Sperm transport, storage and release in the sheep oviduct in relation to the time of ovulation

Sperm migration, selection, survival, and fertilizing ability in the mammalian oviduct†

In vitro fertilization (IVF) gives rise to embryos in a number of mammalian species and is currently widely used for assisted reproduction in humans and for genetic purposes in cattle. However, the rate of polyspermy is generally higher in vitro than in vivo and IVF remains ineffective in some domestic species like pigs and horses, highlighting the importance of the female reproductive tract for gamete quality and fertilization. In this review, the way the female environment modulates sperm selective migration, survival, and acquisition of fertilizing ability in the oviduct is being considered under six aspects: (1) the utero-tubal junction that selects a sperm sub-population entering the oviduct; (2) the presence of sperm binding sites on luminal epithelial cells in the oviduct, which prolong sperm viability and plays a role in limiting polyspermic fertilization; (3) the contractions of the oviduct, which promote sperm migration toward the site of fertilization in the ampulla; (4) the regions of the oviduct, which play different roles in regulating sperm physiology and interactions with oviduct epithelial cells; (5) the time of ovulation, and (6) the steroid hormonal environment which regulates sperm release from the luminal epithelial cells and facilitates capacitation in a finely orchestrated manner.

Prenatal Bisphenol A Exposure Alters Epithelial Cell Composition in the Rhesus Macaque Fetal Oviduct

Bisphenol A (BPA) is an endocrine disrupting compound that is a pervasive environmental contaminant. Although it has been reported to affect the development of a variety of fetal reproductive tissues, data on the effect of fetal BPA exposure on oviducts were extremely limited and were only available in mice. To determine if there are adverse effects of gestational BPA exposure on fetal oviduct, we exposed pregnant rhesus macaques with female fetuses to oral or nonoral BPA during the last trimester of gestation (day 100 to term). After the treatment, fetal oviducts were collected for morphology evaluation. BPA exposure altered the percentages of different cell types (ciliated, nonciliated, and secretory) in the fetal oviduct and resulted in a significant high ciliated cell population in the BPA-exposed fetal oviduct. The distribution of ciliated cells on the epithelium in the BPA-exposed fetal oviduct was also altered. Gestational BPA exposure reduced the expression of mucosubstance and uteroglobin in secretory cells in the fetal oviduct. A comparison of the outcome of the fetal oviduct studies with similar outcomes previously reported in the lung from the same fetuses demonstrates that BPA exhibits opposite effects in these two organs. In conclusion, the BPA-associated alterations in the fetal oviduct could potentially affect the oviduct morphology and function later in life with a negative impact on fertility. The mechanisms of action of the differential response in the oviduct and the lung to BPA exposure require further investigation.

Annexin A2 and S100A10 in the mammalian oviduct

In many mammals, upon entry into the female reproductive tract, a subpopulation of sperm is stored in the oviduct forming a functional reservoir. In the oviducts of pig and cow, Annexin A2 (AnxA2) has been linked to the binding of sperm. This protein may exist as a monomer or bound to S100A10 and both forms are associated with different biological functions. S100A10 has not yet been reported in the oviduct. The objective of this work is to analyze for the presence of S100A10 in the oviduct and to advance the study of AnxA2 and S100A10 in this organ. This work shows the presence of both proteins, AnxA2 and S100A10, in the oviduct of human, pig, cow, cat, dog and rabbit. At least in pig, AnxA2 is found devoid of S100A10 in the outer surface of the apical plasma membrane of oviductal epithelial cells, indicating that it binds to sperm as a monomer or in association with proteins different from S100A10. In the apical cytoplasm of pig oviductal epithelial cells, AnxA2 is associated with S100A10. In primary culture of porcine oviductal cells, the expression of ANXA2 is increased by progesterone, while the expression of S100A10 is increased by progesterone and estradiol. The widespread detection of both proteins in the oviduct of mammals indicates a probable conserved function in this organ. In summary, S100A10 and AnxA2 are widespread in the mammalian oviduct but AnxA2 binds sperm in vivo devoid of S100A10 and may be related to reservoir formation.

Alterations to the bull sperm surface proteins that bind sperm to oviductal epithelium

Three Binder of SPerm proteins (BSP1, BSP3, BSP5) are secreted by bovine seminal vesicles into seminal plasma and adsorbed onto sperm. When sperm inseminated into the female reach the oviduct, the BSP proteins bind them to its epithelial lining, forming a sperm storage reservoir. Previously, we reported that binding of capacitated sperm to oviductal epithelium in vitro is lower than that of uncapacitated sperm and we proposed that reduced binding was due to loss of BSP proteins during capacitation. Because of differences in amino acid sequences, we predicted that each BSP would respond differently to capacitating conditions. To test whether all three BSP proteins were lost from sperm during capacitation and whether the kinetics of loss differed among the three BSP proteins, ejaculated bull sperm were incubated under various capacitating conditions, and then the amounts of BSP proteins remaining on the sperm were assayed by Western blotting. Capacitation was assayed by analysis of protein tyrosine phosphorylation. While loss of BSP1 was not detected, most of the BSP5 was lost from sperm during incubation in TALP medium, even without addition of the capacitation enhancers heparin and dbcAMP-IBMX. Surprisingly, a smaller molecular mass was detected by anti-BSP3 antibodies in extracts of incubated sperm. Its identity was confirmed as BSP3 by mass spectrometry, indicating that BSP3 undergoes modification on the sperm surface. These changes in the composition of BSP proteins on sperm could play a role in releasing sperm from the storage reservoir by modifying sperm interactions with the oviductal epithelium.

Distribution and viability of spermatozoa in the canine female genital tract during post-ovulatory oocyte maturation

BACKGROUND

Unlike other domestic mammals, in which metaphase-II oocytes are ovulated, canine ovulation is characterized by the release of primary oocytes, which may take 12 to up to 36 hours. Further 60 hours are needed for maturation to secondary oocytes which then remain fertile for about 48 hours. Oestrus takes 7 to 10 days on average and may start as early as a week before ovulation. This together with the prolonged process of post-ovulatory oocyte maturation requires an according longevity of spermatozoa in the female genital tract in order to provide a population of fertile sperm when oocytes have matured to fertilizability. Therefore the distribution and viability of spermatozoa in the bitch genital tract was examined during post-ovulatory oocyte maturation.

METHODS

Thirteen beagle bitches were inseminated on the day of sonographically verified ovulation with pooled semen of two beagle dogs containing one billion progressively motile spermatozoa. Ovariohysterectomy was performed two days later (group 1, n = 6) and four days later (group 2, n = 7). The oviduct and uterine horn of one side were flushed separately and the flushing's were checked for the presence of gametes. The oviducts including the utero-tubal junction and the uterine horns, both the flushed and unflushed, were histologically examined for sperm distribution.

RESULTS

The total number of spermatozoa recovered by flushing was low and evaluation of viability was limited. Prophase-I oocytes were collected from oviduct flushing in group 1, whereas unfertilized metaphase-II oocytes were detected in group 2. From day 2 to day 4 after ovulation a significant decrease in the percentage of glands containing sperm (P<0.05) and a marked reduction of the mean sperm number in uterine horn glands were observed. A concomitant diminution of spermatozoa was indicated in the utero-tubal junction accompanied by a slight increase in sperm numbers in the mid oviduct.

CONCLUSIONS

Oocyte maturation to metaphase-II stage is accompanied by a continuous sperm detachment and elimination in the uterine horns. Entrance of spermatozoa into the caudal oviduct seems to be steadily controlled by the utero-tubal junction thus providing a selected sperm population to be shifted towards the site of fertilization when oocyte maturation is completed.

Oviductal, endometrial and embryonic gene expression patterns as molecular clues for pregnancy establishment

In higher animals, the beginning of new life and transfer of genetic material to the next generation occurs in the oviduct when two distinct gametes cells unite resulting in the formation of a zygote. The zygote then undergoes serial developmental processes in the oviduct and enters into the uterus where it faces challenges and scrutiny from the endometrial ecosystem. Thus, embryos that are able to establish an appropriate embryo-maternal dialogue are capable of developing to term whereas the incompetent ones can perish any time during the gestation period. Although several lines of evidences indicated that pregnancy loss is a multi-factorial phenomenon, the biochemical composition of the embryo and maternal environment are the main players to determine pregnancy outcome. Indeed, expression patterns of the genes are the driving forces that induce biochemical composition changes in embryo, oviduct and uterine environment. Thus, examining the molecular signals that are associated with oviductal or endometrial receptivity and embryo implantation is essential for establishing strategies to improve pregnancy success. Therefore, this review focuses on the contribution of oviduct and its transcriptome profile on early stage embryo development and the impact of endometrium and its transcriptome changes on peri and post embryo implantation. In addition, this paper integrates established facts about hormonal and molecular signatures associated with endometrial receptivity. Finally, the blastocyst and pre-conception endometrial gene expression profiles have been discussed in relation to the pregnancy outcome to highlight the potentials of blastocyst and pre-transfer endometrial transcriptome profile approach for selecting appropriate recipient and developmentally competent embryo.

Considerations of viscosity in the preliminaries to mammalian fertilisation

Migration of spermatozoa in the female genital tract will be strongly influenced by the viscosity of the fluids encountered, yet little systematic analysis has been given to such a consideration. This essay reviews the series of milieux confronting a fertilising sperm during its progression to the oviduct ampulla. Two groups are discussed, first those in which ejaculation is into the vagina, second those in which semen enters the uterus during a protracted mating. Viscous glycoprotein secretions that accumulate in the oviduct isthmus of both groups before ovulation are highlighted, as is the environment generated in the ampulla by the post-ovulatory suspension of oocyte(s), cumulus cells and spermatozoa; follicular and peritoneal fluids may also be present. The viscosity of all female tract fluids responds to cyclical variations in temperature, and these exist within the oviduct near the time of ovulation. Gradations in viscosity influence the pattern and strength of sperm flagellar activity and the rate of forward movement. Measurements of sperm motility are currently made in a physiological medium of constant viscosity and temperature, thereby overlooking changes in the female genital tract. A more sophisticated approach might reveal an adequate fertilising potential in a proportion of putatively poor semen samples.

Synchronization of oestrus and ovulation by short time combined FGA, PGF(2α), GnRH, eCG treatments for natural service or AI fixed-time

Two experiments were conducted in ewes in order to develop an oestrus-ovulation short time synchronization protocol based on combined FGA, PGF(2α), GnRH, eCG treatments, for use in dairy sheep before natural service (Experiment 1) or for fixed-time artificial insemination (Experiment 2), during the breeding season. In Experiment 1 seventy-five non-lactating dairy ewes were subdivided into 5 treatment groups (N=15): (1) Group Fe - control, which received FGA vaginal sponges (14 days)+eCG (Day 14); (2) Group FPe, FGA (5 days)+PGF(2α) (Day 5)+eCG (Day 5); (3) Group PFe, PGF(2α) (Day 0)+FGA (5 days)+eCG (Day 5); (4) Group PFG, PGF(2α) (Day 0)+FGA (5 days)+GnRH (30h after sponge removal, s.r.); (5) Group GPe, GnRH (Day 0)+PGF(2α) (Day 5)+eCG (Day 5). Ewes were checked for oestrus and hand-mated. Time of ovulation was recorded by laparoscopy for 10 animals from each treatment. The percentages of female in oestrus and the interval to oestrus (h after treatment), fertility and prolificacy rate were recorded. There were no treatment differences in the percentage of females in oestrus. The interval to oestrus was earlier in Fe Group and delayed in FPe Group (P<0.01). Ovulation time was earlier in GPe Group compared to FPe Group (P<0.05). Fertility rates were significantly different (P<0.05) between the PFe and the FPeG Groups compared with the PFG Group. No significant differences were observed in prolificacy among the treatments. In Experiment 2, sixty dry ewes were subdivided (N=20) into the following three experimental treatment groups: (1) Group FP, FGA (5 days)+PGF(2α) (Day 5); (2) Group FPG, FGA (5 days)+PGF(2α) (Day 5)+GnRH (30hs.r.); (3) Group FPeG, FGA (5 days)+PGF(2α) (Day 5)+eCG (Day 5)+GnRH (30hs.r.). These were further subdivided into two groups (N=10) corresponding to 52 and 60hs.r. fixed-time insemination. Laparoscopic intrauterine insemination was performed with frozen semen (80×10(6)spermatozoa/dose) and ovulation time was recorded in a subgroup (N=10). GnRH resulted in an earlier ovulation time (P<0.05) in FPG and FPeG Groups (53.0h vs 61.6h). Fertility rate was higher in FPeG treated ewes inseminated at 60hs.r. (60%, 6/10). In FP and FPG Groups fertility rates were higher following insemination at 52hs.r. (50.0 and 40.0%).

Selectivity in the transport of spermatozoa to oviductal reservoirs in the menstruating fruit bat, Carollia perspicillata

To better document the timing of ovulation and fertilization, female reproductive tracts were collected every 12 h from captive-bred fruit bats (Carollia perspicillata) on days 1–3 postcoitum and examined histologically. This also permitted observations on sperm transport, storage, and disposition. As the animals had previously been sexually segregated, most had been cycling and possessed menstrual uteri at the time of collection. Menstruation is periovulatory in this species. A widespread, headfirst orientation of spermatozoa to the uterine mucosa was observed in specimens apparently collected soon after insemination. Thereafter, however, this relationship was limited in most cases to the area around the entrance of each uterotubal junction (UTJ). A small number of spermatozoa also colonized the UTJs, which functioned as temporary sperm reservoirs on days 1–2. AlthoughC. perspicillatais monovular, no consistent differences were observed between the two oviducts in the pattern of sperm storage and release. Very few sperm were ever observed in the isthmus or ampulla (the site of fertilization). Menstrual debris (including fine particulate matter) and leukocytes present in the uterine cavity in most tracts did not gain access to the UTJ with the spermatozoa. Smooth muscle and abundant elastic fibers in the wall of the intramural UTJ, as well as receptors on its luminal epithelial cells, may play roles in the selective transport of spermatozoa to the fertilization site. While some spermatozoa are phagocytosed in the uterine lumen or by epithelial cells in the UTJ, the fate of most is probably expulsion into the vagina.

Effects of oviductal proteins, including heat shock 70 kDa protein 8, on survival of ram spermatozoa over 48 h in vitro

Following insemination, ram spermatozoa are transported to the isthmus region of the oviduct where they bind to the oviductal epithelial cells (OEC), remaining viable for several hours. The aim of the present study was to begin to decipher which component(s) of the ewe oviduct actively participates in maintaining the viability of ram spermatozoa. A series of experiments was conducted to investigate whether: (1) soluble OEC apical plasma membrane proteins (sAPM) isolated from ewes prolong survival of ram spermatozoa over an extended (48 h) coincubation period at 39 degrees C; (2) a recombinant form of one of these oviductal proteins, namely heat shock 70 kDa protein 8 (HSPA8), prolongs survival of ram spermatozoa; and (3) pretreatment with HSPA8 antibody compromises the ability of sAPM to prolong the survival of ram spermatozoa. Both sAPM and recombinant HSPA8 had a beneficial effect on the viability of ram spermatozoa during coincubation, although both these effects were dose dependent. In contrast, pretreatment with HSPA8 antibody significantly negated the ability of sAPM to maintain the viability of ram spermatozoa. These findings suggest that HSPA8 is an active component of the ewe oviduct that participates in maintaining the viability of ram spermatozoa. This is a potentially valuable observation given that there is a great deal of room for improving existing diluents for storing fresh ram semen.

Temporal dynamics of ram sperm binding and survival during 48-h coculture with oviducal epithelial cells

Following insemination, ram spermatozoa bind to oviducal epithelial cells (OEC) in vivo and remain viable for several hours before fertilisation. In the present study, we investigated whether OEC monolayers reproduce this effect in vitro, performing an analysis of ram sperm binding and survival over an extended (48 h) period at 39°C. We wanted to determine whether the reproductive cycle phase and/or oviducal region would influence ram sperm binding and survival in coculture with OEC and whether reproductive and non-reproductive epithelial cells bound and maintained the viability of ram spermatozoa equivalently. Oviducts were separated into groups based on their ovarian state (follicular or luteal) and then divided into two parts (isthmus and ampulla) for OEC isolation. Sheep kidney epithelial cells (Madin-Darby ovine kidney; MDOK) were purchased commercially. Reproductive cycle phase, but not oviducal region, affected sperm binding to OEC. Although more spermatozoa bound to luteal OEC than to follicular OEC at 1 h, at 24 h follicular OEC had bound more spermatozoa than luteal OEC. Generally, spermatozoa that were bound to OEC and MDOK had enhanced viability at each of the time points investigated (1, 6, 24 and 48 h), but the viability of the OEC-bound spermatozoa was greater than that of the MDOK-bound spermatozoa at 48 h. In conclusion, ram sperm–epithelial cell interactions are temporal, dynamic and depend on the origin of the epithelial cells.

Sperm release from oviduct epithelial binding is controlled hormonally by peri-ovulatory graafian follicles

To avoid inappropriate conclusions being drawn from the extensive use of in vitro preparations of sperm-oviduct epithelial binding, it is recalled that events in the genital tract of mammals are regulated by the gonads, primarily by their changing secretion of steroid hormones. Key observations from in vivo models are used to emphasise the dynamic interactions between viable sperm cells and the caudal (distal) portion of the oviduct isthmus, the site of the functional sperm reservoir. These include (1) pre-ovulatory arrest and epithelial binding of intact sperm cells and thereby suppression of completion of capacitation, (2) peri-ovulatory activation and release from binding of discrete sub-populations of competent spermatozoa, and (3) post-ovulatory liberation of large numbers of spermatozoa. These observations underline the influence of endocrine regulation of sperm binding and release by peri-ovulatory Graafian follicles, a point brought out by the enhanced sperm release prompted by diverse treatments with solutions of progesterone. In the light of this evidence, the suitability of in vitro preparations for clarifying physiological events should be questioned, especially if myosalpingeal catecholamines diffusing out of the autonomic nervous system contribute to sperm activation and/or release. None of this is to infer that sperm cells themselves are without influence on their epithelial binding reaction(s). Nor is it to suggest that in vitro models of sperm-oviduct binding are without relevance to the development of sperm evaluation technologies. However, pre-ovulatory sperm-epithelial binding and a regulated peri-ovulatory release should be seen as vital tactics in the overall strategy of achieving successful monospermic fertilisation.

Advances in deep uterine insemination: a fruitful way forward to exploit new sperm technologies in cattle

After clarifying regions of the female tract wherein spermatozoa are stored and the egg is fertilised, proposals are made for a modified site of sperm deposition in cattle. A deep pre-ovulatory insemination into the ipsilateral horn of the uterus-the side of the ovulatory follicle-should improve establishment of viable spermatozoa in the caudal region of the oviduct isthmus, the so-called functional sperm reservoir. Suppressed motility within viscous secretions and binding of sperm heads to endosalpingeal microvilli are features of this phase of storage. Activation and release of such spermatozoa would be prompted by imminent ovulation and associated ovarian endocrine programming by both local and systemic routes. Potential advantages of deep insemination include: (1) raising the fertility of genetically valuable bulls whose non-return rates are sub-optimal; (2) reducing the number of spermatozoa in each insemination dose; (3) exploiting the limited numbers of sex-selected sperm cells (X- and Y-chromosome-bearing spermatozoa) available from flow cytometry; (4) breeding from valuable but oligospermic bulls. Putative disadvantages might include: (1) rectal palpation of the ovaries to identify the pre-ovulatory follicle; (2) damage to or even perforation of the uterine wall by the insemination device; (3) the risk of polyspermic fertilisation; (4) specific training in the technique for non-clinically qualified inseminators. Each of these reservations receives comment. In conclusion, a modified technique of insemination should be feasible under commercial conditions, could be coupled with new sperm technologies, and would give a boost to the artificial insemination industry.

Storage of ram semen

Storage of ram semen in liquid and frozen state, the diluents used for both methods, processing, cooling, freezing and thawing of semen are reviewed. Factors influencing the fertility of stored semen and methods used for improvement are discussed, and fertility results of long-term frozen stored ram semen are also given.

A glimpse at sperm function in vivo: sperm transport and epithelial interaction in the female reproductive tract

The process of sperm transport in the female reproductive tract is more than simply a migration of spermatozoa from the site of insemination to the site of fertilization. Rather, it is a complex and dynamic continuum that encompasses phases of sperm distribution within the tract, the accumulation of spermatozoa in reservoirs, the modulation of sperm physiology and acquisition of fertilization competence, the ascent of competent spermatozoa to the site of fertilization, and the elimination of the non-fertilizing sperm population. The dynamic interactions that occur between functional spermatozoa and the luminal fluids and epithelial surfaces of the female genital tract during transit and storage enhance sperm survival and regulate sperm function in the female. The universal nature of this interaction highlights it as a key component of the sperm transport process.

Ovarian follicular fluid, progesterone and Ca2+ ion influences on sperm release from the fallopian tube reservoir

As a means of determining whether ovarian follicular fluid reaches the functional sperm reservoir in the caudal isthmus of the Fallopian tube shortly after ovulation, 0.01-0.02 ml aliquots of whole or steroid-free follicular fluid were introduced into the distal extremity of the isthmus within 1 hr before ovulation. Eggs were recovered during a second intervention 4 hr 45 min-6 hr 10 min after treatment and examined by phase-contrast microscopy for the normality of fertilisation. In a separate experiment, 0.01-0.02 ml aliquots of 10 microM calcium ionophore solution were introduced into the same site in comparable animals. Sixty-nine fertilised eggs were recovered from 12 fallopian tubes treated with whole follicular fluid, of which 24 (34.8%) were polyspermic. The 12 contralateral control tubes (PBS-treated) yielded 47 fertilised eggs, of which only one (2.1%) was polyspermic (P < 0.001). Steroid-free aliquots of the same follicular fluid introduced bilaterally into eight fallopian tubes (4 animals) resulted in recovery of 59 fertilised eggs, of which only one (1.7%) was polyspermic. Treatment with ionophore solution yielded a 41.6% incidence of polyspermy (10 of 24 eggs from four tubes) compared with 3.8% polyspermy (1 egg) from the control tubes (P < 0.01). Dispermy was the principal form of polyspermy. The numbers of accessory spermatozoa on/in the zona pellucida were increased by the experimental treatment. Follicular fluid passing down the fallopian tube ampulla at ovulation was therefore considered not to be the physiological stimulus for an initial, tightly-controlled release of spermatozoa from epithelial binding in the caudal isthmus. Indeed, because such sperm activation commences shortly before ovulation, a locally transmitted ovarian programming with relatively high concentrations of follicular hormones remains the favoured model. Although pre-ovulatory progesterone is considered to be the coordinating steroid of increasing influence in these pre-fertilisation events, its effects are proposed to be modulated in the endosalpinx by mobilisation of Ca2+ ions into a discrete population of bound spermatozoa. Results of the steroid-free follicular fluid and calcium ionophore treatments stand in support.

Fertility and ovum fertilization rate after laparoscopic or transcervical intrauterine artificial insemination of oxytocin-treated ewes

Based on our previous work, we found that exogenous oxytocin induces uterine tetany and cervical dilation, and permits transcervical access to the uterus. However, the oxytocin does not reduce sustained sperm transport from the uterus to the oviducts. Thus, we hypothesized that exogenous oxytocin may be a useful adjunct to transcervical intrauterine AI procedures for sheep: two experiments were conducted to test our hypothesis. In Experiment 1, purebred ewes (n = 75/group) were artificially inseminated intrauterine with either laparoscopic or oxytocin-transcervical (i.e., 200 USP units of oxytocin 30 min before AI) procedures. At 54 h after progestogenated pessaries were removed, ewes were inseminated with 200 x 10(6) sperm/0.25 ml of fresh, extended semen, which was collected from a purebred ram of the corresponding breed. Pregnancy rate was greater (P < 0.05) after laparoscopic (37.5%) than after transcervical AI (0%). Because of the disappointing results of Experiment 1, Experiment 2 was conducted to determine whether oxytocin or the AI procedure per se reduced ovum fertilization rate. Treatments were designed in a 2 x 2 factorial arrangement. At 60 h after norgestomet implant removal and 10 min before either laparoscopic or transcervical (cervical in a saline group) AI with 100 x 10(6) sperm/0.25 ml, ewes (n = 10/group) received an intravenous injection of either isotonic saline or 200 USP units of oxytocin. Fertilization rate, which was determined 72 h after AI, was greater (P < 0.05) after laparoscopic than after transcervical/cervical AI (92.5 vs 28%), but oxytocin treatment did not affect fertilization rate. The results indicate that exogenous oxytocin did not reduce ovum fertilization rate, but the transcervical AI procedure per se seemed to reduce fertilization rate.

Cytofluorescent assay to quantify adhesion of equine spermatozoa to oviduct epithelial cells in vitro

To facilitate the study of interactions between equine spermatozoa and homologous oviduct epithelial cells, we developed an assay to count labelled spermatozoa bound to oviduct epithelial cell (OEC) monolayers and used the assay to compare the binding ability of spermatozoa from different stallions. Washed spermatozoa from three stallions were incubated with the fluorochrome Hoechst 33342 (5 micrograms/ml) for 1 min. Spermatozoa were then layered over confluent monolayers of oviduct epithelial cells in 2 cm2 culture wells. Coculture treatments comprised five concentrations of spermatozoa (10(5), 5 x 10(5), 10(6), 2.5 x 10(6), and 5 x 10(6) per well). Cocultures were incubated for 30 min before unattached spermatozoa were aspirated in coculture supernatant. Fluorescent videoimages of attached spermatozoa were digitized, and attached spermatozoa were counted by image processing and analysis. Four wells (replicates) of each concentration were allocated within each ejaculate, and ejaculates were blocked by stallion for ANOVA. The total number of spermatozoa bound was not different between replicate wells (P > 0.1). Stallion, ejaculate, concentration, and all higher level interactions influenced total spermatozoa bound (P < 0.00001). Coefficients of variation between replicates were lowest for inseminate concentrations between 10(6) and 5 x 10(6) spermatozoa per well. Within the ejaculate, a log linear relationship exists between the number of bound spermatozoa and a spermatozoal concentration of the inseminate between 5 x 10(5) and 5 x 10(6) spermatozoa per well. This assay provides a reliable method of determining numbers of spermatozoa bound to somatic cells in vitro. Furthermore, differences exist in the ability of spermatozoa from different stallions to bind OEC monolayers.

Capacitation in vitro of bovine spermatozoa by oviduct epithelial cell monolayer conditioned medium

The effect of the active capacitating factor secreted from oviduct epithelial cell monolayers (OECM) in different environments on in vitro fertilization was evaluated. Capacitation was determined as the ability of sperm to fertilize bovine oocytes in vitro. When the mTALP was supplemented with glucose during conditioning, the sperm penetration rate was significantly reduced (P < 0.05) compared to the control (7% +/- 1 vs. 30% +/- 4). The percentages of sperm penetrated oocytes were higher following insemination in the OECM-conditioned medium derived from the early stage (48% +/- 7) of the estrous cycle than in the OECM-conditioned medium derived from either mid (35% +/- 2) or late stages (28% +/- 3) of the estrous cycle. When the medium was supplemented with 0.1 or 0.5 microgram/ml estradiol-17 beta during medium conditioning, sperm penetration rates increased (P < 0.05) compared to the control group (55% +/- 4 vs. 40% +/- 3 and 54% +/- 2 vs. 41% +/- 3, respectively). In addition, the percentages of penetrated oocytes significantly decreased (P < 0.05) following insemination when the OECM-conditioned medium was added to 0.01%, 0.05%, and 0.1% ethanol compared to the control (25% +/- 4, 19% +/- 2, 18% +/- 3, and 45% +/- 3, respectively). Sperm penetration rates significantly (P < 0.01) decreased when the OECM-conditioned medium was heated to 100 degrees C for 5 min (10% +/- 1 vs. 40% +/- 3). These results suggest that the active capacitating factor was secreted by the OECM and that this capacitating factor in the OECM-conditioned medium was inhibited by the presence of glucose. This factor was found to be heat-sensitive and its action was affected by ethanol. The OECM derived from the three phases of the estrous cycle as well as the presence of estradiol-17 beta influenced the capacity of the OECM to secrete this capacitating factor in vitro.

Ovarian regulation of sperm progression in the fallopian tubes

Successful liberation and apposition of gametes are essential components of fertility. Normal fertilisation depends upon the establishment of a pre-ovulatory sperm gradient in the female tract between the site of semen deposition and the site of fertilisation in the Fallopian tubes. As a consequence, sperm: egg ratios may be close to unity at the time of activation of most secondary oocytes under conditions of spontaneous mating. In the absence of a sufficient sperm gradient, newly ovulated eggs would be confronted by an excess of spermatozoa resulting in polyspermic fertilisation. Penetration of the vitellus by more than one spermatozoon is pathological in mammals (Beatty, 1957; Austin, 1963). Accordingly, systems that act to regulate sperm progression and competence before the time of ovulation assume a particular importance. During the 1950s, 1960s and 1970s, there was much controversy as to the rate of sperm transport into the Fallopian tubes. Because observations failed to focus on those spermatozoa that could fertilise eggs, the controversy was largely sterile. Nor were the disagreements well founded since some experiments employed artificial insemination whilst others used natural mating. These two quite distinct approaches to introducing a sperm suspension into the female tract could not reasonably form the basis of disagreements on the physiological events of cellular progression. More recent studies have been set in perspective by Overstreet (1983), Harper (1988), Yanagimachi (1988), Hunter (1988, 1991, 1995) and Drobnis & Overstreet (1992)After mating at the onset of oestrus, ram and bull spermatozoa require a minimum of 6–8 h to reach the Fallopian tubes in sufficient numbers to promote suc.cessful fertilisation (Hunter et al., 1980; Hunter & Wilmut, 1982). Spermatozoa displaced to the tubes in a small number of minutes are moribund or dead, not.

Ram spermatozoa cocultured with epithelial cell monolayers: an in vitro model for the study of capacitation and the acrosome reaction

The effects of different epithelial cells, namely, hamster oviduct, sheep oviduct, and pig kidney epithelial cells (IBRS-2), on the viability, percentage of progressive motility (PPM), and acrosome reactions of ejaculated ram spermatozoa were investigated. Sperm aliquots were cultured on cells, cell-conditioned medium 199, or control medium 199. The PPM of unattached spermatozoa was estimated after 0, 3, 6, 9, 12, and 24 hr of incubation at 37 degrees C under 5% CO2 in air. Viability and the occurrence of true acrosome reactions were assessed using a triple-stain technique. Spermatozoa started to attach within 1 hr of coculture with the hamster or sheep oviductal epithelial cell (OEC) monolayers, and these spermatozoa showed vigorous tail motion. No spermatozoa were found to attach to the IBRS-2 monolayer. The PPM of unattached spermatozoa cocultured with the various types of epithelial cell monolayers for 12 hr was significantly higher than that of spermatozoa incubated in conditioned media or medium 199 alone (54% in hamster OEC vs. 40% in conditioned; 68% in sheep OEC vs. 38% in conditioned; 36% in control medium). On the other hand, after 24 hr of incubation, there were no differences in the PPM of spermatozoa cocultured with epithelial cells or incubated in conditioned media. The percentages of cells undergoing a true acrosome reaction reached maximum values (P < 0.05) in spermatozoa incubated for 9 hr in the presence of hamster OEC (22.5%) or for 12 hr on sheep OEC (20.5%) monolayers.(ABSTRACT TRUNCATED AT 250 WORDS)

Rate of establishment of a fertilising population of spermatozoa in the sheep cervix after a single mating at the onset of oestrus

In order to study how soon a population of spermatozoa capable of fertilisation could progress into the cervical canal, the vaginal contents were flushed with a detergent solution at different intervals after mating at the onset of oestrus. Eggs recovered 1 or 2 days later from the oviducts were stained and examined by phase-contrast microscopy. Flushing at 3 minutes after mating did not prevent fertilisation in 44% of instances, whereas similar flushes performed at 6 or 9 minutes completely prevented fertilisation in a total of 26 animals. In the groups flushed at 12 and 15 minutes, the proportion of eggs fertilised was 21% and 24%, respectively, and this increased to 37% after flushing at 18 minutes. An explanation is offered for the paradoxical finding at 3 minutes, and it is concluded that at least 30-60 minutes would be required for adequate colonisation of the cervix with a fertilising population of spermatozoa under the conditions employed in the experiment. However, multiple matings or mating closer to the time of ovulation might act to reduce this interval.

The evolution of eutherian spermatozoa and underlying selective forces: female selection and sperm competition

We have examined sperm morphology and dimensions in Eutherian mammals. In most Eutherians, sperm heads are round or oval and spermatozoa have short tails (average sperm length about 65 microns; range = 33-121 microns). Rodents, however, clearly depart from the typical Eutherian pattern in that they show a broad array of head morphs and an extreme range of sperm dimensions (35-250 microns). In order to trace the evolutionary changes that rodent sperm have undergone, we have used phylogenetic relationships based on biogeographical, morphological, chromosomal and genic data, and we have superimposed onto them the information available on sperm traits. Analyses were carried out for five rodent groups on which enough information was available. The evolutionary trends which emerged from these studies have two main points in common: throughout evolution spermatozoa have become enlarged and morphologically more complex, and this process seems to have taken place independently in different lineages. A general model was developed which outlines the different evolutionary pathways that rodent sperm have undergone. The adaptive significance of the increase in head complexity and the elongation of the sperm tail remains obscure. We have integrated information from evolutionary, physiological and behavioural studies to address this issue. We argue that two main selective forces may have favoured these changes: female selection within the reproductive tract and sperm competition. The female tract represents a formidable barrier for spermatozoa and its provides an environment where numerous interactions take place. The extent of these barriers and the complexity of these poorly understood interactions suggest that females may be exercising a strong selection, which may enable them to favour particular types of spermatozoa or ejaculates from particular males. Throughout their evolution males must have evolved adaptations to overcome these barriers, and the conflicting interests of choosy females. Sperm competition is a potent evolutionary force among mammals, which has influenced not only the evolution of sperm numbers but also changes in sperm dimensions. Thus, sperm competition has favoured the elongation of the sperm tail, which has led to the attainment of faster swimming speed, an important factor when sperm from rival males compete to reach the ova first.

Precontact mammalian sperm-egg communication and role in fertilization

In creatures with external fertilization, e.g., metazoa, it is well established that there is precontact sperm-egg communication in the form of chemotaxis. An intriguing question is whether also in mammals, where fertilization is internal and the need for precontact sperm-egg communication is not self-evident, such a process occurs and what its physiological significance may be. Here we review the evidence related to such a process in mammals, evidence which suggests that sperm attraction to the ovulated egg may indeed occur. On the basis of the available data we propose a hypothesis, according to which a sperm population is heterogeneous with respect to its physiological state; some spermatozoa are at a physiological state ready for fertilizing an egg, while others are premature or overmature. According to the hypothesis this is a dynamic state; the population of fertilizing spermatozoa gradually loses its potency and, at the same time, other spermatozoa mature and acquire fertilizing ability. After ovulation, only the fertilizing spermatozoa are attracted to the egg, while the rest are either repelled or inhibited and thus prevented from reaching the egg. The potential significance of sperm-egg communication is discussed.

Sperm transport in the human female reproductive tract--a dynamic interaction

The interaction between sperm and the human female tract has been largely ignored. This review summarizes the data available from animal species with specific reference to sperm in the oviduct. Our knowledge of sperm transport within the human female tract is explored and, using the data available from animal species, three lines of future experimental design are suggested. Firstly, there is the need to improve and develop techniques to recover sperm successfully from the tract. Second, an in-vitro approach which examines the modulation of reproductive tract fluids on sperm function is advocated. Third, an in-vitro tissue/cell culture system is required to investigate in more detail the interaction between the epithelium and sperm. Using such approaches many of the questions posed in this review can be addressed confidently in the near future.

Effect of prostaglandin F2α at insemination on sperm cell numbers and pregnancy rate in beef cattle

Fourteen cycling, nonlactating, multiparous beef cows were artificially inseminated (AI) 10 to 12 h after the onset of natural estrus. One unit of frozen-thawed semen containing 100 x 10(6) total sperm cells was deposited into the body of the uterus. Immediately after AI, alternating cows were injected i.m. with either 25 mg (5 ml) of prostaglandin F(2)alpha (PGF) or 5 ml of 0.9% saline-benzyl alcohol control solution. Cows were slaughtered 16 +/- 1 h post AI, oviducts were retrieved, segmented into thirds (upper, middle and lower) and flushed with 1 ml of 0.2% gluteraldehyde in phosphate buffered saline. The number of sperm cells was counted using a phase contrast microscope. There were no right or left side effects (P=0.61) on the number of sperm cells recovered per oviduct within cow (389 vs 553; average SEM = 219). PGF had no effect (P=0.77) on the number of sperm cells recovered per oviduct (642 vs 300; average SEM = 231 for PGF and control females, respectively). More sperm cells were recovered from the lower third segment (P<0.05) compared with the middle and upper segments. Ovulation tended to affect (P=0.10) the number of sperm cells recovered per oviduct (742 vs 200; average SEM = 231). Additionally, 114 beef females (68 Angus x Hereford heifers and 46 Chianina crossbred postpartum suckled cows) were treated as described above following AI at natural estrus with 20 x 10(6) motile sperm cells. Pregnancy rates did not differ significantly in heifers (70.6 vs 58.8%) or in Chianina cows (34.8 vs 52.2%) for control and PGF-treated females, respectively. Overall, pregnancy rates were identical between control and PGF-treated females at 56.1%. In this study, PGF treatment immediately following AI in beef cattle had no effect on the number of sperm cells in the oviducts or on the pregnancy rate.

Transport and fate of spermatozoa after insemination of cattle

Sperm capable of fertilizing ova reach the isthmus of cows about 8 h after mating and remain in the caudal 2 cm of the isthmus until ovulation. Then small numbers of sperm move to the site of fertilization at the junction of the isthmus and ampulla. Within a few hours after deposition of semen in the uterine body, most sperm have drained to the exterior in cervical mucus. By 12 to 24 h after insemination, only a few percent of the sperm remain in the reproductive tract, and most of these are in the vagina. Contractions of the reproductive tract appear to be the primary mechanism of sperm transport. Flagellation of sperm is probably required for sperm to enter the folds of the cervix, and flagellation may be helpful or essential for sperm to pass through the uterotubal junction, move from the isthmus to the ampulla, and penetrate ova. High proportions of sperm undergo the acrosome reaction only in the ampulla on the side of ovulation and only after ovulation. The fertilization rate in cattle can be improved by use of semen from high fertility bulls and perhaps by timing insemination with semen from lower fertility bulls after the end of estrus.

Transport of spermatozoa in the sheep oviduct: preovulatory sequestering of cells in the caudal isthmus

Progression of ram spermatozoa within the sheep oviduct has been studied in relation to the time of ovulation. Ewes were mated at the onset of estrus and, at increasing intervals thereafter, the oviduct isthmus was transected 1.5-2.0 cm proximal to the utero-tubal junction. The incidence of fertilization and number of accessory spermatozoa were examined in eggs recovered 1 to 3 days after surgery. Ovulation occurred 24-26 hours after the onset of estrus. None of 52 eggs recovered from 48 oviducts transected up to 21 hours after mating was fertilized, nor were spermatozoa associated with the zona pellucida. Two of 33 eggs (6.1%) from 29 oviducts transected between 22 and 24 hours after mating were fertilized, while 3 of 14 eggs (21.4%) and 13 of 16 eggs (81.3%) were fertilized with transection at 25 and 26 hours, respectively. The mean numbers of accessory spermatozoa on eggs in the latter two groups were 0.7 (range 0-2) and 7.9 (range 0-26). Results from transection at 27-30 hours after mating indicated a progressive release and adovarian movement of spermatozoa. Viable spermatozoa are apparently sequestered in the caudal isthmus for as long as 17-18 hours, until shortly before ovulation, when a local transfer of ovarian follicular hormones is thought to facilitate their redistribution. The adrenergic stimulation of powerful adovarian waves of contraction in the isthmus at this time may also act to provoke the capacitation and hyperactivation of ram spermatozoa.

Regulation of oviduct function in pigs by local transfer of ovarian steroids and prostaglandins: a mechanism to influence sperm transport

Blood was collected from a prominent ear vein and from the arterioles supplying the caudal portion of each oviduct in 5 estrous animals. Sampling was arranged at 4 preovulatory intervals, and just after ovulation in the fifth animal. Steroid hormones and prostaglandins were determined by radioimmunoassay of plasma. Whereas the concentration of cortisol did not differ between peripheral and oviduct blood samples, the overall values for progesterone, androstenedione and estradiol were significantly higher in oviduct samples (P less than 0.001) - frequently by 5- to 10-fold or more. The concentration of these three hormones in oviduct blood corresponded, in most instances, with the number of preovulatory follicles or recent ovulations in the adjacent ovary but suitable statistical correlations could not be performed. Prostaglandin F2 alpha was also present in higher concentrations in oviduct compared with peripheral plasma (P less than 0.005), although pulmonary clearance of prostaglandins would have influenced the peripheral values. Differences in the concentration of prostaglandin E2 were not significant. A local transfer of follicular hormones from the ovarian vein to the ovarian and utero-tubal arteries is proposed as a means of regulating oviduct function. Elevated concentrations of steroids and prostaglandins transferred in this way would permit incisive changes in the patency and contractile activity of the isthmus, thereby facilitating the periovulatory phase of sperm transport from the caudal portion of the oviduct to the site of fertilization.