| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Eutheria Foundation, Cross Plains, Wisconsin 53528
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
conceptus, embryo, endometrial vascular perfusion, endometrium, mares, pregnancy, uterine contractions, uterus
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
The propulsive force for embryo mobility is uterine contraction, as indicated by similar temporal changes in uterine contractility and vesicle mobility [2, 5], reduced mobility after experimental inhibition of contractions [6], and reduced contractions in a uterine horn into which vesicle entry is prevented by experimental cornual ligation [2]. The mobility favors physiologic exchange between the relatively small conceptus and large uterus [4]. In this regard, results of confinement of the conceptus to one uterine horn indicate that the conceptus locally stimulates uterine turgidity and edema as well as contractility [2] and that movement throughout the uterus is needed to prevent the bilaterally active uterine luteolytic mechanism [2, 7].
The cessation of mobility is called fixation, and this occurs on Days 15–17 [8]. The site of fixation is at a flexure in the caudal segment of one of the uterine horns, without regard to the side of ovulation. It has been postulated that fixation occurs at the flexure because it is the greatest impediment to continued mobility of the growing vesicle [8, 9]. A decrease in uterine diameter because of increasing turgidity from the stimulation of the mobile vesicle further contributes to fixation in the most restricted area.
The effects of the mobile equine conceptus on vascular perfusion of the endometrium are unknown. Transrectal Doppler ultrasonography recently was used for noninvasive study of the blood flow in the uterine arteries during early equine pregnancy [10]. Time-averaged maximum velocity (TAMV) was higher, and resistance index (RI) was lower, in the arteries of pregnant mares compared to those of nonpregnant mares beginning on Day 11. From Day 15 to Day 29 of pregnancy, TAMV was higher, and RI was lower, in the uterine artery ipsilateral to the conceptus compared to the opposite artery. The authors [10] indicated that an increase in TAMV represented greater blood flow in the arteries and that a decrease in RI represented reduced resistance to blood flow in the vasculature distal to the site of assessment. It was not determined whether conceptus fixation had occurred in at least some mares by the day that a difference in blood flow was detected between the ipsilateral and the contralateral arteries. Thus, to our knowledge, a local effect of the embryonic vesicle on the uterine vasculature in association with mobility of the conceptus has not been demonstrated.
The purpose of the present study was to test the hypothesis that transient changes in vascular perfusion of the endometrium occur in association with changes in location of the conceptus, as indicated by greater perfusion in the uterine horn containing the conceptus compared to the opposite horn during the maximum mobility phase. In addition, comparisons in vascularity were made between horns that were ipsilateral and contralateral to the corpus luteum on Days 1–8 in bred mares in which an embryo was later detected versus those in which an embryo was not detected and between the horn of embryo fixation and the opposite horn. The time of an effect of the conceptus on vascularity of the endometrium and the time of an effect on uterine contractility were compared for a tentative indication of whether a similar conceptus-generated stimulus is involved in the two uterine responses.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Animals were handled in accordance with the Guide for the Care and Use of Animals in Agricultural Research. Pony mares of mixed breeds (age, 6–15 yr; weight, 290–430 kg) were used during the last half of the ovulatory season. The mares had free access to grass hay, water, and trace-mineralized salt. Mares with docile temperament and no apparent abnormalities of the reproductive tract [11] were selected. The selected mares were scanned daily by ultrasound and bred naturally when a preovulatory follicle reached 35 mm and every other day thereafter until ovulation. Mares with twin embryos were not used.
Ultrasonography
A pulse-wave ultrasound scanner with both B-mode (gray scale) and color Doppler functions was used (Aloka SSD-2000; Aloka America, Wallingford, CT). Uterine contractions were assessed in B-mode using a finger-mounted, 7.5-MHz, convex transducer (UST-995-7.5). The transducer was placed transrectally over the middle segment of each uterine horn in a longitudinal plane. The extent of contractility was scored as described for the uterine body [5]. The scores ranged from 1 to 4, indicating no, minimal, intermediate, and maximal activity, respectively.
Vascular perfusion of the endometrium was evaluated using the color Doppler flow-mode function and a 7.5-MHz, linear-array transducer (UST-5821-7.5) with a beam-field width of 60 mm. The following settings were used: velocity range limit, 9.96 cm/sec; flow filter, 4; and frame rate, 6 Hz. The transducer was placed over a cross-section of the middle segment of each uterine horn. The vascularity or vascular perfusion was estimated subjectively by scoring the extent of colored areas in the endometrium during real-time cross-sectioning of the middle segment of each horn during a continuous span of 1 min; because of animal and uterine movements, multiple cross-sections were viewed. Only the colored areas that appeared to be within the endometrium were considered (Fig. 1). The scores ranged from 1 to 4, indicting no, minimal, intermediate, and maximal involvement, respectively. The 1-min scan was recorded on digital videocassettes (Mini-DV).
|
Vascular perfusion of the endometrium was assessed objectively by off-line measurement of the number of colored pixels as an indicator of blood-flow area. Three still images from cross-sections of the middle segment of each horn were used for determination of the number of colored pixels, and the average was used in the analyses. The images were captured from the videocassettes using Adobe Premiere Pro 1.5 software (TIFF format; Adobe Systems, San Jose, CA). Colored spots or pixel aggregates were selected from the images, extracted, and saved (GIF format) using Adobe PhotoShop 5.5 software (Adobe Systems). ImageJ 1.31v software (National Institutes of Health, Bethesda, MD) was used for calculation of the total number of colored pixels for each GIF-format image.
In addition to color Doppler evaluation of the endometrium, spectral Doppler scans were made of the arteries at the mesometrial attachment. These vessels were outside the uterine horn but within 1 cm of the uterine surface. For the spectral mode, the velocity range limit was set at 19.9 cm/ sec and the Doppler filter at 100 Hz. Spectral waveforms were generated three times for three cardiac cycles by placement of a gate (width, 2 mm) over the most intensely colored area in the color-flow/B-mode image (Fig. 1). One cardiac cycle was arbitrarily chosen from each of the three scans, and the average was used for measurement of TAMV and pulsatility index (PI) using preset functions in the ultrasound scanner. The determination, meaning, and interpretation of TAMV and PI are given in a discussion of blood-flow velocity in the uterine arteries of women [12]. An increase in TAMV and a decrease in PI are reported to indicate increased vascular perfusion of tissues distal to the point of examination of the artery.
Experiment 1
Twenty-four naturally bred mares were examined daily beginning between 1300 and 1800 h with the duplex B-mode/color-mode scanner from Day 1 (Day 0 = ovulation) until Day 16. Examination procedures and data analyses were divided into Days 1–8 and Days 9–16; Day 9 was the earliest day of detection of an embryonic vesicle. On Days 1–8, comparisons were made between the uterine horns that were ipsilateral and contralateral to the corpus luteum. Comparisons were then made between mares in which an embryo was not detected by Day 12 or thereafter (n = 8) and pregnant (n = 16) mares using the average between horns for each mare. On Days 9–16, comparisons were made similarly except that the uterine horn containing the embryonic vesicle and the opposite horn were used. Assignment to the pregnant group could not be made until an embryonic vesicle was detected. Therefore, the number of pregnant mares per day increased over Day 9 (n = 3 mares), Day 10 (n = 11 mares), Day 11 (n = 15 mares), and Days 12–16 (n = 16 mares/day). On each day, the mobility of the embryonic vesicle was monitored every 5 min, as described previously [3], until the vesicle remained in the same uterine horn for five consecutive examinations (i.e., for 20 min). Uterine contractility was scored in B-mode, and the 1-min continuous scanning of the middle segment of each uterine horn was done in color-mode for endometrial vascularity scoring. The color Doppler was set on spectral mode for measuring TAMV and PI at the mesometrial attachment.
Experiment 2
Fourteen mares (different from those used in experiment 1) with an embryonic vesicle on Day 11 or Day 12 were used. A 2-h mobility trial was done on Day 13, beginning between 1730 and 2400 h. The location of the vesicle in one of nine uterine segments of similar length (three for each horn and the body) was recorded every 5 min [3]. Seven of the 14 mares were used to evaluate objectively the reliability of the subjective scoring system that had been used by operator 1 in experiment 1 to estimate the extent of vascular perfusion of the endometrium. In these seven mares, the embryonic vesicle was not in the middle segment of the horn at the time of scoring, so bias associated with the presence of a vesicle was avoided. Operator 2 isolated on videocassette the 1-min continuous scanning of the middle segment of each uterine horn and assigned an identification number to each of the 14 segments. The segments were randomized by operator 2, and an endometrial color Doppler score was made by operator 1 without knowledge of the embryo location and mare identity. In addition, operator 1 selected three images from each segment that seemed to be representative of the extent of colored Doppler areas within the endometrium. These three images of each uterine segment (n = 42 total images) were given an identification and randomized by operator 2. Each randomized endometrial image was evaluated by operator 1 for the number of discrete, colored spots or pixel aggregates and total number of colored pixels.
Initial information regarding the exposure time needed by the embryonic vesicle to stimulate endometrial vascular perfusion and uterine contractility was obtained by scoring the middle segment of each horn for vascularity and contractility on Day 13 in all 14 mares. A scoring session was done every 20 min for 2 h for a total of eight examinations per mare. In the same mares over the same 2-h period, the location of the embryonic vesicle in one of the nine uterine segments had been recorded every 5 min, as described above. Therefore, retrospective examination of these records made it possible to select mares in which the vesicle entered a horn and remained there for a prolonged period, encompassing at least two scoring sessions (i.e., 20 min). Endometrial vascularity and uterine contractility scores for the uterine horn containing the embryo in these mares were taken from three consecutive scoring sessions: session 1, before the embryo entered the horn; session 2, after the embryo had entered; and session 3, with the embryo still in the horn. Complete data involving all three scoring sessions were available for 10 mares. Comparison of scores from sessions 2 and 3 with those from session 1 thus provided some indication of how vascularity and contractility had been affected by the presence of the embryo for various time intervals.
After Day 13, mobility trials were done each day in all 14 mares and continued until the day that no changes occurred among segments during 2 h. The absence of a location change in 2 h was defined as fixation, as reported previously [8]. Fixation was positively confirmed in all mares during another mobility trial on the following day. Daily determinations for the uterine contractions and color Doppler end points (vascularity score, TAMV, and PI) were done from Day 13 until 6 days after fixation for all 14 mares. Data were centralized to the day of fixation, including the horn of the future fixation, extending from 3 days before fixation to 6 days after fixation. In addition to the vascularity assessments of the middle segment of the uterine horns, the vascularity of the endometrium around the vesicle after fixation was assessed by including the vesicle in the continuous, 1-min cross-sectioning of the endometrium. End points for the middle segment of each uterine horn were compared between the horn of fixation (or future fixation) and the opposite horn. In addition, endometrial vascularity comparisons included the group with data from around the vesicle beginning on the day of fixation. Data were analyzed for 3 days before fixation and separately from the day of fixation to 6 days after fixation.
Statistical Analyses
Data were examined for normality with the Kolmogorov-Smirnov test. When the normality test was significant (P < 0.05), data were transformed to natural logarithms. The scores for Doppler vascularity and uterine contractility were considered to be nonparametric and were analyzed by a ranking procedure (Kruskal-Wallis test). The ranked scores for contractility and vascularity and the other Doppler end points were analyzed by the mixed procedure of SAS (version 8.2; SAS Institute, Inc., Cary, NC) to determine the main effects and the interaction using a repeated statement to account for autocorrelation between sequential measurements. Paired and unpaired Student t-tests were used to locate the differences both within and between horns and between pregnant and nonpregnant mares when significant main effects or an interaction were obtained. Discrete data were analyzed by Student t-tests. The proportion of mares for each day in experiment 1 with adequate Doppler color signals for measurement of TAMV and PI were compared between days with chi-square tests. A probability of P 
0.05 indicated a significant difference, and probabilities between P > 0.05 and P < 0.1 indicated a difference approaching significance. All values, unless otherwise stated, are ± SEM.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
The endometrial vascularity scores and contractility scores on Days 1–8 and Days 9–16 and the results of statistical analyses are shown in Figure 2. On Days 1–8, no significant differences were observed for endometrial vascularity. However, contractility progressively increased between Day 2 or Day 3 and Day 8. On Days 9–16, endometrial vascularity increased after Day 11 in the pregnant group, with a more pronounced increase in the horn with the embryo than in the opposite horn; vascularity did not change in the group in which an embryo was not detected. Uterine contractility in the pregnant group increased similarly in both uterine horns between Day 10 and Day 12.
|
The color Doppler signals within the endometrium were inadequate for the production of spectral waveforms in both groups of mares throughout the experiment. Color Doppler signals for vessels in the mesometrial attachment were adequate for spectral analyses in both horns of some mares in each group during Days 1–8; the frequency of an adequate signal initially increased and then decreased (Fig. 3). During Days 9–16, the frequency of adequate signals increased in both uterine horns but only in the pregnant mares. Spectral analyses for TAMV and PI were done for the two horns in pregnant mares with adequate signals on Days 10–16; a significant day effect for both end points reflected an increase over days for TAMV and a decrease for PI (Fig. 4).
|
|
Experiment 2
During the 2-h mobility trials on Day 13, the embryonic vesicle moved from one horn to the other 1.0 ± 0.2 times per trial and between a horn and the body, or vice versa, 3.9 ± 0.5 times. The mean day of fixation was Day 15.8 ± 0.2 (range, Days 15–17). The objective vascularity scores from the real-time video clips were greater (2.1 ± 0.2 vs. 1.7 ± 0.2, P < 0.02), and the subjective vascularity scores also were greater (1.9 ± 0.2 vs. 1.5 ± 0.1, P < 0.02), in the horn with the embryo versus the opposite horn. The number of colored spots in images of endometrial cross-sections in the objective evaluations were greater (P < 0.04) in the horn with the embryo than in the opposite horn and approached significance (P < 0.1) for the total number of colored pixels per endometrial image (Table 1). The continued presence of the vesicle in the same horn for an average of 7 min stimulated an increase (P < 0.004) in vascularity or perfusion of the endometrium of the middle segment of the horn (Table 2); a corresponding increase in contractility approached significance (P < 0.1).
|
|
The endometrial vascularity scores and number of colored pixels in the endometrium, TAMV and PI of the mesometrial attachment, and uterine contractility scores before and after fixation are shown in Figure 5. From 1 to 3 days before fixation, the day effect was significant (P < 0.05) for all end points except contractility. The group effect and interaction were not significant for any end point before fixation. The statistical results are shown for the days of and days after fixation. Endometrial vascularity and number of colored endometrial pixels were progressively higher in the following sequence: horn without the vesicle, horn with the vesicle, and area of endometrium surrounding the fixed vesicle. The TAMV was higher, and the PI was lower, in the horn with the vesicle on most days after fixation.
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
The present results strongly support the hypothesis that changes in vascular perfusion of the endometrium occur locally, in association with location changes of the embryonic vesicle during the mobility phase. Higher vascularity scores were found for the horn with the embryo at the time of examination compared to the opposite horn throughout Days 12–15. The scores in the embryo-containing horn increased between Day 10 and Day 12. Although the scores were higher in the embryo-containing horn than in the opposite horn, scores were higher in both horns of pregnant mares compared with mares in which an embryo was not detected by Day 12 or thereafter. To our knowledge, local and transient vascular perfusion of the endometrium as the mobile equine embryonic vesicle traverses the uterus is a novel finding. At a comparable stage of pregnancy in cattle and sheep, the conceptus expands along the length of the horn on the side of ovulation and does not involve the opposite horn. These species differences appear to be associated with a unilateral uteroluteolytic pathway in cattle and sheep and a systemic pathway in horses [13]. Blood flow increases in the uterine artery ipsilateral, but not contralateral, to the conceptus between Day 13 and Day 15 in sheep [14] and between Day 15 and Day 17 in cattle [15]. Swine have embryos in both horns, and blood flow transiently increases in both uterine arteries 12 and 13 days after insemination. However, when embryos are experimentally confined to one horn, the blood flow increases only on that side [16]; furthermore, blood flow to uterine segments containing a conceptus is greater than that for segments that do not contain a conceptus [17]. The stimulation of the local uterine vascular system by the embryos that has been reported previously for cattle, sheep, and swine and in the present study for ponies occurs at approximately the time the embryos are involved in luteal maintenance. The present study in mares demonstrated the rapid, locally sensitive nature of the phenomenon.
The mechanism involved in local stimulation of uterine vascularity by the conceptus in these species has not been clarified. One consideration is that the early conceptus alters endometrial vascularity by the production of vascular stimulants. In this regard, estrogens stimulate increased uterine blood flow in the sow, cow, and ewe [18]. In vitro studies have shown that Day 12 porcine embryos [19] and Day 16 bovine embryos [20, 21] produce estrogens. The trophoblast of the equine embryonic vesicle that is involved in steroid conversion has been reported as early as Day 8 [22] and Day 13 [23]. A marked in vitro production of estrogen by the equine conceptus occurs as early as Day 12 [24, 25]. Thus, estrogen has vasostimulatory properties, and production by the conceptus occurs on the days that the conceptus of horses, swine, and cattle is stimulating local uterine vascularity. In this regard, a recent study in mares found that PI values were higher for the uterine artery during both estrus and diestrus in estrogen-treated mares compared with nontreated mares [26]. The blastocysts of many species secrete a variety of prostaglandins, and it has been proposed that conceptus prostaglandins stimulate increases in uterine blood flow [27]. Equine embryos secrete prostaglandins F2
and E2 [28–30]. However, it is not known whether prostaglandins, steroids, or other factors account for the increased endometrial vascular perfusion described in the present study. Furthermore, physical stimulation unrelated to direct production of a vasoactive substance by the conceptus cannot be ruled out.
After completion of experiment 1, concern existed that the scoring of endometrial vascularity may have been biased, because the operator was aware of the location of the embryonic vesicle. Therefore, an objective reliability trial was incorporated into experiment 2 on Day 13, wherein the operator scored the endometrial vascularity without knowledge of embryo location or animal identity. Vascularity scores were higher in the horn that contained the embryo for both the objective and subjective scoring systems, indicating that the subjective scoring system used in experiment 1 was useful. Another indication of the reliability of the scoring system was the similar conclusions between scoring vascularity and counting the number of colored spots or pixels in images of endometrial cross-sections in the reliability trial and in comparisons of the horn of fixation and the opposite horn. We concluded that the subjective scoring of endometrial vascularity was a useful and convenient approach.
For the spectral Doppler assessments of the arteries of the mesometrial attachment, the TAMV and PI increased and decreased, respectively, over Days 10–16 of pregnancy; no difference was observed between horns, as indicated by the absence of a group effect and a day-by-group interaction. Results for both end points indicate increased vascular perfusion of the uterus distal to the site of assessment. Even though the highest Doppler shift was assessed, based on selection of the brightest colored area, true blood velocities likely were not expressed by the TAMV values. The angle of insonation was unknown. However, the relative TAMV values are taken as meaningful expressions of vascular perfusion distal to the assessment. It is unlikely that the angle of arterial insonation would have been different between the horns with and without the embryo. In addition, volume of blood flow delivered by the arteries could not be determined, because the diameters of arteries were unknown.
The TAMV and PI end points may have been less sensitive than the scoring of the vascular perfusion of the endometrium and, therefore, did not detect the localized difference between horns during the mobility phase. In this regard, a previous spectral analysis color Doppler study in mares was done for the main uterine arteries [10]: Greater increases in blood flow were found in pregnant mares than in nonpregnant mares after Day 11, but no difference was found between the embryo-containing horn and the opposite horn until Day 15. The frequency of the occurrence of fixation by Day 15 was not determined. In the present study, postfixation endometrial vascularity and number of colored pixels were greatest in the endometrium surrounding the fixed embryonic vesicle and were greater in the middle segment of the horn of fixation than in the opposite horn. No differences were observed before fixation between the horn of future fixation and the opposite horn, indicating that the extent of prefixation vascular perfusion did not play a role in selection of the horn of fixation. The postfixation results for the arteries in the mesometrial attachment and the greater TAMV on the side of fixation are consistent with the previously reported TAMV results for the uterine artery of the horn containing the embryo beginning on Day 15 [10].
The similarity regarding endometrial vascularity between mares in which an embryo was not detected and pregnant mares until the increases in both horns in pregnant mares after Day 11 is consistent with the previous studies of blood flow in the uterine arteries [10]. Furthermore, no differences were observed between horns ipsilateral and contralateral to the corpus luteum in the mares in which an embryo was not detected, as reported previously for nonbred mares [30]. A unimodal increase and decrease in the frequency of adequate Doppler signals for spectral analyses of arteries in the mesometrial attachment of mares with no embryo detected occurred between Day 1 and Day 11; maximum values occurred on approximately Days 4–6. This result likely reflects the transient lower PI reported for the uterine artery on Days 4–6 [31]. In the present study, pregnant mares showed a similar unimodal profile except that number of mesometrial attachments with adequate spectral signals increased again after Day 8, resulting in a significant difference by Day 11 between pregnant mares and mares with no detected embryo. The reason for the transient increased incidence of Doppler spectral displays on Days 4–6 in both groups of mares is not known. In this regard, the presence or absence of an embryo on Days 1– 8 cannot be considered, because embryonic loss could have occurred in the group with no embryo detected by Day 12. To our knowledge, a transient increase in estradiol on Days 4–6 has not been reported; however, some interovulatory intervals have increased follicular activity at this time [32]. Furthermore, early, short-term increases in uterine tone [33] and in estrous-like uterine echotexture [34] have been reported during early diestrus. Further study will be needed to determine if the apparent transient changes in endometrial perfusion, uterine tone, and endometrial echotexture in early diestrus are interrelated and whether estrogens or other factors are involved.
Uterine contractions are active in mares during diestrus, whereas the uterus of other farm species is quiescent [1]. An increase in contractions in the uterine horns during approximately Day 3 to Day 8 in pregnant mares as well as in the mares with no embryo detected was shown in the present study. The further. and more profound, increase in contractility concomitant with increased mobility of the conceptus confirms previous findings [5, 9]. A noteworthy difference in contractility and endometrial perfusion in the present study was the absence of a detected difference between the embryo-containing horn and the opposite horn for contractions versus the greater vascular perfusion in the embryo-containing horn. This result suggests that different factors may be involved in the two phenomena or that endometrial perfusion abates more rapidly than uterine contractions after the conceptus departs from a horn.
In summary, color Doppler ultrasonography was used to study the relationships of endometrial vascular perfusion and uterine blood flow to the mobility of the embryonic vesicle during early pregnancy in mares. Endometrial vascularity scores were similar between mares with no embryo detected and pregnant mares until an increase in scores occurred in both horns of pregnant mares by Day 12. In the pregnant mares, the scores were higher in the embryo-containing horn than in the opposite horn from Day 12 to 6 days after fixation. Spectral analyses of arteries in the mesometrial attachment indicated a gradual increase in TAMV in both horns during the mobility phase and a greater velocity in the horn of fixation than in the opposite horn beginning on the day of fixation.
|
ACKNOWLEDGMENTS |
|---|
|
FOOTNOTES |
|---|
2 Correspondence: O.J. Ginther, Animal Health and Biomedical Sciences, 1656 Linden Drive, University of Wisconsin, Madison, WI 53706. FAX: 608 262 7420; ginther{at}svm.vetmed.wisc.edu
Received: 17 September 2004.
First decision: 5 October 2004.
Accepted: 24 November 2004.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
production by equine conceptuses and concentrations in conceptus fluids and uterine flushings recovered from early pregnant and diestrous mares. Reproduction 2002 123:261-268[Abstract]This article has been cited by other articles:
|
|
 |
|
  J C Ferreira, E L Gastal, and O J Ginther Uterine blood flow and perfusion in mares with uterine cysts: effect of the size of the cystic area and age Reproduction, April 1, 2008; 135(4): 541 - 550. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L.A. Silva and O.J. Ginther An Early Endometrial Vascular Indicator of Completed Orientation of the Embryo and the Role of Dorsal Endometrial Encroachment in Mares Biol Reprod, February 1, 2006; 74(2): 337 - 343. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
