Relationships of mammalian sperm motility and morphology to hydrodynamic aspects of cell function.

Abstract

This study investigated the relationships of sperm body morphology and flagellar beat frequency and shape with the swimming velocity, power output, and stirring of nearby fluid by the spermatozoa of several mammals. Hamster spermatozoa were studied before and after the motility activation which is associated with capacitation and the acrosome reaction in that species. Human spermatozoa were assessed while swimming progressively in semen, and also while exhibiting the figure-of-eight beat pattern seen in cervical mucus and other media of high viscosity. Ram spermatozoa were studied while swimming in diluted semen. Data obtained from high-speed cinemicrography were applied to a computerized mathematical model of the hydrodynamics of sperm movement. The results demonstrate the relationships between sperm hydrodynamics and morphology, flagellar beat frequency, and shape. Many of these relationships are highly nonlinear, so that small differences in geometrical parameters of morphology and movement can produce large differences in hydrodynamic characteristics. Thus, hamster spermatozoa (preactivated) swim faster and expend more energy than ram spermatozoa which, in turn, exceed human spermatozoa in these measures. However, there is sufficient geometrical similarity in the morphologies and movement characteristics of these spermatozoa that appropriate grouping of various parameters results in dimensionless expressions with general applicability. Thus, the conclusions resulting from the present work can be used in studying the spermatozoa of other mammals as well. It was also shown that fluid stirring by spermatozoa, as opposed to smaller microorganisms, is an important mechanism of transfer of dissolved ions, molecules, and gases to and from the cell surface. In this regard, activated hamster sperm stir substantially more fluid than do preactivated hamster sperm, even though their power outputs are not significantly different.