Ovulation-inducing factor in seminal plasma: a review

Area of Science:

• Reproductive biology and endocrinology
• Mammalian ovulation mechanisms
• Hormonal regulation of reproduction

Background:

• Ovulation involves GnRH and LH pulsatile release, with species classified as spontaneous or induced ovulators.
• Induced ovulators typically rely on copulatory stimuli for GnRH release, unlike spontaneous ovulators triggered by estradiol.
• Previous research suggested physical stimulation during copulation is key for ovulation induction in camelids like alpacas and llamas.

Purpose of the Study:

• To investigate the role of seminal plasma components in inducing ovulation.
• To re-examine the mechanisms of ovulation in both induced and spontaneous ovulators.
• To characterize the ovulation-inducing factor (OIF) in seminal plasma.

Main Methods:

• Analysis of seminal plasma for ovulation-inducing activity.
• Characterization of OIF's protein nature, molecular mass, and resistance to degradation.
• In vivo and in vitro studies to assess OIF's effects on LH secretion, ovulation, and ovarian dynamics across various species.

Main Results:

• Direct evidence for an ovulation-inducing factor (OIF) in semen, stimulating LH secretion, ovulation, and luteal development.
• OIF is a heat- and proteinase K-resistant 14kDa protein molecule acting systemically, potentially at the hypothalamus.
• OIF is present in diverse mammalian species and induces ovulation/LH release even in spontaneous ovulators, suggesting a broader role.

Conclusions:

• Seminal plasma OIF is a potent, systemically acting stimulant of ovulation, mediated at the hypothalamic level.
• The discovery of OIF necessitates a re-evaluation of ovulation induction mechanisms across mammalian species.
• OIF's presence and function in spontaneous ovulators indicate it is not merely a phylogenetic vestige but plays a significant reproductive role.