Inability of human sperm to change their orientation in response to external chemical stimuli

Abstract

To investigate whether human sperm can respond to external chemical stimuli by orienting themselves toward chemoattractants or withdrawing from hostile environments. Controlled laboratory assays. Normal human sperm and two other flagellated micro-organisms were exposed to various potential chemoattractant or chemorepellent substances. Human sperm, Euglena viridis, and Escherichia coli were exposed to various substances from the female reproductive system or to various toxic agents by placing them within tiny wells in a sealed minichamber. They were followed by microscopic observation and by intermittent photography. Images of photographed micro-organisms were analyzed for signs of attraction to or withdrawal from the test substances. Human sperm neither changed their orientation toward nor accumulated next to the well that contained cervical mucus, uterine cavity and follicular fluid, cumulus cells, or intact nonfertilized human eggs. Contrary to other micro-organisms that turned away from sources of hydrochloric acid, sodium hydroxide, ethanol, or glutaraldehyde, human sperm did not withdraw from these solutions. They swam along the ascending chemical gradient, facing ahead while becoming immobilized by these agents. It may be implied from the observation that they did not turn away from a hostile environment when expected to do so or turn toward chemoattractants that human sperm do not respond to external chemical stimuli and, most probably, chemotaxis between human sperm and ova in nature does not exist.