
new matrix; during the period of the experiment metachromatic
material did not reappear in the cartilage.
(b) Effect of vitamin A on incorporation of inorganic sulphate by cartilage.
Fell, Mellanby and Pelc (1956) studied the effect of vitamin A on the
uptake of radioactive inorganic sulphate (
3 5
S 0 4 ) by the cartilaginous
limb-bone rudiments of 7-day chick embryos in culture.
The first effect of the vitamin was to prevent sulphate from being
incorporated in the matrix; this was followed by loss of sulphate
that had already been incorporated. The loss of sulphate was closely
correlated with the disappearance of metachromasia in preparations
stained with toluidine blue. This result first led us to suspect that in
hypervitaminosis A, cartilage matrix was broken down under the
influence of enzymes, but how this was accomplished was not known.
(c) Comparison of effects of papain protease and vitamin A on cartilage in
culture. Thomas (1956) found that when papain protease was injected
into rabbits, in a few hours the animals' ears collapsed and hung down
like those of a spaniel. The cartilage of these drooping ears had lost
most of its metachromasia and the intercellular partitions had become
very narrow. This effect closely resembled that of vitamin A on cartilage
in culture. A comparative study was therefore made of the effects of
papain and of vitamin A on cartilage in culture (Fell and Thomas, 1960)
and in rabbits (Thomas, McCluskey, Potter and Weissmann, 1960).
In rabbits, the effects on the cartilage of a small dose of papain and
a large dose of vitamin A were found to be indistinguishable, and the
vitamin even caused a partial collapse of the ears. In the cultures also
there was a close similarity between the effects of the two agents on the
cartilage. The main difference was that the enzyme, which acted
directly on the matrix, had a much more evenly distributed effect
than the vitamin which acted via the cells and produced greater
changes in some parts of the rudiment than in others. When both
compounds were added to the medium simultaneously, they had a
dramatic additive effect on the cartilage.