Phospholipids in ram semen: metabolism of plasmalogen and fatty acids

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Abstract
The effects of lipid-containing fractions obtained from ram semen upon the respiration of ram spermatozoa have been examined. Marked activations were observed with dialysed seminal plasma and dialysed concentrates of fluids used to wash the spermatozoa. These are ascribed to the presence of lipoproteins. Phospholipid fractions sometimes activated sperm respiration to a small extent. However, activation was insignificant when care was taken to prevent impairment of motility during preliminary washing of the spermatozoa. The phospholipids extractable by chloroform-methanol from washed spermatozoa and from seminal plasma have been fractionated on silicic acid columns. We have confirmed our earlier finding that the major phospholipid in extracts of freeze-dried spermatozoa is choline plasmalogen and that lecithin is absent. Extracts of fresh spermatozoa, and of spermatozoa and plasma which have been frozen, contain both plasmalogen and lecithin. For fresh spermatozoa the ratio is approximately 1:1. The lipids extractable from spermatozoa that had been incubated in the absence of sugar under both anaerobic and aerobic conditions have been compared with those from non-incubated spermatozoa. Analyses were made of (1) free fatty acids, (2) choline plasmalogen, (3) phosphorus in the mixed lecithin-plasmalogen fraction. Free fatty acids accumulated during anaerobic incubation, but in the presence of oxygen the accumulation was smaller or there was even a net loss. It was mainly Cl4 and C16 acids which accumulated in the absence of oxygen and that were oxidized in its presence. There was no appreciable decrease in lecithin during incubation for 2.5-3 hr. at 37[degree], but about 25% of the intracellular plasmalogen was hydrolysed. These results strengthen our earlier view that, in the absence of fructose, ram spermatozoa can utilize as a source of energy the fatty acids which derive from breakdown of plasmalogen.