Copper: a biphasic regulator of caprine sperm forward progression.

Copper is essential for spermatogenesis and its presence has been demonstrated in male and female reproductive fluids in several mammalian species. However, little is known about the physiological significance of this trace element in the regulation of forward progression of mammalian sperm cells which is essential for sperm fertility potential in vivo. The purpose of this investigation was to determine the physiological role of the bivalent copper ion (Cu(2+)) on mammalian sperm forward motility using a chemically-defined medium and caprine cauda epididymal sperm model. Sperm forward motility was significantly enhanced by Cu(2+) in a dose-dependent manner; maximal activation (approx 20%) was noted at the 5 µM level of the metal. Above 10 µM Cu(2+) sperm motility decreased, showing that Cu(2+) exerts a biphasic regulation on sperm motility. These findings have been confirmed using a spectrophotometric motility assay, an objective method of motility analysis. At lower concentrations (up to 5 µM), copper enhanced sperm membrane lipid peroxidation as well as the level of intra-sperm cyclic adenosine mono phosphate (c-AMP), but at a higher level it caused marked inhibition of both of the biochemical parameters. The observed correlation of Cu(2+)-dependent biphasic modulation of sperm membrane lipid peroxidation and intrasperm c-AMP with sperm forward motility is consistent with the view that Cu(2+) regulation of sperm motility is mediated by membrane lipid peroxidation, which in turn modulates the level of intra-sperm c-AMP, a well-known activator of sperm motility.