Leptin and leptin receptor are detectable in equine spermatozoa but are not involved in in vitro fertilisation.

This research investigates the presence and role of hormones leptin (OB) and leptin receptors (OB-R) in equine spermatozoa and their impacts on in vitro fertilisation (IVF). The results indicate that while OB and OB-R can be detected in horse sperm, they do not independently contribute to successful fertilisation.

Introduction and Study Objectives

• The study explores the presence, location, and expression of leptin (OB) and leptin receptors (OB-R) — hormones previously identified in human and swine seminal plasma — in horse spermatozoa.
• The role of OB in in vitro fertilisation (IVF) of horses is investigated, specifically in comparison with progesterone (P), a hormone also found in follicular fluid (FF). FF is used as a reference point for in vitro sperm preparation in this study.

Results

• OB and OB-R mRNA and the corresponding proteins were identified in horse spermatozoa for the first time.
• When sperm were treated with OB, three motility parameters (VSL, STR, and LIN) decreased, which are commonly associated with hyperactivation. However, the acrosome reaction rate — a pivotal process for fertilisation — increased.
• Comparison of the fertilisation rates and the percentage of eight-cell stage embryos reveal that OB doesn’t facilitate oocyte fertilisation by itself. The fertilisation rate was 51% with FF, 46.15% with P, 43.64% with P+OB, and 0% with OB alone. Similarly, the percentage of eight-cell stage embryos was 18.7% with FF, 17.1% with P, and 16.7% with P+OB.

Conclusions

• While OB and OB-R are detectable in equine spermatozoa and do affect sperm capacitation and hyperactivation, they don’t enhance the penetration of sperm into the oocyte (egg cell). This is unlike progesterone, which appears to contribute to both capacitation/hyperactivation and successful penetration, therefore leading to higher fertilisation rates.