Temporal correlations between plasma ovarian steroid hormone levels and intrauterine oxygen tension in the guinea pig.

In summary, while arterial and venous pO2 remain constant throughout the estrous cycle, dramatic fluctuations in intrauterine oxygen tension occur, reaching maximal levels on Days 0 and 6 when plasma estrogen levels are elevated. This correlation suggests that ovarian steroids regulate intrauterine pO2 via their actions upon a number of uterine and vascular parameters, the temporal relationships existing between the mid-luteal rise in plasma estrogen, intrauterine pO2 and implantation suggesting that the steroid induced increase in oxygen availability to the blastocyst may participate in the process of implantation in the guinea pig.