Secretions of Ovine Uterus and Oviduct Induce in Vitro Capacitation of Ram Spermatozoa

Abstract

Interaction between spermatozoa and female reproductive tract fluids involves both losses of surface proteins and adsorption of exogenous fluids' components. To study the functional consequences of this interaction, sperm acrosome reaction was evaluated after incubation at 37°C in uterine (UF) and/or oviductal (OF) fluid collected at estrus from conscious ewes. Ram spermatozoa were collected through the catheterized vas deferens. The fluids had previously been diluted with equal volumes of BWW medium or dialyzed against BWW. Control incubations were in BWW. Twenty minutes before the end of incubation, Ca²⁺(2.5 mM) was added to induce the acrosome reaction, which was assessed using a triple stain technique. Results showed that 22–24% of the sperm experienced acrosome reaction after sequential incubation in UF (1 h) and OF (4 h), or in UF alone (5 h). Exposure to OF alone induced 13% of acrosome reaction. When the spermatozoa were preincubated in UF followed by OF, the acrosome reaction percentage increased almost linearly with time. When incubated in UF alone, this percentage increased steadily with time, whereas a plateau was reached after 1 h of incubation in OF alone. Dialysis of the fluids did not modify the results. These results show that ewe reproductive tract secretions may capacitate ram spermatozoa in vitro, evaluated by their efficacy to induce acrosome reaction.

Key Words:

• spermatozoa
• capacitation
• acrosome reaction
• uterine fluid
• oviductal fluid