HYALURONAN IN THE SOW’S OVIDUCT: ITS EFFECT ON BOAR SPERM MORPHOLOGY AND FUNCTION

Abstract

During sperm transport in the female pig, a proportion of the spermatozoa is arrested at the uterotubal junction and the isthmus, where an oviductal sperm reservoir is built up. The sperm reservoir maintains sperm viability and controls the release of fertilizing spermatozoa so that only a small subpopulation reaches the site of fertilization, thus diminishing the risk of polyspermy. In vitro research has focused on sperm binding as the main mechanism of sperm storage, sperm release and modulation of capacitation, but little attention has been paid to the sperm reservoir fluid, its composition and the control of capacitation in vivo. This review provides information about the characteristics of the oviductal sperm reservoir during the estrous cycle and its main luminal content
which is composed of hyaluronan (HA) and includes the effects of HA on porcine spermatozoa. In inseminated sows, the spermatozoa are entrapped in a mucus-like oviductal fluid from the pre-ovulation UTJ and the adjacent isthmus. This fluid contains HA which is synthesized in the epithelium by HA synthase-3. The HA receptor “CD44”
is particularly concentrated in the deep furrows of the sperm reservoir where most spermatozoa are trapped. Massive sperm capacitation does not occur in the sperm reservoir during pre-ovulation and peri-ovulation in vivo. However, the capacitation of spermatozoa in the sperm reservoir is increased post-ovulation, suggesting a role for
HA in modulating sperm capacitation in pigs. The findings support the concept that the sperm reservoir keeps the potentially fertile spermatozoa viable and uncapacitated during their pre-ovulatory arrest and this data may help improve sperm preparation protocols for porcine in vitro fertilization (IVF) and the preservation of boar semen.