Background
Advances in research relating to menstruation and associated disorders (eg, endometriosis
and premenstrual syndrome) have been hindered by the lack of an appropriate animal
model. Menstruation, the cyclical shedding of the decidualized endometrium in the
absence of pregnancy, is believed to be limited to 78 higher-order primates (human
beings and Old World monkeys), 4 species of bat, and the elephant shrew. This represents
only 1.5% of the known 5502 mammalian species and <0.09% of these are nonprimates.
Thus, many aspects of menstruation remain poorly understood, limiting the development
of effective treatments for women with menstrual disorders. Menstruation occurs as
a consequence of progesterone priming of the endometrial stroma and a spontaneous
decidual reaction. At the end of each infertile cycle as progesterone levels decline
the uterus is unable to maintain this terminally differentiated stroma and the superficial
endometrium is shed. True menstruation has never been reported in rodents.
Objective
Here we describe the first observation of menstruation in a rodent, the spiny mouse
(Acomys cahirinus).
Study Design
Virgin female spiny mice (n = 14) aged 12–16 weeks were sampled through daily vaginal
lavage for 2 complete reproductive cycles. Stage-specific collection of reproductive
tissue and plasma was used for histology, prolactin immunohistochemistry, and enzyme-linked
immunosorbent assay of progesterone (n = 4–5/stage of the menstrual cycle). Normally
distributed data are reported as the mean ± SE and significant differences calculated
using a 1-way analysis of variance. Nonnormal data are displayed as the median values
of replicates (with interquartile range) and significant differences calculated using
Kruskal-Wallis test.
Results
Mean menstrual cycle length was 8.7 ± 0.4 days with red blood cells observed in the
lavages over 3.0 ± 0.2 days. Cyclic endometrial shedding and blood in the vaginal
canal concluding with each infertile cycle was confirmed in all virgin females. The
endometrium was thickest during the luteal phase at 322.6 μm (254.8, 512.2), when
plasma progesterone peaked at 102.1 ng/mL (70.1, 198.6) and the optical density for
prolactin immunoreactivity was strongest (0.071 ± 0.01 arbitrary units).
Conclusion
The spiny mouse undergoes spontaneous decidualization, demonstrating for the first
time menstruation in a rodent. The spiny mouse provides a readily accessible nonprimate
model to study the mechanisms of menstrual shedding and repair, and may therefore
be useful in furthering studies of human menstrual and pregnancy-associated disorders.
Key words
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Article Info
Publication History
Published online: August 05, 2016
Accepted:
July 15,
2016
Received in revised form:
July 14,
2016
Received:
June 9,
2016
Footnotes
H.D. is a National Health and Medical Research Council Career Development Fellow. S.E. is funded by a career development fellowship from the Cerebral Palsy Alliance to H.D. Partial funding for this project was obtained from National Health and Medical Research Council of Australia to H.D. and a grant from the Victorian Government Infrastructure Support Fund to the Hudson Institute of Medical Research.
The authors report no conflict of interest.
Cite this article as: Bellofiore N, Ellery SJ, Mamrot J, et al. First evidence of a menstruating rodent: the spiny mouse (Acomys cahirinus). Am J Obstet Gynecol 2017;216:40.e1-11.
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