16. A C T I O N S OF H O R M O N E S
601
that in insulin-treated animals. Its mode of action is still obscure, but
it is possible that at least two different mechanisms are involved:
an inhibition of chondroitin sulphate as suggested by Duraiswami
(1950) which interferes with cartilage differentiation combined with a
growth-promoting effect on epiphysis and the soft tissue surrounding the
rudiments. The temporary stimulation of growth obtained by Hay in
the older embryos suggests that the developmental stage also influences
the hormonal response.
The growth hormone was, with one exception, found to inhibit
the growth of cell cultures of epidermis. This effect could be prevented
or even reversed by addition of insulin to the medium. This latter
finding agrees with Bullough's (1954b) contention that the two hormones
are antagonists, insulin promoting the glucokinase reaction and the
growth hormone inhibiting it selectively. It also lends support to the
view of Ketterer, Randle and Young (1957) that, in the organism,
the presence of insulin is necessary for the growth hormone to become
effective. The increase in protein synthesis in the bone rudiments
treated with the hormone may have been facilitated by small amounts
of insulin present in the medium.
I I I .
E F F E C T S OF T H Y R O T R O P H I N ( T S H ) ,
A D R E N O C O R T I C O T R O P H I N ( A C T H ) A N D G O N A D O T R O P H I N S
In vitro studies have shown that these hormones affect their target
tissues directly and that the responses they evoke are comparable to
those seen in the organism. The evidence for this was obtained in two
ways: by adding the hormones to the culture medium and by the use of
contact cultures in which the target organ was grown in close proximity
to fragments of the anterior pituitary gland.
A. EFFECTS OF T H Y R O T R O P H I N ON T H E E M B R Y O N I C
A N D Y O U N G A D U L T T H Y R O I D G L A N D
The effect of thyrotrophin on the embryonic chick thyroid, explanted
as a whole, was studied by Gaillard (1955a) and by Bakker-Sauer
(1961) (Vol. 2, p. 649). Explants from 6-9-day chick embryos grown in
natural medium without addition of hormones form primary follicles
and secrete colloid within 2-4 days' incubation. This occurs earlier
in vitro than in the organism, probably owing to the presence of small
amounts of thyrotrophic hormones in the medium. Addition of thyrotrophin to the medium in concentrations ranging from 10~
3 to 10~
4
i.u. per culture vessel was followed by an increase in colloid formation
601
that in insulin-treated animals. Its mode of action is still obscure, but
it is possible that at least two different mechanisms are involved:
an inhibition of chondroitin sulphate as suggested by Duraiswami
(1950) which interferes with cartilage differentiation combined with a
growth-promoting effect on epiphysis and the soft tissue surrounding the
rudiments. The temporary stimulation of growth obtained by Hay in
the older embryos suggests that the developmental stage also influences
the hormonal response.
The growth hormone was, with one exception, found to inhibit
the growth of cell cultures of epidermis. This effect could be prevented
or even reversed by addition of insulin to the medium. This latter
finding agrees with Bullough's (1954b) contention that the two hormones
are antagonists, insulin promoting the glucokinase reaction and the
growth hormone inhibiting it selectively. It also lends support to the
view of Ketterer, Randle and Young (1957) that, in the organism,
the presence of insulin is necessary for the growth hormone to become
effective. The increase in protein synthesis in the bone rudiments
treated with the hormone may have been facilitated by small amounts
of insulin present in the medium.
I I I .
E F F E C T S OF T H Y R O T R O P H I N ( T S H ) ,
A D R E N O C O R T I C O T R O P H I N ( A C T H ) A N D G O N A D O T R O P H I N S
In vitro studies have shown that these hormones affect their target
tissues directly and that the responses they evoke are comparable to
those seen in the organism. The evidence for this was obtained in two
ways: by adding the hormones to the culture medium and by the use of
contact cultures in which the target organ was grown in close proximity
to fragments of the anterior pituitary gland.
A. EFFECTS OF T H Y R O T R O P H I N ON T H E E M B R Y O N I C
A N D Y O U N G A D U L T T H Y R O I D G L A N D
The effect of thyrotrophin on the embryonic chick thyroid, explanted
as a whole, was studied by Gaillard (1955a) and by Bakker-Sauer
(1961) (Vol. 2, p. 649). Explants from 6-9-day chick embryos grown in
natural medium without addition of hormones form primary follicles
and secrete colloid within 2-4 days' incubation. This occurs earlier
in vitro than in the organism, probably owing to the presence of small
amounts of thyrotrophic hormones in the medium. Addition of thyrotrophin to the medium in concentrations ranging from 10~
3 to 10~
4
i.u. per culture vessel was followed by an increase in colloid formation