Very long chain polyunsaturated fatty acids are the major acyl groups of sphingomyelins and ceramides located in the head of bull and rat spermatozoa

Abstract

Polyunsaturated fatty acids (VLCPUFA) are important constituents of sphingomyelin (SM) and ceramide (Cer) in testicular germ cells. In the present paper we focused on the SM and Cer and their fatty acids inspermatozoa and their main regions, heads and tails. In bull and ram spermatozoa,SM was the third most abundant phospholipid and VLCPUFA were the major acylgroups ( approximately 70%) of SM and Cer. In rat epididymal spermatozoa the SM/Cer ratio was low in the absence of and could be maintained high in the presence of the cation chelator EDTA, added to the medium used for spermisolation. This fact points to the occurrence of an active divalent cation-dependent sphingomyelinase. Bull and rat sperm had an uneven head-tail distribution of phospholipid, with virtually all the VLCPUFA-rich SM located atthe head, the lower SM content in the rat being determined by the lower spermhead/tail size ratio. Most of the SM from bull sperm heads was readilysolubilized with 1% Triton X-100 at 4 degrees C. The detergent-soluble SMfraction was richer in VLCPUFA than the nonsoluble fraction and richer insaturated fatty acids. Cer was produced at the expense of SM, thus decreasing severalfold the SM/Cer ratio in rat spermatozoa incubated for 2 h in presence ofthe sperm-capacitating agents, calcium, bicarbonate, and albumin. The generationof Cer from SM in the sperm head surface may be an early step among thebiochemical and biophysical changes known to take place in the spermatozoon inthe physiological events preceding fertilization.