600
ILSE LASNITZKI
The effect of insulin on cultures could be completely suppressed by
addition of nicotinamide to the medium. In tibiae from insulininjected embryos nicotinamide almost completely counteracted the
effect on bones removed on the sixth day, only partially on bones
explanted on the seventh day, and was ineffective on the eighth day.
Hay (1958) also studied the influence of growth hormone and of a
combination of insulin and growth hormone on the length, wet and
dry weights and total nitrogen content of femora and tibiae grown in
vitro. Rudiments cultivated in the presence of bovine-pituitary growth
hormone (0-18 mg/ml medium) showed a slight but significant retardation of growth in length after 2 days, but at 8 days there was no longer
a significant difference between treated and control explants. The wet
and dry weights of the treated bones were higher than those of the
control explants. The treated cultures contained more water, but there
was no difference between the percentage water content and that of the
controls. The total nitrogen content of the treated cultures was increased
by 13% over that of the controls, but if expressed as a percentage of
wet or dry weights there was no difference between the two sets of
cultures. Histological preparations showed no difference between
experimental and control cultures. This agrees well with (unpublished)
observations by Chen who failed to find any alterations in histological
structure or interference with differentiation in chick bone rudiments
grown in the presence of growth hormone.
Tibiae and femora exposed to a combination of growth hormone
and insulin (0*18 mg G H and 0-016 i.u./ml) showed a typical insulin
effect. However, the growth hormone seemed to promote the early
stimulation of growth seen after insulin, since, in explants treated with
both substances, the increase in length was 7% greater than in those
grown with insulin alone. But there was no additional effect of the
growth hormone on wet or dry weight or on the nitrogen content.
c. SUMMARY
It may be concluded that insulin is a growth-promoting agent which,
by a direct effect, promotes proliferation in cell and organ cultures alike,
and stimulates glycogen synthesis and lipogenesis. It also increases
RNA synthesis selectively. The promotion of growth is associated
with an increase of glucose uptake and utilization. It is not certain which is the primary effect: stimulation of cell proliferation
followed by a rise in glucose consumption or an increased glucose
utilization which makes a rise in cell multiplication possible.
The hormone has also a direct effect on bone which closely resembles
ILSE LASNITZKI
The effect of insulin on cultures could be completely suppressed by
addition of nicotinamide to the medium. In tibiae from insulininjected embryos nicotinamide almost completely counteracted the
effect on bones removed on the sixth day, only partially on bones
explanted on the seventh day, and was ineffective on the eighth day.
Hay (1958) also studied the influence of growth hormone and of a
combination of insulin and growth hormone on the length, wet and
dry weights and total nitrogen content of femora and tibiae grown in
vitro. Rudiments cultivated in the presence of bovine-pituitary growth
hormone (0-18 mg/ml medium) showed a slight but significant retardation of growth in length after 2 days, but at 8 days there was no longer
a significant difference between treated and control explants. The wet
and dry weights of the treated bones were higher than those of the
control explants. The treated cultures contained more water, but there
was no difference between the percentage water content and that of the
controls. The total nitrogen content of the treated cultures was increased
by 13% over that of the controls, but if expressed as a percentage of
wet or dry weights there was no difference between the two sets of
cultures. Histological preparations showed no difference between
experimental and control cultures. This agrees well with (unpublished)
observations by Chen who failed to find any alterations in histological
structure or interference with differentiation in chick bone rudiments
grown in the presence of growth hormone.
Tibiae and femora exposed to a combination of growth hormone
and insulin (0*18 mg G H and 0-016 i.u./ml) showed a typical insulin
effect. However, the growth hormone seemed to promote the early
stimulation of growth seen after insulin, since, in explants treated with
both substances, the increase in length was 7% greater than in those
grown with insulin alone. But there was no additional effect of the
growth hormone on wet or dry weight or on the nitrogen content.
c. SUMMARY
It may be concluded that insulin is a growth-promoting agent which,
by a direct effect, promotes proliferation in cell and organ cultures alike,
and stimulates glycogen synthesis and lipogenesis. It also increases
RNA synthesis selectively. The promotion of growth is associated
with an increase of glucose uptake and utilization. It is not certain which is the primary effect: stimulation of cell proliferation
followed by a rise in glucose consumption or an increased glucose
utilization which makes a rise in cell multiplication possible.
The hormone has also a direct effect on bone which closely resembles