Suppression of progesterone-enhanced hyperactivation in hamster spermatozoa by estrogen

In this study, I examined whether sperm hyperactivation in hamster is regulated by steroid hormones such as estrogen (estradiol, E(2)) and progesterone. Although sperm hyperactivation was enhanced by progesterone, 17beta-estradiol (17betaE(2)) itself did not affect sperm hyperactivation. However, 17betaE(2) suppressed progesterone-enhanced hyperactivation in a concentration-dependent manner through non-genomic pathways when spermatozoa were exposed to 17betaE(2) at the same time or before exposure to progesterone. When spermatozoa were exposed to 17betaE(2) after exposure to progesterone, 17betaE(2) did not suppress progesterone-enhanced hyperactivation. Moreover, 17alpha-estradiol, an inactive isomer of E(2), did not suppress progesterone-enhanced hyperactivation. Observations using a FITC-conjugated 17betaE(2) showed that it binds to the acrosome region of the sperm head. Binding of 17betaE(2) to spermatozoa was not inhibited by progesterone, although 17betaE(2) did not suppress progesterone-enhanced hyperactivation when spermatozoa were exposed to 17betaE(2) after exposure to progesterone. On the other hand, binding of progesterone to spermatozoa was also not inhibited by 17betaE(2) even if progesterone-enhanced hyperactivation was suppressed by 17betaE(2). Although tyrosine phosphorylations of sperm proteins were enhanced by progesterone, enhancement of tyrosine phosphorylations by progesterone was suppressed by 17betaE(2). Moreover, tyrosine phosphorylations were inhibited by 17betaE(2) when only 17betaE(2) was added to the medium. From these results, it is likely that 17betaE(2) competitively suppresses progesterone-enhanced hyperactivation through the inhibition of tyrosine phosphorylations via non-genomic pathways.