Seminal plasma aids the survival and cervical transit of epididymal ram spermatozoa

Abstract

Seminal plasma purportedly plays a critical role in reproduction, but epididymal spermatozoa are capable of fertilisation following deposition in the uterus, calling into question the biological requirement of this substance. Through a combination of direct observation of spermatozoa in utero using probe-based Confocal Laser Endomicroscopy, in vivo assessment of sperm fertility and in vitro analysis of various sperm functional parameters, this study investigated the role of seminal plasma in spermatozoa transit through the cervix of the ewe. Following deposition in the cervical os, epididymal spermatozoa previously exposed to seminal plasma displayed an enhanced ability to traverse the cervix as evidenced by both significantly higher pregnancy rates and numbers of spermatozoa observed at the utero-tubal junction when compared with epididymal spermatozoa not previously exposed to seminal plasma. The beneficial effect of seminal plasma on sperm transport was clearly localised to transit through the cervix as pregnancy rates of spermatozoa deposited directly into the uterus were unaffected by exposure to seminal plasma. This phenomenon was not explained by changes to sperm motion characteristics, as seminal plasma had no effect on the motility, kinematic parameters or mitochondrial membrane potential of spermatozoa. Rather, in vitro testing revealed that seminal plasma improved the ability of epididymal spermatozoa to penetrate cervical mucus recovered from ewes in oestrus. These results demonstrate that the survival and transport of ram spermatozoa through the cervix of the ewe is not linked to their motility or velocity but rather the presence of some cervical penetration trait conferred by exposure to seminal plasma.

From One Ejaculate to Another: Transference of Sperm Traits via Seminal Plasma Supplementation in the Ram

“…One context in which seminal plasma has received significant research attention is in the application of assisted reproductive technologies (ART). Epididymal sperm can be successfully used to fertilise eggs both in vitro and in vivo [13], demonstrating that seminal plasma is not essential for reproduction [14]. Indeed, seminal plasma is routinely washed from sperm prior to use in ART as its persistent presence in IVF prevents capacitation and sperm-egg fusion [15].…”

“…Indeed, seminal plasma is routinely washed from sperm prior to use in ART as its persistent presence in IVF prevents capacitation and sperm-egg fusion [15]. However, seminal plasma supplementation during sperm processing can also be used to improve sperm function in ART [10,13], although outcomes are inherently variable due to variability in seminal plasma composition and the method of supplementation [16]. For example, the addition of seminal plasma can improve post-thaw sperm quality, but only when the seminal plasma is sourced from males with high freeze-tolerance ejaculates [17,18].…”

Submitted oral and poster presentations

“…Among those, 14 correlated negatively (Pearson correlation coefficients from -0.85 to -0.43; p<0.05) and 4 correlated positively (0.52 to 0.44) with fertility. From this set of 18 proteins, 4 had previously been found to be related to sperm quality, motility and/or freezing ability in sheep (Rickards et al, 2014, 2015, Soleilhavoup et al, 2014. An interesting example is Ubiquitin carboxyl-terminal hydrolase isozyme L3, which increases in abundance with fertility.…”

Physiological function of seminal vesicle secretions on male fecundity

“…These results suggest that the accessory gland secretions regulate the timing of sperm capacitation to improve male fertility. Accessory gland secretions help the survival and cervical transit of epididymal spermatozoa and to prevent an immunological response to spermatozoa in the female reproductive tract …”