Sperm motility within the mammalian epididymis: species variation and correlation with free calcium levels in epididymal plasma.

The region within the epididymis where spontaneous sperm motility first appeared and the extent of later motility within that organ, as shown by microscopic observation of undiluted samples, varied with the species. In the rat, mouse, and hamster, little sperm motility was present. In other species, spontaneously motile sperm were obtained from the caput (rabbit) and corpus (bull and man) regions of the epididymis. Samples from the cauda region of the epididymis were found to contain many motile sperm in the rabbit, bull, and especially man, where most of the sperm were intensely motile. There was a correlation between the amount of free calcium surrounding the sperm within the cauda epididymidis of a given species and the level of sperm motility therein. An inverse relationship was also found between the free calcium concentration in the cauda epididymal plasma of a species and the later inducibility of motility in diluted sperm from that species by calcium ion.