The University of Saskatchewan team of international scientists, led by Gregg Adams, has found that sex and a protein in male semen acts on the female brain to prompt ovulation.
A professor of veterinary biomedical sciences at the Western College of Veterinary Medicine at the Saskatchewan University, Gregg's team has found that the male protein also "regulates the growth, maintenance, and survival of nerve cells." This protein is known as NGF (nerve growth factor).
The study shows that all male mammals have accessory sex glands that are known to contribute seminal fluid to semen. However, the role of the fluid and glands was not well understood until the current study, which is raising questions about fertility in all mammals. The study was published in the August 2, 2012, issue of the "Proceedings of the National Academy of Sciences (PNAS)."
“From the results of our research, we now know that these glands produce large amounts of a protein that has a direct effect on the female,” says Adams.
The large amount of protein perplexed Adams, as the effects of the abundant protein on females have never been recognized prior to the new study. The protein is called the ovulation-inducing factor (OIF), found in the semen of all mammal species. Once the team compared OIF to thousands of other proteins, "To our surprise, it turns out OIF and NGF are the same molecule," Adams says. "Even more surprising is that the effects of NGF in the female were not recognized earlier, since it's so abundant in seminal plasma."
While OIF/NGF may function differently from animal to animal, it is present in all mammals studied so far, from llamas, cattle and koalas to pigs, rabbits, mice, and humans. This implies an important role in reproduction in all mammals. Just how it works, its role in various species, and its clinical relevance to human infertility are a few of the questions that remain to be answered.
Gregg's international team studied cattle and llamas, as llamas are "induced ovulators." This means they ovulate only when they are inseminated. Cows and humans are "spontaneous ovulators," which means they require a regular build-up of hormones in order to stimulate an egg release. The semen acts as a hormonal signal through the hypothalamus of the female brain and its pituitary gland. This triggers the release of other hormones, signaling the ovaries to release eggs or an egg, depending on the species.
The researchers used a wide source of techniques, comparing OIF and NGF. It was found that they had the same size and caused the same effects across all mammal species. “The idea that a substance in mammalian semen has a direct effect on the female brain is a new one,” Adams explains in ScienceCodex. “This latest finding broadens our understanding of the mechanisms that regulate ovulation and raises some intriguing questions about fertility.”