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Growth and regression of corpora lutea during the normal estrous cycle of the rat.

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GROWTH AKD REGRESSION O F CORPORA IJUTEEA
DVRING THE NORMAL ESTROUS
CYCLE O F THE R14T
JOHN L. BOLIPU’G
S e r f 1 0 1 i of S f w o - A i i n t o r n y , Pale University Gcliool of Mrtliciiie,
N e w Hazwn, Connecticut
0SE TEST FIGUXE A N D T\VO PLATES (‘PWEXTY FIGURER)
The study of growth and regression of corpora lutea in
the rat has beeii complicated by the large number of corpora
lutea formed at each estrus and further by the fact that tlic
corpora lutea of one generation a r e still quite large when the
succeeding set is formed.
Long and Evans ( ’22) observed that a change occurred in
thc size aiid number of fat droplets in tlic lutcal cells of oiic
gcncration of “corpora lutea of ovulation’’ at the onset of the
first estrus following their formation. This was interpreted
N S an indication of the cessation of functional activity by that
particular set of corpora lutea. They also stated that, “Succession of tlic corpora lutea by anothcr set is riot immediately
indicated by size regression of the first set Tvhosc dimensions
are indeed not perceptibly reduced even by the second sueceediiig ovulation when their greatest diameter is still about
1mm.” A cursory examination of the corpora lutea in ovaries
prepared for study of the growth of the follicle in tlie r a t
(Boling, Blandau, Soderwall and Young, ’41) indicated that
in the normal cyclc there is a coiisiderablc decrease in the
volume of the corpora lutca of one set about the time of
formation of the succeeding set. I t sccmed advisable, thcwThis investigation was supported bp g r a n t s froin t h e Cotnmittee for Resenrcli
in Problems of Sea, National Research Council, ndministercd by Williaiii C .
Young and 11. S. Rnrr.
131
T H 1’:
132
JOHN L. BOLIKG
fore, to examine further tlie cycle of growth and regression of
the corpora lutea formed during the 4-day estrous cycle of
the rat.
NATERIAL AND hIETHO1)S
The albino ~ a t used
s
in this study were from 3 to 6 months
old and weighed from 160 to 230 gmi. at the beginning of
obseiw~tioiis. Of the fifteen normal animals used, eleven were
observed for heat (as determined by the copulatory response)
at hourly intervals for 6 to 8 cycles previous to autopsy, three
were obsei*rcd for 5 cycles and one for 4 cycles (table 1).
Of the 94 cj-cles observed i n the fifteen animals 72 were 4-day
cycles, 20 were 5-day cycles, and 2 were 6-day cycles. Three
animals were killed at each of the following periods in the
cycle : beginning of’ heat, and 12, 24, 48, and ‘72 hours after the
heginning of lieat (table 1). The three animals killed at tlie
beginning of heat a r e classified in table 1 as killed at 92, 96
and 97 hours after the beginning of heat, which is in cacli
instance the elapsed time betn-ecn the begiiiiiing of the heat
at which they were killed and the beginning of the preceding
heat. I n ten other animals the cycle preceding that during
which they were killed was 4 c l a p long and in the tivo remaiiiing animals it was 5 days long. In addition to tlie fifteen
animals displaying only normal estrous cycles, one animal
was killed at the begiiiiiiiig of heat after a 6-clay cycle diicli
liad been immediately pimetled by ail 11-clay cpclc. Tlic ovaries
were fixed in Zenkcrs without acetic acid, emheclded in paraffin,
serially scctioiietl at 10 p and stained with liacmatoxylin and
eosin.
I n all of the ovaries examined, tlie corpora lutea of tlic most
recently formed set mere readily distingaisliahlc from those
of older generations. A t 12 and 24 hours after the beginning
of heat the corlmra lutca of the next youngest set (approximately 4 days old) are, with the exception of occasional very
small corpora lutea, larger than those of older generations.
I-Iowcver, at 48, 72, and 96 A 4 liours after the beginning of
heat, when the prerious generation is 6, 7 and 8 davs old
GKOIVTII AXD 1:EGBESSlON O F CORPORA LUTEA
1XI
respectively, regression has proceeded so f a r that a distinction in size could not be diawii 1)etweeii the corpora lutea of
this generation and those of older sets. For this reasoii, in
the ovaries removed a t 48, 72 and 96 t 4 hours after tlic
beginniiig of heat the number of recent corpora lutca was
determined first aiid then the same number of the largest old
corpori\ lutca was selected for the calculations of volume
(table 1 ) .
The volumes of the corpora lutea were calculated as follows :
the two diameters of the largest section of a corpus luteum
mere measured with ail ocular micrometer ; the third diameter
was o1)tained by countiiig the sections through which it estended. The three diameters were then multiplied together
and substituted for the value diLin the formula for calculating
the volume of a sphere, 1/6nd3.
The author wishes to ackiio~vledgcthe very substantial assistance given by Dr. R. J. Blandau in observing the animals
and collcctiiig tlie material used in this study.
OBSERVATIONS
Siiice ovulation in tlie albino rat occurs most f i w p n t l y
betiveeii 8 aiid 11hours after the beginning of estrus (Boling,
Rlandau, Soderwall and Young, ’41 ) tlie description of tlic
growth of tlie corpora lutea will begin with those found in
oraries removed 12 hours after the begiiiriing of heat. I n the
ovaries of the two rats which had ovulatcd by 12 hours after
the begiiiniiig of heat the average size of the twenty-one most
i*eceiitly formed corpora lutea was 115 x lO‘+p:j, range 91.5
to 148 X 106p3 (table 1). The walls of the newly formed
corpora lutea are collapsed (fig. a), the typical cordition
immediately following ovulation and the point of rupture is
usually apparent microscopically. The cells are small with
very cleiisely staining or slightly vesicular nuclei (fig. 12).
The arerage volume of the thirty-eight corpora lutca formed
at the orulation 4 days previously was 350 x 106py”,range 122
to 596 x 1OcpCr”.Their size and appearaiice (figs. 7 and 17)
134
JOHN IJ. BOLING
distinguish them from the recently formed corpora lutea
(figs. 2 and 12). With the exception of occasional very small
corpora lutea the 4-day-old set is also easily distinguishablc
from the older corpora lutea (figs. 11 and 21).
The average volume of the thirty-one most recently formed
corpora lutea in three pairs of ovaries removed 24 hours
after the beginning of heat was 337 X 106ps, range 215 to
TABLE 1
The average atid range in voliimes are shown for the two ~ o t r n g e r tsets of
corpora lutea.
CORPORALUTEAOF
HOURS
AXTIER
BEQIN-
MOST RECENT OVULATIOh
NUMBER
-
OF
8
13
Average
"4
10
11
27
45
11
AverAge
NO.
Average
Range
in8
91.5-128
120
115
93.2-148
91.5-148
355
380
277
337
363-444
287-473
3 15-373
21.7-473
11
12
16
AveraEe
"7
447
318
350
108
13
Average
12
12
12
409
318
343
356
4i1
604
384-536
384-635
13
274
228
661
541
532
545
279-686
331-705
434-607
279-705
1"
12
13'
183
242
209
211
972
FOLLICLES
-I
122-355
232-596
173-406
122-596
7
11
8
7
605
470
415-788
381-543
212-819
14
14 l
131
175
176
159
350-465
192-39;
192-444
193-463
5
158-265
144-213
217-346
144-346
5
4
7
I
--
6
--
14
14
10
Rnnae
NUXBER
F CYCLES
IBSERVED
PRIOR TO
AUFOPSY
-10
10
11
I
445-635 13 ' 227
39
48
1 3 535
420-588 10 ' 170
508
10
4R
51
48
xUynEg
Volume x I0"p"
NO.
24
I
CORPORA IrUTEA O F
PRECEDING OVULATION
119-230
171-297
125-313
119-313
--
4.57
10
61-179
149-229
138-257
61-25;
14
13
10
6
7
6
51 7
249-786
The number of most recently formed corpora lutea was deteriiiiiied and the
same number of the largest old corpora was used in calculating the average
volume of the older set.
aAutopsy a t the beginning of heat a t the stated iiumbcr of hours after the
beginning of the prewdiiig heat.
Average
GROWTH AND REGRESSION O F CORPORA L C T E A
135
473 X 10'ip:s (table 1). At this time a layer of luteal cclls surrounds a relatively large inner cavity (figs. 3 and 13). The
thirty-one corpora lutea of the previous generation, now approximately 5 days old, averaged 356 X 106p3, range 192 t o
465 X l o o p 3 (table 1). The glandular cells were undergoing
retrogressive changes and fibrocytes had become more numerous (figs. 8 and 18).
Forty-eight hours after the beginning of heat the average
volume of the thirty-six most recently formed corpora lutea
in three pairs of ovaries was 504 X l o o p 3 , range 384 to 635 X
106p:'. Except for a small central region of connective tissue
elements which is occasionally hemorrhagic, glandular luteal
cells with vascular and supporting tissues make up the entire
corpus luteum (figs. 4 and 14). Thirty-six of the largest old
corpoi-a lutea in these ovaries averaged 228 X l o o p 3 in volume,
~ ~ i n g144
e to 346 x l o o p 3 . Retrogression is marked in these
corpora lntea which mere approximately 6 days old (figs. 9
and 19).
Seventy-two hours after the beginning of heat the average
volume of the thirty-six most recently formed corpora lutea
in three pairs of ovaries was 545 X l o o p 3 , range 279 to 705 X
l o o p 3 . This is the largest average volume observed f o r the
corpora lutea in the normal 4-day estrous cycle. Except for
the difference in staining of a few small areas to be discussed
later the parenchyma appears intact as far as its condition
is clemoiistrated by the techniques employed (figs. 5 and 15).
Tlie average volume of the thirty-six largest old corpora lutea
in these ovaries mas 211 X lo6$, range 119 to 313 x l o o p 3 .
X o distinct difference in size or appearance was observed
hetween the largest old corpora lutea a t the seventy-second
hour (figs. 10 and 20) and those examined at the forty-eighth
hour.
In the tliree pairs of ovaries obtained at the beginning of
heat (92, 96, and 97 hours respectively after onset of preceding heat) the average volume of the thirty-eight most recent corpora lutea was 517 X l o o p 3 , range 212 to 786 x l o o p 3 .
This is ii slight decrease from the average size of the 72-hour
1.36
J O H N 1,. BOLING
group. Thirty-eight of' the largest old coiyora lutea averaged
159 X l o o p s , range 61 to 257 X 106p:'. Regression is pronomiced
in these corpora lutea which a r e 8 days or more old (figs. 11
und 21).
The above observations a r e summarized graphically in
figure 1. The corpora lutea formed approximately 8 to 11
hours after the beginning of heat grow rapidly until about
the forty-eighth hour; subsequently therc is no marked increase in size during the normal 4-day cycle. Eegression
begins near the beginning of the succeeding heat and proceeds
rapidly during the next 12 hours. It continues at a slower
rate during tlie next 4 d a y and by the time corpora lutea a r e
approximately 8 days old regression is pronounced. The
changes in volume parallel changes in the histological character of the corpora lutea. During the phase of rapid growth
of the newly f o r m e i corpora lutea the parencliymal cells increase in size and exhibit more definite cell boundaries wliile
at the same time their nuclei become larger and more vesicular.
Near the onset of the first estrus succeeding the formation of
a set of corpora lutea regression begins in the parenchyma
cell. Fibrocytes increase in prominence as the glanciular cells
regress. The recently formed corpora lutea a r e strong1:- basophilic but near the time of onset of retrogressive clianges
they hccome ii1crcasing1-y more acidophilic.
At no time dui-ing thc. examination of the mtitei*ial from
animals mhicli displayed oiily normal 4- to 6-day cycleh TVCW
any corpo1.a lutea encountered which gave cvidencc of haring
than
retained their maximum 01- near maximum size f o r nio~*e
1 cycle. On the other hand, four of the corpora hitea examined
were considerably smaller than the other coiyora lutca with
wliich tlieir histolo~icalappearance vvoulct classify them. Tn
tlie 72-hour group, two of thirty-six most recently formcd
corpora lutca had the inicroscopical structure of this ceneixtion, but they a r e iii the range of volumes of the oh1 coi*pora
lutea. One of thew in animal 2 had a volume of 379 x
while that of the next smallest corpus luteum in the pair of
ovaries was 499 X 10'p'i. The second was in aiiirniil 21 and
G R O W T H A X D GEGGESSIOK O F CORPORA LCTEA
137
liacl a volume of 331 X 106p3 while the volume of the next
smallest corpus luteum was 503 X lo6$. These corpora lutea
might be coilsidered growing corpora lutea which would later
reach a larger sizc. However, that such is riot the case is
suggested by the occurrence of an unusually small corpus
lutcnm aniong thc thirty-four most recent corpora lutea a t
the beginning of heat when regression of this generation lincl
Fig. 1 The course of growth in volume of the most recently foiincd corpora lutea
is indicated by the solid line. The regression of the generation of corpora lutca
formed at the preceding ovulation is indicatcd by the broken linc.
begun. This corpus luteurn in animal 69 had it volume of
242 X 106vcl".The filial unusually small corpus luteum occurred
in animal 1258 in the 4-day-old set at 12 hours aftcr the begining of heat. Its volume was 122 x l O V + mhile that of the nest
smallest corpus luteum in the set was 194 x
Although
regression proceeds a t a rapid rate during the first 12 hours
after the beginning of heat it does not sccm likely that a
138
1
JOHN L. BOLISG
large corpus luteum would be reduced to such a small volume
during this short period. These data suggest that occasional
corpora lutea remain well below the usual size range at
maturity.
It must be emphasized that the rapid regression of corpora
lutea -\\’as observed only in animals in which 4 o r more cycles
preceding autopsy had been normal 4- to 6-day cycles. I n
addition to the fifteen animals reported above, one animal was
killed at the beginning of heat after a 6-day cycle which had
been immediately preceded by an 11-day cycle. I n the ovaries
from this animal there mas a set of nine corpora lutea with
an average volume of 693 X 10sp”, range 576 to 820 X loop3.
The structure of these corpora lutea is similar to that of a
4-tla;v-old set at the beginning of heat. Besides these there
were fi\-e other large corpora lutea with an average volume
of 595 X 10Rp:I, range 420 to 625 x loo$. The latter have the
histological characteristics of an older set of corpora lutea
although they are larger than tlie lower limit of the range
obserred f o r 4-day-old corpora lutea at the beginning of heat
(table 1). This indicates that corpora lutea formed during
an 11-clay cycle remained large through the succeeding 6-day
cyde, thereby causing a confusion of generations of corpora
lntea as far as size is concerned. Long and Evans (’22)
obscrred that the corpora lutea of the pseudopregnant cycle
were larger than those of the normal cycle; also that those
of pregnancy became still larger and maintained diameters
of over 1mm. for as long as 20 days post-partnm.
It has bcen indicatcd above that the techniques used did
not reveal any definite signs of regression in corpora lutca
before tlie beginning of the lieat succeeding that a t m h i ~ h
they formed. At this time, whcii the generation of corpora
lut ca was approximately 33 days old, a prominent vacuolization was observed in twenty-five of the thirty-seven most recent corpora lutea (figs. 6 and 16). No evidence of a beginning
of this vacuolization was observed in the ovaries removed at
the seventy-second hour unless it is associated with the oc(wrrcnce of very small areas of n1oi.e densely staining cells
GROWTH AKTD REGRESSION O F CORPORA LCTEA
139
which occur in ten of the thirty-eight most recently formed
corpora lutea. Twelve hours after the beginning of heat, the
vacuolization was marked in twenty-one of the thirty-eight
corpora lutea of the generation approximately 4 d a p old
(figs. 7 and 17). Twenty-four hours after tlie beginning of heat
the vacuolization was present in seventeen of the thirty-one
corpora lutea of the generation about 4; days old. The vacuoles
are not as large or prominent at 24 hours after the beginning
of heat as they were a t the beginning of heat. Small vacuoles
are numerous in the later stages of involution of corpora
lutea but they do not present the characteristic appearance
shown in figures 6 and 7. The significance of tlie vacuolizatioii
cannot be determined from the present material. It niay bc
related to the changes in fat droplets observed by Long and
Evans ( ’22).
DISCUSSIOX’
Tlie apparent discrepancy betweeii the observations of
Long and Evans (’22) and the present study may be due to
the method of analysis of size variation rather than to an
actual difference in material observed. The size of the corpora
lutea was recorded by Long and Evans iii terms of millimeters
in diameter and they state that the greatest diameter 1 ) tlic
~
second succeeding ovulation was still “about 1 rnrn.” In tlie
present study, the largest diameter of the largest corpus lutcum
in the set about 8 days old (animal no. 69, table 1) just prior to
the second ovulation succeeding that at which it was formed,
was 0.87 mm. The average of the three diameters of this corpus
luteum was 0.79 mm. and tlic volume 257 x 106pcl“.Eighty-seven
liundredths of a millimeter is in the rangc covered 11)- the
term “about 1 mm.” but the reduction in volume of this tlic
largest corpus luteum in the generation approximately 8 days
old is very striking when it is compared with the nrcrwge
volume of the most recently formed set during the latter part
of the cycle (table 1). On the other hand, it is also possihlC
that the rate and maiincr of regression may be somewhat rlif-
140
JOHR L. BOLIKG
fcrent for the strain used by Long aiid Evans and that used
in the present study. This possibility is suggested by the
observations of Pfeiffer in mice (personal communication).
He observed that in the highly inbred A strain of mice,
corpora lutca l o s ~thcir identity more rapidly than they do
in other strains.
It is beyond tlie scope of the present study to explain the
factors responsible f o r the observed decrease in the size of
one set of corpora lutea about the time of formation of the
succeeding set. Greep ( ’38) observed that injectioiis of luteinizing liormone caused the rapid regression of persistent
corl,oi*n lutea in hypophysectomized rats. This suggests that
the same factor which causes the formation of the new set of
corpora lutea may be associated witli the rapid regression of
the 4-day-old corpora lutea which oecurs during the first 12
hours after the beginning of heat.
su 1tNAR1’
Fifteen albino rats were used in a study of the growth and
regwssion of corpora lutca during the normal 4-day estrous
cycle.
The average volume of the most recently formed sct of
corpora lutea increased at a relatively rapid rate between 12
and 48 hours after the beginning of heat. From the fortyeiglith to approximately the ninety-sixth hour, whcn the sueecwling licat began, there was little change in average volume.
During the first 1 2 hours following the onset of the first
heat period subsequent to their formation, the average volume
of the corpora lutea decreased rapidly. Throughout the rcst
of the cycle regression continued but at a slower rate.
A t no time was more than a single set of corpora lutea of
maximum size observed i n tlie ovaries of animals which had
exhibited only 4- to 6-day estrous cycles during 4 or more
cycles immediately prior to autopsy.
GI:OWT€C
AND REGCESSIOP\’ OF COBPOEA LUTEA
1-41
LITERATURE CITED
I ~ O L I X G,J.
. I,., R. J. I~IASUIU. A. I,. GODERWALL AND W. C. YOUXG 1941 Growth
of the graafian follicle a n d the time of orulation in the albino rat.
Anat. R r c . , rol. 79, pp. 313-331.
G K ~ w . It. 0. 1938 The effect of gonadotropic hormones on the persisting
rorporn lutea in hvpophysec.tomizeil1 rats. Ehdorrinology, vol. 23, pp.
154-163.
Losc,, J . -IAND
., H. 31. EVAXS 1922 The oestrous cycle i n the rat and its
associated phenomena. Mem. Unir. Calif ., vol. 6, pp. 1-148.
PIATE 1
EXPLANATlON OF F'IGUBES
hlagnificstion X 45.
2 Corpus luteuni of most recently formed set 12 liours after beginning of Ilcat,
POI. 113 X 10Epp. Compuro with figure 7. R indicates point of rupture,
3 Corpus Iuteuin of most recently formed set 24 hours a f t e r beginning of heat,
rol. 397 X 10'~'.
Compare with figure 8.
4 Corpus luteuni of most recently formed sct 48 hours after thc begiiining of
heat, vol. 515 X loop'. Compare with figure 9.
5 Corpus luteum of most recently formed set 72 liours after the beginning of
heat, vol. 607 X loopn. Compare with figure 10.
6 Corpus luteum of most recently formed set :kt the beginning of heat (97
hours after thc beginning of the preceding heat), vol. 521 X lo6$'. Conipare with
figure 11.
7 Corpus lutemn of sccond youngest set 13 hours nftcr tlic beginning of hwt,
1-01. 363 X loop'.
8 Corpus luteuni of second youngest sct 24 hours after the beginning of heat,
vol. 361 X loop3.
9 Corpus lutcuin of second youngest sct 48 hours after the beginning of heat,
TO^. 238 X 10np'.
10 Corpus luteuni of second youngest scxt i 2 hours after the brginninp of heat,
vol. 221 x lO"p7.
11 Corpus luteuni of scacond youngest set a t beginning of hrat (97 hours after
tlic beginning of the preceding heat), vol. 153 X 1 0 " ~ ~ .
143
PTA1'E 2
F S P L A S A T I O S OF FIUYRI'S
Xignification X 430
12 ('(~113 friini c'orpiis luteuni of most rcc.eutly foriuetl sct 1 2 hours :ifter beginiiiiig of 1ic:it. .\I i 011 i i i figurt. ? iiic1ic:itrs Irgioii of 1iliotogn1ih. V o m p r r with
figurc 17.
13 Cells froni corpus Iiitciini of most I z r c n t l ~ forinrd set 24 Iiours after
beginning of Iwit. Arro\\ i u figurc 3 indic:ltrs region of photogra1)li. Compare
with figure 18.
14 Pclln froiii ( 0 1 lniq luttuiii of uic,st ieccntly f o ~ i i i c v l set 48 Iiouns :iftrr
I q i n n i n g of 1ic:)t. Arrow in figure. 1 hlic.;itcs region o f 1hotogral)h. Compare
with figure 19.
1.5 Cclls froiii c0rl)us Intriiiii of iiio\t wwiit1)- f o r i w d svt 7 2 I I C I I I ~ Safter
~ 111 figuw 5 iiitlicntcs rcgiou of photogrnpll. ('oinp:ire
I)rgiiiiiiiig (if Iirnt. A l rom
with figure 20.
16 Cells f r o i n corpus Inteuui of most rrc'entl> foiined sct at hegiiining of heat
(97 hours aftcr Iwgiiining of lnwwlilig licit). Arroir in figure 6 intlicntrs rcgioll
of 11hotogr:iph. C o u i p n r ~with
~ figure 21.
17 <'ells froni caorlnis lutcuii of secoiid z oungwt sot 1 2 honi ~i :iftw liegiuning
of heat. Arrnw in figurtb 7 iuclicatrs rrgion of photograpll. ("ouipaw with figure 12.
18 C'clls froiii (*orpus Intcuni of Xccond pouiigest set 24 hours after lwgiiining
of 1ic:it. -2rrow in figui 8 indic.:ltca regloii of p l i o t ~ ~ g ~ : iCoiiipnicl
~ ~ I i . with figure 13.
19 Cells from coi pus Intcuiii of second ?oungrst set 48 hours :iftcr hginiiing
of heat. Arrow in fignrc, !) indicatrs rogioii of photograph. ('oiupare with figure 14.
20 Cells f r o m corlius luteuiu of second >-ouiigest sct 72 hours nftcr beginning
of lirat. A ~ r o wi n figrnv 10 iiiilic itcs region of pliotngr:ipli. ('onipair with figurr 15.
21 Ccllq from c o i p w 1ntc.mii of secontl poungcst set n t lieginning of heat
(97 hours a f t c r l)(~giiiningof 1irccccling heat). Ari ow in figure 11 indic:~tc>srrgion
of photograph. Coinpare wit11 figure 16.
(3
N
..
k
145
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