It isn't just sperm that is present in semen. A protein called NGF might stimulate production of eggs for the sperm to fuse with. [Image Credit:]

Protein in Semen Stimulates Ovulation in Female Brain

A protein being termed ‘Ovulation-inducing Factor’ has been found in the seminal fluid of a variety of male mammals, which stimulates the female brain to produce eggs (the process of which is called ovulation).

Ovulation-Inducing Factor

The presence of such a protein was first discovered when female camels ovulated soon after injection with semen. This experiment was repeated with llamas and alpacas to see the same results. However, the species in which it was first discovered (rabbits and koalas, besides camels) are called ‘induced ovulators’, meaning that the females produce eggs only upon insemination by the male. In other mammals including horses, pigs and humans, ovulation is spontaneous—meaning that there is a biological cycle in the female which leads to a buildup of hormones leading to the release of the egg. It turned out that OIF was also present in the semen of these spontaneous ovulators. Did OIF actually change ovulation rhythms in them?

It isn’t just sperm that is present in semen. A protein called NGF might stimulate production of eggs for the sperm to fuse with. [Image Credit:]

The conservation of this protein must have a biological significance, and one way to determine that was to characterize the protein OIF. Researchers isolated this protein from llamas and bulls and tried to identify it in order to determine how its mechanism of action in the female body. By comparing protein structures, they found that this protein is actually a Nerve Growth Factor (NGF), a protein commonly found in nerve cells of the body. To confirm this finding, they isolated NGF from mice and injected it into llamas, and found that ovulation was induced in the llamas.

NGF Acts as a Hormone on the Female Brain

The NGF protein can act on the hypothalamus of the female brain via a system of hormones. What this means is that a substance that is a part of the male body can interfere with the female’s reproductive cycle. Is this true in humans too? We don’t know, but it might mean that we can rely less on birth control methods relying on abstinence during some days of the menstrual cycle. We know that human semen contains NGF, and that NGF can act on female hormones, but the female reproductive cycle is one that is tightly controlled, and further studies will have to be performed to determine the extent to which OIF/NGF can influence ovulation in spontaneous ovulators. In cows, injection of OIF has shown to alter ovarian function and shortens the ovarian cycles of cows.

“The idea that a substance in mammalian semen has a direct effect on the female brain is a new one,” says Gregg Adams, who headed the research team. “This latest finding broadens our understanding of the mechanisms that regulate ovulation and raises some intriguing questions about fertility.” Perhaps a host of fertility-related issues could be traced back to deficiencies in NGF in male semen, or NGF receptors in females.

You can read about this research here.


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