Incubation of mouse sperm with lactate delays capacitation and hyperactivation and lowers fertilization levels in vitro

Mouse sperm were incubated in medium with or without 24 mM lactate and assessed for 1) motility characteristics including hyperactivation--a computer-assisted motion analysis system was used; 2) capacitation--a chlortetracycline fluorescent dye binding assay was used; and 3) ability to penetrate oocytes. Lactate affected all aspects of motility and delayed the rates of both hyperactivation and capacitation. When a concentration of 8 x 10(3) sperm/ml was used for insemination in vitro, sperm preincubated 60-90 minutes in medium with lactate prior to insemination in lactate-free medium fertilized fewer oocytes than did sperm preincubated in lactate-free medium. Use of a calcium-sensitive electrode demonstrated that lactate chelated appreciable amounts of calcium in the medium. Capacitation was assayed in sperm incubated 60 minutes in medium with various concentrations of lactate or CaCl2. When medium containing lactate was compared to medium without lactate but having a similar level of free calcium, the level of capacitation of sperm incubated with lactate was less than half that of sperm incubated without lactate. These results demonstrate that including 24 mM lactate in the medium can have detrimental effects on mouse sperm hyperactivation and capacitation. The detrimental effects on capacitation are partly but not completely due to the chelation of calcium by lactate.