[Use of a Ca(++) antagonist in noise-induced hearing loss in animal experiment]

Hearing thresholds at 1-2-4-6 and 8 kHz were determined by brainstem evoked response audiometry (BERA) in 24 guinea pigs. The animals were then divided into 6 groups. Group 1 (controls) received no drugs and were not exposed to noise. Group 2 were given 15 mg/24 h/kg diltiazem s.c. for 13 days. Group 4 was exposed to the same noise as group 3 but was also treated with diltiazem 15 mg/kg/24 h from three days before noise exposure until the end of the experiment. Group 5 was exposed to a 110 dB SPL broad-band noise for 3 h daily for 10 days. Group 6 was exposed to the same noise as group 5 and was treated with diltiazem 15 mg/kg/24 h from three days before noise exposure until the end of the experiment. After the last noise exposure hearing thresholds were determined again by BERA and were found to be unchanged in those animals treated with the drug alone and the controls. In those groups with drug administration and noise exposure hearing loss was less than in the animals exposed to noise alone. This difference was more pronounced in the 90 dB groups than in the 110 dB groups.