Lead-induced changes in spermatozoa function and metabolism

The relationships between sperm reactive oxygen species (ROS) generation, the capacitation process and acrosome reaction, and the sperm-oocyte penetration rate (SOPR) were investigated to understand the effect of lead toxicity on sperm functions and the mechanisms of these effects. Male Sprague-Dawley rats received weekly intraperitoneal injections of 20 mg or 50 mg lead acetate/kg or 20 mg or 50 mg sodium acetate/kg (control) for 6 wk. Serum testosterone was measured by radioimmunoassay. In cauda epididymal spermatozoa, the chemiluminescence was measured to evaluate the sperm ROS generation. Chlortetracycline fluorescence assay was used to study the status of capacitation and acrosome reaction on fresh cauda epididymal spermatozoa and after 2, 4, or 24 h of incubation with 5 mg/ml bovine serum albumin. In lead-exposed rats, the serum testosterone levels were reduced, and the percentage of capacitation and the chemiluminescence were significantly increased in fresh cauda epididymal spermatozoa. The serum testosterone levels were negatively associated with the percentage of acrosome-reacted spermatozoa. Sperm chemiluminescence was positively correlated with the percentage of both capacitated and acrosome-reacted spermatozoa. The SOPR was negatively associated with the percentage of both capacitated and acrosome-reacted spermatozoa. In summary, this study showed that male rats exposed to lead had decreased serum testosterone levels and that this metal produced early onset of capacitation by one of the pathways of ROS generation. These effects might consequently result in premature acrosome reaction and reduced zona-intact oocyte-penetrating capability.