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Collagen remodeling in the uterine cervix 75
Braz. J. morphol. Sci. (2003) 20(2), 75-84
ISSN- 0102-9010
COLLAGEN REMODELING DURING CERVICAL RIPENING
IS A KEY EVENT FOR SUCCESSFUL VAGINAL DELIVERY
Mónica Muñoz-de-Toro, Jorgelina Varayoud, Jorge G. Ramos, Horacio A. Rodríguez and Enrique H. Luque
Laboratorio de Endocrinología y Tumores Hormonodependientes (LETH), School of Biochemistry and Biological Sciences,
Universidad Nacional del Litoral, Casilla de Correo 242, (3000) Santa Fe, Argentina.
ABSTRACT
Parturition involves a complex interplay of maternal and fetal factors. An understanding of the physiological mechanisms
involved in maternal adaptations would be of great benefit in the diagnosis, management, and outcome of dystocic
parturition, an important problem in human health care and animal production. In this review, we consider the
histofunctional changes in the uterine cervix that are essential for successful vaginal delivery and focus on work from
our laboratory. The functions of the uterine cervix change considerably during pregnancy. As the uterus enlarges to
accommodate the growing fetus, the cervix behaves essentially as a barrier. At term, however, the cervix softens and
dilates through a process known as cervical ripening. This process is extremely complex and involves interactions
between different cellular compartments and the extracellular matrix, as well as properly timed biochemical cascades,
and stromal infiltration by inflammatory cells. Since the main component of the uterine cervix is connective tissue,
collagen remodeling is a key event for ripening and delivery. Moreover, because of their intrinsic mechanical properties,
elastic fibers may be involved in the recovery of shape immediately after parturition. Despite the advances in our
knowledge of cervical ripening, the signals responsible for initiating these changes remain to be elucidated. By under-
standing the mechanisms involved in these changes, it should be possible to address complex issues such as cervical
incompetence, pre- and post-term delivery, and proper “ripening” of the cervix in order to avoid surgical delivery.
Key words: Collagen remodeling, extracellular matrix, parturition, uterine cervix
Abbreviations: α-smooth muscle actin (α-SMA), basement membrane (BM), blood vessels (bv), cytoplasmic processes
(CP), eosinophils (eos), epithelium (E), estradiol (E2), estrogen receptor (ER), fibroblast (Fib), muscle layer (MS),
myofibroblast (Myof), nucleus (N), progesterone (P4), progesterone receptor (PR), subepithelial stroma (SS).
Correspondence to: Dr. Mónica Muñoz-de-Toro
Laboratorio de Endocrinología y Tumores Hormonodependientes,
School of Biochemistry and Biological Sciences, Casilla de Correo
242, (3000) Santa Fe, Argentina Tel/Fax: (54) (342) 4575207, E-mail:
monicamt@fbcb.unl.edu.ar
Parturition results from a complex interplay of
maternal and fetal factors. Maternal preparation for
parturition involves many events, including cervical
ripening, relaxation of the interpubic joint, induction
of receptors for uterine-activating agents, and the
formation of gap junctions between uterine smooth
muscle cells in order to coordinate myometrial
contractions [15]. The most important issue in peri-
natology is how to predict when a patient at term or
preterm will proceed to active labour. Further
knowledge of uterine contractility and cervical
ripening may be useful in helping to recognize when
the uterus or the cervix is prepared for labour and
thus select effective therapeutic strategies. An
understanding of the physiological mechanisms
involved in maternal adaptations would be of great
benefit in the diagnosis, management, and outcome
of dystocic parturition, an important problem in
human health care and animal production. In this
review, we consider the histofunctional changes in
the uterine cervix that are essential for successful
vaginal delivery and focus on work from our
laboratory.
THE UTERINE CERVIX:
HISTOARCHITECTURE AND FUNCTIONS
The uterine cervix was initially thought to be
merely an anatomic end of the uterus that allowed
drainage of the menstrual flow (when present), sperm
migration and the passage of the conceptus during
delivery. However, numerous studies have shown that
the cervix has an important role in the normal transport
and capacitation of spermatozoa, as well as acting as
a protective barrier, together with the cervical mucus,
against the penetration of microorganisms and toxic
substances into the uterine cavity. The cervix also
serves to prevent the expulsion of the preterm con-
ceptus. At term, however, the cervix softens and
REVIEW ARTICLE
Muñoz-de-Toro et al.
76
Braz. J. morphol. Sci. (2003) 20(2), 75-84
dilates through a process known as cervical ripening
[61]. This process is an active biochemical response
which occurs independently of uterine contractions
and is similar to an inflammatory reaction. Cervical
ripening involves interactions between various
cellular compartments and the extracellular matrix,
as well as properly timed biochemical cascades and
stromal infiltration by inflammatory cells [26,65].
tissue that confers the required mechanical properties
to this segment [18]. This conclusion is reinforced by
observations in species in which the muscular
component is either scant or absent. Connective
tissues have a predominantly mechanical function and
must be able to withstand high tensile or
compressional stress and to recover their shape and
form when the stress is removed [50]. Collagen-
containing fibers add strength to the tissues, whereas
elastin and proteoglycans are essential for matrix
resiliency.
During parturition, the increased amount of water
present obviously helps to soften the uterine cervix,
but proper dilation is dependent on changes in
collagen-containing fibers and other components of
the extracellular matrix [26,29,39,40,55,69]. It is,
therefore, not surprising that connective tissue is the
major component of the uterine cervix (Figs. 1 and
2), and that collagen fibers play an important role in
the functions of this structure. Elastic fibers, the
second most important fibrillar component of the
cervical connective tissue, protect against rupture
during dilation/parturition, thus guaranteeing the
anatomical integrity and continuity between the uterus
and vagina during delivery. These fibers may also be
involved in the recovery of shape during the post-
partum period, particularly in view of their ability to
undergo reversible extension.
Figure 2. Histological section stained with hematoxylin-eosin
showing the different tissue compartments of the guinea pig
uterine cervix: The subepithelial stroma (SS) is the area of
connective tissue from the basement membrane to the muscle
layer (MS). The SS occupies most of the cervical tissue and
collagen fibers play an important role in the physiological
adaptation of the organ. E - epithelium, SS - subepithelial stroma,
MS - smooth muscular stroma. Bar = 150 μm.
Figure 1. Schematic representation of the rat uterine cervix. As
in most other species, including humans, connective tissue was
the predomintat component, with smooth muscle accounting for
10-15% of the rat cervical tissue.
The uterine cervix is a complex organ that under-
goes extensive histoarchitectural changes to allow its
successful adaptation to the different physiological
conditions mentioned above [11,33,36,71]. As shown
in the organization of rat cervical tissue (Fig.1), the
cervix is composed predominantly of connective
tissue [9,10]. The rate and extent to which the cervix
must dilate and efface to allow expulsion of the
fetus(es) vary among species [6]. Since, in some
species, a considerable number of muscle fibers is
observed in the cervix, it was initially believed that
these fibers were responsible for the physiological
valve function of the cervix [57]. Although smooth
muscle fibers may participate in the functional
mechanisms of the uterine cervix, it is the connective
Collagen remodeling in the uterine cervix 77
Braz. J. morphol. Sci. (2003) 20(2), 75-84
Figure 3. Photomicrographs of nonpregnant (A and B) and intrapartum (C and D) rat cervix. In the upper panel the sections were
studied by the Picrosirius-polarization method, a specific procedure to detect oriented collagenous structures. All brightly birefringent
structures shining against a dark background were collagenous material (A). Section of a nonpregnant control cervix in which collagen
appears as thick bundles of continuous, densely packed fibers. Compare the regular arrangement of the collagen fibers in (A) with the
disturbed appearance of the corroded collagenous framework seen in an intrapartum sample (C). In the latter, the collagenous fibers
showed the fragmented and irregular appearance characteristic of collagen remodeling. The section in the lower panel were stained
with Sirius red in alkaline solution in order to detect eosinophils. In the nonpregnant cervix (B), eosinophils were limited to blood
vessels (bv) and no eosinophils were seen in the stroma. In the intrapartum sample (D), a heavy eosinophilic infiltration (eos) was
observed in the connective tissue. Bar = 35 μm.
CERVICAL RIPENING: INVOLVEMENT
OF COLLAGENOLYSIS AND POLYMORPHO-
NUCLEAR LEUKOCYTE INFILTRATION
The dilation and effacement (ripening) of the
cervix are necessary prerequisites for a normal vaginal
delivery [35]. Cervical dilation is accompanied by
disruption of the ordered collagen bundles (Fig. 3A,
C). The cellular response involves modifications of
the extracellular matrix, with cervical stromal cells
and immune cells being responsible, at least in part,
for the enzymatic remodeling of fibrous connective
tissue [26,37-42,47,67].
The physiological mechanisms involved in the
onset of ripening at term are still unclear, although
collagenase has been implicated in this process. There
is good evidence that the activity of collagenase and
other proteolytic enzymes increases at term [28,51].
One of the sources of these enzymes could be the
infiltrating neutrophils seen in women, sheep and
guinea-pigs [21,26,37,47,49] and the eosinophils seen
in rats [38,40,54]. A close spatial and temporal
association between the infiltration of eosinophils and
collagenolysis has been observed in the cervical
stroma of rats during parturition (Fig. 3C,D) [40,54].
Muñoz-de-Toro et al.
78
Braz. J. morphol. Sci. (2003) 20(2), 75-84
The presence of polymorphonuclear leukocytes
in cervical tissue during parturition has been
confirmed by electron microscopy [21,26,37,38] and
by immunohistochemistry using specific antibodies
against granule-associated neutrophil enzymes or
against eosinophil major basic protein [12,47]. In
addition, polymorphonuclear leukocytes degranulate
in the cervical stroma at term and this event coincides
with the widespread collagenolysis seen in the extra-
cellular matrix [26,38]. The changes in the
organization of cervical collagen fibers have been
quantified [39,40] using the picrosirius-polarization
method which allows the morphometric analysis of
collagen fiber organization [25,43]. This method is
specific for orientated collagen molecules since only
these structures show a bright birefringence [43].
Collagen fibers normally form thick bundles of
densely packed, regularly arranged fibers that appear
as brightly birefringent structures throughout the
entire microscopic field. During collagen remodeling,
collagen fibers are not dense or regularly arranged
and show weak birefringence. Figure 3 shows the
appearance of nonpregnant (A) and intrapartum (C)
rat cervix studied with the picrosirius-polarization
method. Note that the greater the collagen remodeling,
the lower the birefringence.
Electron microscopic examination of human [26],
rat [38] and ewe [37] cervical stroma during labor
has revealed dramatic changes in the fine structure of
collagen. The regular arrangement of collagen fibrils,
which is typical of nonpregnant cervix, is markedly
disturbed in intrapartum cervical biopsy specimens
(Fig. 4A,B). Electron micrographs of collagen deg-
radation show fragmented collagen fibrils which, in
cross-section, have a ragged, irregular outline. Fibro-
blast are the main cell type in cervical tissue from
nonpregnant rats, ewes, guinea pigs and women (Fig.
3B). In intrapartum samples there is extensive poly-
morphonuclear leukocyte infiltration of the cervical
stroma (Fig. 3D) with few mast cells and macroph-
ages, in addition to the fibroblasts. Light and elec-
tron microscopy have revealed a series of character-
istics in the appearance and distribution of these poly-
morphonuclear leukocytes. The identity of polymor-
phonuclear leukocytes which varies among species,
was confirmed by electron microscopy, immunohis-
tochemistry and special staining techniques [52].
There is currently no explanation for the differences
in the types of polymorphonuclear leukocytes that in-
filtrate each species or for the variations in their mi-
gration patterns. In the ewe, neutrophils migrate to-
wards the cervical lumen since their highest number
occurs in the luminal mucus [37]. These neutrophils
may be responsible for preventing uterine infections
associated with parturition since they make the cer-
vical mucus less penetrable to microorganisms.
THE MODULATION OF LEUKOCYTE
INFILTRATION BY ESTROGEN AND
PROGESTERONE AND THE INVOLVEMENT OF
RELAXIN IN COLLAGEN REMODELING
The uterine cervix is a dynamic structure with a
high capacity to adapt to different, often opposing,
roles during the physiological events associated with
gestation, parturition and postpartum recovery. To
achieve this adaptation, the cervix responds to changes
in hormone levels [5,16,39,61]. Progesterone (P4) is
essential for the maintenance of pregnancy in most,
if not all, eutherian mammals [62] and reduces the
ability of the female to combat intrauterine bacterial
infections [20,27,58]. This latter effect is thought to
result, at least in part, from the P4-dependent reduction
in uterine leukocyte infiltration [2,21,63].
Parturition in rats and sheep is preceded by a fall
in P4 and an increase in estradiol (E2) plasma levels,
with both steroids being implicated in the regulation
of cervical softening in sheep [30,48]. Estradiol
stimulates whereas P4 inhibits the infiltration of
eosinophils in the rat cervix at term [39,40]. Neither
estrogen nor P4 alone is responsible for collagen
remodeling. Rather, this response is mediated by
relaxin, a hormone with a major role in promoting
the growth and widespread reorganization of collagen
fibers in the rat cervix [7,23,31,39]. Estradiol-induced
eosinophil infiltration in the rat cervix is blocked by
tamoxifen [54], an antagonist that interacts with the
estrogen receptor (ER). Progesterone also antagonizes
the effect of E2. The anti-progestin RU-486 blocks
the inhibitory action of P4 on eosinophil infiltration
in the cervix [54], thus suggesting that the effect of
P4 is mediated by the progestin receptor (PR). The
antagonistic actions of both steroids explain the time
course of the leukocyte invasion in intact pregnant
rats during the last days of pregnancy. Following the
decrease in P4 levels that occurs during the last 36 h
of pregnancy in the rat [45], the increased E2 levels
act through the ER promoting the massive infiltration
seen in cervical tissue at term.
In addition to the serum steroid hormone levels,
the level of the receptors for these mediators also play
Collagen remodeling in the uterine cervix 79
Braz. J. morphol. Sci. (2003) 20(2), 75-84
Figure 4. Photomicrographs of a nonpregnant (A) and intrapartum (B) rat cervix studied by electron microscopy. (A) A fibroblast
(Fib) surrounded by collagen fibers showing the regular arrangement characteristic of nonpregnant cervical tissue. Bar = 1.3 μm. (B)
A myofibroblast (Myof) and collagen fibers with a disturbed appearance and corroded framework characteristic of collagen remodeling
in intrapartum cervical tisssue. A cervical epithelial cell (E) and the basement membrane (BM) are shown. Bar = 0.5 μm.
Muñoz-de-Toro et al.
80
Braz. J. morphol. Sci. (2003) 20(2), 75-84
Figure 5. Photomicrographs of myofibroblastic cells in the lamina propria of human uterine cervix during labor. Electron micrographs
of a subepithelial myofibroblastic cell at low (A) and high (B) magnification. (A) The well-developed rough endoplasmic reticulum
and the Golgi complex (arrowhead) indicate that the myofibroblast is actively involved in secretion. The luminal epithelium (E) and
its basement membrane (arrow) can be seen. Bar = 2.5 μm. (B) A high magnification of the cell shown in (A), with cell surface
features characteristic of myofibroblasts, including a subplasmalemmal web of filaments (arrowheads) and microtubules (arrow)
and plasmalemmal caveolae with pinocytotic vesicles (asterisk). E - epithelium, G - Golgi complex. Bar = 0.4 μm. (C) Myofibroblastic
cells (Myof) immunostained for desmin show a halo arround the nucleus (N) that extends through the cytoplasm up to the cell
membrane. The inset shows cytoplasmic processes (CP) that are an important characteristic of myofibroblastic cells. E - epithelium.
Bar = 25 μm, inset = 10 μm.
pivotal role in the histofunctional changes of the
cervix. Thus, in humans and guinea pigs, in which no
significant changes in the serum concentrations of
either E2 or P4 occur immediately before parturition
[68], there is a significant down-regulation of PR and
ERα [56,64]. Recently, an increase in ERβ but not
ERα mRNA has been reported in the human cervix
at term [72]. Thus, the onset of parturition may involve
changes in the responsiveness of the uterus and cervix
to P4 and E2 through alterations in their receptor
density [56].
For ethical reasons, time course studies during
the entire gestation cannot be done in humans, so an
animal model with responses similar to those in
humans would be a valuable tool for studying
temporal and spatial changes in the expression of ER
and PR in the uterus and cervix from mid pregnancy
to early postpartum. In our laboratory, the guinea pig
has been used to study the profile of ERα and PR
expression and collagen remodeling (as an indicator
of functional changes) in different regions of the
uterus and cervix during pregnancy, parturition and
postpartum [56]. Our findings indicate that, in the
presence of high levels of P4 and E2, the diminished
target organ responsiveness to P4 before parturition
may be caused by a decrease in PR levels in the
subepithelium and muscular region. Alterations in PR
levels could help to coordinate cervical dilatation and
uterine contractions. Indeed, it has been hypothesised
[8,16] that a reduction in P4–mediated inhibition,
either through a decrease in hormone production (rats,
rabbits, sheep) or in hormone activity in the target
organs (primates, guinea-pigs), is the major
mechanism for initiating parturition. Our results [56]
are consistent with the P4 withdrawal theory of
parturition.
PHENOTYPIC MODULATION OF FIBROBLASTS
AND CELL TURNOVER IN THE CELLULAR
COMPARTMENTS OF THE UTERINE CERVIX
As already mentioned, connective tissue cells and
the extracellular matrix play important roles in
cervical functions. Fibroblasts, the most common cells
in the connective tissue, show marked phenotypic
plasticity in architecture and biochemical composition
in various physiological and pathological situations
[59,60]. Changes in the cytoskeletal elements are
prominent features in the morphological alterations
in fibroblasts with desmin, vimentin and α-smooth
muscle actin (α-SMA) frequently being expressed in
specific pathways of differentiation [4,22]. The
contractile machinery represented by cytoskeletal
structures such as microfilaments and intermediate
filaments provides characteristic ultrastructural
features that are useful for defining the myofibroblast
[13,14]. We have examined the ultrastructural and
immunohistochemical characteristics of fibroblasts in
the mucous layer of uterine cervices from rats [70]
and women [44]. The differential expression of
cytoskeletal proteins, and the ultrastructural features
seen in both species, indicate that the resident
fibroblasts seen in the mucous layer of nonpregnant
cervices are replaced by a typical myofibroblastic-
cell phenotype characteristic of intrapartum tissue
(Figs. 4B and 5). The implications of the plasticity of
fibroblastic-myofibroblastic cells in the physiological
changes seen in the uterine cervix during pregnancy,
labour and postpartum involution require further
investigation.
In addition to the phenotypic modulation of
fibroblastic cells, adaptative changes in the uterine
cervix during pregnancy imply a dynamic cell
turnover. In rats, the proliferation and death of
epithelial and stromal cells during pregnancy, at term
and in early postpartum are influenced by hormones
[3,32,53,66,73]. In all stages studied, 1) ERα and PR
have different patterns of expression and responses
to the signals that modulate proliferation and/or
apoptosis, depending on the cellular compartment, and
2) although the epithelium is the region with the
highest cell turnover, the fibroblastic and muscle
stroma are dynamic compartments with their own
patterns of behavior [53].
Collagen remodeling in the uterine cervix 81
Braz. J. morphol. Sci. (2003) 20(2), 75-84
Muñoz-de-Toro et al.
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Braz. J. morphol. Sci. (2003) 20(2), 75-84
MAST CELLS ARE INVOLVED IN CERVICAL
ANGIOGENESIS
Cervical ripening is an extremely complex process
that involves interactions between different cellular
compartments and the extracellular matrix, as well
as properly timed biochemical cascades, and the
infiltration of inflammatory cells into the stroma.
Cervical ripening is an energy-dependent process that
requires an adequate supply of nutrients. The vascular
system and new vessel formation (angiogenesis) are
critical for the cervical histo-architectural changes that
are necessary for a successful vaginal delivery
[24,34,Varayoud et al., unpublished results].
Endothelial cell proliferation assessed by BrdU
incorporation and measurement of the vascular area
showed a significant increase in the subepithelial and
muscular cervical stroma at the end of gestation in
the rat [Varayoud et al., unpublished results].
Although angiogenesis is essentially an endothelial
cell event, other cell types and various mediators are
involved in this process [17]. Studies in vitro and in
vivo have implicated mast cells in angiogenesis
[34,46]. We have also demonstrated that mast cells
are involved in cervical angiogenesis since the
inhibition of mast cell degranulation results in a
significant decrease in endothelial cell proliferation
and in the vascular area [Varayoud et al., unpublished
results]. A better understanding of the regulation of
angiogenesis, would allow the development of
therapeutic strategies for controlling cervical function.
CERVICAL RECOVERING AFTER DELIVERY
Apoptosis is a predominant event during
postpartum cervical involution and may contribute
to the recovery of the uterine cervix after delivery
[53]. In addition, water resorption and a decrease in
the levels of some proteoglycans contribute to this
process [19,29]. However, none of these events can
account for the recovery in uterine cervix shape that
occurs immediately after parturition. The intrinsic
mechanical properties of elastic fibers suggests that
these structures may be involved in cervical rigidity
and in the recovery of form immediately after delivery.
In agreement with this, we recently reported an
increase in the elastic system fibers in the uterine
cervix at the end of pregnancy [1].
CONCLUSIONS
Understanding the complex cellular and
molecular biology underlying the dynamic function
of the uterine cervix is a basic challenge for studies
investigating the physiology of gestation and
parturition. During pregnancy, extensive tissue
remodeling involves both the extracellular matrix and
cells of the cervical tissue. The cellular and
extracellular compartments must rapidly adapt to new
functional demands imposed by gestation and
parturition, and then subsequently return to their
original state during the period of involution. In this
review, we have discussed the histofunctional features
observed in the uterine cervix during gestation,
parturition and early postpartum, and have stressed
the key role of collagen remodeling in adaptations to
different functional demands, particularly during
cervical ripening. Despite advances in our knowledge
of cervical ripening, the precise signals and hormonal
control responsible for initiating these changes remain
to be fully elucidated. If we can understand the
mechanisms responsible for these changes, then we
may be better able to address complex phenomena
such as cervical incompetence, pre- and post-term
delivery, and proper “ripening” of the cervix.
ACKNOWLEDGMENTS
This review is dedicated to the memory of Professor
Gregorio S. Montes (1952-2002) who was an invaluable source
of advice, assistance, and moral support in our work. Professor
Montes instilled in us his passion for the impossible and
introduced us to research in collagen biology. He nourished our
work through his insights and valuable critiques; and this is
reflected in the many papers cited which were joint efforts
between his and our laboratories. All LETH members are
indebted to him for the time and effort he devoted to supporting
the development and expansion of our research group. We were
extremely priviledged to have enjoyed his friendship.
We also thank our fellows whose work contributed to many
of the results discussed in this article. The studies described here
were supported by grants from the Argentine National Council
for Science and Technology (CONICET), the Universidad
Nacional del Litoral, SECyT-CAPES, and the Argentine National
Agency for the Promotion of Science and Technology
(ANPCyT).
REFERENCES
1. Battlehner CN, Caldini EG, Pereira JCR, Luque EH, Montes
GS (2003) How to measure the increase in elastic system
fibres in the lamina propria of the mucous layer of the uterine
cervix of pregnant rats? J. Anat. (in press)
2. Broome AW, Winter AJ, McKnutt SH, Casida LE (1960)
Variations in uterine response to experimental infection due
to the hormonal state of the ovaries. II. The mobilization of
leukocytes and their importance in uterine bactericidal
activity. Am. J. Vet. Res. 21, 675-682.
3. Burger LL, Sherwood OD (1998) Relaxin increases the
accumulation of new epithelial and stromal cells in the rat
cervix during the second half of pregnancy. Endocrinology
139, 3984-3995.
Collagen remodeling in the uterine cervix 83
Braz. J. morphol. Sci. (2003) 20(2), 75-84
4. Can A, Tekelioglu M, Baltaci A (1995) Expression of desmin
and vimentin intermediate filaments in human decidual cells
during first trimester pregnancy. Placenta 16, 261-275.
5. Challis JRG, Matthews SG, Gibb W, Lye SJ (2000) Endocrine
and paracrine regulation of birth at term and preterm. Endocr.
Rev. 21, 514-550.
6. Challis JRG, Olson DM (1988) Parturition. In: The
Physiology of Reproduction (Knobil E, Neill JD, eds). 1st
edn, pp. 2177-2216. Raven Press: New York.
7. Cheah SH, Neg KH, Johgalingam VT, Ragavan M (1995)
The effects of oestradiol and relaxin on extensibility and
collagen organization of the pregnant rat cervix. J.
Endocrinol. 146, 331-337.
8. Csapo AI, Wiest WG (1969) An examination of the
quantitative relationship between progesterone and the
maintenance of pregnancy. Endocrinology 85, 735-746.
9. Danforth DN (1947) The fibrous nature of the human cervix,
and its relation to the isthmic segment in gravid and
nongravid uteri. Am. J. Obstet. Gynecol. 53, 541-560.
10. Danforth DN (1983) The morphology of the human cervix.
Clin. Obstet. Gynecol. 26, 7-13.
11. Danforth DN, Veis A, Breen M , Weinstein HG, Buckingham
JC, Manolo P (1974) The effect of pregnancy and labor on
the human cervix. Changes in collagen, glycoproteins and
glycosaminoglycans. Am. J. Obstet. Gynecol. 120, 641- 651.
12. Duchesne MJ, Badia E (1992) Immunohistochemical local-
ization of the eosinophil major basic protein in the uterus
horn and cervix of the rat at term and after parturition.Cell
Tissue Res. 270, 79-86.
13. Eyden B (2001a) The fibronexus in reactive and tumoral
myofibroblasts: further characterisation by electron
microscopy. Histol. Histopathol. 16, 57-70.
14. Eyden B (2001b) The myofibroblast: an assessment of
controversial issues and a definition useful in diagnosis and
research. Ultrastruct. Pathol. 25, 39-50.
15. Fuchs AR, Fields MJ (1999) Parturition, nonhuman
mammals. In: Encyclopedia of Reproduction, Vo l. 3. (Knobil
E, Neill JD, eds). pp. 703-716. Academic Press: New York.
16. Garfield RE, Saade G, Buhimschi C, Buhimschi I, Shi L,
Shi SQ, Chwalisz K (1998) Control and assessment of the
uterus and cervix during pregnancy and labour. Hum. Reprod.
Update 4, 673-695.
17. Griffioen AW, Molema G (2000) Angiogenesis: potentials
for pharmacologic intervention in the treatment of cancer,
cardiovascular diseases, and chronic inflammation.
Pharmacol. Rev. 52, 237-268.
18. Harkness MLR, Harkness RD (1959) Changes in the physical
properties of the uterine cervix of the rat during pregnancy.
J. Physiol. 148, 524-547.
19. Harkness MLR, Harkness RD (1961) The mechanical
properties of the uterine cervix of the rat during involution
after parturition. J. Physiol. 156, 112-120.
20. Hawk HW, Turner GD, Sykes JF (1960) The effect of ovarian
hormones on the uterine defense mechanism during the early
stages of induced infection. Am. J. Vet. Res. 21, 644-648.
21. Hegele-Hartung C, Chwalisz K, Beier HM, Elger W (1989)
Ripening of the uterine cervix of the guinea-pig after
treatment with the progesterone antagonist onapristone (ZK
98,299): an electron microscopic study. Hum. Reprod. 4, 369-
377.
22. Holstein AF, Maekawa M, Nagano T, Davidoff MS (1996)
Myofibroblasts in the lamina propria of human seminiferous
tubules are dynamic structures of heterogeneous phenotype.
Arch. Histol. Cytol. 59, 109-125.
23. Hwang JJ, Shanks RD, Sherwood OD (1989) Monoclonal
antibodies specific for rat relaxin. IV. Passive
immunization with monoclonal antibodies during the
antepartum period reduces cervical growth and
extensibility, disrupts birth, and reduces pup survival in
intact rats. Endocrinology 125, 260-266.
24. Hyder SM, Stancel GM (2000) Regulation of VEGF in the
reproductive tract by sex-steroid hormones. Histol.
Histopathol. 15, 325-334.
25. Junqueira LCU, Bignolas G, Brentani RR (1979)
Picrosirius staining plus polarization microscopy, a
specific method for collagen detection in tissue sections.
Histochem. J. 11, 447-455.
26. Junqueira LCU, Zugaib M, Montes GS, Toledo OMS,
Krisztan RM, Shigihara KM (1980) Morphologic and
histochemical evidence for the occurrence of collagenolysis
and for the role of neutrophilic polymorphonuclear
leukocytes during cervical dilation. Am. J. Obstet. Gynecol.
138, 273-281.
27. Kelly RW (1994) Pregnancy maintenance and parturition:
the role of prostaglandin in manipulating the immune and
inflammatory response. Endocr. Rev. 15, 684-706.
28. Kitamura K, Ito A, Mori Y, Hirakawa S (1979) Changes in
the human uterine cervical collagenase with specific
reference to cervical ripening. Biochem. Med. 22, 332-338.
29. Kokenyesi R, Woessner JF Jr (1990) Relationship between
dilatation of the rat uterine cervix and a small dermatan
sulfate proteoglycan. Biol. Reprod. 42, 87-97.
30. Ledger WL, Webster MA, Anderson ABM, Turnbull AC
(1985) Effect of inhibition of prostaglandin synthesis on
cervical softening and uterine activity during ovine
parturition resulting from progesterone withdrawal induced
by epostane. J. Endocrinol. 105, 227-233.
31. Lee AB, Hwang J-J, Haab LM, Fields PA, Sherwood OD
(1992) Monoclonal antibodies specific for rat relaxin. VI.
Passive immunization with monoclonal antibodies
throughout the second half of pregnancy disrupts histological
changes associated with cervical softening at parturition in
rats. Endocrinology 130, 2386-2391.
32. Leppert PC (1998a) The biochemistry and physiology of the
uterine cervix during gestation and parturition. Prenat.
Neonat. Med. 3, 103-105.
33. Leppert PC (1998b) Proliferation and apoptosis of fibroblasts
and smooth muscle cells in rat uterine cervix throughout
gestation and the effect of the antiprogesterone onapristone.
Am. J. Obstet. Gynecol. 178, 713-725.
34. Levi-Schaffer F, Pe’er J (2001) Mast cells and angiogenesis.
Clin. Exp. Allergy 31, 521-524.
35. Liggins GC, Forster CS, Grieves SA, Schwartz AL (1977)
Control of parturition in man. Biol. Reprod. 16, 39-56.
36. Ludmir J, Sehdev HM (2000) Anatomy and physiology of
the uterine cervix. Clin. Obstet. Gynecol. 43, 433-439.
37. Luque EH, Bassani MM, Ramos JG, Maffini M, Canal A,
Kass L, Caldini EG, Ferreira Jr JMC, Muñoz-de-Toro M,
Montes GS (1997) Leukocyte infiltration and collagenolysis
in cervical tissue from intrapartum sheep. J. Vet. Med. 44,
501-510.
38. Luque EH, Montes GS (1989) Progesterone promotes a
massive infiltration of the rat uterine cervix by the
eosinophilic polymorphonuclear leukocytes. Anat. Rec. 223,
257-265.
39. Luque EH, Muñoz-de-Toro M, Ramos JG, Rodríguez HA,
Sherwood OD (1998) Role of relaxin and estrogen in the
control of eosinophilic invasion and collagen remodeling in
rat cervical tissue at term. Biol. Reprod. 59, 795-800.
Muñoz-de-Toro et al.
84
Braz. J. morphol. Sci. (2003) 20(2), 75-84
40. Luque EH, Ramos JG, Rodriguez HA, Muñoz-de-Toro M
(1996) Dissociation in the control of cervical eosinophilic
infiltration and collagenolysis at the end of pregnancy or
after pseudopregnancy in ovariectomized steroid-treated rats.
Biol. Reprod. 55, 1206-1212.
41. Maymon E, Romero R, Pacora P, Gomez R, Athayde N,
Edwin S, Yoon BH (2000) Human neutrophil collagenase
(matrix metalloproteinase 8) in parturition, premature rupture
of the membranes, and intrauterine infection. Am. J. Obstet.
Gynecol. 183, 94-99.
42. Minamoto T, Arai K, Hirakawa S, Nagai Y (1987)
Immunohistochemical studies on collagen types in the uterine
cervix in pregnant and nonpregnant states. Am. J. Obstet.
Gynecol. 156, 138-144.
43. Montes GS (1996) Structural biology of the fibres of the
collagenous and elastic systems. Cell Biol. Int. 20, 15-27.
44. Montes GS, Zugaib M, Joazeiro PP, Varayoud J, Ramos JG,
Muñoz-de-Toro M, Luque EH (2002) Phenotypic modulation
of fibroblastic cells in the mucous layer of the human uterine
cervix at term. Reproduction 124, 783-790.
45. Morishige WK, Pepe GJ, Rothchild I (1973) Serum
luteinizing hormone, prolactin and progesterone levels during
pregnancy in the rat. Endocrinology 92, 1527-1530.
46. Norrby K (2002) Mast cells and angiogenesis. APMIS 110,
355-371.
47. Osmer R, Rath W, Adelmann-Grill BC, Fittkow C, Kuloczik
M, Szeverenyi M, Tschesche H, Kuhn W (1992) Origin of
cervical collagenase during parturition. Am. J. Obstet.
Gynecol. 166, 1455-1460.
48. Owiny JR, Fitzpatrick RJ, Spiller DG, Appleton J (1987)
Scanning electron microscopy of the wall of the ovine cervix
uteri in relation to tensile strength at parturition. Res. Vet.
Sci. 43, 36-43.
49. Owiny JR, Gilbert RO, Wahl CH, Nathanielsz PW (1995)
Leukocytic invasion of the ovine cervix at parturition. J. Soc.
Gynecol. Investig. 2, 593-596.
50. Parry DAD, Craig AS (1988) Collagen fibrils during
development and maturation and their contribution to the
mechanical attributes of connective tissue. In: Collagen. Vol
II. (Nimni ME, ed). pp.1-23. CRC Press: Boca Raton.
51. Rajabi MR, Dean DD, Beydoun SN, Woessner Jr JF (1988)
Elevated tissue levels of collagenase during dilation of uterine
cervix in human parturition. Am. J. Obstet. Gynecol. 159,
971-976.
52. Ramos JG (2001) Factores que mejoran la eficiencia
reproductiva: regulación endócrina del mecanismo de
dilatación del cuello uterino durante el parto. Doctoral Thesis,
Facultad de Bioquímica y Ciencias Biológicas, Universidad
Nacional del Litoral, Santa Fe, Argentina.
53. Ramos JG, Varayoud J, Bosquiazzo VL, Luque EH, Muñoz-
de-Toro M (2002) Cellular turnover in the rat uterine cervix
and its relationship to estrogen and progesterone receptor
dynamics. Biol. Reprod. 67, 735-742.
54. Ramos JG, Varayoud J, Kass L, Rodríguez H, Muñoz-de-
Toro M, Montes GS, Luque EH (2000) Estrogen and
progesterone modulation of eosinophilic infiltration of the
rat uterine cervix. Steroids 65, 409-414.
55. Rechberger T, Woessner Jr JF (1993) Collagenase, its
inhibitors, and decorin in the lower uterine segment in
pregnant women. Am. J. Obstet. Gynecol. 168, 1598-1603.
56. Rodríguez HA, Kass L, Varayoud J, Ramos JG, Ortega HH,
Durando M, Muñoz-de-Toro M, Luque EH (2003) Collagen
remodelling in the guinea pig uterine cervix at term is
associated with a decrease in PR expression. Mol. Hum.
Reprod. (in press).
57. Rorie DK, Newton M (1967) Histologic and chemical studies
of the smooth muscle in the human cervix and uterus. Am. J.
Obstet. Gynecol. 99, 466-469.
58. Rowson LEA, Lamming GE, Fry RM (1953) The influence of
ovarian hormones on uterine infection. Nature 171, 749-750.
59. Sappino AP, Schürch W, Gabbiani G (1990) Differentiation
repertoire of fibroblastic cells: expression of cytoskeletal
proteins as marker of phenotypic modulations. Lab. Invest.
63, 144-161.
60. Schmitt-Graff A, Desmouliere A, Gabbiani G (1994)
Heterogeneity of myofibroblast phenotypic features: an
example of fibroblastic cell plasticity. Virchows Arch. 425,
3-24.
61. Shi L, Shi SQ, Saade GR, Chwalisz K, Garfield RE (2000)
Studies of cervical ripening in pregnant rats: effects of various
treatments. Mol. Hum. Reprod. 6, 382-389.
62. Short RV (1969) Implantation and the maternal recognition
of pregnancy. In: Ciba Foundation Symposium on Foetal
Autonomy (Wolstenholme GEW, O´Connor MO, eds). pp.
2-26. Churchill Livingstone: London.
63. Staples LD, Heap RB, Wooding FBP, King GJ (1983)
Migration of leukocytes into the uterus after acute removal
of ovarian progesterone during early pregnancy in the sheep.
Placenta 4, 339-349.
64. Stjernholm Y, Sahlin L, Akerberg S, Elinder A, Eriksson HA,
Malmström A, Ekman G (1996) Cervical ripening in humans:
potential roles of estrogen, progesterone, and insulin-like
growth factor-I. Am. J. Obstet. Gynecol. 174, 1065-1071.
65. Stygar D, Wang H, Stjernholm Vladic YS, Ekman G,
Eriksson H, Sahlin L (2002) Increased level of matrix
metalloproteinases 2 and 9 in the ripening process of the
human cervix. Biol. Reprod. 67, 889-894.
66. Takamoto N, Leppert PC, Yu SY (1998) Cell death and
proliferation and its relation to collagen degradation in uterine
involution of rat. Connect. Tissue Res. 37, 163-175.
67. Thomson AJ, Telfer JF, Young A, Campbell S, Stewart CJR,
Cameron IT, Greer IA, Norman JE (1999) Leukocytes
infiltrate the myometrium during human parturition: further
evidence that labour is an inflammatory process. Hum.
Reprod. 14, 229-236.
68. Trewin AL, Hutz RJ (1999) Guinea pig female. In:
Encyclopedia of Reproduction. Vol. 3 . (Knobil E, Neill JD,
eds). pp. 583-588. Academic Press: New York.
69. Uldbjerg N, Ekman G, Malmström A, Olsson K, Ulmsten U
(1983) Ripening of the human uterine cervix related to
changes in collagen, glycosaminoglycans, and collagenolytic
activity. Am. J. Obstet. Gynecol. 147, 662-666.
70. Varayoud J, Ramos JG, Joazeiro PP, Montes GS, Muñoz-de-
Toro M, Luque EH (2001) Characterization of fibroblastic
cell plasticity in the lamina propria of the rat uterine cervix
at term. Biol. Reprod. 65, 375-383.
71. Wang H, Eriksson H, Sahlin L (2000) Estrogen receptor alpha
and beta in the female reproductive tract of the rat during
the estrous cycle. Biol. Reprod. 63, 1331-1340.
72. Wang H, Stejernholm Y, Ekman G, Eriksson H, Sahlin L
(2001) Different regulation of oestrogen receptors alpha and
beta in the human cervix at term pregnancy. Mol. Hum.
Reprod. 7, 293-300.
73. Zhao S, Fields PA, Sherwood OD (2001) Evidence that
relaxin inhibits apoptosis in the cervix and the vagina during
the second half of pregnancy in the rat. Endocrinology 142,
2221-2229.
Received: April 30, 2003
Accepted: July 1, 2003
