Changes in expression and activity levels of ecto-5'-nucleotidase/CD73 along the mouse female estrous cycle.

Aim:  Extracellular ATP and its hydrolysis product adenosine modulate various reproductive functions such as those requiring contraction, hormone synthesis and maintenance of fluid composition. Moreover, adenosine is a key molecule for sperm capacitation. Extracellular nucleotide and nucleoside levels are affected by cell surface ectonucleotidases, amongst which the ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) family is the most abundant and effective to hydrolyse ATP and ADP to AMP. In the female reproductive tract three members of this family have been recently identified: NTPDase1, NTPDase2 and NTPDase3 (Histochem. Cell Biol.131, 2009, 615). The purpose of the present study was to characterize in this system the expression profile of ecto-5′-nucleotidase (CD73), the enzyme generating adenosine from AMP. Methods:  Immunological techniques and in situ enzymatic assays were used to characterize the ecto-5′-nucleotidase expression in the mouse female reproductive tract along the four stages of the estrous cycle, that were determined by vaginal smear examination. Results:  Ecto-5′-nucleotidase was abundantly detected in the corpora lutea of the ovaries, as well as in several epithelia, such as that of oviducts, uterus and endometrial glands. Marked changes in endometrial ecto-5′-nucleotidase expression and activity along the estrous cycle are described, these being maximum at estrus phase, coinciding with optimal female sexual receptivity. Conclusion:  The adenosine generated thereby, besides other functions, might contribute to sperm capacitation, thus significantly influencing fertility.