Sperm chemotaxis accumulation assays

The accumulation-based assays for sperm chemotaxis can be divided into three main categories. 

In this assay, the spermatozoa in the well are suspended in a solution containing the chemoattractant. The capillary, containing either a control buffer or the chemoattractant, is immersed in the sperm suspension. When the capillary contains buffer only, the spermatozoa sense a descending gradient of the chemoattractant as they move from the well to the capillary (Figure 7). When the chemoattractant is in both the capillary and the well, they sense no gradient at all. A comparison is made between these two conditions. This assay thus measures the sperm tendency to leave the chemoattractant rather than to accumulate in it. In the case of sperm chemotaxis, sperm accumulation in the capillary is... 

ANP is a polypeptide hormone that is secreted in large quantities by the atrial portion of the heart and from a variety of other mammalian cell types. It exerts many of its actions via activation of particulate guanylate cyclase [16, 134]. ANP is present in human follicular fluids [163] and specific ANP receptors have been identified in human spermatozoa [144]. Sperm chemotaxis to ANP was demonstrated by sperm accumulation in capillaries with ascending [6] and descending [192] gradients and by choice assays [192] (Table 4). It is not yet known whether ANP is involved in sperm chemotaxis in vivo and whether the physiological chemoattractant for human spermatozoa is an ANP-like substance. Since chemotaxis to ANP at physiological concentrations can be observed only in the presence of a neutral endopeptidase inhibitor such... 

In conclusion, follicular fluid, bourgeonal, ANP, and RANTES are the only substances that have been demonstrated to act as chemoattractants for spermatozoa by assays that differentiate between chemotaxis and other processes causing accumulation (Table 1). ANP may not be a direct physiological chemoattractant but rather a guanylate cyclase activator. The significance of sperm chemotaxis to bourgeonal and RANTES is an open question. The identity of the chemoattractant(s) in follicular fluid has yet to be revealed. 

A similar technique that does distinguish between chemotaxis and other means of sperm accumulation is the inverted capillary assay (Figure 7). 

In a series of studies, Sliwa [146-149, 151] demonstrated mouse sperm accumulation in acetylcholine, adrenaline, calcitonin, -endorphin, oj ocin, and substance P. Negative mouse sperm accumulation (i.e., apparent repulsion) was demonstrated with glucagon and vasopressin. However, since only a single assay was used in these studies (a choice assay that did not distinguish between chemotaxis and trapping), the significance of these observations with respect to chemotaxis is not clear. 

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