牛精子の生存性におよぼすカフェインの影響

The purpose of the present study was to examine the effects of caffeine on motility of ejaculated bull spermatozoa. Bull semen was diluted with egg yolk-sodium citrate dilutor (ECD) in the presence or absence of caffeine and, in some cases, diluted with Ca-free KRP solution. Di1uted semen was incubated for 6-8 hr at 37°C or stored for 7days at 4°C. Some samples were frozen to -196°C. The results obtained are summarized as follows. 1. Bull spermatozoa were washed with Ca-free KRP solution, suspended in this solution and incubated for 8hr at 37°C with various substrates in the presence or absence of 10mM caffeine. Sperm motility index was enhanced for 2 hr by caffeine without exogenous substrate. Motility index of caffeine-treated spermatozoa, however, decreased as compared with that of control after incubation of 4 or more hr without exogenous substrate. Caffeine markedly increased and maintained motility index of spermatozoa incubated with glucose, fructose, pyruvate or lactate for about 5 hr. Caffeine also increased the grade of motile sperm activity. 2. When bull semen was diluted with ECD and incubated for 6 hr at 37°C or stored for 7 days at 4°C, greater stimulation of sperm motility by caffeine appeared at 5. 4-18mM or 5.4-13.5mM, respectively. In these experiments caffeine increased and maintained sperm motility index. An increase in the grade of sperm activity by caffeine was also observed. 3. Bull semen diluted with ECD was stored at 4°C and caffeine was added to diluted semen on the 3rd day of storage at 4°C to give a final concentration of 4, 10, or 20mM. An immediate improvement of the sperm motility index and the grade of sperm activity occurred with the addition of caffeine to aged spermatozoa. The addition of caffeine increased longevity of aged spermatozoa stored at 4°C. Maximal stimulation of motility index of aged spermatozoa apgeared at 10mM caffeine. 4. Bull semen was diluted with ECD and frozen to -196°C. When glycerol was added to caffeine-treated spermatozoa to give a concentration of 7% before freezing, pre-freeze and post-thaw motility indices of caffeine-treated spermatozoa were decreased as compared with those of caffeine-untreated spermatozoa. To the contrary, the addition of caffeine to frozen-thawed spermatozoa in the presence of glyceorl enhanced motility index and longevity of spermatozoa when compared to the control samples. Maximal stimulation of motility of frozenthawed spermatozoa appeared at 10mM caffeine. 5. Bull spermatozoa treated with various concentrations of glycerol in the presence or absence of 10mM caffeine was stored at 4°C for 24hr. Spermatozoa, stored at 4°C with 2% glycerol plus caffeine, showed enhanced motility index as compared with the caffeine-untreated spermatozoa with 2% glvicerol. Spermatozoa. stored at 4°C with 7 or 10% glycerol plus caffeine, however, showed decreased motility index as compared with the caffeine-untreated spermatozoa with 7 or 10% glycerol. The effect of caffeine on sperm motility, therefore, may have relation to the glycerol level in diluted semen. In conclusion, caffeine increased and maintained the motility index of ejaculated bull spermatozoa which were diluted with Ca-free KRP solution or ECD. Caffeine also increased the grade of motile sperm activity.