Effects of Caffeine on Mitotic Delay of Sea Urchin Eggs Fertilized with X-irradiated Sperm

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When sea urchin eggs were fertilized with X-irradiated sperm, the prolongation of streak stage in the first cleavage was induced. Caffeine reduced the prolonged streak stage only when the chemical was administered during the period of the prolongation. This effect of caffeine was observed at the concentrations higher than 0.13mM and reached the maximum at approximately 2 mM. Other methylxanthines such as theophylline and theobromine, which are generally known to increase c-AMP contents in the cell, exhibited similar effects upon the mitotic delay. On the other hand, aminophylline which is also considered to increase c-AMP level in sea urchin eggs, had not such effect. Whitfield, Rixon and Youdale have reported that in normal and irradiated thymocyte populations, somatotropic hormone and elevated concentrations of calcium stimulate the flow of the cell into mitosis, when they are administered into the medium. The increase in mitotic activity in normal cells both by hormones such as growth hormone or parathyroid hormone and by calcium or magnesium ion is shown to result from the stimulation of the initiation of DNA synthetic phase.
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