Storage and Release of Spermatozoa from the Pre-Uterine Tube Reservoir

Abstract

In mammals, after coitus a small number of spermatozoa enter the uterine tube and following attachment to uterine tube epithelium are arrested in a non-capacitated state until peri-ovulatory signalling induces their detachment. Whilst awaiting release low numbers of spermatozoa continually detach from the epithelium and the uterine tube reservoir risks depletion. There is evidence of attachment of spermatozoa to uterine epithelium in several species which might form a potential pre-uterine tube reservoir. In this study we demonstrate that: (1) dog spermatozoa attach to uterine epithelium and maintain flagellar activity, (2) in non-capacitating conditions spermatozoa progressively detach with a variety of motility characteristics, (3) attachment is not influenced by epithelial changes occurring around ovulation, (4) attachment to uterine epithelium slows capacitation, (5) capacitated spermatozoa have reduced ability to attach to uterine epithelium, (6) under capacitating conditions increased numbers of spermatozoa detach and exhibit transitional and hyperactive motility which differ to those seen in non-capacitating conditions, (7) detachment of spermatozoa and motility changes can be induced by post-ovulation but not pre-ovulation uterine tube flush fluid and by components of follicular fluid and solubilised zona pellucida, (8) prolonged culture does not change the nature of the progressive detachment seen in non-capacitating conditions nor the potential for increased detachment in capacitating conditions. We postulate that in some species binding of spermatozoa to uterine epithelium is an important component of the transport of spermatozoa. Before ovulation low numbers of spermatozoa continually detach, including those which are non-capacitated with fast forward progressive motility allowing the re-population of the uterine tube, whilst around the time of ovulation, signalling from as-yet unknown factors associated with follicular fluid, oocytes and uterine tube secretion promotes the detachment of large numbers of capacitated spermatozoa with hyperactive motility that may contribute to the fertilising pool.

Effect of calcium, bicarbonate, and albumin on capacitation-related events in equine sperm

“…Capacitation can be achieved in vitro in most species by incubation of sperm in a medium that imitates the environment of the female reproductive tract (Yanagimachi 1994, Freeman & England 2013, typically the one containing BSA, calcium, and bicarbonate (standard capacitating medium). Addition of BSA, a cholesterol acceptor, is associated with cholesterol efflux from the sperm plasma membrane in boar, human, and mice (Boerke et al 2008, Tulsiani & Abou-Haila 2011.…”

Oviduct Binding and Elevated Environmental pH Induce Protein Tyrosine Phosphorylation in Stallion Spermatozoa1

“…During natural mating, mammalian spermatozoa are deposited in the female reproductive tract and subsequently migrate to a sperm reservoir, which, in many species, is located in the isthmus of the oviduct [1][2][3], although there are exceptions, such as the dog [4,5]. In the sperm reservoir, spermatozoa bind via the apical region of the head to oviduct epithelial cells (OECs) [6][7][8].…”

Uterine fluid from bitches with mating-induced endometritis reduces the attachment of spermatozoa to the uterine epithelium

“…However, the long period of sexual receptivity in the bitch means that mating frequently occurs many days before ovulation. Arguably, the development of a hostile uterine environment after an 'early' mating might be more significant than the 'on time' inseminations of the present study; at early breedings the role of the uterine epithelium as a storage site for spermatozoa becomes more important (England et al, 2013b;Freeman and England, 2013). In the instance of an early mating or insemination, it might be appropriate to consider reducing the potential impact of any mating-induced endometritis by large-volume lavage of the uterus prior to a second mating, as has been proposed in the management of this condition in mares (Vanderwall and Woods, 2003), but clearly this contention needs further study in bitches.…”

“…The bitch uterine epithelium is an important storage site for spermatozoa (England et al, 2013a;Freeman and England, 2013), and so the possibility of a hostile uterine environment influencing the survival of spermatozoa was the key focus of this study. We collected uterine lavage fluid from bitches that had been monitored at a previous oestrous cycle where either no uterine fluid was detected and the bitches had become pregnant, or where uterine fluid was detected in bitches with endometrial hyperplasia and they had not become pregnant.…”