Influences of 5-Hydroxytryptamine Receptor Agonists on Spermatozoal Hyperactivation and In Vitro Fertilization...

In mice, 5-hydroxytryptamine (5-HT) enhances hyperactivation through 5-HT₂, 5-HT₃, 5-HT₄, and 5-HT₇ receptors and increases in vitro fertilization (IVF) success through the 5-HT₄ receptor. In the present study, we examined the effects of 5-HT receptor agonists on motility, hyperactivation, motility kinematics, and IVF success in mice.

Spermatozoa were incubated for 4 h at 37°C under 5% CO₂ in modified Tyrode's albumin lactate pyruvate medium to induce hyperactivation. Motility and hyperactivation were analyzed using a video microscope. Motility kinematics were evaluated using the Sperm Motility Analysis System. IVF was performed by co-incubation of spermatozoa and oocytes for 0.5 and 5 h.

5-HT receptors were detected. 5-HT₂, 5-HT_2A, 5-HT_2B, and 5-HT₄ receptor agonists significantly enhanced hyperactivation and increased IVF success. 5-HT₃ and 5-HT₇ receptor agonists slightly enhanced hyperactivation but did not affect IVF success. These agonists did not affect motility. During hyperactivation, the velocities of motility kinematics decreased. 5-HT₂, 5-HT_2A, 5-HT_2B, and 5-HT₄ receptor agonists accelerated the decrease in velocities.

These results suggest that 5-HT₂ and 5-HT₄ receptors participate in the enhancement of hyperactivation and the increase in IVF success in mice. The influence of the 5-HT₄ receptor agonist is stronger than that of the 5-HT₂ receptor agonists.