Plasmalogen in ram semen, and its role in sperm metabolism.

Whole semen can be stored successfully under both aerobic and anaerobic conditions, owing to the presence of glycolysable carbohydrate in the seminal plasma. However, if mammalian spermatozoa are separated from the seminal plasma by centrifuging and washing, they can maintain their motility only in the presence of oxygen. From this it has been inferred that when spermatozoa are deprived of fructose, which is the usual glycolysable carbohydrate in seminal plasma, they utilize the oxidation of intracellular reserves as a source of energy for motility. Lardy & Phillips (1941a, b, 1945) assigned this role of energy reserve to the phospholipids, pointing out that (i) the lipidphosphorus content diminishes during the aerobic storage of bull spermatozoa and (ii) the rate and duration of oxygen consumption are markedly increased when egg phospholipids, known to be composed chiefly of lecithin, are added to sperm suspensions in a sugar-free medium. These results were contradicted by Bomstein & Steberl (1957), who were unable to detect any appreciable changes in lipid phosphorus of washed bull spermatozoa during aerobic storage. These authors also concluded that the stimulation of oxygen consumption by exogenous phospholipids was not due to oxidation of these phospholipids. In similar experiments with ram spermatozoa analysis of phosphorus fractions gave no indication that the lipidphosphorus content diminishes during aerobic metabolism (Mann, 1958). The early experimental approaches to the participation of phospholipids in sperm metabolism were based upon two assumptions. The first of these, well entrenched since the early work by Miescher (1878, 1897), Mathews (1897) and Sano (1922), was that sperm phospholipids consist mainly of lecithin; the second was that any utilization of phospholipid during sperm metabolism would lead to liberation of the phosphorus in a non-lipid, acid-soluble form. Quite recently, however, investigations on the chemical nature of lipids present in ram spermatozoa have shown that there is no evidence for the presence of lecithin in the sperm cells and that the predominant intracellular lipid is of aldehydogenic nature, resembling the plasmalogens of brain and muscle (Lovern, Olley, Hartree & Mann, 1957). These findings, together with an earlier observation that a plasmalogen-like lipid is also present in bull semen (Boguth, 1952), made it desirable to reinvestigate the problem of the alleged relationship between lipids and the aerobic metabolism of mammalian spermatozoa. In this paper are reported analyses of plasmalogen and acyl ester in the lipids of ram semen with special reference to the behaviour of these substances during the aerobic as well as the anaerobic metabolism of spermatozoa.