close

Вход

Забыли?

вход по аккаунту

?

The experimental shortening of delayed pregnancy in the albino rat.

код для вставкиСкачать
THE EXPERIMENTAL SHORTENING O F DELAYED
PREGNANCY I N T H E ALBINO RAT
CHARLES K. WEICHERT
2001ogicnl Laboratory, Universiiy of Cinciniiati, Ohio
THREE PLATES
The normal gestation period of the albino rats in our colony
is 22 days but occasional individuals may have 21-day or 23-day
gestation periods. Long and Evans ('22) first discovered that
in the r a t oestrus and ovulation occur shortly after parturition,
usually within 2 6 3 6 hours. It does not seem to be very generally known, however, that if copulation and conception occur
during this post-partum oestrus the gestation period which
follows and during which the young of the first litter are being
suckled, may be prolonged and extend over a period ranging
from 22 to 36 or more days.
Pinard ('05) apparently was the first investigator t o report
the occurrence of prolonged gestation or delayed pregnancy
in rodents. I n some of his cases the period of gestation was
half again as along as the normal duration. Daniel ('10) reported the occurrence of delayed pregnancy in lactating mice
and stated that gestation was prolonged by 1 day for each
mouse being suckled. King ( '13) reported similar observations
on the albino rat. These early workers attributed the prolongation of gestation to nutritive disturbances and implied
that the suckling young received nutrition a t the expense of
those developing i.11 utero, thus preventing them from growiiig
at the normal rate.
Kirkham ( '16 a, b, '18) working with mice discovered that
ovulation and fertilization in the majority of cases occur normally during the post-partum oestrus of lactating females.
He reports a rather high percentage of failures, however.
31
32
CHARLES K. WEICHERT
Segrncntation of tlic f crtilized eggs arid thcir passage down
the Fallopian tubes occurs at the same rate in both nursing
and non-nursing mothers. Kirkham found that the prolongation of gestation was due to delayed implantation and stated
that the fertilized eggs of lactating fernales lie free in the
lumen of the uterus from the sixth to the fourteenth days. He
believed that the uterine cells would not react t o the blastocysts and enable them to become implanted before the fourteenth day. He interpreted this as being due to a withdrawal
of nourishment from the parent by the suckling young. Kirkham also noted that the embryos in the uteri of pregnant
females suckling the same number of young did not always
develop a t the same rate. He attributed this t o individual
variation in the influence of the mammary glands.
Mirskaia and Crew ('30) report that the degree of prolongation of gestation in lactating mice is variable but that it has no
relation to the number of young in the uterus nor to the number suckling. They do not find any support to the contention
that there is some inhibitory action exerted by the mammary
gland. They suggest that delayed implantation and prolonged
pregnancy are due to the inability of the corpus luteum to cater
adequately for implantation and lactation at the same time.
Hain ('34) also finds that when the pregnant albino r a t is
suckling pregnancy is prolonged but he reports that its duration bears no relation to the number of young being suckled.
Enzmann, Saphir and Pincus ( '32) confirmed Kirkham's
observation that prolonged gestation in mice is due to delayed
implantation. They found, however, that the time of implantation in inseminated lactating mice does not always occur on
the fourteenth day but may take place any time between the
sixth and sixteenth days and that the time of implantation
depends on the number of suckling young. Furthermore, they
state that each of the suckling young delays the ensuing parturition 21 hours rather than 1 day as reported by Daniel.
These investigators also report that very little, if any, growth
takes place in the blastocysts a s they lie free in the uterine
SHORTENING O F DELAYED PREGNANCY
33
lumen but that after implantation finally occurs the growth
curve of the developing young is indistinguishable from that
of an embryo during normal pregnancy. The birth weight of
young from a prolonged gestation is the same as the weight
of young born at normal term. Detailed data are given in
another paper (Enzmann, '35).
Hamlett ('3.5) reviewing the entire subject of delayed implantation and discontinuous development in mammals, suggests that the delay may be due to an alteration of hormonal
conditions in lactating females rather than to such a simple
phenomenon as withdrawal of nourishment through the mammary glands. He believes that the corpus luteum through its
influence on the uterus plays an important r6le in delayed
pregnancy. Since the activity of the corpus luteum depends
on the hypophysis, alterations in hypophyseal activity may
account for all of these unusual findings. Hamlett reports that
attempts to shorten the free vesicle stage by the use of hypophyseal extracts or other hormones (luteal extracts, AntuitrinS) have completely failed. Pincus ('36) by injecting oestronefree corpus luteum extracts into lactating pregnant mice also
failed to bring about the desired results.
It seemed to the writer that in the light of recent endocrine
discoveries the entire problem was worth reinvestigating. The
albino rat rather than the mouse was chosen as a subject since
so few observations have been made on that animal. He wishes
t o thank Dr. Elizabeth Ward for permission t o include some
data gathered by her, in this paper. He is indebted to his wife
for her technical assistance and constant help in making daily
observations of the experimental animals. Mr. Anselm Schurgast very kindly assisted in the preparation of the plates. The
writer wishes to take this means to express his appreciation
to Dr. Oliver Kamm of the Parke-Davis Laboratories for his
interest in contributing a generous supply of Antuitrin-S for
this work and to Dr. Max Gilbert of the Schering Corporation
for supplying liberal quantities of Proluton (crystalline progesterone in sesame oil).
34
C H A R L E S li. WEICHERT
PRELIMJNAHT OBSERVATIOXS
In some preliminary work, observations were made 011 thc
length of fifty-six gestation periods in rats suckling various
numbers of young. These data were obtained by Dr. Elizabeth
TAELE 1
Variations in the length of gestation period in. pregwaat rats szicPling 1-12 ?lozing
NUMBER OF
CASES
4
3
9
I
2
3
1
3
1
3
2
2
2
3
1
2
2
3
2
3
2
1
3
2
1
2
1
NrMBlCR OF
GESTATIOX
S O U X U FJLICKI.TNG
(DAYS)
1
2
2
3
3
4
4
4
5
5
5
6
6
7
7
'7
7
8
9
9
9
9
10
10
10
10
22
22
234
24
25
25
26;
28
26
2G3
27
27
28
273
28
284
29
31
32+
33
335
34
33
31
35
36
Ward. H c r figures which a r e given in table 1 liavc been supplemented by some obtained by tlie author. In all of these cases
spermatozoa were fonrid in the vagina within 24-36 hours after
parturition. The male was then removed from thc breeding
cage.
Examination of the above table shows clearly that the more
young that are suckling the greater is the prolongation of the
SHORTENING O F DELAYED PREGNANCY
35
gestation period. Discrepancies occur but the general trend
is unmistakable.
I n order to study the conditions of the reproductive organs
during delayed pregnancy, forty-two inseminated lactating
rats which were suckling various numbers of young, were
sacrificed on the day before parturition would be expected to
occur (twenty-first day of gestation). Ten of these were not
pregnant. This fairly high percentage of negative results is
in keeping with reports of other investigators who believe
that in many cases ovulation fails to occur a t the post-partum
oestrus o r else the fertilized eggs die prior to implantation.
I t may be too, that the spermatozoa sometinies fail to reach
the upper limits of the Fallopian tubes. Typical pregnant
uteri were selected to be photographed and are shown in plate
1 (compare with plate 3, fig. H).
Although in this series of thirty-two uteri, discrepancies
occur, nevertheless it is clear that on the twenty-first day of
gestation, the greater number of young being suckled, the
smaller are the developing embryos.
Careful examination of the ovaries of the thirty-two rats
obtained in this series revealed that the corpora lutea of those
suckling large numbers of young are definitely smaller than
those of rats suckling smaller numbers (see plate 2 ) . I n order
to obtain definite quantitative data on the size of the corpora
lutea, the diameters of eight corpora lutea chosen at random
from each animal were measured with a Vernier caliper and
a n average taken. The data are presented in table 2.
Again, discrepancies occur but there can be no doubt as to
the trend. It appears that there may be a minimum size for
the corpora lutea, f o r there is less variation among those suckling large numbers of young than among those suckling smaller
numbers.
oe numThese observations suggested that perhaps when larc;
bers of young a r e being suckled the delay in implantation may
be directly related to the fact that the endometrium is not
properly prepared for the reception of the fertilized ovum and
that failure of a progestational endometrium to appear a t thc
36
CHARLES Ei. WEICHERT
normal time may be due to insufficient amounts of progesterone being secreted by the smaller corpora lutea.
Accordingly some experiments were undertaken in an
attempt to bring about implantation at the normal time by
properly preparing the endometrium in rats suckling between
six and thirteen young.
TABLE 2
Varintions in cliunwter of corpora lutea in pregnant rats suckling 1-12 yozlng
AVERAGE DIAMETER
OF CORPORA LUTEA
N U M B E R O F YOUNG
SUCKLIKG
2.261 mrn.
2.025 mm.
2.025 mm.
2.012 mm.
1.931 mm.
1.643 mm.
1.637 mm.
1.654 mm.
1.562 mm.
1.556 mm.
1.437 mm.
1.487 mm.
1.425 mm.
0
1
2
3
4
5
6
7
8
9
10
11
13
EXPERIMENTAL
Seventeen inseminated lactating rats were injected intramuscularly with various amounts of crystalline progesterone
in sesame oil (Proluton; Schering Corporation) and for varying lengths of time. All animals were sacrificed on the twentyfirst day after spermatozoa were found in the vagina. Of these,
nine failed to become pregnant. The data f o r the remaining
eight are included in table 3.
Injections of small quantities of another corpus luteum
preparation (Lipo-lutin ; Parke-Davis) gave similar results in
two out of three cases.
These observations are interesting because they indicate
that small quantities of progesterone are insufficient, under
the conditions described here, to prepare the endometrium of
inseminated lactating rats for an early and normal implanta-
37
S H O R T E N I N G O F DELAYED PREGNANCY
tion. Large dosages (1t o 3 mg. daily) seem to be required but
the length of time over which such injections should be administered has not a s yet been determined. This is in keeping
with the results of other investigators who find that relatively
large doses of progesterone are required to inhibit normal
oestrus and ovulation (Selye, Browne and Collip, '36 ;Lahr and
Riddle, '36, and Phillips, '37).
I n these experiments in which progesterone alone was administered no fully developed living foetuses were found on
the twenty-first day of gestation (see plate 3 ) . The percentage
TABLE 3
Resulis of injecting various amounts of progesterone for different lengths of time
in rats suckling 6-13 young. Acceleration refers t o time of implantation w h a
compared with minjected rats suckling similar numbers of young
RAT
N'~~$~GoF
SUOKLING
AMOUNT
PROGESTERONE
GIVEN AT EACH
DAYS
ADMINIBTERED
RESULTS
INJECTION
days
D 255
D 275
D 297
D 251
D.296
D 294
D 328
6
10
9
13
10
10
0.2
0.2
0.2
0.5
0.5
1.0
20
3-5-7-9
3-5-7-9
8
3-5-7-9
8
20
D 335
12
3.0
20
Slight acceleration
Some acceleration
No acceleration
Some acceleration
Slight acceleration
No acceleration
Good acceleration but
death and resorption
Marked acceleration but
death and resorption
of animals in which pregnancy failed to occur is considerably
higher in these experimental animals than in the normal
controls.
The next procedure was an attempt to stimulate the secretion
of the animals' own corpora lutea by injecting some luteinizing
gonadotropic agent. Accordingly twenty-five inseminated lactating rats were injected for different lengths of time with
various amounts of Antuitrin-S. All were sacrificed on the
twenty-first day after spermatozoa were found in the vagina.
The data for this experiment are given in table 4.
38
CHABLES I<. WEICHERT
The results show that daily injections of 20 rat units of
Antuitrin-S for the first 7 o r 8 days after insemination are
effective in bringing about implantation a t the normal time
in these lactating rats. I n one case similar results were obtained when 20 rat units were injected daily for 20 days.
TABLE 4
Resiilts of injecting carious amounts of Antuitrin-S for different lengths of time
in insmii?ratrd rats suckling 6-12 yozing
RAT
D 240
D 816
D 257
D 249
D 261
D 256
D 259
D 244
D 260
D 254
II 258
D 302
D 250
D 221
D 276
n 248
D 222
D 213
D 232
D 228
D 229
I3 265
TI 263
I3 265
D 266
NCMRER O P
YOYSG
SLICIi1,INC:
6
12
9
9
8
r
6
8
6
11
10
10
8
8
11
8
8
11
9
9
c
9
10
8
12
A.MOONT
4NTCITRIN-S
LV’EI AT EACH
I1JBCTION
DAYS
ADMIhTSTER’EU
rut u n i t x
doys
10
10
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
50
100
20
50
100
20
8
20
first day
first day
0
2
4
4
4
6
6
r
8
8
8
8
8
20
20
20
20
3rd day only
3rd day only
3rd day only
5-6-7-8
RESt’I’TS
Yegative
Negative
Negative
Negative
Negative
Negative
Negative
Negative
Negative
Negative
Delayed implantatioii
3 full term foetuses
1 full term foetus
2 full term foetuses
1 full term foetus
Pregnant but resorbing
2 full term foetuses
3 full term foetuses
Negative
Pregnant but resorbing
Negative
Negative
Negative
Nega tive
Delayed implantation
Although fully developed viable foetuses were present in the
uteri of these animals on the twenty-first day of gestation,
nevertheless none of the pregnant uteri appeared normal. The
number of foetuses T ~ always
S
small and resorption areas
were common (see plate 3). Apparently the stimulated ovaries
SHORTENING OF DELAYED PREGNANCY
39
with their large numbers of corpora lutea were not adequate
t o support the continuous development of more than a few
embryos even after normal implantation had occurred. The
experiment shows, however, that a gonadotropic luteinizing
hormone may be effective in bringing about implantation at
the normal time in inseminated rats suckling fairly large numbers of young.
Since even larger doses of Antuitrin-S failed to produce
normal appearing uteri, it was decided to supplement Antuitrin-S injections with small doses of progesterone.
Accordingly nine inseminated lactating rats suckling eight
to twelve young were injected daily for the first 8 days with
20 rat units of Antuitrin-S. Following this period of injection
each rat was injected intramuscularly every other day with
0.2 mg. of progesterone. Two of these failed to become pregnant. Five of the remaining seven were sacrificed on the
twenty-first day. Of these, four had uteri that were indistinguishable from a normal uterus at term (see plate 3, I;
compare with H). They contained two, two, five and eight fully
developed living foetuses respectively. The fifth rat had but
one living foetus and one resorption area. The two remaining
rats were permitted t o go to term. D 314, suckling ten young
was delivered of two normal living offspring early on the
twenty-third day of pregnancy. These young died after 4 days,
apparently from malnutrition. The mother retained her maternal instincts for she continued to retrieve and cuddle the
young but seemed incapable of nursing them. D 311, suckling
eleven young, delivered four offspring toward the end of the
twenty-second day, 13 to 14 days earlier than would have been
the case had no injections been given. One of these lived for
only 12 days but the other three were successfully reared and
appeared normal in every respect except that their eyes opened
2 days earlier than the average for our colony.
Thus, it has been demonstrated that when proper hormonal
conditions are supplied it is possible to bring about normal
implantation, gestation, delivery and rearing of young in inseminated lactating rats suckling large numbers of young.
40
CHARLES K. WEICHERT
I n some additional and similar experiments, nine rats injected with estrogenic substances (theelin ; stilboestrol) or
pregnant mare serum gave only negative results.
nIsCUssrON
The mechanism controlling delayed implantation in inseminated lactating rats is undoubtedly complicated. The experiments cited above throw some light upon the problem and
indicate that hormonal imbalance is the mison r l ' p t r e for the
phenomenon.
It is well known at the present time that ovariectomy has no
influence upon normal established lactation (Selye and McKeown, '34). Hence, the contention of Mirskaia and Crew
('30) that delayed implantation and prolonged pregnancy are
due to the inability of the corpus luteum to maintain lactation
and at the same time prepare the uterus for implantation, is
without foundation.
Selye ( '34) and Selye and McKeown ( '34) have shown that
the act of suckling reflexly maintains lactation in the rat.
Removal of the pituitary gland brings about a cessation of
milk secretion. These investigators believe that the act of
suckling stimulates the production of prolactin by the hypophysis. Prolactin in turn stimulates and maintains the
secretory activity of the mammary glands.
It is possible that with the increased activity of the hypophysis in producing prolactin, there is a corresponding suppression
in secretion or release, of the hypophyseal gonadotropic hormones. This might result in a failure of the corpora lutea to
develop properly or else bring about a slower development
and thus account for the failure of the uterus to respond t o
the presence of the fertilized eggs. Furthermore, the larger
the number of young, the greater would be the suckling stimulus and the greater the suppression of the gonadotropic hormones. This might very well explain the variation in time of
implantation between rats suckling small litters and those
suckling large numbers.
S H O R T E N I N G OF DELAYED P R E G N A N C Y
41
There is one good argument against this conception. It has
been shown by Corner and Warren ('19), Long and Evans
( '22), Lyon and Allen ( '38) and Leonard and Meyer ( '39) that
placentomata can be produced in lactating rats from the fourth
day to as long as the twenty-fourth day post-partum. I n some
additional experiments the author has found that if threads
are inserted in the uterus on the fourth day after parturition,
placentomata may be produced as readily in rats suckling ten
young as in those suckling smaller numbers. This would seem
to indicate that the uterus is fully capable of responding to
the presence of fertilized eggs by the fourth day post-partum
even when large numbers of young are being suckled. This,
however, is contrary to what actually occurs. It is of course
possible, that the mechanical injury produced by threading the
uterus might be a much stronger stimulus than the presence
of the fertilized ovum. Further experiments are being carried
out in an attempt to clarify this point.
The fact that placentomata may be produced as late as the
twenty-fourth day post-partum checks well with the fact that
implantation may be delayed until 16 or more days after parturition.
Teel ('26) injected anterior hypopliyseal fluid into normal
pregnant rats and caused a delay in implantation and prolongation of gestation from 2-6 days. I n most of his cases the
birth mechanism was interfered with. If the injections were
not continued too long the young were born alive. The results
which Teel obtained really duplicated what occurs naturally
when inseminated rats are suckling young from a previous
litter. He believed that his results were due to the luteinizing
gonadotropic agent in the hypophyseal extracts. It seems
strange that one lnteinizing factor should cause a delay in
implantation whereas another brings about an early implantation. At the time when Teel performed his experiments the
extracts containing gonadotropic hormones were necessarily
crude. It is possible that some factor in the extracts, other tlian
gonadotropic, may have been responsible for bringing about
the delay in implantation which he observed. The author., in
42
CHARLES K. WEICHERT
some additional experiments, is attempting to correlate Teel’s
findings with those recorded here.
CONCLUSIONS
1. The length of the prolonged gestation of inseminated lactating rats is closely correlated with the number of suckling
young.
2. The size of the corpora lutea in the ovaries of lactating
rats on the twenty-first day of pregnancy is inversely correlated with the number of suckling young.
3. Injection of large doses of corpus luteum hormone (progesterone) may possibly bring about a normal and early implantation of fertilized eggs.
4. Injection of the pregnancy urine gonadotropic factor
( Antuitrin-S) brings about normal and early implantation and
is successful in maintaining viable foetuses iiz zctero. Resorption areas are common.
5 . Injection of Antuitrin-S supplemented by progesterone
is effective in bringing about normal implantation, gestation,
delivery and rearing of young in rats suckling large numbers
of young.
6. It is suggested that the act of suckling may stimulate the
production of prolactin by the hypophysis with a corresponding
inhibition of secretion or release, of gonadotropic hormones.
The time when ovarian hormones necessary for nidation are
released may thus vary with the strength of the suckling stimulus and therefore be dependent upon the number of suckling
young.
LITERATURE CITED
CORNEI, G. W., AND S. L. WARREN 1919 Influence of the ovaries upon the production of artificial dcciduomata ; confirmatory studies. Anat. Rec.,
vol. 16, p. 168.
1910 Observations on the period of gestation in white mice.
DANIEL,J. FRANK
J. Exp. Zoo]., vol. 9, p. 865.
ENZMANN,
E. V., N. R. SAPHIR
AND G. PINCUS1932 Delayed pregnancy in mice.
Anat. Rec.,
54, p. 325.
ENZMANN,
E. V. 1935 Intrauterine growth of albino mice in normal and. in
delayed pregnancy. Anat. Rcc., vol. 62, p. 31.
1701.
S H O R T E N I N G O F DELAYED PREGNANCY
43
HAIN,A. RI. 1934 The effect of suckling on the duration of pregnancy in the rat.
J. Exp. Biol., rol. 11, p. 279.
HAIILETT,
G. W. D. 1935 Delayed implantation and discontinuous development
in the mammals. Quart. Rev. of Biol., vol. 10, p. 432.
KING,HELEND. 1913 Some anomalies in the gestation of the albino rat. Biol.
Bull., vol. 24, 1). 37i.
KIRKHAM,
W. B. 1916 a The prolonged gcstation pcriotl in nursing inice. Anat.
Re<..,rol. 10, p. 219.
1916 b The prolonged gcstation period i n suckling micc. Anat. Rec.,
1-01. 11, p. 31.
1918 Observation on the relation betwcen suckling and tlie rate o f
embryonic developrncnt in mice. J. Exp. Zoo]., rol. 27, 1'. 49.
LAHR,E. L., AND 0. RIDDLE 1936 Tcinporary suppression of oestrous cycles in
the rat by prolactin. Proc. SOC.Exper. Biol. and Med., vol. 34, p. 880.
LEONARD,
S. L., AYD R. K. MEYER 1939 Cit : Sex and Tnternal Secretions. Second
edition, I). 490.
LONG,.J. A,, AXD H. M. EVANS 1922 Thc oestrous rycle in the rat and its associated phenomena. Ifmi. Univ. Calif. 6, p. 1.
LYON,R. A., AND W. M. ALLEN 1938 Duration of sensitivity of tlie endometrium
during lactation in thc rat. Am. J. Physiol., rol. 122, p. 624.
MIRSKAIA,
L., AND F. A. E. CREW 1930 On the pregnancy rate in the lactating
niouw and the effcct of sucking on the duration of pregnancy. Proc.
Roy. 8oc. of Edinburgh, vol. 51, p. 1.
PHILLIPS,
W. A. 1937 The inhibition of estrous cycles in the albino rat by
progesterone. Am. .J. Physiol., vol. 119, p. 623.
PINARD 190.5 Gestation. Richct 's Dictionaire de Physiologic, T. 7. Paris. (Compare Marshall.)
PINCUS,
GREGORY
1936 The Eggs of Mammals. The 1\Iacmillan Co.
SELI'E,HANS 1934 On thr nervous control of lactution. Ani. J. Physiol., vol. 107,
p. 535.
RELYE, HANS,J. S. 1,. BROWNIT
AND J. B. COLLIP 1936 Effect of large doses of
progesterone i n the female rat. Proc. SOP.Expcr. Riol. and Med., rol.
34, p. 4 i 2 .
SELYE,
H a ~ s AND
,
T. MCKEOWN1934 Further studies on the influence of suckling. Anat. Rec., vol. 60, p. 323.
TEEL, H. M. 1926 The effects of injecting anterior hypophyseal fluid on the
course of gestation in the rat. Am. J. Physiol., vol. i 9 , p. 170.
PLATE 1
Shoming t h r \ari:iti(~iii n sizr of utcii on the twcnty-first d a y of pregiianry of rats suckling
different numbers of young. The numher in the lower right hand corner of earl1 figure indicates
the nuniher of suckling youiig from t h e previous litter.
44
Ovaries removed f r o m laetitting rats 011 thr twenty-first day of 1myyi:incy. The
nuriiher i n the lowrr right hand coriic1' o f each fiyurc indicates thc nuniber o f
sucltliiig young frorri the previous litter. The progrcssire dirniiiutiou iii size of the
corpora lutea is uiiinist:ikalde.
1.5
PLATE 3
E.\PIJANATION OF FIGURES
Uteri of espcriniciital 1act:iting rats secrificed o n the twenty-first day of prpgn:rncy. Thr numbrr in the lower right liand corner of each figurr reprcscnts the
nunibcr of suckling ynung from tlir prrrious littrr.
A Utcius of rat suckling tcn youiig; injected with 0.2 nig. progesterone on days
3-5-7-9 a f t r r insemination.
B Uterus of rat suckling ten >oung; i n j w t r d daily with 0.5 xng. 1)”ogcstrrone
foi the first 8 days after inseniiiiation.
C Uterus of rat suckling tell young; injected daily f o r 20 days after inseniin:~tion with 1.0 ing. progesterone. Thc embryos are bring resorbed.
Jl I‘terus of rat suckling twelve young; injected ilaily for 20 d a j s after insemination with 3.0 mg. progcsterone. Resorption is taking place.
E Uterus of r a t suckling tni young; in)ectcd daily with 20 rat units of Antuitrin-S for the first 6 days after insemination, Implantation has been delayed.
F Uterus of r a t surkling elwen poiiiig; injected daily with 20 nit unity of
Antuitrin S for the fiist 8 days a f t r r insemination. Notc resoqition arras.
G Vterus of rat suckling eleven young; injtsctecl daily with 20 i:>t nnits of
Antnitria-S f o r 20 days after insemination. Note resorption areas.
II Utelus of noinial control j)regn:mt rat o n twenty first day of grstatiou. Tell
foetuses :ire present.
I r t e r u s of rat .;uc.kliiig ten ynung; injccted daily with 20 rat units of Antuitriii S for the first 8 d:iys nftcr inaenii1i:ition. This was followed by iiijectioii of
0.2 nig. progrsternne oii days 10-l2-1-2-l~i-l8-00.
Eight foctuses are prescnt.
4G
47
Документ
Категория
Без категории
Просмотров
2
Размер файла
852 Кб
Теги
pregnancy, albina, experimentov, delayed, shortening, rat
1/--страниц
Пожаловаться на содержимое документа