Motility of rat spermatozoa at the site of fertilization

This study was undertaken to examine the factors that may affect the numbers and motility patterns of spermatozoa at the site of fertilization. The contents of the oviductal ampullae of previously mated cycling or superovulated immature rats were examined microscopically. We determined whether spermatozoa were free or associated with cells and whether they exhibited hyperactivated motility, forward progressive motility, or were immotile. These data were correlated with the percentage of fertilized eggs. In addition, the beat pattern of hyperactivated spermatozoa was characterized by using high-speed video microscopy. At the time when half of the eggs were fertilized, ampullae of cycling rats contained an average of less than one motile spermatozoon per ampulla. Most of these motile spermatozoa were hyperactivated. About half of these were free in the ampulla and about half were in the cumulus or zona pellucida. Hyperactivated spermatozoa displayed a nonprogressive whiplash wave form with a high amplitude recovery stroke similar to that described in hamster and guinea pig spermatozoa capacitated in vitro. In addition to motile spermatozoa, we counted about three immotile spermatozoa for each motile spermatozoon. In superovulated, immature female rats, we found about ten times as many spermatozoa in each category as in cycling rats. From our observations, it is clear that very few spermatozoa reach the ampulla of the oviduct. Furthermore our observations suggest that in cycling rats progressively swimming spermatozoa may become hyperactivated shortly after entering the ampulla of the oviduct. They probably enter the cumulus mass within a short time or become immotile.(ABSTRACT TRUNCATED AT 250 WORDS)