Phospholipid metabolism in boar spermatozoa and role of diacylglycerol species in the de novo formation of phosphatidylcholine.

We have investigated pathways of lipid metabolism in boar spermatozoa sperm cells incubated for up to 3 days with [14C]palmitic acid, [14C]glycerol, [14C]choline, or [14C]arachidonic acid or incorporated these precursors into diglycerides and/or phospholipids. When spermatozoa were incubated with [14C]palmitic acid or [14C]glycerol, there was first an incorporation into phosphatidic acid, followed by labelling of 1,2-diacylglycerol (DAG) and then phosphatidylcholine (PC). This indicates that the de novo pathway of phospholipid synthesis is active in these cells. However, not all DAG was converted to PC. A pool of di-saturated DAG, which represented a considerable proportion of the high basal levels of DAG, accumulated the majority of label. Another DAG pool, containing saturated fatty acids in position 1 and unsaturated fatty acids in position 2 and representing the remaining basal DAG, was in equilibrium with PC. When spermatozoa were incubated with [14C]arachidonic acid, there was a considerable incorporation of label into PC, which indicates the presence of an active deacylation/ reacylation cycle. The behaviour of certain lipid pools varied depending on the temperature at which spermatozoa were incubated. For example, in the presence of [14C]palmitic acid or [14C]arachidonic acid, there was more incorporation of label into PC when spermatozoa were incubated at 25 degrees C than when incubated at 17 degrees C. Taken together, these results indicate that spermatozoa have an active lipid synthetic capacity. It may therefore be possible to design methods to evaluate the metabolic activity of boar spermatozoa based on the incorporation of lipid precursors under standardized conditions.