Laser Light-Scattering Study of the Effect of Progesterone on Sperm Motility

Abstract

It is known that progestins can induce in the secretory cells of the cervix the excretion of a mucus that is highly viscuos, scanty, and impenetrable to spermatozoa. Mucus of this type is similar to that excreted during the luteal phase of the normal human menstrual cycle and the cow estrous cycle. It is a natural sequence to ask the question, do progestins also have a direct effect on sperm motility? With dynamic laser light-scattering we measured the motility of freshly washed human spermatozoa and of spermatozoa in the presence of a progesterone, both in terms of their swimming speed distribution as expressed in the spectrum of scattered light. The swimming speed was significantly reduced when the concentration of progesterone was three orders of magnitude greater than that of the physiologic level. This finding confirms the finding in earlier biochemical studies that progesterone has a distinct spermiostatic effect. We suggest this answer to the above question: progestin-releasing contraceptive devices may act on spermatozoa directly as well as in the secretory cells of the cervix.Laser light scattering was used to determine the concentrations of progesterone that would inhibit sperm motility in vitro to judge whether the mechanism of progesterone action as a contraceptive was due to alterations of cervical mucus and, hence, sperm transport inhibition. 2 methods were used: one dissolved progesterone in a semen sample obtained by human masturbation, and one required implantation of a progesterone-containing silicone rod in cow uterine tissue in vitro. Swimming speed of spermatozoa was determined. From a control sample, it was found that the decay of sperm ability to swim was an exponential function of frequency. The swimming speed of washed sperm and treated sperm was measured by the spectrum of scattered light. Overall, the swimming speed was significantly reduced when the concentrations of progesterone were 3 orders of magnitude greater than the physiological level, confirming progesterone's spermiostatic effect. Apparently, progesterone acts on receptors of the sperm plasma membrane, causing sperm stasis. Since laser light scattering is noninvasive, it has a place in evaluations of sperm motility. This study showed that the concentration of progesterone can be as high as 2 mcg/ml in the cervix without causing an appreciable effect on sperm motility, but inhibition occurs at higher progesterone concentrations.