Sex is complicated. Scientists know there’s a lot happening during reproduction, but a recent finding reveals an even more surprising event taking place during intercourse. Dr. Gregg Adams and his team have found a component in the seminal fluid that actually prepares the female body for ovulation!
In 2005, Adams and his team discovered a protein in seminal fluid that could induce ovulation in llamas and alpacas. They called this protein, Ovulation-Inducing Factor (OIF). In Adams’ latest study, he and his team discovered that this protein is actually a chemical called Nerve Growth Factor (NGF) — a protein that is crucial for the development and survival of sensory neurons — and that it also exists in humans.
Mammals can be divided into two groups: induced ovulators (i.e. camels, llamas and rabbits, which release eggs in response to sex) and spontaneous ovulators (i.e. humans or mammals with regular menstrual cycles and a regularly scheduled release of eggs). The researchers were able to isolate the OIF protein in semen from both llama (induced ovulators) and cattle (spontaneous ovulators) and, through a series of experiments, found that the OIF in seminal fluid worked across species. For example, seminal fluid from llamas induced ovulation in mice!
But, how is OIF inducing ovulation? It was always assumed that NGF did not cross the blood-brain barrier and only acted locally on the sensory areas of the nervous system. However, when the OIF protein is introduced into the uterus, it travels to the hypothalamus and pituitary gland triggering a hormonal response that activates ovulation. This study suggests that OIF is traveling through the bloodstream, crossing the blood-brain barrier and activating the hypothalamus and pituitary gland to release hormones necessary for pregnancy. How exactly the OIF is crossing the blood-brain barrier is not yet known and requires more study, but it is clear that NGF is playing a role in reproduction.
The discovery of NGF in seminal plasma helps to answer the evolutionary question of the existence of the male accessory gland system as more than a mere vestige. OIF in semen effects ovarian function and gonadotropin release and has a direct effect on the hypothalamo-pituitary-gondal axis of females making the male gland system much more of a team member than earlier thought.
Spontaneous ovulators do not need NGF to ovulate, but it does still have an effect on fertility. The OIF protein aids the growth of ovary follicles which release eggs. It also affects the growth of the corpus luteum – a structure formed from the collapsed follicle after an egg is released – which produces progesterone, a hormone crucial for maintaining a pregnancy. Progesterone is important in both the male and female for fertility and pregnancy. Adams hopes to conduct more research on how NGF in the seminal fluid is related to issues of fertility. His team plans to see if the level of OIF in semen has a direct relation to infertility (i.e. do higher levels of OIF in semen equal more fertile). Such research promises to be helpful in the field of infertility and for couples experiencing difficulties in getting pregnant.