Antioxidant capacity of follicular fluid in relation to follicular size and stage of estrous cycle in buffaloes

The present study was designed to evaluate the changes in the concentrations of different antioxidants, such as glutathione (GSH), glutathione reductase (GR), superoxide dismutase (SOD), and catalase (CAT), in the follicular fluid collected from different follicular size categories in relation to stage of estrous cycle in buffaloes. In addition, malondialdehyde (MDA) as an indicator for lipid peroxidation was also estimated. Fifty pairs of buffalo ovaries were collected from a local slaughterhouse. Based on ovarian structures, the cycle was divided into follicular and luteal phase. The follicles on each pair were classified into three groups; small (≤3 mm), medium (4-9 mm) and large (≥10 mm). The concentrations of SOD, CAT, GSH, and GR in the follicular fluid of each group as well as MDA were estimated. Results indicated that there was a significant decrease (P < 0.05) in the average numbers of small follicles obtained at the follicular phase than those obtained at the luteal phase of the cycle. However, the mean numbers of the large sized follicles was significantly increased (P < 0.05) in the follicular phase than in the luteal phase. Large follicles obtained at the luteal phase had a significantly higher (P < 0.05) concentration of GSH than that obtained from small ones. A significant (P < 0.05) effect of follicular size on GR concentrations was observed. The concentration of SOD tended to be higher in large follicles obtained at the follicular phase than that collected at the luteal phase (56.7 ± 3.7 vs. 28.1 ± 6.7 U/mL, respectively). On the contrary, a significantly higher concentration (P < 0.05) of SOD was recorded in small follicles as compared with medium and large follicles collected at the luteal phase. CAT concentrations did not significantly differ among different follicular sizes between follicular and luteal phases as well as within each phase. Malondialdehyde concentration was significantly decreased (P < 0.05) in the follicular fluid obtained from small follicles collected at the follicular phase compared with those obtained at the luteal phase. In conclusion, the present study showed that the concentrations of enzymatic antioxidants except for CAT vary according to the follicle size and the stage of the estrous cycle suggesting their possible role in the process of follicular development during estrous cycle in buffaloes.     

Effect of the season on some aspects of the estrous cycle in Martina Franca donkey

The Martina Franca (MF) donkey breed, with 48 jackasses and 515 jennies, is considered an endangered breed according to the data from the Monitoring Institute for Rare Breeds and Seeds in Europe. The knowledge of the estrous cycle characteristics has a great impact for assisted reproduction, especially in endangered species. In this study, the estrous cycle characteristics were investigated in 12 MF jennies throughout the year. Estrous cycle, estrous and diestrous lengths, follicular growth and ovulation, and estradiol-17β (E2) and progesterone (P4) plasma concentrations were monitored in MF jennies and compared in different seasons. In all jennies (100%) estrous cycle was detected during the whole year, with no differences in the estrous cycle length among seasons. However, a significant increase of estrous length in spring and summer compared with autumn and winter was found. Diestrus was shorter in summer than in the other seasons. Estrous behavior was always shown and characterized by rhythmic eversion of the vulvar labia (winking) with exhibition of the clitoris, urination, male receptivity and clapping, with sialorrhoea, neck and head extension, and back ears. Estrus was characterized by the ovulation of a larger follicle in spring and summer than in autumn and winter. The pattern of E2 and P4 plasma concentrations during the estrous cycle were similar to that reported for the mare, but without differences among the four seasons, so that a negligible effect of environmental conditions on ovarian E2 and P4 secretion was hypothesized, despite the larger diameter of the ovulating follicle in spring and summer.     

The expression of angiogenic growth factors and their receptors in ovarian follicles throughout the estrous cycle in the ewe

Healthy follicles are highly vascularized whereas those undergoing atresia have poor vascularity, suggesting a relationship between follicular vascularization and follicular function. Vascularization is regulated by angiogenic factors, and among them vascular endothelial growth factor (VEGF) and angiopoietin-Tie (Ang-Tie) systems are of central importance. The objectives of this study were to determine if VEGF, VEGF receptor-2 (VEGFR-2), and components of the Ang-Tie system are expressed in ovarian follicles at both the protein and mRNA levels and to explore if their expression is related to the stage of the estrous cycle in the ewe. Ovaries from cyclic ewes were collected during the luteal phase (n = 5) or before (n = 5), during (n = 4), and after (n = 4) the preovulatory luteinizing hormone (LH) surge. After fixation, ovaries were wax-embedded, serially sectioned, and analyzed for both protein and mRNA expression of VEGF, VEGFR-2, angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), Tie-1 (mRNA only), and Tie-2. mRNA was studied by in situ hybridization using digoxigenin-11-UTP-labeled ovine riboprobes. A similar pattern of expression was observed for mRNA and protein for all of the factors. Both mRNA and protein expression of VEGF, VEGFR-2, Ang-1, Ang-2, Tie-1 (mRNA only), and Tie-2 in the granulosa and theca cells of follicles ≥2 mm in diameter was significantly different among the stages of the estrous cycle, with the highest expression detected at the post-LH surge stage. Theca cells expressed significantly greater levels of the six angiogenic factors compared with granulosa cells at all stages of the estrous cycle. Expression levels in granulosa and theca cells were comparable between small (2.0 to 2.5 mm) and medium (2.5 to 4.0 mm) follicles, but large follicles (>4.0 mm) expressed higher mRNA and protein levels (all P < 0.05) for all factors at all stages of the estrous cycle. These data show (i) that VEGF, VEGFR-2, and the Ang-Tie system are present in both granulosa and theca cells of the ovarian follicle, (ii) that thecal cells consistently express greater levels of all of these factors compared with granulosa cells, and (iii) that their levels of expression are related to the stage of the estrous cycle and to follicle size.     

Ovarian antral follicular dynamics in sheep revisited: Comparison among estrous cycles with three or four follicular waves

In this study, the characteristics of ovarian follicular waves and patterns of serum concentrations of follicle-stimulating hormone (FSH), estradiol, and progesterone were compared between cycles with three (n = 9) or four (n = 10) follicular waves in Western White Face (WWF) ewes (Ovis aries). Transrectal ultrasonography and blood sampling were performed daily during one cycle. Estrous cycles were 17.11 ± 0.3 and 17.20 ± 0.2 d long in cycles with three and four waves, respectively (P > 0.05). The first interwave interval and the interval from the emergence of the final wave to the day of ovulation were longer in cycles with three waves compared with those in cycles with four waves (P < 0.05). The growth phase (5.1 ± 0.5 vs. 3.1 ± 0.4 d) and life span (5.67 ± 0.3 vs. 4.3 ± 0.3 d) of the largest follicle growing in the last or ovulatory wave was longer in cycles with three waves compared with that in cycles with four waves (P < 0.05). The maximum diameter of the largest follicle was greater in the first wave and the ovulatory wave compared with that in other waves of the cycle (P < 0.05). The regression phase of the largest follicle growing in the first wave was longer in cycles with three waves compared with that in cycles with four waves (4.44 ± 0.4 vs. 3.4 ± 0.4 d; P < 0.05). The length of the life span, regression phase, and, although not significant in every case, FSH peak concentration and amplitude decreased across the cycle (P < 0.05). We concluded that estrous cycles with three or four follicular waves were confined within the same length of cycle in WWF ewes. In this study, there were no apparent endocrine or follicular characteristics that could explain the regulation of the different number of follicular waves (three vs. four) during cycles of similar length.     

Apoptosis in the canine endometrium during the estrous cycle

Apoptotic cell death in the endometria of 58 female dogs in different stages of the estrous cycle was assessed (in formalin-fixed, paraffin-embedded sections) with both the terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labeling (TUNEL) assay and immunohistochemical detection of caspase-3 activity. For both techniques, the apoptotic index was determined in the surface epithelium, stroma, crypts, and basal glands by counting the percentage of stained cells in a total of 500 cells in each category. In the surface epithelium and stroma, TUNEL- and caspase-3-positive cells were rare (apoptotic index<1) throughout the estrous cycle. However, caspase-3 detection showed a significant increase in the apoptotic index in the stroma during anestrus as well as an increase in the index in both the stroma and surface epithelium in late metestrus. The apoptotic index increased during late metestrus and anestrus in the crypts and basal glands; in the crypts, this increase was significant only when caspase-3 detection was used, whereas in basal glands, significant differences were found for both techniques. In conclusion, apoptosis was present in canine endometrial cells during the estrous cycle, but caspase-3 detection showed more significant differences than the TUNEL assay. Furthermore, a high apoptotic index (suggestive of endometrial desquamation) was not detected in the surface epithelium and there was no significant correlation between the apoptotic index in any cell group and serum progesterone concentrations.     

Investigation of individual and group variability in estrous cycle characteristics in female Asian elephants (Elephas maximus) at the Oregon Zoo

Evaluating ovarian cycle activity through longitudinal progestagen monitoring is important for optimizing breeding management of captive elephants and understanding impact of life events (births, deaths, and transfers) on reproductive function. This study summarized serum progestagen profiles for eight Asian mainland elephants (Elephas maximus indicus) and one Bornean elephant (E. maximus borneensis) at the Oregon Zoo over a 20-yr interval, and represents the longest longitudinal dataset evaluated to date. Estrous cycle characteristics were more varied than previously reported for this species, with an overall duration of 12 to 19 wk, luteal phase duration of 4 to 15 wk, and follicular phase duration of 2 to 12 wk. In general, there was more cycle variability across than within individual elephants. Compared with other elephants in the group, the Borneo female exhibited consistently longer cycle lengths, higher progestagen concentrations, and greater cycle variability; however, it is not known if this represents a subspecies or an individual difference. Cycle durations did not appear to change over time or with age, and the first pubertal cycle was similar to subsequent cycles. Variability in duration of the follicular phase was greater than that of the luteal phase. In addition, there was a significant negative relationship between luteal and follicular phase durations, suggesting a possible regulatory role of the follicular phase in maintaining a relatively consistent cycle duration within individuals. Overall, we found these elephants to be highly resilient in that major life events (births, deaths, and changes in herd structure) had minimal effect on cycle dynamics over time. In conclusion, the higher range in cycle phase characteristics is likely because of the larger number of elephants studied and longer duration of longitudinal monitoring, and may be more representative of the captive population as a whole. Furthermore, identification of significant interanimal variability suggests that understanding the complexities of herd reproductive characteristics could facilitate development of more effective institution-specific breeding management strategies.     

Repeatability of 2-wave and 3-wave patterns of ovarian follicular development during the bovine estrous cycle

Characteristics predictive of a 2-wave versus 3-wave pattern of ovarian follicular development during the interovulatory interval (IOI) were examined by ultrasonographic monitoring of 91 IOIs from 31 beef heifers. Repeatability of the wave pattern within individuals and the effects of season and age were determined using a subset of 75 IOIs from 15 heifers examined for multiple IOIs. The 2-wave pattern was detected in 62 of 91 (68%) IOIs, and the 3-wave pattern was detected in 29 of 91 (32%) IOIs. The preponderance of the 2-wave versus 3-wave pattern (P < 0.05) was not influenced by season (P = 0.61) but was even greater in the more mature age group (P = 0.02). The majority of IOIs ≤21 d was of the 2-wave pattern (88%; P < 0.05), whereas the majority of IOIs ≥22 d was of the 3-wave pattern (78%; P < 0.05). The proportion of nonalternating patterns (repeatability) was more than twofold greater than the proportion of alternating patterns (70% vs. 30%; P < 0.01). This relationship was consistent among seasons (P < 0.01) and even more marked in the more mature age group (P = 0.01). Emergence and follicular dominance of Wave 2 were delayed (P < 0.01), and the onset of corpus luteum regression was earlier (P < 0.01) in 2-wave versus 3-wave IOI. In conclusion, the duration of the IOI was predictive of the wave pattern, and the pattern was repeatable within individuals. Factors influencing the period of follicular dominance of Wave 1 in 2-wave versus 3-wave IOI may be responsible for regulating the wave pattern and may be associated with heifer maturity or relative nutritional demand during the postpubertal period. The impact of greater follicular attrition recorded in 3-wave versus 2-wave IOI on ovarian depletion and reproductive senescence is worthy of critical evaluation.     

Characterization of ovarian follicular dynamics in dromedary camels (Camelus dromedarius)

Ovarian follicular dynamics was monitored by transrectal ultrasonography, for a period of 60 to 90 days, and its correlation with plasma estradiol-17β (E2) and progesterone (P4) were studied in seventeen, multiparous, non-lactating, 12 to 20-year-old dromedary camels. The average number of follicles recruited (12.77 ± 0.93) in each wave between animals varied (P < 0.001). The number of follicles recruited during different follicular waves was highly repeatable (0.95) within individual animals. The growth and mature phase periods of the dominant follicle (DF) were 6.10 ± 0.15 and 10.20 ± 0.47 days, respectively with a linear growth rate of 1.17 ± 0.02 mm/day between Day 0 and 10 of the follicular wave. There was an inverse relationship between the diameter of the largest DF and number of follicles (r = −0.95, P < 0.001). The DF development did not regularly alternate between the ovaries and the incidence of codominance was 45%. The mean maximum diameter of DF during its mature phase was 27.30 ± 0.78 mm and oversized follicle was 38.43 ± 1.41 mm. In 73.3% waves, the DF continued its growth for a period of 10.64 ± 1.53 days even after losing its dominance and developed into oversized follicle. The duration of the regression phase of DF and oversized follicle were 24.71 ± 3.79 and 18.50 ± 2.23 days. The mean duration of a complete follicular wave was 47.11 ± 2.94 days with an interwave interval (IWI) of 16.36 ± 0.37 days. The IWI within an individual was repeatable (0.88) and between the animals was variable (P < 0.001). Plasma E2 concentration profiles showed a wave like pattern. The peak plasma E2 concentrations were attained approximately 12 days after beginning of the growth phase, when the largest DF grew to a diameter of 18.7 mm. Plasma concentration of P4 was below 1.0 ng/mL in 85% of waves and above 1.0 ng/mL in 15% of the waves for a period of 3 to 6 days in the absence of spontaneous ovulation. It is concluded that ovarian follicular development and plasma E2 concentrations occurs in a wave like pattern in dromedary camels and the IWI and follicle numbers recruited per wave are variable between the animals and repeatable within an individual animal.     

A stereological study of medium antral follicles during the bovine estrous cycle

Stereological methods were applied to bovine cumulus-oocyte complexes (COCs) in order to characterize them quantitatively during the estrous cycle. COCs from medium (4-8mm) antral follicles with a compact and complete cumulus mass, and with an uniform or a non-visible ooplasm were aspirated from ovaries of Holstein-Friesian cows, fixed in glutaraldehyde, randomly embedded in glycol-methacrylate, and sectioned at 20 microm. The unbiased nucleator principle was used for estimating the mean volumes of complexes, oocytes, cumulus cells, and nuclei of oocytes and cumulus cells. The thickness of the zona pellucida and the relative numerical percentages of the several morphological types (C1-C3) of cumulus cells were also evaluated. The optical disector procedure was used for cumulus cell sampling. Quantitative data show that COCs appear heterogeneous for all studied parameters. From metestrus to proestrus the volumes of COCs and oocytes remained constant, the volumes of oocytes and oocyte nuclei were correlated, the thickness of the outer zona pellucida decreased, and the relative numerical frequency of follicular type C3 cells increased. Results suggest that COCs from distinct estrus stages are structurally different, with type C3 follicular cells gradually differentiating from cell types C1 and C2.     

Expression of VEGF-A,Flt-1, and Flk-1 in the arterial endothelial cells of the uterine broad ligament throughout the estrous cycle

The aim of the present study was to determine the immunoreactivity of vascular endothelial growth factor (VEGF-A) and its two receptors, viz., Flt-1 (fms-like tyrosine kinase) and Flk-1 (fetal liver kinase), on the surface of endothelial cells of the uterine artery and its branches and of the arcuate arteries in the area of the uterine broad ligament during various phases of the estrous cycle in the pig. We also investigated their expression to determine whether this was phase-related. The highest immunoreactivity for VEGF-A was observed in the uterine artery and arcuate arteries at the early luteal phase and in the branches of the uterine artery during the follicular phase of the estrous cycle. The strongest immunostaining intensity of Flt-1 was found in the uterine artery and its branches at the follicular phase and in arcuate arteries at the mid-luteal phase, whereas Flk-1 immunostaining was at its highest in the uterine artery at the mid-luteal phase and in the branches of the uterine artery and arcuate arteries at the follicular phase. Additionally, VEGF-A expression was assessed by semi-quantitative Western blot analysis, which revealed significantly higher levels of VEGF-A protein during the early luteal and the follicular phase of the estrous cycle (P < 0.001). The phase-related differences in the immunoreactivity and expression of VEGF-A and VEGF receptors suggest that these factors are hormone-dependent during the estrous cycle in the pig.     

Plasma follicle stimulating hormone and luteinizing hormone patterns during the estrous cycle of ewes

Fifteen Suffolk ewes were used in three experiments to compare plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) patterns during the estrous cycle and to determine whether FSH levels undergo changes in pulse frequency. Luteinizing hormone changed inversely with progesterone levels whereas FSH and progesterone concentrations revealed no obvious relationship. Unlike LH, FSH levels did not pulsate during the follicular phase. Higher FSH levels were detected on days 1, 6 and 12 and lower levels on days 0, 4 and 16. Coincident preovulatory LH and FSH surges were observed and this was the only time FSH and LH levels appeared to be jointly controlled.     

Ovarian follicular and luteal dynamics in wapiti during the estrous cycle

The reproductive tracts of 13 mature hinds were examined daily by transrectal ultrasonography and blood samples were taken daily from October to January to characterize follicular, luteal, and endocrine dynamics in wapiti during the estrous season. Follicle development occurred in waves characterized by regular, synchronous development of a group of follicles in temporal succession to a surge in serum FSH concentration. The mean interovulatory interval was 21.3 +/- 0.1 d, but was shorter in hinds exhibiting two follicular waves than in hinds exhibiting three and four waves (P < 0.05). The interwave interval was similar among waves in two-wave cycles and the first wave of three-wave cycles. All other interwave intervals in three- and four-wave cycles were shorter (P < 0.05). The maximum diameter of the dominant follicle of the first wave was similar among two-, three-, and four-wave cycles. For all other waves in three- and four-wave cycles, the maximum diameter was smaller (P < 0.05). Corpus luteum diameter and plasma progesterone concentrations were similar between two- and three-wave cycles, but the luteal phase was longer (P < 0.05) in four-wave cycles. The dominant follicle emerged at a diameter of 4 mm at 0.4 +/- 0.1 and 0.8 +/- 0.1 d before the largest and second largest subordinate follicles, respectively. The follicle destined to become dominant was larger (P < 0.05) than the largest subordinate follicle one day after emergence, which coincided with the first significant decrease in serum FSH concentration. We concluded that the estrous cycle in wapiti is characterized by two, three, or four waves of follicular development (each preceded by a surge in circulating FSH), that there is a positive relationship between the number of waves and the duration of the cycle, and an inverse relationship between the number of waves and the magnitude of follicular dominance (diameter and duration of the dominant follicle).     

Lymphocyte number and distribution in the rat uterine epithelium during estrous cycle and early pregnancy

Summary The number of intraepithelial lymphocytes (IEL) in the luminal and glandular epithelium of the uterus of virgin rats was analysed in diestrus, proestrus and estrus, and in nulliparous rats on days 5, 7 and 9 of pregnancy. IEL number was calculated either with respect to the number of epithelial cells or to the length of epithelium section. It was found that in diestrus, the number of IEL was, on average, 3.7 per 100 luminal epithelial cells or 6.7 per 1 mm of epithelium section, whereas in proestrus, it decreased to 0.9 and 1.2 IEL, respectively. On day 5 of pregnancy (before implantation) the number of IEL decreased further to 0.45 per 100 luminal epithelial cells or 0.9 per 1 mm of epithelium. On days 7 and 9 of pregnancy, IEL number further decreased in implantation sites, whereas in interimplantation sites it remained at the level calculated for day 5 of pregnancy. The population of uterine IEL consisted of small (82–99%) and large (1–18%) lymphocytes. In all stages of the estrous cycle, IEL occurred with a frequency of 68–87% in the basal region, 8–20% in the middle region and 4–12% in the apical region of the luminal epithelium width.     

Systemic and intraovarian effects of corpus luteum on follicular dynamics during estrous cycle in hair breed sheep

The present study aimed to determine systemic and local effects of corpora lutea (CL), on follicular dynamics throughout the estrous cycle. All follicles >or=2 mm and CL were assessed by daily transrectal ultrasonography in 12 West African ewes. Blood samples were collected to determine plasma concentration of progesterone. Fifteen estrous cycles were evaluated with a mean interovulatory interval of 16.8+/-0.2 days. Two (13.3%), 10 (66.7%) and 3 (20%) of the estrous cycles had 2, 3 and 4 waves of follicular development, respectively. In sheep with three waves of follicular development, both the length of growing phase and the growth rate of dominant follicles from midluteal wave II were diminished (3.4+/-0.3 days, P<0.0001, and 0.4+/-0.1 mm/day, P<0.01, respectively) when compared to follicles from early luteal phase (wave I, 4.1+/-0.2 days, and 0.7+/-0.1 mm/day) or late luteal phase (wave III, 6.3+/-0.4 mm and 0.6+/-0.1 mm/day). The diameter of the dominant follicle was smaller during the midluteal phase (3.9+/-0.1 mm, P<0.0001) than in the early and late luteal phase (5.0+/-0.2 and 5.7+/-0.2 mm; respectively). The effect of the dominant follicle was less during midluteal phase, because number of accompanying smaller follicles was fewer (P<0.01) in waves I and III (6.3+/-0.9 compared with 3.4+/-0.8 and 2.3+/-0.7). The number of follicles was also different between ovaries that had CL and those that did not. The total number of large follicles during the luteal phase was less in ovaries with CL (0.9+/-0.5 compared with 2.7+/-0.3; P<0.01), as was the mean daily number of both large (0.1+/-0.02 compared with 0.2+/-0.02; P<0.001) and total number of follicles >or=2 mm (2.5+/-0.1 compared with 3.3+/-0.1; P<0.01). Current results indicate that the presence of a functional CL may exert both systemic and local effects on the population of follicles, affecting the dominance exerted by large follicles.     

Diffusion barriers in the vaginal epithelium during the estrous cycle in guinea pigs

Summary In the present study the permeability barriers of the multilayered vaginal epithelium were examined using tracer perfusion techniques, freeze-fracture and thin sectioning. During diestrus and proestrus the upper layers of mucified epithelial cells exhibit tight-junctional belts, which restrict tracer molecules such as lanthanum and horseradish peroxidase. When the highly mucified cells begin to degenerate toward the end of proestrus the underlying epithelium is already keratinized as typical for estrus. The keratinized epithelial cells have a tight-junctional network that joins the basal plasma membranes with the apical membranes of subjacent cells and blocks paracellular diffusion of the tracer molecules. During conversion of the cornified epithelium to a mucified epithelium in metestrus the intercellular space of the epithelium is stained by tracer molecules even though tight-junctional belts can be observed.These results indicate that during cyclic changes of the vaginal epithelium tight junctions can, in general, be considered for the restriction of paracellular diffusion. In metestrus, however, junctions become functionally leaky although they remain morphologically intact.Intercellular lipids, which are normally common in cornified epithelia, are extremely rare and cannot constitute an effective barrier to diffusion in the vagina of the guinea pig. The significance of a strategy that bases the regulation of the permeability on tight junctions rather than on intercellular lipids is discussed.     

A collaboration of aquaporins handles water transport in relation to the estrous cycle in the bitch uterus

Fluid movement through uterine cell membranes is crucial, as it can modulate the tissue imbibition pattern in the different phases of the estrous cycle. To gain insight into the mechanisms underlying steroid-controlled water handling, the presence and distribution of aquaporins (AQPs), integral membrane channel proteins permitting rapid passive water movement, was explored in bitch uterine tissues. Immunohistochemistry and Western immunoblot analysis were used to study the presence of AQP1, AQP2, and AQP5 in the layers of the bitch uterine wall during the different estrous phases. Presence of endothelial nitric oxide-generating enzyme NO synthase (NOS3) was also investigated, as it is known that the vasodilator NOS3 might be involved in the development of uterine edema. The results demonstrated the following: (1) AQP1, AQP2, and AQP5 were present in the uterus of cycling bitches. (2) AQP1 was localized within uterine mesometrial, myometrial, and endometrial blood vessels and in the circular and longitudinal layers of myometrium. AQP1 localization and expression were unaffected by the estrous cycle. (3) The estrogenic milieu was probably at the basis of AQP2 expression in the glandular and luminal epithelium of the endometrium. (4) AQP5 water channels were present in the apical plasma membrane of uterine epithelial cells in coincidence with plasma progesterone increase. (5) NOS3 was localized in the myometrial and epithelial tissues as well as in blood vessels indicating a contribution of this vasoactive peptide to the uterine imbibition processes. Thus, we can hypothesize that a functional and distinctive collaboration exists among diverse AQPs in water handling during the different functional uterine phases.