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 studie s 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 mug/ml) or chromium (0.0, 5.0, 10.0 and 2 0.0 mug/ml) for 2 h in the culture medium. The sperm that became attached t o the ova in the presence of these metals were scored. Synthesis of DNA, RN A and protein was assessed during this process by labelling the cells with [H-3]thymidine (20 mu Ci/ml), [H-3]uridine (50 mu Ci/ml) and [S-35]methioni ne (10 mu Ci/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 s perm attaching to the ova in both exposed groups along with a decrease in t he incorporation of radiolabelled thymidine, uridine and methionine. The re sults indicate that DNA, RNA and protein synthesis under sperm-zona binding conditions are affected by the presence of these two metals. The physiolog y of the gametes is altered resulting in a low frequency of sperm attachmen t to the ova, which in turn leads to a risk of reproductive failure. (C) 20 01 Elsevier Science Ltd. All rights reserved.