The inhibitory effect of gossypol acetic acid on human sperm motility was studied with a transmembrane migration method. Gossypol decreased sperm motility after it had been incubated with semen for more than 15 min. However, when sperm motility was evaluated immediately after semen had been mixed with gossypol, no inhibitory effect could be found. We consider that the sperm immobilizing potency of gossypol is much less than our previously studied sperm immobilizing agents. It is unlikely that gossypol can be developed as a vaginal spermicide. The importance of time course in the pharmacological study of sperm motility is emphasized in this study.
PIP: Medical researchers collected and tested fresh human semen samples (sperm concentration of 20 million/mi; basal motility 20%) from healthy donors to measure the potency of gossypol in inhibiting human sperm motility. They used the transmembrane migration method to test the preparation of racemic gossypol acetic acid. The data revealed that the more concentrated the gossypol solution the more it inhibited sperm motility. For example, a concentration of .01mM gossypol incubated at 37 degrees celsius (body temperature) for 120 minutes sperm motility was 75% of the control. Sperm motility fell to 38% at .1mM gossypol and to 10% at 1mM gossypol at the same time and temperature. Moreover duration and temperature of incubation also inhibited sperm motility. for example, at 25 degrees celsius (room temperature), overall sperm motility fell only 35% even if the researchers kept the semen for 2 hours in 1mM gossypol. The percentage increased to 50% overall at body temperature and 30, 60, and 120 minutes and gossypol concentrations of .5mM, .15mM, .05mM. No inhibition of sperm motility occurred immediately after researchers mixed semen with gossypol, however. This study demonstrated that the contraceptive mode of action may involve an enzymatic process. The researchers concluded that the sperm immobilizing potency of gossypol is considerably less than other studied sperm immobilizing agents therefore gossypol could probably not be developed as a vaginal spermicide. Other research has indicated that placing gossypol in the vagina does inhibit the effect of herpes simplex virus type 2 infection, however.