308
J . A . L U C Y
taneous de-repression of enzyme systems and such a change may
complicate the interpretation of experimental observations. Mueller,
Herranen and Jervell (1958) observed that incorporation of glycine
into segments of rat uterus was greater in tissue from animals that had
been treated with oestradiol than in tissue obtained from control
animals. On the other hand, uterine segments from control animals
exhibited a striking increase during cultivation for 18 h in Eagle's
medium in the ability to incorporate glycine into protein, while
segments from animals previously treated with oestradiol showed little
capacity for further activation during incubation in vitro. It appeared
that incubation of the segments in tissue-culture medium accomplished
much the same effect as the oestrogen produced in vivo. The authors
suggested that the specialized hormonal mechanism for inducing an
anabolic response in the uterus was possibly by-passed in vitro by
metabolic alterations that were even more fundamental to the induction of growth among cells in general.
The increased ability to incorporate glycine into protein that occurred
during cultivation of uterine segments in vitro, appears to be similar to
the increase in the level of arginase activity that was observed on
cultivation of explants of mouse prostate glands (Lasnitzki and Lucy,
1961). The arginase activity of the freshly excised prostate gland was
low, but on cultivation in "natural" media for 9 days there was an
increase in activity of from ten to twenty times. The typical histological
structure of the prostate gland which consisted of ducts and alveoli
surrounded by fibromuscular stroma, and lined by one row of epithelial
cells, was preserved during cultivation. The increase in arginase
activity was unaffected by the inclusion of testosterone in the medium.
Since the difference in arginase activities between the prostates of
normal and castrated mice was small, it was unlikely that lack of
direct hormonal control was responsible for the rise in enzyme activity
of the gland in vitro, and it is possible that an induction of arginase
synthesis may have occurred. Cultures grown in the presence of
methylcholanthrene showed a much smaller increase in arginase
activity; in these explants many hyperplastic alveoli could be distinguished in which the cells had multiplied to form several layers that
projected into the lumen. Substrate-induced synthesis of arginase has
been reported in experiments with freshly isolated embryonic chick
and mouse cells (Klein, 1960), and also with a number of established
cell-strains (Klein, 1961). Addition of arginine alone to the culture
medium used with the cell strains did not lead to greater activity,
but when yeast R N A was included in the medium, the addition of
arginine caused a 7-10-fold increase in arginase activity per mg of
total nitrogen in the tissue. Addition of R N A and arginine did not
J . A . L U C Y
taneous de-repression of enzyme systems and such a change may
complicate the interpretation of experimental observations. Mueller,
Herranen and Jervell (1958) observed that incorporation of glycine
into segments of rat uterus was greater in tissue from animals that had
been treated with oestradiol than in tissue obtained from control
animals. On the other hand, uterine segments from control animals
exhibited a striking increase during cultivation for 18 h in Eagle's
medium in the ability to incorporate glycine into protein, while
segments from animals previously treated with oestradiol showed little
capacity for further activation during incubation in vitro. It appeared
that incubation of the segments in tissue-culture medium accomplished
much the same effect as the oestrogen produced in vivo. The authors
suggested that the specialized hormonal mechanism for inducing an
anabolic response in the uterus was possibly by-passed in vitro by
metabolic alterations that were even more fundamental to the induction of growth among cells in general.
The increased ability to incorporate glycine into protein that occurred
during cultivation of uterine segments in vitro, appears to be similar to
the increase in the level of arginase activity that was observed on
cultivation of explants of mouse prostate glands (Lasnitzki and Lucy,
1961). The arginase activity of the freshly excised prostate gland was
low, but on cultivation in "natural" media for 9 days there was an
increase in activity of from ten to twenty times. The typical histological
structure of the prostate gland which consisted of ducts and alveoli
surrounded by fibromuscular stroma, and lined by one row of epithelial
cells, was preserved during cultivation. The increase in arginase
activity was unaffected by the inclusion of testosterone in the medium.
Since the difference in arginase activities between the prostates of
normal and castrated mice was small, it was unlikely that lack of
direct hormonal control was responsible for the rise in enzyme activity
of the gland in vitro, and it is possible that an induction of arginase
synthesis may have occurred. Cultures grown in the presence of
methylcholanthrene showed a much smaller increase in arginase
activity; in these explants many hyperplastic alveoli could be distinguished in which the cells had multiplied to form several layers that
projected into the lumen. Substrate-induced synthesis of arginase has
been reported in experiments with freshly isolated embryonic chick
and mouse cells (Klein, 1960), and also with a number of established
cell-strains (Klein, 1961). Addition of arginine alone to the culture
medium used with the cell strains did not lead to greater activity,
but when yeast R N A was included in the medium, the addition of
arginine caused a 7-10-fold increase in arginase activity per mg of
total nitrogen in the tissue. Addition of R N A and arginine did not