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Effects of estrogen on pituitary morphology in goitrogen treated rats. An electron microscopic study

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Effects of Estrogen on Pituitary Morphology
- - in
Goitrogen Treated Rats. An Electron
Microscopic Study '
Labomtoire universitaire d'anatomie pathologique, H6pital Brugmann and
Fondation medicale Reine Elisabeth, Brussels, Belgium
The influence on pituitary cytology of propylthiouracil (PTU) and
estradiol benzoate (EB) administered singly and in combination was studied by
electron microscopy in adult female rats. PTU alone induced striking changes in the
morphology of thyrotroph cells, which were all transformed into typical thyroidectomy
cells, characterized by enormously dilated ergastoplasmic sacs; the acidophils were
degranulated and some of them took the appearance of relatively quiescent prolactin
cells rather than degranulated somatotrophs. EB alone caused no definite changes in
the morphology of thyrotroph cells; its essential effect was the development of a large
number of prolactin cells. When both treatments were combined, thyroidectomy cells
were found, existing side by side with untransformed thyrotrophs and exhibiting less
dilated ergastoplasmic sacs than after PTU alone; prolactin cells were present in
great number and showed a more developed ergastoplasm than after EB alone. Thyroid
weight and height of the follicular cells were not changed by EB given singly; they
were both increased under the influence of PTU; thyroid weight but not mean height
of the follicular cells was slightly less increased when EB was added to PTU. It is
tentatively concluded that estrogen may have a dual action on the thyro-pituitary
axis: on one hand, a depressing influence on thyrotroph cells and on the other hand
a direct stimulatory effect on the thyroid gland.
A relationship between ovarian and thyroidal functions has long been suspected
on clinical grounds. Experimental studies
in this field have led to conflicting or inconclusive results due in part to varying
dosage and duration of estrogen treatments
and to differences in methods used in
evaluating thyroid function. A summary
of the earlier literature dealing with this
subject may be found in Noach ('55a,b)
and in Feldman ('65). In a more recent
period, an increasing number of investigators have reported a stimulatory effect
of estrogens on thyroid gland activity as
measured by an increased uptake of radioactive iodine (Soliman and Reineke, '55;
Noach, '55a,b; Feldman, '56; Nataf et al.,
'57; Florsheim, '58; Brown-Grant, '62;
Amesbury et al., '65; Yamada et al., '66)
or an increased secretion rate (Grosvenor
and Turner, '59; Moon and Turner, '60;
Grosvenor, '62). However the precise
mode of action of estrogens has not been
clearly elucidated by these studies. Some
authors have claimed that the ovarian
hormone affects the thyroid via the pituitary gland (Soliman and Reineke, '54;
h n r . RE.,
160: 595-606.
Grosvenor, '62; Yamada et al., '66). Others
have denied this (Noach, '55a,b; Feldman,
'56; Florsheim, '58). An intermediate view
has been expressed by Brown-Grant ('62).
According to him, the most probable explanation for the changes in thyroid gland
activity observed during the estrus cycle
in the rat is an increase in thyrotrophic
hormone (TSH) secretion during the proestrus and in the early estrous stages;
however the increase in thyroid function
which can be obtained in spayed rats by
the administration of exogenous estrogen
was apparently not mediated by the pituitary gland.
The problem of a possible influence exerted by estrogens on pituitary thyrotrophic
activity has been approached by morphological methods. For this, advantage has
been taken of the striking cytological
changes that occur in the adenohypophysis
of the rat following thyroidectomy or goitrogen administration. It is well known
1This investigation was partly supported by grant
699 from the Belgian Fonds de la Recherche scientiflque medicale.
2 Estradiol benzoate was kindly supplied by the
"Laboratories Roussel-Labunis."
that these experimental procedures rapidly
lead to the appearance in the adenohypophysis of enlarged, regranulated and
vacuolated basophils which, in the final
stage of their transformation, assume the
typical aspect of thyroidectomy cells
(Purves, '61). It has been established that
these changes affect a specific class of
cells (Zeckwer, '37, '38) and are evidence
of an increased rate of TSH production
and output (Contopoulos et al., '58). The
results of estrogen administration on the
development of thyroidectomy cells in the
rat have been studied since an early date,
initially as a mean to ascertain whether
there is any difference between these and
the morphologically comparable castration
cells. Hohlweg and Junkman ('33) followed by Zeckwer ('38) claimed that estrogens were without effect on the development of thyroidectomy, but inhibited the
development of castration cells. On the
other hand, Nelson and Hickman ('57),
like Severinghaus and Smelser ('37),
reported that the changes in pituitary
basophil cells which followed either thyroidectomy or castration were similarly corrected and prevented by estrogens. Desclin
and Ermans ('50) obtained comparable
results; in addition, having used thiouracil
treatment rather than thyroidectomy to
induce a hypothyroid state, they were able
to make the observation that despite its
effectiveness in preventing the development of thyroidectomy cells, estrogen did
not reduce the goiter resulting from thiouracil treatment. This last result however
has been disputed (Chamono, '44). According to Eskin and Bogdanove ('56)
estrogen is capable of reducing but not of
abolishing the hyperplastic response of the
thyroid gland to goitrogen administration,
depending on the relative amounts of hormone and goitrogen.
These controversial statements and the
absence of any electron microscopic study
on the Muence of estrogen on the cytology of thyroidectomy cells prompted the
following experiment.
Animals. A total of 32 female white
rats, of inbred stock, weighing between
155 gm and 175 gm and randomly distributed into four experimental groups were
used. In a preliminary step, the experiment was made on five animals in each
group. After a study of the results had
shown that each of the different treatments
produced a characteristic and clear-cut
effect, the entire experiment was repeated,
under exactly similar conditions, on an
additional set of three animals in each
group, the pituitary glands of which were
examined by electron-microscopy. The
measurements made in the two successive
experiments were pooled for a final statistical analysis of the variances.
Treatments. All treatments were given
during 15 successive days, at the end of
which period, all animals were sacrificed
by ether anesthesia. Estradiol benzoate
was injected subcutaneously at a daily
dose of 15 vg dissolved in 0.15 ml of oil.
Propylthiouracil (PTU)3was given through
a stomach tube, passed under light ether
anesthesia, at a daily dose of 20 mg suspended in 2 ml of tap water. Group 1
received estradiol benzoate alone. Group
2 was given estradiol benzoate and PTU.
Group 3 received PTU alone. Group 4
served as controls and were administered
oil and water under similar conditions as
the animals of group 2. Before and during
the experiment, the rats were fed a commercial food preparation and drank tap
water ad libitum.
Measurements and morphological investigations. In all animals, the following
data were recorded: body weights at the
beginning and at the end of the experiment; weights of thyroids, adrenals and
ovaries. The pituitary glands were weighed
only in the 20 animals that served for the
preliminary investigation. A histological
study was made of the following organs in
all animals: thyroid glands, in each of
which the mean height of 100 follicular
cells was measured under a 500 X magnification, mammary glands and reproductive tracts. A histological study of the
pituitary gIands, fixed in Hollande-sublimate without acetic acid, was made in the
20 rats that served for the preliminary
investigation and on the halves of some of
the pituitary glands removed for electronmicroscopy in the second set of animals;
sections were stained with Herlant's tetras Propylthiouracil was kindly supplied by the "Etablissements H. V. Mees."
chrome ('60), aldehyde-fuchsin, Alcian
blue in acid solution and azocarmine.
EEectron microscopy. The adenohypophyses, separated from the posterior
lobe, were fixed for 45 minutes at room
temperature in a 1% solution of osmium
tetroxide in phosphate buffer at pH 7.2.
The material was imbedded in Dow epoxy
resins according to the method of Lockwood ('64). Ultrathin sections were cut by
glass knives and examined after lead acetate staining (Millonig, '61) in a Zeiss
EM-9 electron microscope.
The results of our measurements are
recorded in table 1.
Estradiol benzoate, whether given singly
or in combination with PTU, influenced
particularly the pituitary glands and
ovaries, the weights of which increased
to a highly significant degree. PTU on the
other hand, administered singly or in combination with estradiol benzoate, markedly
increased thyroid weight and height of
the follicular cells; at the same time, it
significantly decreased adrenal weight.
When comparing the mean thyroid weight
obtained in group 3, where PTU was given
singly, with that obtained in group 2,
where PTU was associated with estradiol
benzoate, it appears that under the influence of the estrogen, the hyperplastic
response of the thyroid was reduced; the
difference, however was small and was
statistically significant only at the 0.05
level (F = 6.46 for 28" of liberty); the
mean height of the follicular cells on the
other hand, was the same in these two
Histology of reproductive tracts and
m a m m a r y glands
In the groups of estrogen-treated rats
the vaginae always showed an important
mucification of their mucosae; this was
associated with a corresponding development of acini in the mammary glands
that also exhibited signs of active secretion.
Comparable, although somewhat less
pronounced changes were found in two of
the eight rats that had been given PTU
singly. They were entirely absent in the
control animals.
Pituitary histology
(a) After estradiol-benzoate treatment,
the histological picture of the adenohypophysis was dominated by the presence,
Means and standard deviations
Estr.' alone
Estr.1 and PTU
PTU alone
2 and 1
3 and4
Body weight
162.5 174.6
k 3 . 6 &9.2
165.0 169.4
e 7 . 2 216.1
165.0 166.8
2 7 . 2 rt6.1
164.4 172.5
24.2 f12.5
163.8 172.0
2 4 . 7 213.0
164.7 169.6
24.6 210.0
No estradiol
165.0 168.1
2 5 . 2 211.9
163.4 173.6
k 3 . 9 "10.7
1 Estradiol benzoate 15 It.g/day during 15 days.
3 Propylthiouracil 20 mg/day dunng 15 days.
3 Significant difference (P
Yighly significant difference (P < 0.01).
f 7.3
2 8.1
k 4.8
+- 4.4
+- 8.9
f 1.14
k 0.72
57 1.00
rt 0.84
+- 3.4
f6.1F4 "7.0
-C 4.5t4
f 9.5
2 2.36
k 1.71
2 1.05
in overwhelming numbers, of poorly granulated acidophil cells, the cytoplasm of
which was bordered by a filamentous rim of
basophilia and contained a large central
Golgi area. They were typical prolactin
(b) After PTU treatment administered
singly, the adenohypophysis contained
numerous conspicuously enlarged basophils, generally arranged in small clusters.
Their main cytological characteristics were
a great size (up to 15 ~1 diameter), an oval
form, a foamy cytoplasm containing a
large Golgi area and a few rather indistinct small granules that stained with aldehyde-fuchsin and with Alcian blue in acid
solution. They were typical thyroidectomy
cells. Changes were also observed in the
class of acidophil cells: most of them
were less granulated than in controls. The
tetrachrome stain of Herlant (’60) stained
these poorly granulated cells a shade of red.
(c) After both treatments had been combined, the main changes occurred in the
acidophil cells which, in their great majority, took the characteristic appearance of
prolactin cells; typical thyroidectomy cells
could no longer be found.
Pituitary ultrastructure
The main cell types which are of interest
to our purpose were identifled by the following criteria as set out by Farquhar
(‘54) and Purves (’61). Thyroidectomy
cells attain huge sizes and contain cystically dilated ergastoplasmic sacs surrounding a large central Golgi area. The dilated
vesicles are separated by thin cytoplasmic
lamellae and their shapes are altered by
mutual compression; they are fdled by an
electron transparent material of indistinct,
rather filamentous structure. Secretory
material is scant and appears under the
form of small (150 to 180 mw in size)
granules of varying density, which are
lined up under the cell membrane or are
scattered in the Golgi area. An occasional
ergastoplasmic sac contains small osmiophilic droplets that are not membranebound. Normally active thyrotrophs are
of a stellate shape and contain small (up
to 250 mu in size), rather scant and
variably dense granules that tend to line
up along the cell membrane; their relatively electron transparent cytoplasm con-
tains a poorly developed endoplasmic
reticulum and thin, rod-like mitochondria.
Prolactin cells have a well developed
ergastoplasm composed of flattened cisternae arranged in parallel arrays under the
cell membrane or in more centrally placed
concentric whorls (“Nebenkerne”); they
contain relatively few granules that are
densely osmiophilic and show a characteristic variability in shapes and sizes (up
to 600 mv), the smallest tending to accumulate inside a large Golgi area. Somatotroph cells can be differentiated from prolactin cells by their larger number of
densely osmiophilic secretory granules
that also have a more uniform shape and
a smaller size (up to 350 mp in diameter).
Ultrastructural effects of the
different treatments
Thyroidectomy cells were present in the
adenohypophyses of rats treated by PTU
whether it was given singly or in combination with estradiol benzoate. When comparing these two experimental groups
however, it was readily apparent that,
under the influence of the estrogen, thyroidectomy cells became far less numerous,
remained of a much lesser size and contained less dilated ergastoplasmic sacs
(figs. 1, 2).
Normally active thyrotrophs were not
seen in animals treated by PTU alone:
apparently they had all transformed into
thyroidectomy cells. By contrast, they
were present in rats given the combined
PTU and estrogen treatment (fig. 3) where
they existed side by side with more or less
fully developed thyroidectomy cells. They
were also present in the two other experimental groups, between which we could
detect no definite difference in their cytological appearance.
Prolactin cells were present in great
numbers after estrogen treatment. There
was a definite difference in their ultrastructure according to whether estrogen had or
had not been supplemented by PTU. In the
former case, their size was greater and
their cytoplasm regularly contained a
greater number of ergastoplasmic Nebenkerne (fig. 4). In the animals treated by
PTU alone, a special type of cells was
seen to emerge from the class of poorly
granulated acidophils; they could be dis-
tinguished from normal somatotrophs by gen does not potentiate the thyroid stimutheir particularly scanty granulation and lating action of goitrogens.
by the large size of their granules, some of
The changes in thyroidectomy cells cytowhich attained 650 mp in their longest logy and the decrease in weight of the
axis (fig. 5). The endoplasmic reticulum thyroid glands of rats given estradiol
of these cells never attained the develop- benzoate in addition to PTU are consistent
ment reached in the typical prolactin cells with a depressing influence of estrogen
as were seen in the estrogen-treated on pituitary thyrotrophic function. It appears unlikely however, that the over-all
effect of estrogen on thyroid activity may
be explained by this sole mechanism. In
Our experiment clearly showed that in rats given estradiol benzoate alone, we
female rats, estradiol benzoate given dur- could detect no cytological evidence of
ing 15 days at a daily dose of 15 pg de- decreased activity in thyrotroph cells.
pressed the thyroprivic response of the Admittedly, electron microscopy can hardly
pituitary to a simultaneous dose of 20 mg be expected to give a proper evaluation of
/day of propylthiouracil. This was demon- the level of function of cells that, even in
strated by the histological study of the their normal state, show no particular
adenohypophyses and was even better cytological evidence of activity and that,
evidenced by electron microscopical obser- after estrogen treatment, become difficult
vation which showed that the effect was to find amidst the proliferated prolactin
of a quantitative rather than a qualitative cells. Of more significance therefore, was
order: under the influence of estrogen, the absence, in our experiments, of any
a smaller number of thyrotrophs were decrease in weight of the thyroid glands
transformed into thyroidectomy cells and after estrogen treatment alone. More imthese were individually less fully developed portant still are the many reports that
than in animals treated by PTU alone. At estrogen administered singly stimulates the
the same time that it depressed the pitui- thyroid gland of the rat as evidenced by
tary thyroprivic reaction, estrogen also either an elevation of different paramdecreased the hyperplastic response of the eters measuring thyroidal activity (Solithyroid gland to PTU administration. This man and Reineke, '55; Noach, '55; Feldeffect was small, of low statistical signifi- man, '56; Nataf et al., '57; Florsheim, '58;
cance and was seemingly not proportional Grosvenor and Turner, '59; Moon and
to the striking changes in pituitary cytol- Turner, '60; Grosvenor, '62; Brown-Grant,
ogy; furthermore, the decline in weight '62; Amesbury et al., '65; Yamada et al.,
was not accompanied by a corresponding '66), an increased height of the follicular
decrease in the height of the follicular cells (Desclin and Ermans, '51) or a gain
cells. No significant changes, either in in weight of the total gland (Desclin and
thyroid weight or in height of the follicular Ermans, '51; Noach, '55; Yamada et al.,
cells were observed when an identical dose '66). Putting together all these results,
we would believe that the ovarian hormone
of estradiol benzoate was given singly.
Our observations on pituitary morphol- influences the thyroid in two counterbalogy are in good agreement with those ancing ways: on one hand directly by
reported by Desclin and Ermans, ('51) and stimulating the thyroid gland, as best
by Amesbury et al., ('65). Previously appears when estrogen is given singly and
reported studies on the influence of estro- on the other hand indirectly, by inhibiting
gen on goiter induction have resulted pituitary thyrotrophic activity, as is best
either in no effect (Desclin and Ermans, demonstrated when estrogen is given in
'51) or in an inhibitory effect (Chamorro, combination with PTU. A comparable view
'49; Eskin and Bogdanove, '56), depending has been expressed by Noach ('55a,b) who
in part on varying time-dose relationships based his conception on quite different
and potencies of drug preparations. Such experimental evidence; he found that
differences make a comparison with our estradiol benzoate increased the uptake of
results difficult. However it seems safe to radioactive iodine by the thyroid of intact,
admit, as a general conclusion, that estro- but not of hypophysectomized rats; in the
latter however, its stimulatory influence
could be restored by the administration
of a constant, low maintenance dose of
TSH and it was in these circumstances
only that a correlation became evident
between thyroid response and estrogen
dosage. Using bioassay procedures, Amesbury et al. (’65) have studied the hormonal
outputs of the pituitaries of estrogentreated male rats. Their results bring no
positive support to our view of a dual
action of estrogen on thyroid function;
but neither do they contradict it. They
reported that in castrated animals, estrogen lowered the TSH content of the pituitary; unfortunately, the corresponding
plasma level of TSH was not examined,
so that no conclusion can be drawn from
this fragmentary information. They further report that in thyroidectomized animals, estrogen does not alter the TSH
contents of pituitary and plasma; their
figures however seem to indicate that both
values were lowered when high doses
(150 ug/day for 20 or 40 days) of estradiol
benzoate were given and such results
would be more in keeping with our morphological findings in the pituitary gland.
The adenohypophyses of our rats which
had been treated by PTU alone showed a
degranulation of the acidophil cells. This
is a well known accompaniment of the
thyroprivic state; it has been demonstrated
to correlate with a decrease in somatotrophin secretion and therefore is generally
considered as indicating a specific inactivation of the somatotroph cells (Contopoulos
and Koneff, ’63). When examining the
ultrastructure of these pituitary glands we
were surprised however to find that a
number of degranulated acidophils exhibited cytological signs of activity rather than
disuse : their Golgi areas and ergastoplasmic cisternae were rather well developed;
furthermore, their sparse granules were
large, some of them attaining a size of
650 mp which, according to Farquhar
(Purves, ’61) lies outside the range seen
in typical somatotrophs. These observations make us suspect that they might well
be prolactin cells which were difficult to
differentiate from degranulated somatotrophs because, being in a state of relative
functional quiescence, they lacked the
characteristic small immature granules
accumulated in an enlarged Golgi area.
Some support for this interpretation could
be found in the mucification of the vaginal
mucosae of some of our PTU-treated rats
and in the better development of their
mammary glands when compared with
those of controls. Furthermore, in the
groups of estrogen treated animals, when
a comparison was made between the
pituitary cytology of those rats that had
received estrogen alone and those that in
addition had been given PTU, it was seen
that in the latter, the prolactin cells had
a more elaborated ergastoplasm with a
greater number of larger “Nebenkerne”.
Our results raise the question of the
locus of effect of estrogen on pituitary
thyrotrophic activity. To this problem, our
experiments bring no definite answer. It
might be conceived that estrogen exerts
an inhibitory influence directly on the
thyrotroph cells. Another explanation is
that estrogen alters the feed-back mechanism governing TSH secretion, possibly by
depressing the hypothalamic centers regulating thyrotrophic function. The second
hypothesis would be in keeping with the
view that estrogen induces the development of prolactin cells through a depressing action on the hypothalamus (Everett,
’54; Pasteels, ’63). We found that prolactin cells apparently also stand under the
influence of PTU: when given singly, the
goitrogen induced their appearance in the
adenohypophysis and, when combined
with estrogen, it increased the development
of their ergastoplasms. This raises the
possibility that the inhibition of thyrotroph
cell activity, which occurs after a combined
estrogen and goitrogen treatment, might
result from a cumulative depressing effect
on the hypothalamic centers.
Sincere thanks are due to Prof. L. Desclin, Universit6 Libre de Bruxelles and
Fondation Reine Elisabeth, for helpful
criticism and encouragement at all times,
and to Miss Delfiasse and M. C . Cortier
for technical assistance.
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All preparations were fixed in osmium tetroxide buffered with phosphate
at pH 7.2 and embedded i n Dow epoxy resin; the sections were stained
by lead acetate (Millonig, '61).
Adenohypophysis of a rat treated by PTU alone. Part of a thyroidectomy cells is shown; at the right is a voluminous Golgi area containing several small secretory granules and two multivesicular bodies.
At the left, numerous greatly dilated ergastoplasmic sacs may be seen;
they are separated by thin cytoplasmic lamellae studded with ribosomes. x 14,000.
Adenohypophysis of a rat given a combined PTU and estradiol
benzoate treatment. Part of a thyroidectomy cell is seen at exactly
the same magnification as in the preceding figure. The ergastoplasmic
sacs are much smaller; some pale secretory granules are lined up
along the cell membrane. x 14,000.
Paul R. Potvliege
Adenohypophysis of a rat given a combined PTU and estradiol
benzoate treatment. A normally active thyrotroph is seen, surrounded
by portions of four prolactin cells and one somatotroph cell, the latter
occupying the upper right corner. The thyrotroph cell is stellate in
shape, contains a small number of secretory granules together with
a poorly developed ergastoplasm. The prolactin cells are identified
by virtue of their highly developed ergastoplasm and their dense
granules, of varying shapes and sizes. The somatotroph cell contains
numerous dense granules. x 9,600.
Adenohypophysis of a rat given a combined PTU and estradiol
benzoate treatment. Part of a prolactin cell is seen: it contains a
large number of ergastoplasmic Nebenkerne; such a n enormously
developed ergastoplasm was never seen in the prolactin cells of rats
treated by estradiol benzoate alone. X 9,200.
Adenohypophysis of a rat treated by PTU alone. Portion of a n
acidophil cell recognizable by its flattened ergastoplasmic cisternae
lined up along the cell membrane and by its densely osmiophilic
granules. The presence of a large number of free ribosomes is
noticeable: the secretory granules are large and attain a size of 650
mp. The cytological appearance is more that of a prolactin cell than
that of a quiescent somatotroph cell. X 9,600.
Paul R. Potvliege
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estrogen, morphology, effect, pituitary, stud, microscopy, goitrogen, electro, rats, treated
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