Hyperactivated sperm progress in the mouse oviduct.

Sperm from naturally mated mice were observed and videotaped moving within mouse oviducts. The typical pattern of sperm progress involved intermittently breaking free and swimming a short distance, then reattaching to the epithelium. The proportion of sperm that swam freely (were not attached to the epithelium) was calculated and analyzed for effects of oviductal region, ovulation status, and sperm location relative to the lumen. A significantly higher proportion of sperm were free in the ampulla than in the isthmus (26.3% +/- 0.8% vs. 11.8% +/- 1.0%; p less than 0.0001) and in post-ovulatory than pre-ovulatory (16.2% +/- 2.0% vs. 10.6% +/- 1.6%; p less than 0.05) oviducts. Flagellar curvature ratio values showed that free sperm (0.716 +/- 0.024) had more sharply curved tails than stuck sperm (0.782 +/- 0.013). While this difference is significant (p = 0.01), the effect of attachment status interacted significantly (p less than 0.05) with the oviductal region such that there was a greater difference in the isthmus than in the ampulla. Only sperm using the more curved tail beats of hyperactivation were seen to break free from the epithelium and to progress along the oviduct. These results indicate that hyperactivation plays a role in moving sperm out of the isthmic reservoir and to the site of fertilization.