Validation of an amphibian sperm inhibition toxicological test method using zinc

Analysis of sperm has been investigated as a possible method to examine the toxicity of environmental contaminants. The amphibian sperm inhibition toxicological test (ASITT) method examines the effects of contaminants on Xenopus laevis (African clawed frog) sperm motility and path trajectories. As part of a preliminary validation of the method, the effects of increasing divalent metal ion, zinc (Zn2+), on X. laevis sperm motility were examined. We hypothesized that Zn2+ concentration would have significant inhibitory effects on percent sperm motility, velocities, and trajectories. The Zn2+ was added to a control solution in concentrations from 0 to 1,417 microg/L. Sperm cells were videotaped at 30 frames per second under x 400 microscope, and percent motility was recorded and paths were mapped by marking the change in position of the sperm head over a period of 1 s. Sperm motility was categorized as progressive, hyperactivated, idle, or nonmotile, and velocities and trajectories were calculated on the basis of x,y coordinates. Increasing Zn2+ concentrations caused a significant exponential decay in percent total motility and progressive motility. Straight-line velocity increased with increasing Zn2+ concentrations. Overall, results suggest that Zn2+ may be interfering with cellular processes, such as cellular respiration, flagellar bending, or ion exchange, thereby inhibiting sperm motility.