Fallopian tube fluid stickiness may affect fertility

Variations in the viscosity, or 'stickiness', of fluid in the fallopian tubes influence the behaviour of cells lining the tubes, potentially impacting fertility.

The viscosity of extracellular fluid in the fallopian tubes is controlled by components such as glucose and proteins, secreted by fallopian tube epithelial cells (FTEC) that line the tract. While its effects on sperm swimming behaviour have been explored, the role of fluid viscosity on the FTEC was unknown before a study recently published in Nature Communications.

'When the fluid is thicker, the extra resistance causes the cells to change their behaviour' said lead author Melati Abdul Halim, a PhD candidate at Monash University in Melbourne, Australia. 'Some cells start growing tiny hair-like structures called cilia, which help move things like eggs along the reproductive tract. The thicker the fluid, the more cilia these cells produce, and the more coordinated their movements become.'

To simulate different viscosities in the fallopian tube, researchers used a 2D microfluidic culture model. They discovered that higher viscosities lead to a fourfold increase in the proportion of FTEC that differentiate into ciliated cells, despite a reduction in overall cell density. This increasing ciliation trend is consistent with natural changes during the menstrual cycle, where both ciliation and fluid viscosity peak during ovulation.

Overall, these findings suggest that at high viscosities, ciliated cells in the fallopian tube self-organise their beating behaviour, forming waves of similar frequency, direction and wavelength. This coordination potentially facilitates the formation of the 'metachronal waves', crucial for producing a unidirectional flow from the ovary towards the uterus.

'The study suggests that the elevated viscosity at certain stages of the menstrual cycle could be a natural mechanism to enhance the formation and coordination of cilia, thus facilitating fertilisation,' said corresponding author Dr Reza Nosrati.

Dr Nosrati suggested that more research in this areas is needed, so that eventually the role of fluid viscosity in the fallopian tubes could be evaluated 'as part of infertility diagnosis and assisted reproduction practices.'