Experimental hypercholesterolaemia in rabbits. Effect on lipid domains in homologous spermatozoa

Summary. The distribution of membrane filipin sterol complexes (FSC) in the plasma membrane of the acrosomal region (PMAR) of rabbit sperm from epididymis and testis, in normal and hypercholesterolaemic rabbits, was examined at ultrastructural level. Membrane FSC were quantitatively analysed on freeze fracture replicas of filipin-treated cells. Cauda epididymal sperm shows a significant increase in filipin sterol complexes concentration in PMAR of hypercholesterolaemic animals compared to normal rabbits. Hypercholesterolaemic animals had 0.53±0.08 FSC μm⁻² in the marginal segment of PMAR and 0.26±0.03 FSC μm⁻² for normal animals. In the principal piece we found 0.70±0.07 FSC μm⁻² for hypercholesterolaemic and 0.43±0.03 FSC μm⁻² for control animals. We also counted 0.58±0.04 FSC μm⁻² in the equatorial segment of PMAR for hypercholesterolaemic and 0.38±0.03 FSC μm⁻² for normal animals respectively. The FSC concentration of testicular sperm, like sperm from corpus and caput of epididymis in hypercholesterolaemic animals, did not differ from the controls. Cholesterol, phospholipids and cholesterol: phospholipid ratio in caudal epididymal sperm from treated males did not differ from controls. Only the sphingomyelin concentration decreases in cauda epididymal sperm from hypercholesterolaemic males compared to controls.
The results presented in this paper suggest that the lipidic domains in PMAR of hypercholesterolaemic rabbits changes when the gametes go through the epididymis.—