A key component of the female reproductive system may have been overlooked. Research into the rete ovarii, an appendage of the ovaries that has previously been dismissed as useless, suggests it has an important role after all.
鈥淲e think it is regulating the timing or rate of ovulation,鈥� says at Duke University in North Carolina. 鈥淚t may control how many [ovarian] follicles are activated in one鈥檚 cycle or when they are activated.鈥�
Her team plans to do further studies to try to confirm this. 鈥淲e haven鈥檛 proved all of this, but there are several smoking guns here,鈥� she says.
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Capel and her colleagues聽 while creating 3D images of developing mouse ovaries and surrounding material.
These images are created by using fluorescent antibodies to light up specific tissues. When the team used one that binds to a protein called PAX8, it showed up a large tubular structure next to the ovaries that extended into it.
鈥淲hen we first found it, we thought, what is this?鈥� says Capel. It turned out to be the rete ovarii, a structure that was first described in 1870, says team member , also at Duke University. It seems to be common to all mammals and was included in the 1914 edition of Gray鈥檚 Anatomy, a standard medical textbook on the human body.
But much of the attention the rete ovarii has received is related to rare abnormalities, such as cysts and tumours. With some studies concluding it is a vestigial structure with no function, it has been dropped from modern editions of the book.
Part of the problem is that even in large animals, the rete ovarii is extremely difficult to see with the naked eye, says Anbarci. It is only because the team was creating 3D images with PAX8 that it could be seen in mice, she says. 鈥淚t was just the luck of using the right antibody.鈥�
While continuing to study the development, structure and function of the rete ovarii, mostly in mice, the researchers found nerves connecting to the appendage. Anbarci is now trying to establish whether these are sending information or receiving it.
In another experiment, Anbarci injected a fluorescent dye into the part of the rete ovarii furthest from the ovaries, finding that it was transported all the way to the organ to which it is attached.
鈥淪o it can actively transport fluid into the ovary,鈥� says Capel. 鈥淭hat suggests that it really does function. It鈥檚 also surrounded by macrophages, which are really interesting cells that communicate a lot around the body.鈥�
We know the ovaries respond to what is happening elsewhere in the body. Extreme exercise can halt ovulation, while obesity can result in irregular ovulation, for instance.
It is assumed that the ovaries respond directly to chemical signals in the blood, but it could be the rete ovarii that is relaying signals, says Capel. 鈥淚t may be a sensory mechanism for the ovary to keep tabs on what鈥檚 going on in the rest of the body,鈥� she says. 鈥淜ind of like an antenna.鈥�
If this is true, it might also play a role in determining when the menopause occurs, says Capel. 鈥淚f it plays a role in regulating the number of follicles that are ovulated, it could be regulating the female reproductive lifespan,鈥� she says. 鈥淪o we could perhaps use it somehow to extend the female reproductive lifespan.鈥�
In the latest study, the researchers call for the rete ovarii to be added to the list of structures that make up the female reproductive tract 鈥� along with the vulva, vagina, cervix, uterus, oviduct and ovaries 鈥� and for its role to be investigated. There is a related structure in the testes called the rete testis, but the team says its research shows the rete ovarii is more complex.
at the University of Pavia in Italy says the role of the rete ovarii is worth exploring. 鈥淐apel鈥檚 hypothesis is quite reasonable and merits investigation,鈥� she says.
bioRxiv
