Effects of gossypol acetic acid on the activity of LDH-C4 from human and rabbit spermatozoa.

PIP: This report focuses on the effect of gossypol acetic acid on LDH-C4 from human and rabbit spermatozoa. Human semen was obtained by masturbation after 3-5 days of abstinence. Semen from successfully vasectomized healthy men was used for studies on the LDH isoenzymes other than LDH-C4 in seminal plasma. Rabbit semen was collected by an artificial vagina. Human samples containing less than 100 million spermatozoa/ml were pooled to obtain a sufficient number of spermatozoa. Rabbit samples were not pooled. LDH activity was analyzed spectrophotometrically. Gossypol acetic acid was obtained from the Special Program of Research on Human Reproduction, World Health Organization, Switzerland through their collaboration with the National Institute of Health in the US and was dissolved in ethanol. Freshly prepared solutions were used for each experiment and 20 mcl added to the cuvette. LDH-C4 from human spermatozoa was inhibited by GAA in a dose dependent manner, with 50% inhibition noted between 50-75 mcm. LDH-C4 from rabbit spermatozoa was slightly less sensitive to GAA as 50% inhibition was observed at concentrations between 75-100 mcm. The interindividual differences in sensitivity to GAA was small in human samples but in the experiment with rabbit semen the interindividual and the intraindividual differences were great. The total LDH activity in seminal plasma from both human (normal and vasectomized men) and rabbit was insensitive to GAA but a minor inhibition was sometimes noted at 100 mcm. It has been proposed that inhibition of LDH-C4 in the testis and/or in ejaculated spermatozoa could provide a possible explanation for the antifertility effect of gossypol. Gossypol has been reported to be much less effective as a male contraceptive in the rabbit than in man. In this study gossypol was slightly less active as an inhibitor of sperm LDH-C4 from rabbits than from humans. This could indicate that an effect by gossypol on sperm LDH-C4 activity is not a major mode of action for its antifertility action. The mode of action of gossypol is most likely complex, involving a number of essential enzyme systems.^ieng