Effects of Caffeine on In-Vitro Fertilization of Pig Follicular Oocytes.

Experiments were conducted to assess the effects of caffeine on the ability of frozen-thawed boar epididymal spermatozoa to penetrate oocytes that had been matured in culture. The spermatozoa were preincubated in modified TCM199 medium and subsequently incubated for 2 h in either a fertilization medium with 2 mM caffeine or in a fertilization medium without caffeine. Then a sample of the spermatozoa in the caffeine-containing medium was introduced into another caffeine-containing medium that contained matured oocytes, while another sample was introduced into a medium with matured oocytes without caffeine. This procedure was repeated for the spermatozoa that had been incubated in the caffeine-free medium. The two sets of manipulations resulted in higher rates of penetration of oocytes inseminated in the caffeine-containing medium than of oocytes in the caffeine-free medium. Furthermore, when oocytes with attaching spermatozoa were washed and transferred to caffeine-free medium after 1, 2 and 3 h of incubation in the presence of caffeine, penetration rates were 14%, 76% and 94%, respectively. Addition of caffeine to the fertilization medium caused as much as a 1.4-fold elevation in levels of cyclic AMP in sperm, the effect being maximal within about 0.5 h of incubation. These results indicate that during 2 to 3 h of incubation with oocytes in the caffeine-containing medium, the spermatozoa become highly fertile, and that a high concentration of cyclic AMP in sperm might not have any direct effects on the ability of sperm to penetrate oocytes.