Researchers at the
Researchers studied the effect that uterine disease has on the reproductive system in cows. Their findings, published in the November issue of the journal Reproduction, suggest that the cow's innate immune system may affect key stages in the reproductive cycle, including suppressing the release of the female sex hormone estrogen and causing failure to ovulate.
In cows, bacteria that enter the uterus after the cow has given birth usually cause uterine disease. The same route of infection can also occur in women; however, humans may also be affected by sexually transmitted infections such as Chlamydia. Although the infections are usually successfully treated with antibiotics, the infertility often persists.
Using the bacterium E. coli, the researchers examined the effect that bacteria have on the granulosa cells that line each egg-containing follicle in the ovary. These granulosa cells nurture the egg until the follicle bursts to release the egg, and they make estradiol (a form of estrogen), which encourages the female to copulate. The researchers found that even after treatment of uterine disease, the follicle still contains a toxin left over from the breakdown of the pathogen.
The researchers also found that granulosa cells, which protect the egg inside the follicle, play a part in the immune response to infection by recognizing that the toxin has entered the follicle and inhibiting production of estradiol.
The researchers say they believe that granulosa cells may play a role in 'quality control' relating to ovulation. Infection can potentially damage the genetic make-up of an egg, and these 'errors' would be passed down from generation to generation. By suppressing the release of estrogen — in effect, reducing sexual behavior — the granulosa are preventing those defects being passed on.
The scientists theorize that these findings open up a new, previously overlooked, avenue for treating uterine disease in cows.
The emphasis on treating uterine disease has so far always been on clearing infection in the uterus. The researchers say that everyone needs to remember that the infection also affects the ovaries and may cause lasting damage.
The findings mirror those from research previously carried out in mice, suggesting that granulosa may be a part of the innate immune system in other mammals, possibly including humans.
It appears that bacteria have a lasting effect on fertility in cattle and possibly humans, say researchers. Their work suggests a mechanism for how this may occur and offers hope for developing new treatments to prevent this from happening.
The Wellcome Trust and the Biotechnology and Biological Sciences Research Council funded this research.