In vivo measurement of pH, CO2 and HCO3- levels in the uterus of non-anesthetized sows through the estrous cycle and after insemination

Abstract Background The pH-CO2-HCO3− system is a ubiquitous biological regulator with important functional implications for reproduction. Knowledge of the physiological values of its components is relevant for reproductive biology and the optimization of Assistant Reproductive Techniques (ARTs). In vivo pH of the oviduct and uterus has been estimated by direct in situ measurements in a few species. However, regarding the levels of CO2 and HCO3−, information is very scarce and, when available, it comes from fluid samples instead of in vivo estimations. This study describes a non-invasive method to measure pH and % of CO2 in the uterus of sows with cutting-edge technology and no medication. Sows were at three different reproductive conditions, estrous with no insemination E(-)AI and after insemination E(+)AI, and diestrous (non-estrous, NE). From pH and CO2 data, HCO3− concentration was estimated. Results The designed methodology allowed for in situ time-lapse recording of pH and % of CO2 within the uterus of non-anesthetized sows. Variable oscillatory patterns of pH, CO2 and HCO3− were found independently of the estrous condition. Insemination did not changed the levels of uterine pH, % of CO2 and HCO3− concentration, -E(-)AI = E(+)AI-, but all the values were affected by the estrous cycle in a way that decreased significantly at diestrous condition - E(-)AI and E(+)AI > NE-. Conclusions A non-invasive approach to the porcine uterus with novel optical probes allowed the obtaining of in situ physiological values of pH, CO2, and HCO3− at different reproductive conditions. While the short-time presence of sperm in the uterus did not change the physiological milieu, the whole pH-CO2-HCO3− system was affected by the estrous cycle. This study contributes to a better understanding of the in vivo regulation of the pH/CO2/HCO3− system in the uterus and may help to optimize the protocols of sperm treatment for in vitro fertilization.