SEQUENTIAL ACQUISITION OF CHEMOTACTIC RESPONSIVENESS BY HUMAN SPERMATOZOA

Recent studies have indicated that human spermatozoa respond to follic ular fluid by attraction to chemotactic factors in the fluid, accompan ied by enhancement of motility and ultimately hyperactivation. In this study, we quantified the sperm response. We exposed spermatozoa to a gradient of a chemotactically active fraction of follicular fluid (den oted as ''the attractant'') and separated the spermatozoa that accumul ated in the attractant and those that did not. We thus obtained two su bpopulations: one enriched with chemotactically responsive spermatozoa , and one deficient in such spermatozoa. The fraction of the responsiv e spermatozoa out of the total sperm population was 2-12% at any measu red time point. With time, the responsive spermatozoa lost their abili ty to be attracted, while such activity was gradually acquired by the subpopulation originally deficient in responsive spermatozoa. These re sults indicate that the identity of responsive spermatozoa is continuo usly changing. If the in vitro results are representative of the physi ological conditions in vivo, they imply that the role of sperm chemota xis combined with enhanced motility may be to select capacitated sperm atozoa and bring them to the egg. Such a mechanism may, over an extend ed period of time, increase the prospect that an egg will meet capacit ated spermatozoa as soon as it ovulates.