Reproduction in Domestic Animals

246 K-P Bru¨ ssow, J Rátky and H Rodriguez-MartinezTable 1. Sperm subpopulations (as %; LSM ± SE) in the porcine SRat pre-, peri- and post-ovulatory oestrus (modified from Tienthai et al.2004)RetrievedSR-spermatozoa (%)Oestrous stage at sperm retrieval (accounted formspontaneous ovulation)Preovulatory()8 h)Periovulatory(±4 h)Postovulatory(+8 h)Number of sows 7 10 7Viable, non-capacitated 72.8 ± 6.9 * 69.0 ± 6.8 * 70.9 ± 7.4 *Viable, capacitated 4.9 ± 3.0 * 1.4 ± 3.0 * 13.7 ± 3.0 *Dead 15.5 ± 5.3 * 16.9 ± 5.2 * 12.8 ± 5.7 **p < 0.05.mucus, hyperactive sperm motility, increased flow oftubal fluid and re-directed oviductal contractions(Rodriguez-Martinez et al. 1998). On the other hand,there is no evidence of a massive sperm release orcapacitation during the pre- and periovulatory periods(Table 1), but rather a constant sperm release towardsthe site of fertilization in relation to the occurrence ofspontaneous ovulation (Mburu et al. 1997; Tienthaiet al. 2004).What Controls Sperm Release from the SR?It is yet to be determined which are mechanism(s) thatinduce the sperm release from the porcine SR. The mostmentioned is the proposed presence of discrete signalsacting as transduced endocrine information from thepre-ovulatory Graafian follicles (Hunter et al. 1983;Hunter 1990), although experimental evidence backingthis mechanism is yet scarce.Experimental evidence for an ovarian influence on spermrelease from the SRMicroinjection of exogenous progesterone or progesterone-richfollicular fluid (FF) under the serosal layer ofthe oviduct surrounding the SR or directly into the SRprovoked a prominent release of spermatozoa and a34% incidence of polyspermy vs 2% in controls,injected with steroid-free FF or medium (Hunter 1972;Hunter et al. 1999). This has lead to the assumptionthat progesterone could be the key effector of spermrelease from the pig SR. Progesterone concentrationsare 100 to 1000 times higher in the FF than inperipheral blood (Eiler and Nalbandov 1977; Blo¨ dowet al. 1990), and thus could stimulate sperm releasefrom the SR when entering the oviduct at ovulation.However, FF does not (or only in a negligible amount,Hansen et al. 1991) enter the porcine oviduct, asdemonstrated by our own experiments, where the entryof FF into the tube was prevented by unilateralendoscopic ligation of the oviduct on the uterine sideof the infundibulum or FF-aspiration before ovulation(Bru¨ ssow et al. 1999a, 2003). Analyses of progesteroneconcentration in FF and oviductal fluid showed thatwhile progesterone levels were similarly low prior to orafter ovulation (0.09 ± 0.13 vs 0.12 ± 0.16 ng ⁄ ml) anddid not differ from the contra-lateral control side (groupFF aspiration: 0.29 ± 0.17 vs 0.24 ± 0.35 ng ⁄ ml;Table 2. Percentages of spermatozoa detected in the ampulla andisthmus of inseminated gilts (n = 12) where FF entry into the oviductwas prevented by aspiration of the FF or ligation of the oviduct on theuterine side of the infundibulum vs sham-ligation (Bru¨ ssow et al. 2003)Group(treatment vs control)Spermatozoa (%) within oviductalsectionAmpullaIsthmusOviduct ligation 0 * 100 *Intact control 35.5 * 64.5 *FF aspiration 0 * 100 *Intact control 29.6 * 70.4 *Sham ligation 42.1 57.9Intact control 45.7 54.3*p < 0.05 vs control.group oviduct ligation: 0.22 ± 0.19 vs 0.21 ±0.22 ng ⁄ ml); those in FF were significantly higher(269.7 ± 67.9 and 389.6 ± 226.5 ng ⁄ ml) albeit notreflected in the oviductal fluid. Likewise, Hansen et al.(1991) found only 0.03 to 0.07% of the progesteroneconcentration of the FF was present within the oviductalflushing. Therefore, although a direct role ofprogesterone in eliciting sperm release from the SR isyet to be determined, a series of interesting results haveemanated from studies testing the involvement of FF inthe process of fertilization. The effect of withdrawingthe FF by aspiration of pre-ovulatory follicles or byoviduct ligation before ovulation was compared for itsrelation to the way spermatozoa were distributed withinthe oviduct right after ovulation vs in sham-manipulatedor intact oviducts (Bru¨ ssow et al. 1999b, 2003).Both a ligature of the oviduct or the FF-aspirationreduced the proportion of spermatozoa within theampullar ⁄ AIJ tubal segment (Table 2), thus suggestingthe sperm release from the SR was constrained. However,it is yet to be clarified whether an absentprogesterone-rich FF was the factor behind this difference.The FF is able to stimulate in vivo fertilization, asdemonstrated in a follow-up study (Bru¨ ssow et al. 2003)in which 6 to 10 cumulus-oocyte-complexes (COCs)recovered from donor gilts were transferred into theoviducts of inseminated recipient gilts – either togetherwith 0.6 ml of FF in one oviduct (FF group – localinfluence of FF) or together with 0.6 ml of PBS into thecontra-lateral oviduct (PBS group – without FF influence,within-animal controls). Another group of giltsserved as sham-operated control-group. The FF wascollected from both ovaries in the recipient gilts andpooled, but the COCs were rejected, to diminishconfounding effects. From this experiment, it wasevident that similarly to controls, the presence of FFcomponentswithin the oviduct increased fertilizationrate (Table 3). However, since a direct effect of FF isalready excluded in vivo, owing to the fact that the FFdoes not significantly enter the oviduct, neither it is anobligatory carrier of porcine oocytes at ovulation(Bru¨ ssow et al. 1998a, 1999a); the influence of FFcomponents on sperm migration and fertilization ispossibly generated by local counter-current transfer intothe blood and lymph circulation, as suggested by HunterÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag