Effect of lead and chromium on nucleic acid and protein synthesis during sperm-zona binding in mice

Lead and chromium are ubiquitous environmental pollutants and their effects on reproductive physiology as shown by animal experiments and human studies is well documented. The present study was conducted to ascertain the role of these metals on gamete physiology during the sperm-zona binding process, Superovulated ova and capacitated sperm from BALB/c mice were exposed to lead (0.0, 0.2, 0. 5, 1.0 and 2.0 microg/ml) or chromium (0.0, 5.0, 10.0 and 20.0 microg/ml) for 2 h in the culture medium. The sperm that became attached to the ova in the presence of these metals were scored. Synthesis of DNA, RNA and protein was assessed during this process by labelling the cells with [3H]thymidine (20 microCi/ml), [3H]uridine (50 microCi/ml) and [35S]methionine (10 microCi/ml) in the culture medium after exposure to the metals for 2 h. Our studies show a significant dose-dependent decrease in the number of sperm attaching to the ova in both exposed groups along with a decrease in the incorporation of radiolabelled thymidine, uridine and methionine. The results indicate that DNA, RNA and protein synthesis under sperm-zona binding conditions are affected by the presence of these two metals. The physiology of the gametes is altered resulting in a low frequency of sperm attachment to the ova, which in turn leads to a risk of reproductive failure.