Entry of glycerol into the rat epididymis and its utilization by epididymal spermatozoa

The availability of glycerol in the epididymal lumen, and the extent of its utilization by spermatozoa, was studied by measurement of the substrate concentration in epididymal fluid and its oxidation in vitro. The source of luminal glycerol was sought by examining its penetration through the epididymal epithelium of a sperm-free tubule by the technique of luminal perfusion during intravenous infusion of glycerol. [3H]Glycerol was rapidly metabolized to a volatile and mobile molecule that quickly equilibrated between blood plasma and the epididymal lumen and so could not be used to monitor transfer. When blood levels of glycerol were raised by infusion of large amounts of the unlabelled compound, glycerol was detected in epididymal perfusates and a positive linear correlation existed between the rate of secretion into the epididymal lumen and the blood plasma concentration, suggesting that passive diffusion across the epithelium from blood could occur. In normal rats, however, the concentration of glycerol in sperm-free epididymal fluid (1.15 mM) exceeded that in blood plasma (0.35 mM). Luminal glycerol is therefore thought to arise from degradation of epididymal lipid.