Effects of cadmium on the hearing system

The functional resemblance between kidney proximal tubular and inner ear ep ithelial cells which has often been pointed out in the literature led us to hypothesize that nephrotoxic agents that cause renal tubular injury might also impair the function of inner ear cells. As one of the most toxic envir onmental nephrotoxic agents is cadmium, we aimed to study its effects on he aring experimentally in rats. In this study, increased blood and renal cort ical cadmium levels were associated with high cadmium accumulation in ear o ssicles and labyrinth in rats exposed to cadmium. The changes in auditory b rainstem response (ABR) and otoacoustic emission in 2-month-old male rats e xposed to drinking water containing 5 and 15 ppm CdCl2 for 30 days showed t hat cadmium-induced nephrotoxicity was associated with signs of defective h earing at a concentration of 15 ppm CdCl2 but that 5 ppm CdCl2 caused heari ng loss without affecting kidney function. The mean latency of ABR wave I, which indicates the function of the cochlea, was 1.335 +/- 0.31 ms in the c ontrol group and 1.641 +/- 0.052 and 1.74 +/- 0.88 ms in the rats subjected to 5 and 15 ppm CdCl2, respectively (p < 0.001). In the cadmium-treated gr oups short interpeak wave I - III latencies (p < 0.01) indicated cochlear d ysfunction and this was also supported by the distortion product otoacousti c emission results (p < 0.001). Non-significant changes in wave III and V l atencies were accepted as evidence of unaltered function of the other parts of the auditory system. These results suggest that hair cells are more sen sitive to cadmium than kidney tubule cells and that the cochlear component of hearing is more vulnerable to cadmium toxicity than other parts of the a uditory system.