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Passage of thyroid hormone across the placenta in intact and hypophysectomized rats.

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Passage of Thyroid Hormone Across the Placenta in
Intact and Hypophysectomized Rats'
MAX HAMBURGH, EDNA H. SOBEL, ROBERT KOBLIN AND
ALAN RINESTONE
Department of Anatomy and Department of Pediatrics, Albert Einstein
College of Medicine, New York, New York
ABSTRACT
The studies were designed to determine whether thyroid hormone
traverses the placenta of the rat.
1. Pregnant rats were hypophysectomized on the twelfth day of the gestation
period. The histological appearance and wet weights of the fetal thyroids at term
were determined and found to be the same as that of fetuses of intact mothers. These
results indicate that maternal TSH is not required for maturation of the fetal thyroid.
2. Intact and hypophysectomized pregnant rats were provided with a diet supplemented with 0.2% propylthiouracil (PTU) added in powdered form starting on the
fifteenth day of gestation until term. This treatment led to enlargement of thyroids
of fetuses of intact and hypophysectomized mothers.
3. Groups of intact and hypophysectomized pregnant rats given the same goitrogenic treatment as group 2 were injected daily with 100, 50, 25 and 12.5 fig of 1-thyroxin
in suspension. Twenty-five pg of thyroxin were sufficient to inhibit goiter development
in fetuses of hypophysectomized rats, while 50 pg was required to prevent the goiter
formation in fetuses obtained from intact non-hypophysectomized pregnant rats.
These results suggest that maternal thyroid hormone passes the placenta from
mother to fetus. The effectiveness with which thyroid hormone passes from the mother
t o the fetal circulation is probably influenced in some way by the maternal pituitary.
The availablity of maternal thyroid hormone to the fetus has been studied in several species with inconsistent results, some
investigators finding evidence for placental
passage, Carr et al. ('59), Grumbach and
Werner ('56), Knobil and Josimovich
('58), Mitskevitch ('57), Nataf et al.
('56), Noumura ('59) and Peterson and
Young ('52), while others have not, Hall
and Myant ('56), Hirvonen and Lybeck
('56), Lybeck ('56) and Postel ('57). Normal development of the fetus may require
thyroid hormone which could be of fetal
or maternal origin. It has been suggested
that the occurrence of severe mental deficiency in the majority of congenitally
hypothyroid children may reflect intrauterine hypothyroidism, Smith, Blizzard
and Wilkens ('57). Efforts to demonstrate
placental passage of thyroid hormone in
human beings suggest that the transfer is
very slow, Carr, Beierwaltes, Raman, Dodson, Tanton, Betts and Stambaugh ('59)
and Grumbach and Werner ('56).
The present study was designed to determine whether thyroid hormone traverses
the placenta of the rat and whether maternal or fetal thyrotrophic hormone is in-
volved in the development of the fetal thyroid gland. The experimental design was
based on the induction of goiters in the
fetuses of hypophysectomized animals and
determination of whether treatment of the
mothers with thyroxine inhibited the delopment of goiters. Prevention of goiters
could be accomplished only if thyroxine
crossed the placenta to inhibit production
of thyrotrophin by the fetal pituitary gland.
Preliminary reports have been published
by Hamburgh and Sobel ('61) and Sobel,
Hamburgh and Koblin ('60).
MATERIALS AND METHODS
A. Materials
Pregnant rats of the Charles River
Breeding Laboratories Caesarian-Derived
(CD) strain, which are Sprague-Dawley
descendants, were used for all experiments. Animals were housed individually
in an air-conditioned room, and provided
with Rockland mouse diet (ground) and
water ad lib unless otherwise indicated.
1This investigation was supported by a research
grant from the United States Public Health Service
N.I.H. A-3489. and by an institutional =ant of the
American Cancer Society.
219
220
M . HAMBURGH, E. H. SOBEL, R. XOBLIN AND A. RINESTONE
Hypophysectomy was performed on the
twelfth day of pregnancy by the commercial supplier. The sella turcicas of the
rats were examined by us for completeness of hypophysectomy at the termination
of pregnancy. The absence of all or a
major portion of the pituitary tissue within the sella turcicas of the operated experimental animals was taken as criterion
of successful hypophysectomy. The fetuses
of each litter were weighed OR the day
of birth and their thyroid glands rapidly
removed by one observer with the aid of
a dissecting microscope. One-half of each
gland was weighed wet on a Mettler semimicrobalance (accuracy 0.001gm) by another observer; the other half was placed
in formaldehyde for subsequent histological examination. Results were calculated
as 2 X the wet weight of one-half gland,
mg/lO gm of body weight and are exone standard error
pressed as the mean
for each group,
*
Thyroxin* (T) (free acid base of l-thyroxin) dissolved in 8.7 ml of physiological saline to which was added 1.3 ml of
0.01 N NaOH, adjusted to pH 8-8.5 was
given by daily injection in 1 rnl of fluid.
This material was poorly soluble and
was given as a suspension. Treatment
was initiated on the fifteenth day of gestation and continued until delivery. Dosages
administered ranged from 12.5 pgm, 25
pgm, 50 pgm, and 300 pgm thyroxin suspension in 1 ml fluid to different groups
of experimental rats.
There were several control groups of
intact and hypophysectomized animals :
(1) Animals maintained on a normal diet.
( 2 ) Animals given PTU mixed with their
regular food and injected with 1 rnl d k a line saline (made up in the same proportion as the fluid in which thyroxin was
dissolved). ( 3 ) Animals maintained on an
unsupplemented diet and given daily thyroxin injections. (4) Hypophysectomized
rats given PTU and injected daily with 85
ugm NaI, instead of thyroxin. This dosage
of NaI was chosen because it contains an
amount of Iodine equivalent to that of 100
pgm thyroxin. ( 5 ) Hypophysectomized rats
maintained on a restricted food intake to
see whether the goitrogen or hormone
treatment might exert its effect on thyroid
weight by inffuencing food intake of the
animals.
B. Experimental methods
1. The role of T S H for differentiationof
the thyroid. In a preliminary series of experiments designed to determine whether
the presence of a maternal pituitary is required during pregnancy for normal differentiation of the thyroid of the offspring,
giands of newborn rats derived from normal and from hypophysectomized mothers
were examined histologically and their wet
RESULTS
weights recorded.
2. Placental transfer of thyroid hormone
Untreated pregnant animals (groups 1A
across the placenta. Intact (non-hypophy- und 1B). The weights of the thyroid
sectomized) and hypophysectomized preg- glands of the fetuses of hypophysectomized
nant rats were offered a goitrogenic diet animals were not different from those of
beginning on the fifteenth day of gesta- the fetuses of intact mothers, (table 1, l A ,
tion. Goiter induction was initially accom- 1B). The size of follicles was not reduced
plished by the provision of drinking water in newborns obtained from hypophysectccontaining 0.05% propylthiouracil (PTU) mized as compared with thyroids of newand 0.5% potassium perchlorate (KClOa) borns of intact mothers (fig. 1 and 2).
Sobel, Hamburgh and K o b h ('60). This Since the thyroid of the fetal rat does not
combination was poorly tolerated by hy- begin to differentiate until the eighteenth
pophysectomized animals. In later experi- day these results indicate that maternal
ments, therefore, PTU (0.2% ) was added TSH is not essential for the differentiation
in powered form mixed with a finely of the fetal thyroid.
ground Rockland mouse diet. The addiTreatment with goitrogens (groups 2 A
tion of KCIO, in the drinking water was und 2B). Ingestion of PTU by the mother
dispensed with. The latter method was resuIted i n enlargement and disorganizaequally effective as a means of goiter in2 Grateful acknowledgment i s made to Smith Kline
duction, and was accompanied by a lower
and French Laboratories for supplying thyroxih used
mortality rate.
in this investigation.
22 1
PASSAGE O F THYROXIN ACROSS T H E PLACENTA
tion of the follicular structure of the thyroid glands of all the fetuses (table 1,
2A-B, fig. 3 and 4 ) . Since these fetal
goiters developed in the absence of the
maternal hypophysis as well as when the
mother was intact (tabIe 1, 1A-2A, 1B2 B ) (P = < O . O O l ) , TSH production by
the fetal hypophysis must have increased
in response to decreased production of
thyroid hormone by the fetal thyroid gland,
since maternal thyroid function in the
hypophysectomized animal is minimal.
Treatment of pregnant animals with
thyroxin (gToups 3A and 3 B ) . There were
differences in response to the treatment
with thyroxin between intact and hypophysectomized animals. Daily injection of 100
wgm of thyroxin to pregnant intact rats
maintained on a normal diet did not affect
the weights of the fetal thyroids (table 1,
l A , 3A). On the other hand there was a
small but statistically significant hypoplasia of fetal thyroids in litters of hy-
pophysectomized mothers treated in the
same manner (table 1, 1B-3B) ( P =
< 0.001).
Treatment with thyroxin in combination
with PTU (groups 4-7A and 4-7B)
Intact mothers (groups 4A-7A). Onehundred micrograms of T given to intact
pregnant rats maintained on a goitrogenic
diet reduced the thyroid weight of newborn
animals to less than that found when the
mother was untreated (table 1, 1A-4A)
( P < 0,001). With a dose of 50 pgm the
fetal thyroid weights were nearly the same
as those of fetuses of untreated mothers
(table 1, 5A), while 25 Ngm did not inhibit
the development of fetal goiters appreciably (table 1, 6A). The massive doses
(100 pgm) of thyroxin administered to
the mother prevented to a small extent the
follicular disorganization of the fetal thyroid that results from PTU treatment
(fig. 5 ) .
TABLE 1
Mean thyroid weight -C standard error in newborn rats
Treatment
Mean
S.E.
Thyroid
weight m g
per 10 g m
body weight
1. Control
N
Number
of fetuses
Number
litters
Of
7
Group 1A intact
Group 1B hypox
1.93f0.07
1.88f0.04
28
85
20
2. PTU
Group 2A intact
Group 2B hypox
4.73f0.18
5.28f0.17
32
88
8
17
3. 100 ggm Thyroxin in normal diet
Group 3A intact
Group 3B hypox
1.98-C 0.05
1.502 0.03
30
20
3
1.28? 0.11
1.8620.14
16
44
4
8
2.24f0.20
1.64?0.11
32
33
8
7
3.60 '-t 0.20
1.93f0.11
31
30
8
6
+
4. PTU 100 pgm Thyroxin
Group 4A intact
Group 4B hypox
5.
+
PTU 50 pgm Thyroxin
Group 5A intact
Group 5B hypox
+
6. PTU 25 pgm Thyroxin
Group 6A intact
Group 6B hypox
7. PTU
+ 12.5pgm Thyroxin
intact
Group 7B hypox
8. PTU
+85 pgm NaI
intact
Group 8B hypox
7
-
-
3.63f0.20
12
3
-
-
-
5.92-C 0.30
14
3
222
M . HAMBURGH, E. H. SOBEL, R. KOBLIN AND A. RINESTONE
TABLE 2
“t” Tests for significance between two means
n
Grouos
1A-2A
2A4A
2A-5A
2A-6A
1A-4A
1A-5A
1A-6A
1A-3A
Intact
Intact
Intact
Intact
Intact
Intact
Intact
Intact
signif.
signif.
signif.
signif.
signif.
not signif.
signif.
not signif.
58
46
62
61
42
58
57
56
1B-2B
2B-4B
2B-5B
2B-6B
2B-7B
2B-SB
1B-4B
1B-5B
1B-6B
1B-7B
1B-8B
1B-3B
Hypox.
Hypox.
Hypox.
Hypox.
Hypox.
Hypox.
Hypox.
Hypox.
Hypox.
Hypox.
Hypox.
Hypox.
signif.
signif.
signif.
signif.
signif.
not signif.
not signif.
signif.
not signif.
signif.
signif.
signif.
171
130
119
116
98
100
127
116
1I3
95
97
103
not signif.
signif.
111
1A-1B
2A-2B
H ypophysectomized mothers ( g r o u p s
4B-7B).
As little as 2 5 clgm T was effective in inhibiting the development of fetal
goiters (table 1, 2B-6B) ( P < 0.001) as
was the dose of 50 wgm (table 1, 2B-5B)
( P < 0.001). With 50 pgm the weight of
the thyroid at term was less than that
found in the fetuses of untreated hypophysectomized rats (table 1, 1B-5B) (P <
0.05). With 12.5 wgm there was partial inhibition of goiter development; the
fetal glands were larger than when the
mother received no treatment (table 1,
1B-7B) (P<O.OOl) but were smaller
than the goiters found when PTU was
given without T (table 1, 2B-7B) (P <
0.001). The follicular disorganization of
the fetal thyroid induced by PTU treatment was less severe when thyroxin was
administered simultaneously ( 100 Hgm)
(fig. 6).
Since, in the hypophysectomized animals, goiter development could have been
prevented only by inhibition of production
of TSH by the fetal pituitary, the observations suggest that thyroid hormone can
cross the placenta when an excess is given
to the mother. The amount of T required
is apparently larger in intact than in
hypophysectomized mothers.
11s
P
< 0.001
< 0.001
< 0,001
< 0.001
< 0.001
> 0.10
< 0.001
> 0.50
< 0,001
< 0.001
< 0.001
< 0.001
< 0.001
> 0.05
> 0.70
< 0.05
> 0.50
< 0.001
< 0.001
< 0.001
> 0.50
< 0.05
Treatment with goiterogerz and Nu1
(group 8B). One group of hypothysectomized mothers maintained on PTU supplemented diet was injected with 85 pgm
NaI daily, to provide the amount of iodine
present in 100 p g m T. There was no inhibition of goiter development (table 1,
2B-8B) (P > 0.05), which indicates that
the effect of the thyroxin treatment could
not have been the result of deiodination of
T with placental passage of iodide rather
than of the intact hormone molecule.
Effect of nutrition (groups 9-11). A
group of hypophysectomized pregnant rats
was maintained on a restricted food intake
of 5 . 5 gm of ground mouse diet per day
to see whether the effect of the goitrogen
or hormone treatment on thyroid weights
of newborn animals was perhaps mediated
through differences in food intake (table
3 ) . The amount of food aIIowed was equal
to the total daily food consumption of one
of our experimental groups (table 3, l o b ) .
Although restrictions in the food intake
depressed total body weight of the newborn rats by about 20% the lowered body
weight was not reflected in the absolute
thyroid weight of the young. The magnitude and the direction of the treatment
with PTU and with PTU and thyroxin on
223
PASSAGE OF THYROXIN ACROSS THE PLACENTA
TABLE 3
Mean thyroid and body weights i n newborn rats
Group
9A
Control
1OA
PTU in food
11A
+
PTU
100 P g m
thyroxin
Treatment
No. of
Mean
body wt.
Mean
aEgte thyroid
wt.
thyroid wt. %5i;ow$
pregnant
mothers
f"".
of
etuses
5
20
5.02
1.08
2.24
7
34
4.48
2.30
5.23
4
20
4.41
0.61
1.37
37
6.14
1.07
1.76
30
4.42
2.21
5.03
24
4.24
0.91
2.28
mg
Animals of groups 9A, lOA, 11A
hypophysectomized
Pregnant mothers kept on
restricted food intake of
5.5 gm daily from 16th
day of pregnancy till term
~~
9B
Control
1OB
PTU in food
11B
PTU
100P g m
thyroxin
+
9
Animals of groups 9B, 10B, 11B
hypophysectomized
Mother fed ad. lib.
4
ditions become more favorable for the
passage of the hormone across the placental barrier toward the end of pregnancy. Most of the experiments cited with
DISCUSSION
negative results were carried out during
Our observations show that maternal the early part of the gestation period,
TSH is not essential for thyroid differentia- while results confirming transfer of hortion in the rat, but they do not indicate mone across the placenta were obtained
whether the rat thyroid differentiates au- in experiments conducted during the lattonomously or whether fetal TSH is re- ter part of pregnancy.
Our results furthermore showed that
quired for its maturation. Dependence of
the developing thyroid on fetal TSH has thyroxin traverses the placental barrier
been shown by Jost ('57, '59) for the rat in hypophysectomized animals more easily
than in intact ones. There are several
thyroid and also for the rabbit thyroid.
Our results can be interpreted as show- possible explanations for this unexpected
ing that thyroxin can cross the placenta finding.
( 1 ) The presence of the maternal pituiof the rat when given to the mother in the
later stages of gestation. Our findings are tary in the pregnant animal might exert
are in agreement with those of Carr et al. an effect on the permeability of the pla('59) on humans, Grumbach and Werner centa to the hormone.
(2) The maternal pituitary may con('56) on humans, Knobil and Josimovich
('58) in rats, Noumura ('59) on rats, centrate some of the exogenously adminMitskevitch ('57) on rabbits and guinea istered thyroid hormone, so that in the inpigs and Peterson and Young ('52) on tact animal relatively less hormone would
guinea pigs. They are not necessarily at be available to reach the fetal circulation.
variance with the negative findings re- Evidence that the pituitary traps circuported by Hall and Myant ('56) on rabbits, lating hormone has been cited by PittHirvonen and Lybeck ('56) on guinea pigs, Rivers ('59).
( 3 ) The maternal pituitary may influLybeck ('56), and Postel ('57) on guinea
pigs.. It is possible that in most of the ence the composition of plasma proteins
species which have been tested so far, con- which bind circulating hormone. Yamada
thyroid weight was essentially alike in the
group fed ad lib and in the group maintained on restricted food intake.
224
M . HAMBURGH, E. H. SOBEL, R. KOBLIN AND A. RINESTONE
('60) has recently presented data which
indicate that agents such as trypan blue,
which interfere with the binding of the
thyroxin molecule to a and @ globulins
operate via the hypophysis.
No estimate of thyroid hormone production of the pregnant rat are available.
Grosvenor and Turner ('58) calculating
thyroid secretion rate by the use of radioiodine technique and measuring subsequent suppression of thyroidal
output,
estimated the daily thyroxin level of lactating rats to be about 2.2 Ng/lOO g and
that of non-lactating rats to be about 1.3
vg/100 g. The body weights of the rats in
our experiment were between 350-400 g.
If pregent rats produce about as much
thyroid homone as lactating rats the daily
requirements of 7.7 vg to 8.8 Ugm in animals weighing between 350-400 g is about
one-third to one-sixth the amount of thyroxin which was effective in inhibiting the
development of fetal goiters in our experiment. It is likely that with the sodium
salt of thyroxin, which is more soluble
than the free acid base of 1-thyroxin which
we used, smaller doses would be adequate.
Knobil and Josimovich ('58) employing
a procedure similar to our own estimated
3 vgm as the effective dose for passage
across the placenta. Dempsey and Astwood ('43) have shown that a daily dose
of 5.2 v g m exogenously administered thyroxin is required to maintain normal thyroid weight in young male rats kept on a
PTU supplemented diet.
The demonstration that thyroid hormone
given to the mother is made available to
the mammalian fetus does not prove that
the mammalian embryo's need for thyroxin is normally satisfied by the maternal
gland.
The frequently reported observations
(Chu, '44 and Davenport and Swingle, '27),
that thyroidectomized animals are able to
conceive and bear normal young has been
interpreted to mean that in many mammals fetal development can take place without thyroid hormone until the fetus begins
to make its own. This view has been challenged, however, by Weiss and Noback
('49) who demonstrated that in the absence of maternal thyroid hormone ossification of bones is delayed and retarded
in the 16 day old fetal rat, at an age when
the fetal thyroid is not yet functioning.
In the light of evidence presented in
this paper, which shows that in later stages
of gestation thyroid hormone can pass
across the placenta, it would appear that
in the rat the embryo's requirements for
thyroid hormone prior to the onset of
function of the fetal gland, can be satisfied at least partially by the mother's thyroid gland.
LITERATURE CITED
Carr, E. A., Jr., W. H. Beierwaltes, G. Raman,
V. N. Dodson, J. Tanton, J. S. Betts and R. A.
Stambaugh 1959 The effect of maternal thyroid function on fetal thyroid function and development. J. Clin. Endocrinol. Metab., 19:
1-18.
Chu, J. P. 1944 Influence of the thyroid gland
on pituitary gonadotrophic activity in the rabbit. Endocrinol., 34: 90-102.
Davenport, C. B., and W. W. Swingle 1927
Effects of operations upon the thyroid glands
of female mice on the growth of their offspring.
J. Exp. Zool., 48: 395440.
Dempsey, E. W.,and E. B. Astwood 1943 Determination of the rate of thyroid hormone
secretion at various environmental temperatures. Endocrinol., 32: 509-518.
Grumbach, M. M., and S. C. Werner 1956
Transfer of thyroid hormone across the human
placenta at term. J. Clin. Endocrinol. Metab.,
16: 1392.
Grosvenor, C. E., and C.W. Turner 1958 Effect
of lactation upon thyroid secretion rate in the
rat. Proc. SOC.Exp. Biol. and Med., 99: 517519.
Hall, P. F.,and N. B. Myant 1956 Passage of
exogenous thyroxine and of iodide between
mothers and fetuses in pregnant rabbits. J.
Physiol., 133: 181-193.
Hamburgh, M.,and E. Sobel 1961 Evidence for
placental transfer of thyroxine and of fetal
pituitary thyroid interaction. Anat. Rec., 139:
234-235.
Hirvonen, L., and H. Lybeck 1956 On the
permeability of guinea pig placenta for thyroxine. Acta physiol. Scand., 36: 17-21.
Jost, A. 1957 Action du propylthiouracile sur
la thyroide de foetus de rat intacts ou dbcapitbs.
Compt. rend. SOC.Biol., 151: 1295-1298.
1959 Action du propylthiouracile sur
la thyroide du foetus de lapin intact, decapitb
ou inject6 de thyroxine. Ibid., 153: 1900-1902.
Knobil, E., and J. B. Josimovich 1958 Placental transfer of thyrotrophic hormone, thyroxine, triiodothyronine and insulin in the rat.
Ann. N. Y. Acad. Sci., 75: 895-904.
Lybeck, H. 1956 On the permeability of guinea
pig placenta for triiodothyronine. Acta physiol.
Scand., 37: 215-219.
Mitskevitch, M. S. 1957 Experimental analysis
of the functional interrelationship between the
hypophysis and thyroid glands during the period of embryonic development of birds and
PASSAGE OF THYROXIN ACROSS T H E PLACENTA
mammals. In: Glands of internal secretion in
the embryonic development of birds and mammals: 104-151 (Chapt. 5) Acad. of Sciences
of U.S.S.R. Institute of Animal Morphology.
Publ. for the Nat. Science Foundation and the
Department of Health, Education and Welfare
by the Israel. Programs for Scientific Translations, 1959.
Nataf, B., M. Sfez, R. Michel and J. Roche 1956
Sur la permeabilitee du placenta B la 3,5,3triiodothyronine. Comp. rend. SOC. Biol., 150:
1088-1090.
Noumura, T. 1959 Development of the hypophyseal - thyroidal system in the rat embryo
and its relation to the maternal system. Japanese J. of Zool., 12: 301-318.
Peterson, R. R., and W. C. Young 1952 The
problem of placental permeability for thyrotrophin, propylthiouracil and thyroxine in the
guinea pig. Endocrinology, 50: 218-225.
Pitt-Rivers, R., and J. R. Tata 1959 Extrathyroidal Distribution and Metabolism of Iodine. In: The Thyroid Hormones: 124-140
(Chap. 7) Pergamon Press.
225
Postel, S. 1957 Placental transfer of perchlorate and triiodothyronine in the guinea pig.
Endocrinology, 60: 53-66.
Smith, D. W.,R. M. Blizzard and L. Wilkens
1957 The mental prognosis in hypothyroidism
of infancy and childhood. Pediatrics, 19: 10111012.
Sobel, E. H., M. Hamburgh and R. Koblin 1960
Development of the fetal thyroid gland. Acta
endocrinol., Suppl. 51: 1207.
1960 Development of fetal thyroids in
rats: evidence for placental transfer of thyroxine. A.M.A. Amer. J. Diseases of Children,
100: 709-710.
Yamada, T. 1960a The effect of trypan blue on
thyroid function in the rat. Endocrinology, 67:
204-211.
1960b Mechanism of action of trypan
blue in suppressing thyroid function. Ibid.,
67: 212-221.
Weiss, R. M.,and C. R. Noback 1949 The effect of thyroxin and thiouracil on the time of
appearance of ossification centers of rat fetuses.
Endocrinol., 45: 289.
PLATE 1
EXPLANATION OF FIGURES
1 Thyroid of newborn rat of a n intact (non-hypophysectomized) untreated mother. Magnification 120 X. Parathyroid shown on right side.
2
Thyroid of a newborn rat of a hypophysectomized untreated mother.
Magnification 120 x. Parathyroid shown on right side.
3
Thyroid of a newborn rat of an intact mother. Mother given 0.2%
propylthiouracil (PTU) mixed in the food beginning on the fifteenth
day of gestation. Magnification 120 X. Follicular arrangement disorganized. Parathyroid on lower right side.
4 Thyroid of newborn rat of a hypophysectomized mother. Mother
treated as in 3. Magnacation 120 X. Follicular arrangement destroyed. Parathyroid in upper right corner.
5
Thyroid of a newborn rat of an intact mother. Mother given PTU as
in 3. Daily injections of 100 pgm of thyroxin were administered from
the fifteenth day of gestation until term. Magnification 120 x. Follicular arrangement disorganized but to a lesser degree than thyroid
shown in figure 3.
6 Thyroid of a newborn rat of a hypophysectomized mother. Mother
treated as in 5. Magnification 120 X. Picture essentially the same as
5. Follicular arrangement disorganized, but to a lesser degree than
thyroid shown in figure 4. Parathyroid in upper right corner.
226
PASSAGE OF THYROXIN ACROSS THE PLACENTA
Max Hamburgh, Edna H. Sobel, Robert Koblin a n d A l a n Rinestone
PLATE 1
227
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