Studies on changes in plasma membrane fluidity during epididymal sperm maturation of rat

During epididymal sperm maturation, the sperm structure and function were modified. The changes in plasma membrane fluidity of spermatozoa from epididymal caput, corpus and cauda of adult SD rats were studied with spin label, 5-Doxyl-stearic acid (5-DSA) and 16-Doxyl-stearic acid (16-DSA), and ESR spectroscopy technique. The hypoosmotic swelling (HOS) test was designed to measure the ability of the sperm plasma membrane to respond osmotically. The results showed that the fluidity of sperm membrane lipid declined gradually from caput to cauda. There was obvious difference between sperm in corpus and in cauda ( P 0.01). The ability of sperm membrane to respond osmotically also decreased, especially from caput to corpus ( P 0.01). The lipid peroxidation reaction during sperm maturation may be one of the causes declining the membrane lipid fuidity.