Oxidative metabolism of spermatozoa from inbred and random bred mice

Epididymal spermatozoa from the random-bred CFW and from the inbred C57 BL/6 strains of mice were treated either hypotonically or with the antibiotic filipin in order to study the mitochondrial oxidative activities of the two strains in the absence of permeability barriers imposed by the plasma membrane. The percentage of motile spermatozoa from C57BL/6 mice was consistently higher than that of CFW mice, but sperm from the latter fertilized a higher percentage of eggs in vitro. In vivo, there was no apparent difference in fertilizing capacity in vivo: no significant difference between strains was observed. There is a strategy of oxidative metabolism in mouse spermatozoa which is common to the two genetic strains of the species tested, but which differs from that of rabbit and bull spermatozoa. The mitochondria of mouse spermatozoa oxidize L--3-glycerolphosphate but not glutamate in the presence of malate; both activities are present in bull spermatozoa but neither are present in rabbit spermatozoa. In common wit those of the mammalian species thus far studied, the mitochondria of mouse spermatozoa readily oxidize lactate and pyruvate in the presence of malate. They also oxidize acetyl CoA, acetyl carnitine, and long-chain acyl CoA esters directly, without the intermediacy of the carnitine esters. Mouse spermatozoa, therefore, have access to endogenous acyl CoA esters as a source of metabolic energy, which is consistent with their ability to maintain motility for 4-6 hours in the absence of added energy sources. Mouse spermatozoa are self-sufficient with regard to oxidative metabolism, which suggests that energy sources are not readily available to them in the mouse female reproductive tract.