17β-Estradiol and environmental estrogens significantly affect mammalian sperm function

Background: Compounds with estrogenic activity can affect reproductive function in mammals. This study investigated possible effects of 17β-estradiol (E₂) and three weakly estrogenic environmental estrogens on mammalian sperm capacitation and fertilizing ability in vitro. Methods: Uncapacitated and capacitated mouse sperm suspensions were incubated for 30 min in the presence of E₂, genistein (Gen), 8-prenylnaringenin (8-PN) and nonylphenol (NP), and then assessed using chlortetracycline (CTC) fluorescence analysis. In addition, treated uncapacitated sperm suspensions were tested for changes in fertilizing ability. Results: In uncapacitated cells, E₂ at ≥1 μmol/l and Gen, 8-PN and NP at ≥0.001 μmol/l, significantly stimulated capacitation and acrosome reactions. Hydroxytamoxifen (an estrogen antagonist) did not inhibit responses to any of these compounds. In capacitated cells, E₂ had no effect, but the other three compounds significantly stimulated acrosome reactions. Added to uncapacitated suspensions, 10 μmol/l E₂, 0.1 μmol/l Gen and 0.1 μmol/l 8-PN all significantly stimulated sperm fertilizing ability (∼76% oocytes fertilized) compared with untreated control sperm (∼36%). Conclusions: This study provides the first evidence that E₂ and environmental estrogens can significantly stimulate mammalian sperm capacitation, acrosome reactions and fertilizing ability, with the environmental estrogens being much more potent than E₂. The inability of hydroxytamoxifen to block these responses suggests that classical estrogen receptors may not be involved. Whether these responses have effects on fertility in vivo remains to be determined, along with the mechanisms of action involved.