Vol.3 No.1, 66-72 (2011) Health
Copyright © 2011 SciRes. Openly accessible at http://www. scirp.org/journal/HEALTH/
The effect of progesterone on uterine fluid ph &
endometrial nhe-1 protein expression in rats
Salleh Naguib1*, Vivi Noryati Ahmad1, Norfadila Kasim1, Salim Muhammad Amri2, Yeong Soh
1Department of Physiology, University of Malaya, Lembah Pantai, Kuala Lumpur, Malaysia;
*Corresponding Author: naguibsalleh@um.edu.my
2Department of Anatomy, University of Malaya, Lembah Pantai, Kuala Lumpur, Malaysia.
Received 26 October 2010; revised 25 November 2010; accepted 24 December 2010
A precise regulation of the uterine fluid volume
and pH is essential for a successful embryo
implantation. Progesterone has been reported
to participate in uterine fluid volume regulation
during this period, however its effect on the
uterine fluid pH is unknown. As endometrial
fluid absorption has been proposed to occur
secondary to sodium (Na+) absorption under
progesterone mediated effect, we therefore hy-
pothesize that there may be a concomitant changes
in fluid volume and pH if sodium-hydrogen ex-
changer (NHE), a protein responsible for both
luminal Na+ absorption and H+ extrusion is in-
volved. In view of these, our study aimed to in-
vestigate the possibility that progesterone af-
fect the uterine fluid pH and endometrial NHE
expression. Ovariectomised female Sprague-
Dawley (SD) rats were treated with peanut oil
(vehicle), oestradiol-3-benzoate and progester-
one for three consecutive days. On the fourth
day, in-vivo uterine perfusions were performed
on anaesthetized rats. The collected perfusate
were analyzed for the changes in pH. The effect
of amiloride, a non-specific Na+-channel blocker
on the pH was investigated. The expression of
uterine NHE-1 protein was detected by Western
blotting and immunohistochemistry. Our find-
ings indicate that the fluid pH is the lowest in
progesterone-treated group and amiloride ad-
ministration significantly increased the pH in
the same treatment group (p < 0.05). NHE-1
proteins were significantly expressed in the
progesterone-treated group. In conclusion,
progesterone induces a reduction of the uterine
fluid pH and is amiloride-sensitive. The up-r eg ul a -
tion of NHE-1 under a common progesterone
effect may explain the role of this exchanger in
regulating the uterine fluid pH.
Keywords: Progesterone; Uterine-Fluid pH; NHE-1;
Implantation is a complex process that requires a pre-
cise control of the uterine fluid volume, pH and its
composition. It occurs within a limited period following
fertilization known as the implantation window period
[1]. During this period, a reduction of the uterine luminal
fluid volume has been documented in both rodents [2,3]
and primates [4]. Multiple molecular mechanisms such
as the increased expression of pinopodes [5], aquoporins
channels [6,7] and the membrane Na+ channel such as
the epithelial Na+ channel (ENaC) [8] have been pro-
posed to play a role in fluid movements across the en-
dometrium under a common progesterone mediated ef-
fect [9].
Since long ago, uterine luminal fluid has been ob-
served to contain a high amount of HCO-
3 as compared
to plasma [10]. Apical HCO-
3 transporters such as cys-
tic fibrosis transmembrane regulator (CFTR) [11] and
the bicarbonate- chloride exchanger (HCO-
[12,13] may be involved in luminal HCO-
3 extrusion.
A continuous HCO-
3 extrusion should be followed by a
concomitant H+ extrusion to maintain a normal intra-
cellular pH [14]. In many absorptive and secretory
epithelia where HCO-
3 extrusion occur, such as in the
proximal tubule of the nephron [15], pancreatic duct
[16] and epididymis [17], apical NHE plays an impor-
tant role in maintaining a normal intracellular pH.
Despite of the reported alkalinity of the uterine luminal
fluid, the changes of the pH under different sex steroids
S. Naguib et al. / Health 3 (2011) 66-72
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
effect and the underlying mechanism involved in uterine
fluid pH regulation is not fully understood. As
sex-steroids in particular progesterone play an important
role in regulating uterine luminal fluid volume, we specu-
late that this hormone may as well affect the pH of this
fluid. Although ENaC has been proposed to be involved in
Na+ absorption and therefore concomitant H2O absorption
[8,18], however NHE may be an alternative route for Na+
absorption which can create osmotic gradient to drive
H2O movement across the epithelia. Additionally NHE
may also be involved in the uterine fluid pH regulation as
similar observations has been made in rats’ kidney [19]
and epididymis [17] as well as in the intestines of rabbits
[20] and mice [21]. Therefore, the aim of this study is to
investigate the effect of sex-steroids on uterine fluid pH as
well as on the expression of NHE proteins.
2.1. Animals and Hormone Treatments
Adult Wistar rats weighing 200-250 g were maintained
under 12:12 lighting conditions, with free access to food
and water. Ovariectomies were performed under isofluorane
anesthesia to eliminate the effect of endogenous steroids.
Ovariectomies were normally performed at least 10 days
before initiating any hormone treatment. Steroids were
dissolved in peanut oil and injected sub-cutaneously in a
volume of 0.1 ml. Steroid treatment involved daily injec-
tions of 0.2 g oestradiol and 4 mg progesterone for 3 con-
secutive days. Vehicle treated animals (control) received 3
daily injections of peanut oil. Oestradiol-3-benzoate and
progesterone were purchased from Sigma-Aldrich.
2.2. Uterine Perfusion
The rats were anesthetized with intraperitoneal injec-
tion of 0.1 ml (80 mg/kg) ketamine and 0.15 ml (10 mg/
kg) xylazine HCl and maintained under anesthesia on a
thermo-statically controlled heat pad for the duration of
the experiment. Body temperature was monitored using a
rectal thermometer. At the end of the perfusion period, the
animals were killed. All procedures were approved by a
local ethic committee. Uterine perfusion was achieved
after tying in place fine-bore polythene tubing (ID 0.38
mm; OD 1.09 mm), pre-filled with perfusate, in both the
anterior and cervical ends of the uterine horn. The cannula
had minimal insertion into the lumen but had slightly
heat-flared endings to prevent them being expelled by any
ongoing uterine contractions. A syringe-driven infusion
pump (Harvard Apparatus) was used to deliver perfusion
medium (with and without amiloride) into the anterior
cannula at a constant rate of 1.5 l/min. The composition of
the perfusion medium was based on published data on the
composition of rat uterine fluid that contained low Na+
and high K+ concentrations [22-24]. It consisted of:
(mmol/l) 110 NaCl, 14.3 NaHCO3, 1 NaHPO4 (total Na+
125.3), 15 KCl, 0.8 MgSO4, 1.8 CaCl2, 5.5 mmol/l glu-
cose and a pH of 7.45. Amiloride was dissolved at a con-
centration of 100 mol/l into the perfusion fluid. Perfusate
collections were made after 3 hours and delivered into
small, covered, pre-weighed polythene tubes. The uterine
luminal fluid pH was measured using the HI8424 Portable
pH/mV/˚C Meter, which was purchased from HANNA
Instrument, Singapore. Micro miniature pH probe (HAN-
NA Instrument, Singapore) was connected to the pH me-
ter and the pH of a minute volume of uterine fluid col-
lected was directly measured.
2.3. Protein Expression
At the end of the treatment period, the rats were killed
by cervical dislocation (procedure approved by local
ethic committee) and the uterine horns and kidneys were
immediately removed and proteins prepared for Western
blotting analysis by homogenization in tissue lysis buffer
(100 mM Tris pH 6.8, 1 mM EDTA pH 8.0, 10% v/v
glycerol and 10 ml/l protease inhibitor cocktail (Sigma,
UK). Samples were subjected to centrifugation (5 min,
250 g) to remove nuclei. Supernatants from each prepa-
ration were heated to 94˚C for 5 min in denaturing buf-
fer (Novex, Invitrogen UK). 30 mg protein from the ute-
rine and kidney samples were separated using Novex
Bis-Tris gels (Invitrogen, UK). Fractionated proteins were
transferred to nitrocellulose membrane (Biorad, UK) by
electroblotting and immunostained with anti NHE-1
(Ab-Cam, UK) 1:500. Immunostained proteins were visu-
alized by enhanced chemiluminescence (Amersham, UK)
and exposure to auto-radiographic film. The size of im-
munostained proteins was calculated by comparison to
protein size markers (BioRad, UK) on the same blots.
For immunohisto-chemistry, uterine horns were fixed in
4% paraformaldehyde for 4 h at 4˚C. The tissues were
then processed through to wax blocks and 5 mm sections
cut. The sections were dewaxed in xylene and
re-hydrated. The tissues were incubated in 10% H2O2 in
methanol to quench endogenous peroxidase activity and
incubated overnight with primary antibodies (rat poly-
clonal IgG) at the following concentrations in PBS;
(1:10 for NHE-1) at 4˚C in a humidified chamber. The
tissues were then incubated with secondary antibody,
bio-tinylated rabbit anti-rat IgG Amersham) at 1:500 for
1 h at room temperature and with tertiary antibody,
streptavidin-horseradish peroxidase (Amersham) at 1:500
for 1 h at room temperature. The sites of antibody bind-
ing were visualized with DAB (Diamino-benzidine HCl),
which gave a dark-brown stain. The sections were coun-
S. Naguib et al. / Health 3(2011) 66- 72
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terstained with hematoxylin for nuclear staining.
2.4. Statistical Analysis
Data are expressed as means ± SEM. Comparisons be-
tween groups of data were made with the Student t-test,
with P < 0.05 considered to be statistically significant.
3.1. The Effect of Amiloride on Uterine Fluid
In Figure 1, it was observed that the pH of the col-
lected perfusates were basic for all treatment groups,
despite the pH of the perfused solution being 7.45. The
alkalinity however seems to differ between each treat-
ment groups with the perfusate in progesterone treated
group being the least alkaline (pH 8.20) (p < 0.05). No
significant differences in pH were observed between the
oestradiol (pH 8.55) and vehicle (pH 8.45) treated
groups. Intraluminal administration of amiloride at 100 m
significantly inhibits the reduction of pH in the proges-
terone treated group (p < 0.05), however not in the vehi-
cle and oestradiol treated groups. The low perfusion rate
at 1.5 l/minute provides adequate time for the action of
amiloride on the folded luminal epithelium. In each ex-
periment, the pH obtained was the mean pH of the col-
lected fluid from both uteri in the same animal.
3.2. Protein Expression
Western blotting of protein isolated from rat uteri in-
dicated the presence of NHE-1 protein in the uterus, and
a protein of predicted size was detected in kidney. In the
uterus, the immunostained NHE-1 protein product has a
molecular weight of 95 kDa, which is similar to the
product detected in kidney control samples (Figure 2).
Immunohisto-chemistry indicated that NHE-1 protein
was expressed mainly at the luminal epithelium under
the influence of progesterone (Figures 3(c) and 3(e)).
Little NHE-1 proteins were detected in the luminal epi-
thelium after vehicle and oestradiol treatment (Figures
3(a) and 3(b)). NHE-1 was also present in a high amount
in the glandular epithelia after progesterone treatment
(Figure 3(c) and 3(e)). The intensity of immunoreactiv-
ity (as shown in Figure 3) and a quantitative assessment
of the immunostaining for NHE-1 isoform are scaled
from 0 with no staining to 4 to the most intense staining
Figure 1. Comparison of the intraluminal fluid pH from the collected fluid between the vehicle, progesterone and
oestradiol treatment respectively and the effect of amiloride on the fluid pH in each treatment groups (see Meth-
ods for detail). Each point represents the mean value (± SEM) of each set of observations (n = 6 rats per point).
**p < 0.05 (comparison between treatment groups in the absence of amiloride), *p < 0.05 (comparison between
the presence and absence of amiloride in the progesterone-treated group).
no amiloride
progesterone oestradiol
S. Naguib et al. / Health 3 (2011) 66-72
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Figure 2. The effect of sex steroids treatment on NHE-1 protein expression in the uterus of ovariec-
tomised rats. The picture above is a representative image of Western blotting analysis of protein expres-
sion under different steroid treatment, C for control, P for progesterone and E2 for oestradiol. The graph
shows the analysis of the relative density for each band. Data were expressed as mean S.E.M (n = 3 per
treatment group. *indicates p < 0.05 as compared to C group for the particular band).
(a) Vehicle (40 ×) (b) Oestradiol (40 ×)
(c) Progesterone (40 ×) (d) Negative control (40 ×)
vehicleoestradiol progesterone
relative band densi
2 P
S. Naguib et al. / Health 3(2011) 66- 72
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(e) Progesterone (100 ×) (f) Negative control (100 ×)
Figure 3. Immunohistochemical localization of NHE-1 in the uterus of (a) vehicle, (b) oestradiol- and (c)
progesterone-treated ovariectomized rats. The pictures are representative images showing the distribution of
NHE-1 in the luminal and glandular epithelia. Bound antibody is stained dark brown and marked with arrows
(n = 6 animals per treatment group). The control image represents incubation without primary antibody, and
the vehicle control represents uterine sections from non-steroid-treated ovariectomized animals. G = gland, L
= lumen. (a, b, c & d are at 40 × magnification, e & f are at 100 × magnification).
Table 1. A semiquantitative assessment of immunostaining
(DAB) of Na+/H+ exchanger-1 in the luminal and glandular
epithelia of rats’ uterus.
Vehicle Progesterone Oestradiol
luminal 1 4 1
glandular 1 4 1
as shown in Table 1.
The alkalinity of the uterine luminal fluid as observed
in all the treatment groups is consistent with the previous
reports that this fluid contains a high amount of HCO-
[25] which is essential for sperm capacitation and acro-
somal reaction during fertilization [26]. Despite this fact,
we have however observed a significant difference in the
pH of the uterine fluid between the progesterone-treated
groups and those rats receiving vehicle or oestradiol in-
jections. Our findings indicated that progesterone re-
duces the alkalinity of the uterine luminal fluid. The sig-
nificance of this pH reduction under progesterone medi-
ated effect is not clear. A less alkaline environment could
be important for embryo implantation that requires an
elevated progesterone level [27] in a species such as
rodents, in which implantation has been reported to oc-
cur 4 to 5 days after fertilization [28]. Furthermore, em-
bryo-endometrial interaction is known to involve multi-
ple factors such as a decrease in the thickness of the cell
glycocalyx as well as cell surface charges [29,30]. In
addition, there has been a reported loss of apico-basal
polarity without a concurrent loss in cell adhesion mo-
lecules that allow interactions and attachment between
the endometrium and the embryo [31]. The changes in
the cell surface charges and polarity could be associated
with the changes in the pH induced by a high level of
progesterone during this phase.
Administration of amiloride, a non-specific Na+
channel blocker significantly inhibit pH reduction in the
progesterone treated group but not the groups that were
treated with vehicle or oestradiol. This suggests the
presence of an amiloride-sensitive Na+ channels at the
apical surface of the endometrium of the progesterone
treated rats. There is no significant changes in the lu-
minal fluid in pH or volume in oestradiol or vehicle
treated rats indicated that Na+ channels were not present
or present in too small an amount to exert a change in
the uterine fluid environment under the regulation of
oestradiol or without hormonal influence. Despite the
presence of amiloride-sensitive ENaC which has been
reported under the progesterone dominant state [18],
however ENaC mediate luminal fluid loss without al-
teration of the luminal fluid pH. This raises suspicion
that other amiloride-sensitive Na+ channels such as the
NHE may be involved.
The presence of NHE-1 in the endometrium in the
progesterone-treated group was further confirmed by
Western blotting and immunohistochemistry. NHE-1
S. Naguib et al. / Health 3 (2011) 66-72
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was localized in the cytoplasm and brush border of the
luminal epithelial cells as well as in the glandular epithe-
lia. The apical distribution of NHE-1 in the endometrium
is similar to those seen in the rats kidney, jejunum and
colon [32]. In the rats cecum however, NHE-1 and
NHE-3 are found only on the brush border cells lining
the apical surface [33]. In addition to maintaining intra-
cellular pH homeostasis, NHE could also be involved in
uterine luminal fluid volume regulation. This has been
reported to occur in the epididymis whereby despite the
absence of ENaC, NHE is responsible for most of semi-
nal fluid reabsorption [17].
We concluded that progesterone induces the expres-
sion of NHE-1 in the endometrial epithelial cells. This
protein could be involved in pH regulation of the uterine
luminal fluid thus creating an environment that is suit-
able for a successful implantation. The understanding of
a molecular mechanism regulating uterine fluid pH is of
clinical relevance because this may lead to strategies to
correct implantation failure and to improve pregnancy
rates. In addition, this could also help in identifying a
new marker for the period of uterine receptivity. How-
ever more works need to be done to confirm the in-
volvement of NHE in uterine fluid pH regulation despite
of a limited data available from our study.
This project is supported by the FRGS grant, Ministry of Higher
Education Malaysia.
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