Retardation of Guinea Pig Sperm Acrosome Reaction by Glucose: The Possible Importance of Pyruvate and Lactate Metabolism in Capacitation and the Acrosome Reaction
The occurrence of the acrosome reaction was used as an index of the completion of capacitation in vitro of guinea pig spermatozoa. Glucose, an energy source which has been used in almost every sperm-capacitation and fertilization medium devised, was found to retard the initiation of the acrosome reaction in media that allow capacitation of guinea pig spermatozoa. Media containing only pyruvate or pyruvate plus lactate as energy sources induced the earliest acrosome reaction. The presence of glucose in addition to pyruvate and lactate retarded the occurrence of the acrosome reaction, and an even longer delay was observed when glucose was the only energy source. Fructose and mannose, which are metabolizable sugars, had a retarding effect on the onset of the acrosome reaction similar to that obtained with glucose. By contrast, sucrose, fucose, lactose, L-glucose and galactose, which are all nonmetabolized or only slightly metabolized sugars, did not retard the occurrence of the acrosome reaction. The metabolism of pyruvate and/or lactate appears to be necessary for the capacitation and the physiological acrosome reaction in guinea pig spermatozoa. The implications of these findings in regard to the control of capacitation in vivo are discussed. The metabolic state of the spermatozoon may influence or regulate the ability of the spermatozoon to undergo the acrosome reaction and thus its ability to fertilize an egg.