Coincident increases in oxytocin receptor expression and EMG responsiveness to oxytocin in the ovine cervix at oestrus

Topical application of cervix with hyaluronan improves fertility in goats inseminated with frozen-thawed semen

Objective

Artificial insemination plays an important role in genetic improvement in the goat farming system. The aim of this study was to investigate the effect of cervical application of hyaluronan (HA) on the fertility in goats after cervical artificial insemination using frozen-thawed (F-T) semen.

Methods

After oestrous synchronisation with progesterone sponges and pregnant mare serum gonadotropin injection, both nulli- and multi-parous goats, were randomly allocated to 2 groups, and were inseminated with 0.25 mL of F-T semen (150×10⁶ spermatozoa) twice at 52 h and 56 h after sponge removal. Prior to the insemination, goats in Group 1 only were given topical cervical HA application at 48 h after sponge removal. Site of insemination was recorded as os-cervix or intra-cervix or intra-uterus. Pregnancy was tested ultrasonographically 42 days after insemination. The data on pregnancy rates and percentage of animals according to the site of semen deposition were compared by Chi-square analysis.

Results

The overall pregnancy rate was significantly (p<0.004) higher in goats with prior application to the cervix with HA (63.3%) than without (36.0%). Same pattern was observed in the pregnancy rates of nulli- and multi-parous goats in both the groups. Percentage of nulliparous goats according to the site of insemination in the HA group did not differ between first and the second insemination. However, in multiparous goats the percentage of animals inseminated intra-cervically was significantly increased (p≤0.05) between the first and the second inseminations.

Conclusion

The results suggest that significantly higher fertility rate in the “HA goats” compared to the “without HA” group was because of deeper insemination facilitated by topical cervical application of HA. The deeper insemination into the cervical canal increase the rate of fertilisation when the cervical artificial insemination is performed.

Comparison of the intravenous and intravaginal route of oxytocin administration for cervical dilation protocol and non-surgical embryo recovery in oestrous-induced Santa Inês ewes

This study compared the effects of intravaginal and intravenous routes of oxytocin (OT) administration in 46 oestrous-induced Santa Inês ewes (6-day treatment with progestin-releasing intravaginal sponges and a single injection of 200 IU of eCG at the time of sponge removal) that underwent transcervical embryo recovery 6-7 days after oestrous onset and mating. All ewes received 37.5 μg of d-cloprostenol via latero-vulvar route, and 1 mg of oestradiol benzoate i.m. 16 hr before and 50 IU of OT 20 min before non-surgical embryo recovery (NSER), with OT being administered intravenously (n = 21) or intravaginally (n = 21). An overall oestrous response was 95.6% (44/46), and adequate cervical retraction could be accomplished in 78.6% (33/42) of ewes. The percentage of successful NSER procedures was 57% (24/42) or 72.7% (24/33) of animals with sufficient cervical retraction. The duration of NSER procedure averaged 28 min (range: 17-40 min) and ~96% of flushing fluid could be recovered (range: 85%-100%). Out of 18 ewes that could not undergo NSER, 12 (66.6%) presented various anatomical barriers, whilst the other 33.4% did not present these barriers and still could not be traversed. Excluding the ewes with those anatomical features, the overall success rate of NSER was 80% (24/30). The route of OT administration had no effect on NSER efficiency or the ease with which transcervical embryo flushing was performed. Both routes of OT administration can be used for cervical dilation protocol. Discarding ewes with anatomical features precluding cervical penetration is highly recommended to increase the efficacy of NSER in sheep.

An in vitro investigation of the actions of reproductive hormones on the cervix of the ewe in the follicular stage: the effects of 17β-estradiol, oxytocin, FSH, and arachidonic acid on the cervical pathway for the synthesis of prostaglandin E2

During the periovulatory period, the cervix of the ewe relaxes and this mechanism is thought to be mediated by oxytocin and prostaglandin E2 (PGE2) in response to increased concentrations of 17β-estradiol and perhaps FSH. The aim of the study was to determine the in vitro effects of 17β-estradiol, FSH, oxytocin, and arachidonic acid (AA) on the synthesis of PGE2 and on the expression of oxytocin receptor (OTR), cytoplasmic phospholipase A2 (cPLA2), and cyclooxygenase 2 (COX-2) in explants of cervical tissue collected from ewes in the periovulatory phase of the estrous cycle. Cervical minces from ewes in the follicular phase of the estrous cycle were cultured in supplemented Eagle's Minimum Essential Medium for 48 hours with 17β-estradiol, FSH, oxytocin, or AA. After incubation, the tissue was stored at -80 °C and the media at -20 °C. Western immunoblotting was used to determine relative levels of OTR, cPLA2, and COX-2 in cervical tissue, and the media was analyzed by RIA, to determine the concentration of PGE2. The addition of 17β-estradiol increased the concentration of PGE2 in the media (P = 0.001), the levels of COX-2 (P = 0.02) and OTR (P = 0.006) but not those of cPLA2 (P = 0.15). The addition of FSH increased the levels of COX-2 (P = 0.01) but, it had no effect on the concentration of PGE2 (P = 0.08) or on the levels of OTR (P = 0.07) and cPLA2 (P = 0.15). Oxytocin did not increase the levels of COX-2 (P = 0.38) but increased those of OTR (P = 0.001) and cPLA2 (P = 0.01) but not on the concentration of PGE2 in the media. Arachidonic acid increased the levels of cPLA2 (P = 0.01) and those of COX-2 (P = 0.02) but not the concentration of PGE2 in the media. Our findings suggest that the PGE2-mediated mechanisms of cervical relaxation in the ewe during the follicular phase are stimulated by FSH, 17β-estradiol, oxytocin, and AA. They all appear to act by inducing receptors and enzymes along the synthetic pathway for PGE2.

Traversing the ovine cervix - a challenge for cryopreserved semen and creative science

This review brings together research findings on cervical relaxation in the ewe and its pharmacological stimulation for enhancement of the penetration needed for transcervical insemination and embryo transfer. On the basis that the success of artificial insemination is the percentage of ewes lambing, a review is made of recent research aimed at understanding and minimising the sub-lethal effects of freezing and thawing on the viability of spermatozoa, their membrane integrity and their ability to migrate through cervical mucus, as these characteristics have a major influence on fertility, particularly when semen is deposited, artificially, in the os cervix. Milestones of achievement are given for transcervical intrauterine insemination, embryo recovery and transfer and the birth of lambs of pre-determined sex, firstly following intracytoplasmic sperm injection, then laparoscopic intrauterine insemination using highly diluted flow-cytometrically sorted fresh semen and subsequently by os cervix insemination using sexed semen that had been frozen and thawed. Diversity of research endeavour (applied, cellular, molecular), research discipline (anatomy, histology, immunology, endocrinology) and research focus (cell, tissue, organ, whole animal) is embraced within the review as each has significant contributions to make in advancing recent scientific findings from the laboratory into robust on-farm transcervical insemination and embryo transfer techniques.

The effects of the prostaglandin E analogue Misoprostol and follicle-stimulating hormone on cervical penetrability in ewes during the peri-ovulatory period

Two experiments in parous Welsh Mountain ewes determined the pattern of natural cervical relaxation over the peri-ovulatory period and investigated FSH and Misoprostol as cervical relaxants to facilitate transcervical passage of an insemination pipette into the uterine cavity. Following synchronisation of oestrus using progestagen sponges and PMSG (500 IU) the depth of cervical penetration was determined using a modified cattle insemination pipette as a measuring device. Penetration of the cervix was least at the time of sponge removal and increased to a maximum at 72 h after sponge removal and then declined. Intra-cervical administrations of either ovine FSH (Ovagen; 2mg) or Misoprostol (1mg; a Prostaglandin E(1) analogue) facilitated cervical penetration. Ovagen given 24h after sponge removal allowed transcervical intrauterine penetration in 100% of ewes at 54 and 60 h after sponge removal while Misoprostol given 48 h after sponge removal allowed trans-cervical penetration in 100% of ewes at 54 h. A combination of Ovagen and Misoprostol was as effective but not more so than Ovagen or Misoprostol alone. These results show that there is natural relaxation of the cervix at oestrus and that maximum relaxation occurs 72 h after sponge removal, which is too late for the correct timing of insemination. The intra-cervical administration of FSH or Misoprostol enhanced relaxation of the cervix and both were able to relax the cervix to allow intrauterine penetration 54 h after sponge removal, the optimum time for insemination. The results also show that FSH is biologically active after intracervical, topical application.

The Expression of Prostaglandin Endoperoxide Synthase 2 Messenger RNA and the Proportion of Smooth Muscle and Collagen in the Sheep Cervix During the Estrous Cycle

The use of transcervical artificial insemination in sheep is limited because of the anatomy of the cervix, which restricts the passage of an inseminating pipette into the uterine lumen. There is a degree of natural cervical relaxation at estrus that enables greater penetration with an inseminating pipette. We hypothesize that this relaxation may be regulated by cervical prostaglandin synthesis and remodeling of the cervical extracellular matrix. The present study investigated the changes in prostaglandin endoperoxide synthase 2 (PTGS2) mRNA expression and the proportion of smooth muscle and collagen in the sheep cervix during the estrous cycle. Sheep cervices were collected at four stages of the estrous cycle: prior to the LH surge, during the LH surge, after the LH surge, and during the luteal phase. The expression of cervical PTGS2 mRNA was determined by in situ hybridization, and the proportion of smooth muscle and collagen in the cervix was investigated by Masson trichrome staining. The expression of PTGS2 mRNA in the sheep cervix was greatest prior to the LH surge, when estradiol concentrations were also greatest. The increase in PTGS2 mRNA expression was associated with an increase in the proportion of collagen in the sheep cervix. We propose that prior to the LH surge, estradiol may stimulate PTGS2 mRNA expression and hence prostaglandin E2 synthesis in the sheep cervix to regulate cervical relaxation, most likely through the rearrangement of collagen bundles within the cervical extracellular matrix.

Increased cervical electrical activity during oestrus in progestagen treated ewes: Possible role in sperm transport

The aim of this investigation was to characterize the pattern of cervical myoelectrical activity (EMG) in the sheep, during the periovulatory period, after synchronization of oestrus with progestagen and eCG. EMG was measured with a computerised modular system in five ewes previously fitted with a pair of monopolar Teflon needle electrodes in the muscle layers of the cervix. Each ewe was submitted to oestrus synchronization treatment with intravaginal progestagen sponge during 12 days, and the administration of 500 IU of eCG at the withdrawal of sponge. EMG was recorded in each animal during 19 h, starting 44 h after withdrawal of sponge. The number and duration of events were determined every hour during the experiment. Two distinct event durations were identified: one lasting less than 200 s and another lasting between 300 and 500 s. The two types of events analysed (less than 200 s and lasting between 300 and 500 s) had a similar pattern during the period of observation although they were not in synchrony. For events lasting less than 200 s, activity increased between 48 and 50 h after sponge withdrawal, with the peak of activity being observed between 51 and 53 h. For events of 300-500 s duration, the peak of activity was observed between 48 and 50h after sponge withdrawal and activity was maintained until 51-53 h. The increase in cervical motility observed in progestagen-eCG treated ewes is in keeping with the increase in cervical activity observed by others in natural cycling animals, and suggests that exogenous hormones used in synchronization protocols had no deleterious action on cervical motility during periovulatory period. The enhanced activity of cervical muscle layer found around the time of mating and/or AI suggests it may play an important role as a regulatory mechanism of sperm transport. Taking advantage of the cervical responsiveness to various drugs, experimental modulation of cervical activity could be used to facilitate cervical sperm transport and consequent improve of fertility after cervical AI.

The anatomy of the sheep cervix and its influence on the transcervical passage of an inseminating pipette into the uterine lumen

The anatomy of the sheep cervix is highly variable between animals and may explain the differing success of transcervical AI between individuals. This study aims to quantify the variation in cervical morphology between ewes and investigate the relationship between cervical anatomy and cervical penetration. Two series of reproductive tracts were collected. Series A: 132 adult anoestrous ewes, and series B: 165 cycling adult ewes and ewe lambs which were identified as luteal or non-luteal based on the presence of a corpus luteum. The morphology of the cervical external os was classified as slit, papilla, duckbill, flap or rose. An inseminating pipette was inserted into the lumen and the depth of penetration recorded. The cervix was opened longitudinally, its length recorded, the number of cervical rings counted and the arrangement of those rings graded. The maximum depth of cervical penetration was affected by cervical grade (series A: P=0.021; series B: P=0.037) and the stage of the oestrous cycle (P=0.008). Grade 1 cervices were more penetrable than grade 2, with grade 3 the least penetrable and non-luteal cervices could be penetrated further than luteal cervices. The distribution of os types differed with age, with rose types more common in adult ewes, and papilla os types more common in ewe lambs. These results indicate that the depth of cervical penetration is affected by the anatomy of the cervical lumen. Cervices with a less convoluted lumen (grade 1) were more penetrable. Non-luteal cervices are likely to have higher oestradiol concentrations than luteal, stimulating cervical relaxation and enabling deeper penetration. The difference in os types with age may be contributable to a morphological alteration at parturition.