BIOLOGY OF REPRODUCTION 69, 1273–1280 (2003)
Published online before print 11 June 2003.
Mimicking the Events of Menstruation in the Murine Uterus1
M. Brasted,3C.A. White,3T.G. Kennedy,4and L.A. Salamonsen2,3
Uterine Biology Laboratory,3Prince Henry’s Institute of Medical Research, Clayton, Victoria 3168, Australia
Department of Physiology & Pharmacology,4The University of Western Ontario, London, Ontario, Canada N6A 5C1
Menstruation and endometrial regeneration occur during ev-
ery normal reproductive cycle in women and some Old World
primates. Many of the cellular and molecular events of men-
struation have been identified by correlative or in vitro studies,
but the lack of a convenient model for menstruation in a labo-
ratory animal has restricted functional studies. In this study, a
mouse model for menstruation first described by Finn in the
1980s has been modified for use in a commonly used inbred
strain of mouse. A decidual stimulus was applied into the uterine
lumen of appropriately primed mice and leukocyte numbers and
apoptosis were examined over time following progesterone
withdrawal. Endometrial tissue breakdown was initiated after
12–16 h, and by 24 h, the entire decidual zone had been shed.
Re-epithelialization was nearly complete by 36 h and the en-
dometrium was fully restored by 48 h. Leukocyte numbers in-
creased significantly in the basal zone by 12 h after progester-
one withdrawal, preceding stromal destruction. Stromal apopto-
sis was detected by TUNEL staining at 0 and 12 h but decreased
by 16 h after progesterone withdrawal. This mouse model thus
mimics many of the events of human menstruation and has the
potential to assist in elucidation of the functional roles of a va-
riety of factors thought to be important in both menstruation
and endometrial repair.
apoptosis, female reproductive tract, menstrual cycle, uterus
With every reproductive cycle, the human endometrium
undergoes extensive remodeling that is unparalleled in any
other adult organ. Following menstruation, when most of
the functional layer of the endometrium is shed, tissue res-
toration occurs, initially by very rapid re-epithelialization
of the exposed surface. Increased estrogen levels then stim-
ulate proliferation and reestablishment of the stromal and
vascular components of the tissue. Following ovulation, as
progesterone levels rise, there is considerable cellular dif-
ferentiation, which prepares the endometrium for blastocyst
implantation; this includes decidualization of the stroma,
elongation and increased tortuosity of the glands, and an-
giogenesis producing specialized spiral arterioles. In the ab-
sence of an implanting blastocyst, the corpus luteum, the
1This work was supported by the NH&MRC of Australia (grants 169003,
143798). T.G.K. contributed to this work while on sabbatical leave from
the University of Western Ontario. He was supported in part by a Hudson
2Correspondence: L.A. Salamonsen, Prince Henry’s Institute of Medical
Research, Level 4, Block E, Monash Medical Centre, 246 Clayton Road,
Clayton, Victoria 3168, Australia. FAX: 61 3 9594 6125;
Received: 19 February 2003.
First decision: 20 March 2003.
Accepted: 16 May 2003.
? 2003 by the Society for the Study of Reproduction, Inc.
ISSN: 0006-3363. http://www.biolreprod.org
primary source of circulating progesterone, degenerates and
serum progesterone levels fall, providing a critical trigger
for menstruation .
Many of the molecular and cellular events of menstru-
ation have now been identified [2, 3]. Leukocyte numbers
increase dramatically immediately premenstrually and can
contribute as much as 40% of the total cellular composition
of the tissue at this time . Other events include actions
of matrix metalloproteinases (MMPs) to degrade the tissue
matrix, of vasoactive substances such as prostaglandins, en-
dothelin, and nitric oxide, and of products of a variety of
leukocytes. However, as menstruation occurs naturally only
in women, some Old World primates, the elephant shrew
(Elephantus myuras jamesoni) and the bat (Glossophaga
soricina) , most of the data supporting roles for such
factors, is either correlative or based on in vitro experiments
using tissue explants or cell cultures. Old World primates
are not widely available for experimentation. There is thus
a clear need for a nonprimate animal model of menstrua-
tion, in which the sequence of events leading to menstru-
ation can be established and which can also be used for
functional studies to examine the relevance of individual
molecules to the processes of menstruation and endometrial
During the 1980s, Finn and Pope  developed a model
of endometrial breakdown in the mouse, in which proges-
terone support was withdrawn from artificially decidualized
endometrium, to mimic the fall in serum progesterone that
occurs in women following luteal regression. Features that
occur in the endometrium of women at the time of men-
struation, including influx of leukocytes and tissue degen-
eration, were observed in this model. However, consider-
able temporal variation in events was observed and the
model was not further used.
The purpose of the present study was to optimize this
mouse model for menstruation in an inbred strain of mouse
commonly used for genetic manipulation, to establish the
temporal sequence of events of tissue breakdown and res-
toration, and to assess the numbers of leukocytes and extent
of apoptosis during the phase of tissue breakdown. Proges-
terone was delivered via silastic implants, providing an op-
portunity to induce a rapid decline in serum progesterone
levels and thus reduce variability in responses.
MATERIALS AND METHODS
Female C57BL/6 mice of 8–12 wk of age were obtained from Monash
University Animal Services. Mice were housed in standard conditions with
food and water provided ad libitum and a constant light cycle of 12 h
(lights-on from 0800 h to 2000 h). Ethics approval for this project was
granted by the Monash University/Monash Medical Centre Animal Ethics
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