Incubation of sperm with UPA at concentrations around the expected plasma levels after ingestion of this EC pill (˜100-200 ng/ml) did not modify the signal transduction of TyrP involved in sperm capacitation. Moreover, UPA showed no agonist effect on progesterone receptors because it did not induce AR. Considering that progesterone in hFF is essential for AR induction, and UPA did not prevent the hFF-induced AR, an antagonist action of UPA on the AR is unlikely.