Reproduction in Domestic Animals

248 K-P Bru¨ ssow, J Rátky and H Rodriguez-Martinezinflammatory-like process initiated by a surge in gonadotropichormones, followed by structural changes in thefollicular wall and vascular microcirculation, consequenceof the action of proteolytic enzymes andprostaglandins (Espey and Lipner 1994). At ovulation,oocytes at the metaphase II stage are picked up by thecilia-covered fimbria and guided through the infundibulumand ampulla (Oxenreider and Day 1965; Alanko1974). Thereby oocytes with their cumulus vestmentaggregate within an ‘egg plug’ (Tanabe et al. 1949;Spalding et al. 1955). The rate of ovum transporttowards the AIJ is rapid (30–45 min, Andersen 1927;Alanko 1965), with the initial speed of ovum transportcalculated as 76 mm ⁄ h (Bru¨ ssow 1985). It is still notclear how ovum pick-up and transport are regulated, asCOCs are conveyed against a flow of tubal fluid.Possibly, this is accomplished by a concerted interactionbetween cumulus cells and the extracellular matrix theysynthesize (mainly HA) which, by dramatically increasingthe size of the egg plug, makes ciliary beating(Talbot et al. 1999), as well as myosalpingeal peristalsis(Rodriguez-Martinez et al. 1982) very effective in movingthe ova to the AIJ. Cumulus cells disperse within 6 hpost-ovulation (Hunter and Dziuk 1968; Hunter 1974;Bru¨ ssow et al. 1987); a process which is stronglyinfluenced by the presence of spermatozoa in the oviduct(Rodriguez-Martinez et al. 2001).The fertilization process within the AIJ includes thebinding of spermatozoa to the glycoprotein covering ofthe oocyte, the ZP-penetration, and finally the fusionwith the oolemma. This generates the cortical reactionand subsequent a ZP-hardening to prevent polyspermicpenetrations, a very effective system in vivo, but still aserious constrain in vitro (Funahashi et al. 2000, 2001).Gamete recognition, binding and fusion are highlyregulated processes involving a number of biochemicalevents (Jansen et al. 2001; Miller and Burkin 2001; Rathet al. 2006). The chronological and cytological details offertilization and early embryonic development in the pighave been thoroughly described by Hunter (1974). Earlyembryo development up to the 4-cell stage occurs withinthe Fallopian tube. Fertilized embryos (appearance oftwo pronuclei) can be observed approximately 5–8 hafter ovulation in the AIJ and isthmus and remain for alonger time (up to 26 h) in the one-cell stage. The 2-cellembryo stage is of short duration (6–8 h) and withinfurther 6–8 h they develop into 4-cell embryos. Earlycleavage of embryos occurs in the isthmus, and mostlyat the 4-cell stage they leave the oviduct 50–60 h postovulation(Hancock 1961; Alanko 1974; Hunter 1974;Bru¨ ssow 1985). Blastulation is impeded in the oviduct(Oxenreider and Day 1965; Rodriguez-Martinez et al.1985), for reasons still unknown.Data on the transport of fertilized and non-fertilizedova through the porcine oviduct are scarce and originateonly from experiments with either inseminated or noninseminatedsows. Some influence of fertilized embryoson oviductal transport was observed (Bru¨ ssow andRa´tky 1996), contrary to other authors (Mwanza et al.2002). However, other factors may influence ovumtransport. As such, PMSG-induced superovulation(SO) alters the distribution of embryos in the oviductwith retardation in the ampulla on d1 after hCGinduced ovulation and an accelerated transport on d3(Bru¨ ssow et al. 1987). It remains unclear if this alterationis due to the higher number of oocytes releasedand ⁄ or an altered hormonal environment in the oviductafter SO. Stress-induced alteration of cortisol levels byfood deprivation (Mburu et al. 1998) or exogenous-ACTH administration (Razdan et al. 2002; Brandt et al.2007) influenced embryo development and distributionwithin the oviduct, as well as disturbed sperm transport,estimated on accessory sperm count (Brandt et al. 2006).Contribution of Oviductal Fluid on SpermCapacitation, Fertilization and EmbryoDevelopmentOviductal fluid (ODF) is formed by selective transudationfrom the blood and specific secretion from theoviduct epithelium; it differs from blood plasma interms of ionic composition, pH, osmolarity and macromolecularcontent, and it varies with the endocrinestatus during the oestrous cycle (Leese 1988; Leese et al.2001). Two areas important to prepare sperm forfertilization, such as sperm quiescence (ensuring spermatozoaare kept alive and potentially fertile) andcapacitation (a destabilizing process, particularly relatedto the apical sperm plasma membrane; see reviewby Rodriguez-Martinez 2007). They are subscribed tobe influenced by the ODF; namely the presence ofdifferent pH environments and the presence of GAGs.For the first named, data from our laboratories indicatethe SR possesses (at least pre-ovulation) an acidic pH,with low levels of local bicarbonate (Rodriguez-Martinez2007), which might be responsible for maintainingsperm quiescence and which prevents sperm capacitationin the SR shortly before ovulation (Mburu et al.1996; Tienthai et al. 2004). Our current results suggest asignificant proportion of boar spermatozoa retrievedfrom the pre-ovulatory SR and exposed to homologousODF of either pre-, peri- or post-ovulatory oestroussows only capacitate, when exposed to post-ovulatoryODF (Tienthai et al. 2004). Capacitation is, however,triggered if these SR-spermatozoa were exposed tobicarbonate (at levels recorded to be present in theAIJ ⁄ ampulla in vivo, e.g. 33–35 mM; Tienthai et al.2004). Bicarbonate is, therefore, considered a specificeffector of the process not only in pigs but also in otherspecies, such as the bovine (Bergqvist et al. 2006). Suchexposure induces sperm membrane destabilization and,ultimately, primes them to acrosomal exocytosis, asdemonstrated in vitro, and expected in vivo. It istherefore postulated that the constant release of individualspermatozoa out of the SR is sufficient to inducetheir capacitation when adequate levels of the effectorare encountered outside of the SR area (Rodriguez-Martinez et al. 2005), thus marking capacitation as aperiovulatory process in vivo (Hunter and Rodriguez-Martinez 2004).The pig ODF contains GAGs, either non-sulphated(HA) or sulphated (S-GAGs, e.g. chondroitin sulphate,dermatan sulphate, keratan sulphate, heparan sulphateand heparin) (Tienthai et al. 2001; Buhi 2002). Themean concentrations of total S-GAGs in ODF differbetween isthmus and ampulla and vary also in relationÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag