METABOLISM OF LACTATE BY MATURE BOAR SPERMATOZOA

Boar sperm oxidatively metabolized fructose, glucose, glycerol, glycer ol 3-phosphate and lactate to CO2 but pyruvate produced only small amo unts of CO2 and this was almost completely prevented when endogenous g lycolytic metabolism was inhibited. Lactate was the preferred substrat e over fructose, glycerol and glycerol 3-phosphate and when lactate wa s offered in the presence of pyruvate, lactate was preferentially oxid ized to CO2. The rate of oxidation of fructose, glycerol and glycerol 3-phosphate was approximately halved in the presence of equi-molar con centrations of lactate and the metabolism of lactate was progressively decreased in the presence of increasing concentrations of mersalyl, a n inhibitor of lactate transport. Sperm maintained a high energy charg e potential when incubated with lactate as substrate in the presence o r absence of bromopyruvate, an inhibitor of endogenous glycolytic meta bolism. This evidence confirms that it is lactate, rather than pyruvat e, that enters the mitochondria thereby constituting a lactate-pyruvat e transport system in these cells for regenerating cytoplasmic nicotin amide adenine dinucleotide (NAD(+)). Electrophoretic examination of th e lactate dehydrogenase isozymes from sperm and several other tissues of the boar showed that sperm contained almost entirely an isozyme whi ch was not present in the other tissues.