The inhibitory effects of gossypol on human sperm motility characteristics: possible modes of reversibility of those effects.

Gossypol (GOS) is a polyphenolic compound derived mainly from cottonseed oil, which has been found to have anti-fertility effects in males. It has been reported to induce disturbances of the hypothalamicpituitary axis, disruption of spermatogenesis in the testes, and inhibition of postejaculatory spermatozoa motility. The inhibition of human sperm motility by GOS has been documented both in vivo and in vitro, although the exact mechanism and possible reversibility of such inhibition is unknown. The objectives of the present study were 1) to examine the in vitro dose response of human sperm motility to GOS, and 2) to determine if the motility inhibition of GOS was reversible, using agents which alter the second messenger cyclic adenosine monophosphate (cAMP), such as, 8-bromo-cAMP (8-Br-cAMP), and forskolin, and adenylate cyclase stimulator. Fresh spermatozoa were obtained from males of known fertility. Motile spermatozoa were recovered via the SpermPrep (SP) method and used further in all experiments. Quantitative and qualitative sperm parameters were recorded at collection, post-SP filtration and post-treatment. Motile spermatozoa were resuspended in either media (SP), or in increasing concentrations of GOS (10, 20, 30 and 50 micrograms/ml) as gossypol acetic acid in media. To study the possible reversibility of the GOS effects, spematozoa already exposed to GOS for 2 hr (at the concentrations mentioned above) were centrifuged and reconstituted in media containing either 10 mM 8-Br-cAMP or 100 microM forskolin and measurements of percent motility and grade of motility (0-4) were taken at 0 time and at 30 min intervals for a total of 2 hr. Each experiment was replicated 8 times. The results obtained in this study showed that GOS inhibited sperm motility in a dose and time dependent manner. The motility characteristics of the 50 micrograms/ml GOS group were lower than all other groups (p < 0.001) and the spermatozoa were completely immobilized within 60 min. Cyclic AMP somewhat rescued the GOS-treated sperm, whereas exposure of GOS-treated sperm to forskolin had no such effects. The data generated in the present study suggest that GOS inhibits cAMP formation, which subsequently decreases sperm motility characteristics. At low concentrations (up to 20 micrograms/ml for 30 min), GOS inhibition is reversibile and compounds that act to increase cAMP seem to be partially responsible for the reversal of GOS inhibition. However, GOS inhibitory effects at levels higher than 20 micrograms/ml (exposed for 30 min) were impossible to reverse, which suggest that GOS at those levels could be an effective agent for vaginal contraception.