The Role of Phosphate Esters in Male Fertility

Abstract

Spermatozoa do not achieve full maturation and fertilizing capacity until passage through the epididymis. During this time they also gain motility, although spermatozoa do not move until after ejaculation. The organic fraction of human seminal plasma contains phosphate esters, particularly glycerylphosphorylcholine (GPC), phosphorylcholine (PCh), and inorganic phosphate (Pi). GPC is found in relatively high concentrations in the semen of many male animals, including man. GPC is synthesized by the epithelial cells of the epididymis, apparently under androgenic control. Consequently, it has been suggested that GPC might be a useful indicator of epididymal function. We have measured GPC, Pi, and PCh in fresh and frozen semen samples, using phosphorus nuclear magnetic resonance (31P NMR). All samples were assayed for phosphate esters. It was found that PCh was totally hydrolized to Pi. The average ratio of GPC to total phosphate (TP = GPC + Pi) remained constant at a value of about 0.1 for sperm counts over 20 million/ml. The ratio for azoospermic specimens was 0.02 or less; the same results were obtained from vasectomy specimens. This finding indicates that most of the GPC comes from the epididymis. There was a significant correlation between motility, progression, and the GPC ratio. Poor motility and progression in the specimens were accompanied by low GPC ratios regardless of the sperm counts.