ENERGY REQUIREMENT OF BOVINE SPERMATOZOA FOR IN-VITRO CAPACITATION

The oxidative energy requirements of bovine spermatozoa capacitated wi th dilauroil-phosphatidylcholine liposomes (PC 12) and the effect of t hese liposomes on acrosome reaction necessary for in vitro fertilizati on were studied. Mitochondrial respiration was measured using 3 differ ent substrates (pyruvate-lactate-glucose) and endogenous substrates. T he samples were either treated with PC 12 or were left untreated and u sed as the control. A 2.8-fold increase in the consumption of oxygen w as observed in the PC 12 treated spermatozoa in the presence of the 3 combined substrates (pyruvate-lactate-glucose). Respiration changes we re not observed when the spermatozoa were capacitated with only 2 of t he 3 substrates or with glucose alone. When endogenous substrates were used, the consumption of oxygen increased 1.7 times, and mitochondria l uncoupling was observed in the treated samples. The hypermotility ch aracteristic of the capacitation process was not observed when glucose or endogenous substrates were used. When the percentage of intact acr osomes was determined using differential-interferential contrast (DIC) microscopy, it was found that in the presence of oxidative substrates there was a 26% decrease compared with that of the control sample. Th e proportion of reacted acrosomes was in the range of 41.3 to 49.6%, a s measured by the chlortetracycline epifluorescence method in the pres ence of calcium ionophore A23187. Only 4% of the spermatozoa showed ac rosome reaction with endogenous substrates. A higher percentage of fer tilized oocytes were observed when the spermatozoa were capacitated in the presence of the 3 substrates (pyruvate-lactate-glucose), confirmi ng that the success of in vitro fertilization depends on the energy co nditions associated with the capacitation process. The results of thes e experiments indicate that the presence of oxidative energy is necess ary to produce capacitation and the hyperactivation characteristic in frozen-thawed bovine spermatozoa treated with liposomes.