Intraovarian spatial and vascular harmony between follicles and corpus luteum in monovulatory heifers, mares, and women

The recipient metabolome explains the asymmetric ovarian impact on fetal sex development after embryo transfer in cattle

In cattle, lateral asymmetry affects ovarian function and embryonic sex, but the underlying molecular mechanisms remain unknown. The plasma metabolome of recipients serves to predict pregnancy after embryo transfer (ET). Thus, the aim of this study was to investigate whether the plasma metabolome exhibits distinct lateral patterns according to the sex of the fetus carried by the recipient and the active ovary side (AOS), i.e., the right ovary (RO) or the left ovary (LO). We analyzed the plasma of synchronized recipients by 1H+NMR on day 0 (estrus, n = 366) and day 7 (hours prior to ET; n = 367). Thereafter, a subset of samples from recipients that calved female (n = 50) or male (n = 69) was used to test the effects of embryonic sex and laterality on pregnancy establishment. Within the RO, the sex ratio of pregnancies carried was biased toward males. Significant differences (P < 0.05) in metabolite levels were evaluated based on the day of blood sample collection (days 0, 7 and day 7/day 0 ratio) using mixed generalized models for metabolite concentration. The most striking differences in metabolite concentrations were associated with the RO, both obtained by multivariate (OPLS-DA) and univariate (mixed generalized) analyses, mainly with metabolites measured on day 0. The metabolites consistently identified through the OPLS-DA with a higher variable importance in projection score, which allowed for discrimination between male fetus- and female fetus-carrying recipients, were hippuric acid, l-phenylalanine, and propionic acid. The concentrations of hydroxyisobutyric acid, propionic acid, l-lysine, methylhistidine, and hippuric acid were lowest when male fetuses were carried, in particular when the RO acted as AOS. No pathways were significantly regulated according to the AOS. In contrast, six pathways were found enriched for calf sex in the day 0 dataset, three for day 7, and nine for day 7/day 0 ratio. However, when the AOS was the right, 20 pathways were regulated on day 0, 8 on day 7, and 13 within the day 7/day 0 ratio, most of which were related to amino acid metabolism, with phenylalanine, tyrosine, and tryptophan biosynthesis and phenylalanine metabolism pathways being identified throughout. Our study shows that certain metabolites in the recipient plasma are influenced by the AOS and can predict the likelihood of carrying male or female embryos to term, suggesting that maternal metabolism prior to or at the time of ET could favor the implantation and/or development of either male or female embryos.

The vascular endothelial growth factor (VEGF) system as a key regulator of ovarian follicle angiogenesis and growth

The vascular endothelial growth factor-A (VEGFA) system is a complex set of proteins, with multiple isoforms and receptors, including both angiogenic (VEGFxxx, VEGFR2) and antiangiogenic members (VEGFxxxb, VEGFR1 and soluble forms of VEGFR). The members of the VEGF system affect the proliferation, survival, and migration of endothelial and nonendothelial cells and are involved in the regulation of follicular angiogenesis and development. The production of VEGF by secondary follicles stimulates preantral follicular development by directly affecting follicular cells and promoting the acquisition of the follicular vasculature and downstream antrum formation. Additionally, the pattern of expression of the components of the VEGF system may provide a proangiogenic milieu capable of triggering angiogenesis and stimulating follicular cells to promote antral follicle growth, whereas, during atresia, this milieu becomes antiangiogenic and blocks follicular development.

Current Animal Model Systems for Ovarian Aging Research

Ovarian aging leads to menopause, loss of fertility and other disorders in multiple organs, which brings great distress to women. For ethical reasons, it is impossible to use humans as direct study subjects for aging research. Therefore, biomedical researchers have employed different non-human organisms to study ovarian aging, including worms, fruit flies, fishes, amphibians, birds, mice, rats, cavies, rabbits, pigs, sheep, cows, horses, monkeys, and apes. Because each of these model organisms has its own features, multiple factors, such as size, anatomical structure, cost, ease of operation, fertility, generation time, lifespan, and gene heredity, should be carefully considered when selecting a model system to study ovarian aging. An appropriate model organism would help researchers explore the risk factors and elucidate molecular mechanisms underlying declined ovarian functions, which might be conducive to preventing or delaying the ovarian aging process. This article will offer an overview on several currently available and commonly used model organisms for ovarian aging research by comparing their pros and cons. In doing so, we hope to provide useful information for ovarian aging researchers.

Fertility restoration of racing mare with persistent corpus luteum

Background and Aim:

Persistent corpus luteum (PCL) causes anestrus in mares. This study aimed to determine the effect of intrauterine prostaglandin F2α (PGF2α) treatment on PCL of racing mares to restore fertility.

Materials and Methods:

Twelve racing mares suspected with PCL were diagnosed using transrectal palpation and confirmed by serum progesterone (P4) concentration measurement. PGF2α was infused intrauterine, followed by serum collection at 24, 48, and 72 h after. Estrous symptoms were monitored, and mating was conducted on day 3 of estrus with an earlier injection of 8.4 μg gonadotropin-releasing hormone twice a day. Transrectal palpation was performed on days 21-30 to observe the corpus luteum. Pregnancy diagnosis was performed rectally on 40-45 days post-mating and confirmed using Doppler ultrasound scanning.

Results:

Eleven of the 12 mares had PCL. There was a dramatic reduction in the P4 concentration following PGF2α treatment of mares with PCL. All mares exhibited estrus 2.6±0.55 days post-treatment with a P4 concentration of 0.12±0.12 ng/mL. Rectal palpation and P4 concentration on 21-30 days after estrous onset showed that all mares were ovulating. The evaluation of P4 concentration on days 40-45 post-mating showed that all mares were still in the luteal phase. However, the pregnancy rate was only 54.5% based on rectal palpation and Doppler ultrasound scanning.

Conclusion:

Treatment of PCL in racing mares with an intrauterine infusion of PGF2α restored the estrous cycle and induced ovulation and pregnancy.

Equine embryo mobility. A game changer

The equine embryo or embryonic vesicle on Days 11-15 postovulation travels with profound physiologic purpose throughout the lumen of the two uterine horns and uterine body making 12 to 22 trips between the two uterine horns per day. This phenomenon is termed embryo mobility and is unique in equids among domestic species. Apparently, the embryo first reaches the uterine body on Days 8 or 9. Mobility increases to maximum by Days 11 or 12 and continues until an abrupt cessation of mobility (fixation) on Days 15 (ponies) or 16 (horses and donkeys). The embryo is propelled by uterine contractions in response to the production of apparently both PGF2α and PGE2 by both the embryo and uterus. An increase in endometrial vascular perfusion accompanies the mobile embryo as it moves from horn to horn. Restricting the embryo to one uterine horn by a ligature has indicated that specific roles of the traveling embryo include the stimulation of uterine contractions, tone, vascularity, and edema and to curtail the production of the luteolysin (PGF2α) by the uterus. The increase in uterine tone, decrease in diameter of the uterine horns, and a flexure in the caudal portion of each horn collaborate in the selection of a horn of fixation. Embryo mobility is a game changer that has solved several long-time enigmas in mare reproduction and has provided a needed and effective finger/thumb compression method for eliminating one member of a twin set.

Switching of follicle destiny so that the second largest follicle becomes dominant in monovulatory species

During an ovulatory follicular wave in the monovulatory species of heifers, mares, and women, the two largest follicles deviate in diameter at the end of a common follicle growth phase. The largest follicle before deviation becomes the future ovulatory follicle in most ovulatory waves. In 10-30% of the ovulatory waves, the destiny of the two follicles switches just before or at deviation so that the second-largest follicle becomes the future ovulatory follicle, and the largest follicle becomes a subordinate. In FSH-driven switching in heifers, mares, and women, the wave-stimulating FSH surge decreases to a low concentration before the largest follicle has developed the ability to utilize the low concentrations. The concentrations of FSH then increase (mares, women) or cease to decrease (heifers), and the next largest follicle acquires the capability of becoming the future ovulatory follicle. Luteolysis-driven switching has been reported in heifers but not in mares and women. The switching in heifers occurs during ovulatory wave 3 of three wave interovulatory intervals (IOI) when the wave of follicles is in the common growth phase in synchrony with the time of luteolysis. Regression of the CL during the common growth phase of ovulatory wave 3 is accompanied by decreased activity of follicles that are adjacent to the regressing CL but not when follicles and CL are separated or in opposite ovaries. The role of luteolysis in switching in heifers has been tested by treating with PGF2α when the largest follicle of wave 2 was near the end of the common growth phase. Switching in destiny of the largest follicle from the expected future dominant to a future subordinate occurred in most waves (10 of 17) when the largest follicle and regressing CL were in the same ovary and adjacent but not when separated in the same ovary or when in opposite ovaries (0 of 11). The newly selected future ovulatory follicle may develop in the opposite ovary. Thereby, frequency of the contralateral vs ipsilateral relationship between the preovulatory follicle and CL in heifers is greater in three-wave IOI than in two-wave IOI. In summary, the second largest predeviation follicle becomes the postdeviation dominant follicle when the decreasing FSH is out of phase with the largest predeviation follicle in heifers, mares, and women or when luteolysis and predeviation are in synchrony in heifers.

Side of ovulation at each end of two- and three-wave interovulatory intervals and before and after pregnancy in cattle

The side of ovulation (left ovary, LO; right ovary, RO) and side of the next ovulation were compared between (1) beginning and end of an interovulatory interval (IOI) and beginning and end of consecutive sets of two and three IOI (n = 900 IOI), (2) beginning and end of the IOI for two and three follicular waves per IOI (n = 1300), and (3) beginning of pregnancy and first postpartum ovulation (n = 793). Pairs of sides of ovulation were designated LL (LO and LO), RR, LR, and RL. The frequency of ovulation pairs for two ends of an IOI was not different from two ends of two or three consecutive IOI indicating that differences between LO and RO were more likely inherent than from factors that developed in each IOI. For each end of an IOI or two consecutive IOI, the least frequency (P < 0.05) was for LL (16 %) with no differences among RR, LR, and RL (28 % for each). Frequencies between ipsilateral (LL, RR) and contralateral (LR, RL) ovulations pairs were not different for two-wave IOI (48 % compared with 52 %) but differed (P < 0.0001) for three-wave IOI (32 % compared with 68 %) and for pregnancy/postpartum (34 % compared with 66 %). In pregnancy/postpartum, each pair was different (P < 0.05) from each other: LL (13 %), RR (21 %), LR (30 %), RL (36 %). The lesser frequency for LL than for any of the others for an IOI, consecutive IOI, and pregnancy/postpartum indicated a ubiquity of the small propensity for LO ovulation.

Relationships among the corpus luteum, follicles and conceptus in sheep

This study aimed to investigate the intra- and interovarian relationships among the corpus luteum (CL), the largest follicle (LF) and follicular population in non-pregnant and between the conceptus and ovarian structures in pregnant ewes. In experiment 1, the follicular and luteal structures were examined in 538 reproductive systems of non-pregnant Awassi ewes. The follicular population was categorised into small (SF), medium (MF) and large (LF) groups. Inter-relationships between CL and follicular population and between LF and subordinate follicles were determined. In experiment 2, the location and number of conceptuses were identified and correlated with the ovarian structures in 58 reproductive systems of pregnant ewes. Effects of pregnancy status, stage of pregnancy, pregnancy side and conceptual number on follicular population were determined. The results showed that the right ovary was more active than the left ovary. CL had intraovarian positive effect on the number of medium and large follicles. LF had no local suppressive effect on the subordinate follicles. Side and stage of pregnancy and the conceptual number did not affect the follicular population. Accordingly, it can be concluded that the LF has no local suppressive effect on the subordinate follicles. The CL has intraovarian positive effect on the follicular population. Follicular population does not show remarkable changes during the first term of pregnancy. The present study probably provides information which may help in the understanding of the ovarian dynamics during pregnancy in sheep.

Selection of side of ovulation by intraovarianism in Bos taurus heifers†

Intraovarianism refers to mechanisms within an ovary that affect the local follicle and luteal dynamics and is well-represented in heifers by greater frequency of ovulation from the right ovary (RO) than the left ovary (LO). On average, the RO has more 6-mm follicles than the LO before one follicle is selected to deviate in diameter and become the future ovulatory follicle. Therefore, the ovulatory follicle is more frequently selected from the RO. More follicles in the RO likely develop before birth as indicated by greater weight of the RO with more 0.3- to 4.8-mm follicles in recently born calves. It has been proposed that differences in intraovarianism between sides are a consequence of differences between sides in the inherent intraovarian angioarchitecture. The frequency of the pair of ovulations at the beginning and end of 900 interovulatory intervals (IOI) was lowest for the left/left (LL) pair (16%) and higher and similar among the RR, LR, and RL pairs (28% each). The lower frequency of LO ovulation was entirely a function of the LL pair as indicated by the lower frequency of the LL than RR pairs without a difference among the RR, LR, and RL pairs. Ovulations from the opposite sides at the beginning and end of an IOI (LR and RL pairs) would not have contributed to a difference in ovulation frequency between LO and RO. In conclusion, the greater frequency of RO (56%) than LO (44%) ovulation was mathematically and functionally a direct consequence of the low frequency of the LL pair of ovulations.

Intraovarianism and differences in ovulation frequency between left and right ovaries in Bos taurus heifers

Sides of ovulation at beginning and end of an interovulatory interval (IOI) were studied for 10 successive ovulations in each of 100 heifers (1000 ovulations, 900 IOI). The frequency of side for 1000 ovulations was less (P < 0.0002) for the left ovary (LO or L; 44.4 %) than for the right ovary (RO or R; 55.6 %). Number of observed ratios of L to R was determined within each of 100 sets of 10 ovulations per set (eg, L2 to R8, L6 to R4). Expected ratios were calculated by combinatorics using the criterion that side of ovulation was an independent event. Differences in ratios between observed and expected were significant supporting the hypothesis that side of ovulation is dependent on the side of the previous ovulation. Number of pairs of ovulations for each end of the 900 IOI was significantly less for the LL pair (144, 16.0 %) than for the pairs of RR (255, 28.3 %), LR (247, 27.5 %), and RL (254, 28.2 %). The hypothesis was supported that the frequency of the pairs of ovulations at the beginning and end of an IOI differed among LL, RR, LR, and RL pairs. Novel observations were that frequency was lowest for the LL pair and similar among the the RR, LR, and RL pairs. These observations indicated that the greater frequency of RO ovulation was mathematically and functionally related to lower frequency of LO ovulation. The interpretation was that intraovarianism in the LL pair accounted for the lower frequency of LO than RO ovulation.

Relationship between more follicles in right than left ovary in recently born calves and right ovary propensity for ovulation in cattle

The mechanism for more frequent ovulation from right ovary (RO) than left ovary (LO) was considered by determining if RO of recently born calves had a propensity for more follicles. Rationale was from reports that RO in heifers has more 6-mm follicles before selection of the future ovulatory follicle as well as greater frequency of RO ovulation. Dimensions, weight, and number of follicles per ovary were compared between LO and RO in 10 Holstein calves (age, 1 to 7 days). Weight of an ovary was greater (P < 0.05) for RO (0.393 ± 0.04 g) than LO (0.355 ± 0.05 g). Follicles were delineated by translucency of follicular fluid from transmitted light. Follicles from 0.3 mm diameter (smallest identified) to 4.8 mm (largest present) were counted. Mean number of translucent antral follicles (8.1 ± 1.8 vs 5.3 ± 1.2 follicles) and means for follicle diameter, fluid volume, and surface area were each greater (P < 0.01) for RO than LO. Combined for all diameters (0.3-4.8 mm), the hypothesis was supported that more follicles are present in RO than LO in calves 1 to 7 days of age. Although follicle activity in the fetus has not been compared between LO and RO, more follicles in RO than LO in recently born calves is consistent with the concept that the propensity for RO ovulation is congenital.

Use of color-Doppler ultrasonography for selection of recipients in timed-embryo transfer programs in beef cattle

We aimed to study the association between CL characteristics assessed by color-Doppler ultrasonography (Doppler-US) at the time of embryo transfer (ET) and pregnancy rate (P/ET) in beef recipients. Estrous cycles of crossbred beef recipients were synchronized for timed-ET. On the day of ET (Day 7), CL area, proportion of luteal blood perfusion (BP), and the relationship between the largest dominant follicle (DF) and CL (ipsilateral or contralateral) were determined. Animals (n = 444) received an in vitro produced embryo from Nelore donors, placed in the uterine horn ipsilateral to the CL. Recipients were split retrospectively in three subgroups according to CL area [small (<3 cm²), medium (3-4 cm²), or large (>4 cm²)] and three subgroups according to luteal signals of BP [low (≤40%), medium (45-50%) or high (≥55%)]. Pregnancy was detected on Days 30-45 by transrectal ultrasonography and P/ET was analyzed considering the effects of cow's category (suckling or non-suckling), CL area, luteal BP and side of DF. P/ET increased along with BP category [low, 45.9%^B, (62/135); medium, 54.1%^AB (93/172); and high, 58.4%^A (80/137)]. When luteal BP was evaluated as a continuous variable, a significant (P < 0.05) linear and positive effect was observed on P/ET. A greater (P < 0.05) CL area and serum progesterone concentrations were observed in the medium and high BP than in the low BP category. Although an effect of luteal size category was not significant on P/ET [small, 49% (76/155); medium, 59.7% (83/139); and large, 50.7% (75/148); P > 0.1], when CL area was evaluated as a continuous variable, a quadratic effect (P < 0.05) indicated a positive relationship between P/ET and CL area until luteal tissue reached 4.07 cm², followed by a negative relationship. The location of the first-wave DF in relation to the CL did not affect P/ET (P > 0.1). In conclusion, Doppler-US is an innovative tool that has the potential to be used for selection of suitable embryo recipients based on luteal BP. Selection of recipients that have a greater chance of maintaining pregnancy will increase the success of timed-ET programs.

Role of intraovarian mechanisms and side of ovary on characteristics of follicle selection in Bos taurus heifers

Intraovarian effects on diameter of future dominant follicle (DF or F1) and future largest subordinate follicle (F2) during the few days before selection of the future DF and subordinate follicles were studied in 147 bovine interovulatory intervals. Follicle selection involves diameter deviation or the beginning of separation of growth rates between F1 and F2. Diameter deviation is classified as conventional (F2 ≥ 7.0 mm when F1 is 8.5 mm or at expected deviation) and as undersized (F2 < 7.0 mm when F1 is 8.5 mm). Diameter separation of F1 and F2 in conventional and undersized deviations is characteristically abrupt and gradual, respectively. The predeviation diameter of F2 when located in an ovary that later becomes the F1 intraovarian patterns of DF-CL, devoid (ovary without a DF or CL), DF alone, or CL alone and in left or right ovaries (LO, RO) was compared between conventional and undersized deviations. In conventional deviation, ovaries with the future DF (combined DF-CL and DF patterns) were associated with greater (P < 0.02) predeviation growth rate of F2 when the DF was in the right ovary (DF/RO, 1.6 ± 0.1 mm/d) than when in the left ovary (DF/LO, 1.2 ± 0.1 mm/d). The F2 was in DF/RO more frequently (75%, P < 0.002) than in non-DF/RO. When F2 was in the future devoid F1 pattern and F1 was 6 mm, F2 was smaller (P < 0.002) in the undersized class (5.3 ± 0.2 mm) than in the conventional class (6.3 ± 0.1) but not when F2 was in one of the other future F1 patterns. Only the devoid pattern was greater in frequency (P < 0.03) in the undersized class than in the conventional class. The novel hypothesis was supported that location of F2 in ovaries with different future F1 intraovarian patterns and on different sides affects the predeviation diameter and growth rate of F2 and thereby the frequencies of conventional and undersized deviations during follicle selection.