Spermatozoa normally encounter the egg at the fertilization site (in the Fallopian tube) within 24 hr after ovulation. A considerable fraction of the spermatozoa ejaculated into the female reproductive tract of mammals remains motionless in storage sites until ovulation, when the spermatozoa resume maximal motility and reach the fertilization site within minutes. The nature of the signal for sperm movement is not known, but one possible mechanism is attraction of spermatozoa to a factor(s) released from the egg. We have obtained evidence in favor of such a possibility by showing that human spermatozoa accumulate in follicular fluid in vitro. This accumulation into follicular fluid was higher by 30-260% than that observed with buffer alone and was highly significant (P < 10-8). Not all of the follicular fluids caused sperm accumulation; however, there was a remarkably strong correlation (P < 0.0001) between the ability of follicular fluid from a particular follicle to cause sperm accumulation and the ability of the egg, obtained from the same follicle, to be fertilized. These findings suggest that attraction may be a key event in the fertilization process and may give an insight into the mechanism underlying early egg-sperm communication.Spermatozoa normally meet the egg at the fertilization site (isthmic-ampullary junction of the Fallopian tube) within 24 hr after ovulation (1)(2)(3). In women, cervical spermatozoa have been reported to possess prolonged acrosomal integrity (in vivo), and this has led to the suggestion that the human cervix may serve as a site of sperm storage (4). In cattle, pigs, and rabbits it has been shown that a considerable fraction of the spermatozoa ejaculated into the female reproductive tract remain in the isthmus of the Fallopian tube until ovulation occurs; they then resume their motility and reach the fertilization site of the ampulla within minutes (2). The mechanisms for sperm selection and the synchronization between ovulation and sperm movement in the female reproductive tract are not known. One plausible mechanism for directed sperm movement would be the attraction of mammalian spermatozoa to factor(s) released from the egg. In vivo studies are currently difficult or impossible, and the many techniques available for measuring leukocyte chemotaxis in vitro (5) appear to be inadequate for studies on mammalian sperm chemotaxis, primarily because of the complexity and rapidity of sperm motion, which subsequently results in poor signal-to-noise ratios. On the other hand, microscopic methods have been useful for demonstrating chemoattraction of invertebrate spermatozoa to the egg (6, 7). Such studies in the mammal have not been reported to our knowledge. Here we examine the possibility of sperm attraction to follicular factor(s) by measuring sperm accumulation in follicular fluid in vitro. We show that human spermatozoa indeed accumulate in follicular fluid and that this accumulation correlates with the ability of the egg to be fertilized. MATERIALS AND METHODSPreparations o...

Spermatozoa normally encounter the egg at the fertilization site (in the Fallopian tube) within 24 hr after ovulation. A considerable fraction of the spermatozoa ejaculated into the female reproductive tract of mammals remains motionless in storage sites until ovulation, when the spermatozoa resume maximal motility and reach the fertilization site within minutes. The nature of the signal for sperm movement is not known, but one possible mechanism is attraction of spermatozoa to a factor(s) released from the egg. We have obtained evidence in favor of such a possibility by showing that human spermatozoa accumulate in follicular fluid in vitro. This accumulation into follicular fluid was higher by 30-260% than that observed with buffer alone and was highly significant (P < 10-8). Not all of the follicular fluids caused sperm accumulation; however, there was a remarkably strong correlation (P < 0.0001) between the ability of follicular fluid from a particular follicle to cause sperm accumulation and the ability of the egg, obtained from the same follicle, to be fertilized. These findings suggest that attraction may be a key event in the fertilization process and may give an insight into the mechanism underlying early egg-sperm communication.