Reproduction in Domestic Animals

Fertilization in the Porcine Fallopian Tube 247Table 3. In vivo fertilization and cleavage rates of porcine cumulusoocyte-complexes(COCs) transferred together with FF or PBS(n = 35 gilts; Bru¨ ssow et al. 2003)FF-treatedoviductsPBS-treatedoviductsControloviductsNumber of oviducts (n) 24 22 24Number of COCs transferred (n) 206 144 –Number of oocytes recovered (n) 138 70 235Recovery rate (%) 67.0 * 45.5 * 73.4 aNumber of oocytes fertilized (n) 78 26 119Fertilization rate (%) 56.5 * 31.7 * 50.6 *Number of cleaved embryos (n) 76 26 113Cleavage rate b (%) 97.4 100 98.3a Relative to the number of ovulated follicles.b Relative to the number of fertilized oocytes.*p < 0.05.et al. (1983), Hunter (1996). However, such hypothesisis yet to be proven.Involvement of oocytes and their cumulus cells in spermrelease form the SRThat oocytes and their cumulus vestment divert spermatozoatowards the ova has been considered previously(Austin and Walton 1960; Harper 1973; Bedfordand Kim 1985), but putative molecular mechanisms arestill speculative (Hunter 1993), and experimental evidenceof an association of oocytes with SR-spermrelease in the pig is missing. Therefore, we created amodel in which ova from donor gilts were transferred atthe periovulatory period into only one oviduct – theother serving as a control – of bilaterally ovectomized(aspiration of oocytes from the follicle) recipient giltsthat previously underwent endoscopic intrauterineinsemination (endo-IUI) with low sperm-doses intoboth uterine horns (Bru¨ ssow et al. 2006). Such a modelavoids ovulation of the recipient’s COCs, and enablesassessment of how the transfer of ova would influencesperm release from the SR. The most important findingof this study was that the presence of COCs in theoviduct significantly increased the percentages of spermatozoain the ampullar and isthmic segments, comparedto control oviducts. Both total numbers andproportions of spermatozoa were always higher, indicatingthat the presence of ova affected sperm releasefrom the SR (Table 4). However, this result does notexplain which component(s) of the oocytes promptedthe spermatozoa to leave the SR.Which components are involved in the sperm release formthe SR?One of the components of the oocytes that mayinfluence spermatozoa to leave the SR could be glycosaminoglycans(GAGs), especially the non-sulfatedGAG hyaluronan (HA) (Tienthai et al. 2004; Liberdaet al. 2006). The HA, a major component of the porcineextracellular matrix of the cumulus and zona pellucida(ZP) (Yokoo et al. 2002) is increasingly synthesized byCOCs during cumulus expansion (Kimura et al. 2002;Yokoo et al. 2007). It is thought to participate in spermcapacitation and release towards the site of fertilization(Tienthai et al. 2000a). Since the level of HA in theporcine ampullar fluid increases around ovulation(Tienthai et al. 2000b), it is possible that additionalHA enters the oviduct together with the COCs. Therefore,we experimentally analysed both the influence oftransferred ovum quality (COCs or cumulus cellremovedoocytes) and addition of HA (COCs + HA,oocytes + HA) on fertilization and the numbers ofZP-accessory spermatozoa in previously ovectomizedendo-IUI gilts (Bru¨ ssow et al. 2003, 2006). Embryodevelopment was not affected by ova quality or exogenousHA. The numbers of accessory spermatozoa werehighest in those COCs transferred together with HA(COC+HA), which did not differ from controls(Table 5). Comparable results have been achieved inprevious experiments (Bru¨ ssow et al. 2003) where additionof exogenous HA, together with cumulus-freeoocytes increased fertilization rates and the number ofaccessory spermatozoa compared to oocytes or COCs.One explanation for these results was that washingand ⁄ or manipulation of COCs in vitro, removed componentsimportant for fertilization. An alternativeinterpretation was that the proposed impact of FF viacounter-current transfer (Hunter 1972) on sperm releaseis missing in gilts from which FF was withdrawn.Summarizing the experimental data, the higher numberof accessory spermatozoa may strengthen the evidencethat HA participates in the process of sperm releasefrom the SR (Rodriguez-Martinez et al. 2005; Liberdaet al. 2006).Ovum Transport and Fertilization in theOviductOvulation, i.e. the ‘flow out’ of a mature folliclereleasing a COC into the oviduct, is a multifacetedTable 4. Distribution of boar spermatozoa (mean ± SE) withinoviductal sections in gilts (n = 10) with transferred COCs (treatedoviducts) or without COCs (control oviducts) (Bru¨ ssow et al. 2006)Treated oviducts (withCOCs)Control oviducts (withoutCOCs)n % n %Total sperm count 63 869 100 85 049 100Sperm reservoir 52 696 82.5 ± 0.5 * 80 921 95.2 ± 0.06 *Isthmus 5699 8.9 ± 0.11 * 2754 3.2 ± 0.06 *Ampulla 5474 8.6 ± 0.11 * 1374 1.6 ± 0.04 *Isthmus + Ampulla 11 173 17.5 ± 0.15 * 4128 4.9 ± 0.07 **p < 0.01 (chi-square).Table 5. Mean numbers (LSMeans ± SEM) of blastomeres and ofaccessory spermatozoa within the zona pellucida in embryos developingin vivo following oocyte or COC transfer, with or withoutexogenous HA (Bru¨ ssow et al. 2006)GroupBlastomeresAccessoryspermatozoaOocyte 2.6 ± 0.2 29.1 ± 3.1 *Oocyte + HA 2.9 ± 0.2 26.2 ± 3.9 *COC 3.1 ± 0.2 22.2 ± 3.3 *COC + HA 2.9 ± 0.2 46.2 ± 5.0 *Control 2.9 ± 0.2 45.2 ± 3.1 **p < 0.05.Ó 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag