Role of seminal osmolarity in the regulation of human sperm motility

Abstract

Mammalian sperm at ejaculation are suspended in the seminal plasma, a heterogeneous mixture deriving from the testicular/epididymal fluid and from secretions of seminal vesicles, prostate and bulbourethral glands. Biochemical characteristics of seminal fluid change along the male reproductive tract when considering its inorganic and organic composition and pH but it is known that in each region of the male genital tract seminal osmolarity is higher than that of serum. It has been previously demonstrated that in invertebrate and vertebrate sperm, seminal plasma osmolarity influences sperm motility and activity, and human sperm have been shown to possess osmosensitive calcium entry pathway that controls important functions such as acrosome reaction and oocyte penetration. In the present study, we have determined seminal plasma osmolarity in a large number of normozoospermic fertile and asthenozoospermic infertile subjects correlating it with sperm motility percentages and kinematic characteristics determined utilizing a computerized motion analysis system. Our results confirm that seminal plasma osmolarity is higher than that of serum (336.1 +/- 20.2 vs. 291.1 +/- 6.9 mOsm/L, respectively). Normozoospermic subjects show seminal osmolarity values that are significantly lower with respect to asthenozoospermic patients (317.8 +/- 12.2 vs. 345.2 +/- 22.6 mOsm/L, p<0.001), irrespective of the cause of asthenozoospermia. Seminal plasma osmolarity negatively correlates with sperm progressive motility percentages and kinetic characteristics (curvilinear velocity, linear velocity, linear coefficient and lateral displacements of sperm head). Furthermore, when sperm from fertile subjects were suspended in medium with an osmolarity increasing from 300 to 600 mOsm, sperm motility percentages and kinetics characteristics were progressively reduced and nearly abolished when medium osmolarity was 600 mOsm. On the contrary, when sperm from asthenozoospermic subjects with high semen osmolarity were resuspended in medium with lower osmolarity, sperm motility parameters improved significantly. Sperm motility parameters did not correlate with seminal plasma concentrations of sodium, potassium, chloride with a weak correlation only with seminal calcium concentration. No correlations are present between seminal plasma osmolarity and ionic composition. In conclusion, the present study confirms and extends the knowledge that, in human, seminal plasma osmolarity is higher than that of serum and demonstrates that seminal osmolarity influences sperm motility characteristics and then it may contribute to the pathogenesis of some forms of asthenozoospermia and male infertility.

The seminal coagulum favours passage of fast-moving sperm into the uterus in the black-handed spider monkey

“…Such a view is supported by the fact that is a major trait showing variability (Sato et al 2007, Hernández-Ló pez et al 2008, providing females (or their reproductive tracts) a substrate for male quality assessment. Since different glands contribute to its formation, a small variation in the amounts of constituents contributed by each gland yields structurally diverse seminal coagula, where changes in its components, independently from sperm concentration, severely impair fertility (Rossato et al 2002, Mikhailichenko & Esipov 2005, Khosrowbeygi & Zarghami 2007, de Lamiranda 2007.…”

“…The seminal coagulum also provides a viscous matrix preventing sperm diffusion out of the ejaculate, and in many primate species contains semenogelins as well as prostate-specific antigen and prostatic acid phosphatase, the enzymes needed to induce ejaculate clotting and its further liquefaction respectively (Lilja 1993, Dorus et al 2004, Clark & Swanson 2005. In addition, semenogelins induce sperm quiescence to avoid spending energy during migration throughout the male tract (Robert & Gagnon 1996, Cooper 1998, Rossato et al 2002, de Lamiranda 2007. Furthermore, prostaglandins found in the seminal coagulum induce contractions of the smooth musculature of the female tract to enhance sperm transport (Prins 1998, Suarez & Pacey 2006.…”

Components of stallion seminal plasma and their influence on spermatozoa

“…No differences are seen in sodium or potassium concentrations between ejaculatory fractions (Kareskoski et al 2005). The addition of potassium to semen extenders improves motility of stallion (Padilla and Foote 1991) and human sperm (Karow et al 1992), but Rossato et al (2002) found no correlation between the ionic composition and the osmolarity of human seminal plasma. Intracellular concentrations of potassium are higher than those of seminal plasma, and therefore potassium levels are linked to sperm concentration.…”

Spontaneously developed tail swellings (SDTS) influence the accuracy of the hypo-osmotic swelling test (HOS-test) in determining membrane integrity and viability of human spermatozoa

“…Cryopreserved sperm underwent the standard freeze-thaw procedure using enhanced sperm freeze solution (Conception Technology). Sperm in semen or in vitro reagents were handled in such a way that physiological osmolarity was not compromised [13][14][15]. SDTS was assessed by observing the sample under a phase contrast microscope at 400X magnification.…”

“…The difference between SDTS and HOS is that both are tail swellings, but it is considered SDTS when swelling is unexpectedly exhibited in fluids holding physiological osmolarities, while HOS occurs if sperm are exposed to hypo-osmotic conditions [1,13]. Physiological osmolarity in this context refers to the osmolarity values of body fluid like semen, and in vitro developed reagents in which human cells, including spermatozoa, maintain their cellular integrity and perform normal physiological functions [13][14][15]. Our study investigated the prevalence of SDTS in sperm samples that are commonly encountered in an andrology laboratory, and secondly the influence of SDTS in HOS-test results.…”