Novel molecular species of sphingomyelin containing 2-hydroxylated polyenoic very-long-chain fatty acids in mammalian testes and spermatozoa.

Polyenoic very-long-chain fatty acids (VLCFA) have been shown to be localized in unusual molecular species of sphingomyelin in the testes and spermatozoa of the ram, bull, rat, and boar and in the spermatozoa of man. The composition of polyenoic VLCFA-sphingomyelin was comparable in the testes and spermatozoa of each mammalian species; however, the sphingolipid was more concentrated in spermatozoa. The composition of testicular and spermatozoan polyenoic VLCFA-sphingomyelin differed considerably between animal types. Human spermatozoa mainly contained n-6 polyenoic VLCFA with two to four double bonds and even-carbon chain lengths up to 32. In ram and bull testes and spermatozoa, n-3 and n-6, tetra-, penta-, and hexaenoic VLCFA with even-carbon chain lengths up to 34 predominated. In rat and boar testes and spermatozoa, the polyenoic VLCFA were mainly n-6 derivatives with three to five double bonds and even- and odd-carbon chain lengths up to 34. The testes and spermatozoa of the latter two animal species contained 2-hydroxylated, in addition to non-hydroxylated, polyenoic VLCFA in sphingomyelin. This is the first time that 2-hydroxylated polyenoic VLCFA have been recognized in biological systems. Non-hydroxylated polyenoic VLCFA were initially observed in the sphingomyelin of rat testes 25 days after birth, followed by 2-hydroxylated derivatives at 30 days. The total amount of polyenoic VLCFA associated with rat testicular sphingomyelin increased dramatically from 25 to 40 days of postnatal life and then remained constant to 60 days (sexual maturity). The ratio of 2-hydroxylated to non-hydroxylated polyenoic VLCFA increased during this period. Polyenoic VLCFA-sphingomyelin seems to occur exclusively in the testes and spermatozoa of mammals, and it is postulated that this lipid plays a role in reproduction.