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

Abstract

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.

Role of NHERF1, Cystic Fibrosis Transmembrane Conductance Regulator, and cAMP in the Regulation of Aquaporin 9

“…Interestingly, AQP9 is not only permeant to water, but it also allows permeation of neutral solutes such as glycerol (35). Glycerol is accumulated in the lumen of the epididymis (14), and may serve as a metabolic substrate for epididymal sperm. Thus, both the neutral solute permeability and water permeability of AQP9 might represent important functions for the preservation and storage of sperm in the lumen of the epididymis.…”

“…Significant water reabsorption leading to a marked increase in sperm concentration and luminal hypertonicity occurs in the epididymis (5,(11)(12)(13). In addition, glycerol, a metabolic substrate for epididymal sperm, is accumulated in the lumen of the distal epididymis (14). In the more distal regions of the epididymis and in the vas deferens, water secretion driven by cystic fibrosis transmembrane conductance regulator (CFTR) 2 dependent chloride transport occurs and controls the fluidity of the luminal content (15,16).…”

Subcellular Localization of Selectively Permeable Aquaporins in the Male Germ Line of a Marine Teleost Reveals Spatial Redistribution in Activated Spermatozoa1

“…In the efferent duct of spermiating seabream, we could only consistently detect Aqp10b polypeptides, which were localized in the plasma membrane of the luminal epithelial cells. As suggested for the rat epididymis [74], the expression of the glycerol-transporting Aqp10b paralog in the seabream efferent duct may mediate water transport and provide glycerol as an aerobic metabolic substrate for spermatozoa [75,76]. Representative Western blots of sperm total protein extracts (S-TP; 60 lg) and plasma membrane extracts (PM; 40 lg) of intact sperm (S) and spermatozoa head (H) and flagellum (F) probed with the different aquaporin antibodies as indicated.…”

Aquaporins in spermatozoa and testicular germ cells: identification and potential role

“…The presence of glycerol in the rat epididymis and its metabolism by spermatozoa has been reported [75]. In a study of 22 infertile men, sperm AQP7 was nondetectable in five of them who showed slightly lower sperm motility than the other patients [76].…”