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ILSE LASNITZKI
during the first 2 days of treatment. At later periods the difference
between control and treated cultures diminished but there was more
vacuolation of the colloid in explants grown with the higher concentrations of the hormone. The hormone did not accelerate the beginning
of colloid formation nor did it influence follicle formation.
Thyroid explants grown in contact with fragments of anterior
pituitary gland from 1-year-old cocks showed a similar response (Gaillard, 1955a) indicating that the pituitary gland releases thyrotrophin
into the culture medium.
Tixier-Vidal (1957) showed that this function of the pituitary
developed in vitro, independently of the organism. In vivo, thyrotrophin
production in the chick embryo begins, usually, after the seventh day
of incubation; in pituitary fragments explanted before this stage,
thyrotrophic activity, as measured by the stimulation of colloid formation in confronted thyroid cultures, appeared at the same time as it
would have started in the embryo. Addition of hypothalamic tissue
which in vivo controls the pituitary functions did not accelerate or
increase the effect (see also Vol. 2, p. 643).
Bakker-Sauer (1961) also describes the formation of antra in thyroid
cells in glands from young chick embryos shortly after addition of
thyrotrophin to the medium. These are PAS- and Gomori-negative
lacunar structures within the cytoplasm close to the nucleus. They are
only of short duration and disappear, usually, after 12-18 h and their
number is greater and their duration longer in glands from younger
embryos and after the higher doses of hormone. Bakker-Sauer attributes antra formation to a proteolytic enzyme which is reabsorbed by
the cytoplasm before colloid formation starts (but see Vol. 2, p. 652).
The stimulation of colloid secretion by thyrotrophin is not confined
to the embryonic organ. Junqueira (1947) has shown that the hormone
evokes similar changes in the thyroid glands of young rats grown in
vitro. The stimulation occurs shortly after addition of the hormone and
ceases after 1 day's growth. Thirty minutes after application of the
hormone the intracellular colloid droplets are increased; at 90 min
large droplets are extruded from the cytoplasm into the follicular
cavity: this is then reabsorbed by the cells which become filled with
colloid. These two phases, release into the lumen and reabsorption,
are not sharply defined, but both processes seem to take place simultaneously. After 1 day's growth in the presence of the hormone the
colloid released into the intrafollicular spaces is no longer reabsorbed
but taken up by macrophages (see also Vol. 2, p. 648).
The fact that the stimulation ceases after comparatively short
periods in both chick and rat thyroids may be caused by an inactivation of the hormone by the thyroid itself. Thus, thyroid tissue incubated
ILSE LASNITZKI
during the first 2 days of treatment. At later periods the difference
between control and treated cultures diminished but there was more
vacuolation of the colloid in explants grown with the higher concentrations of the hormone. The hormone did not accelerate the beginning
of colloid formation nor did it influence follicle formation.
Thyroid explants grown in contact with fragments of anterior
pituitary gland from 1-year-old cocks showed a similar response (Gaillard, 1955a) indicating that the pituitary gland releases thyrotrophin
into the culture medium.
Tixier-Vidal (1957) showed that this function of the pituitary
developed in vitro, independently of the organism. In vivo, thyrotrophin
production in the chick embryo begins, usually, after the seventh day
of incubation; in pituitary fragments explanted before this stage,
thyrotrophic activity, as measured by the stimulation of colloid formation in confronted thyroid cultures, appeared at the same time as it
would have started in the embryo. Addition of hypothalamic tissue
which in vivo controls the pituitary functions did not accelerate or
increase the effect (see also Vol. 2, p. 643).
Bakker-Sauer (1961) also describes the formation of antra in thyroid
cells in glands from young chick embryos shortly after addition of
thyrotrophin to the medium. These are PAS- and Gomori-negative
lacunar structures within the cytoplasm close to the nucleus. They are
only of short duration and disappear, usually, after 12-18 h and their
number is greater and their duration longer in glands from younger
embryos and after the higher doses of hormone. Bakker-Sauer attributes antra formation to a proteolytic enzyme which is reabsorbed by
the cytoplasm before colloid formation starts (but see Vol. 2, p. 652).
The stimulation of colloid secretion by thyrotrophin is not confined
to the embryonic organ. Junqueira (1947) has shown that the hormone
evokes similar changes in the thyroid glands of young rats grown in
vitro. The stimulation occurs shortly after addition of the hormone and
ceases after 1 day's growth. Thirty minutes after application of the
hormone the intracellular colloid droplets are increased; at 90 min
large droplets are extruded from the cytoplasm into the follicular
cavity: this is then reabsorbed by the cells which become filled with
colloid. These two phases, release into the lumen and reabsorption,
are not sharply defined, but both processes seem to take place simultaneously. After 1 day's growth in the presence of the hormone the
colloid released into the intrafollicular spaces is no longer reabsorbed
but taken up by macrophages (see also Vol. 2, p. 648).
The fact that the stimulation ceases after comparatively short
periods in both chick and rat thyroids may be caused by an inactivation of the hormone by the thyroid itself. Thus, thyroid tissue incubated