COMBINED EFFECTS OF ADRENALECTOMY AND NOISE EXPOSURE ON COMPOUND ACTION-POTENTIALS, ENDOCOCHLEAR POTENTIALS AND ENDOLYMPHATIC POTASSIUM CONCENTRATIONS

The effects of removal of endogenous corticosteroids via bilateral adr enalectomy in combination with noise exposure (30 min at 100 dB) were determined by recording compound action potentials (CAP) and endocochl ear potentials (EP), and by measuring potassium concentrations (K-e(+) ) within the endolymph. Thirty-eight Long-Evans rats were divided into groups according to experimental treatments: adrenalectomy (ADX) or n on-ADX and noise exposure or non-noise exposure. CAP thresholds, EP an d K-e(+) values were subjected to repeated-measures analysis of varian ce with group and time as factors classifying the measurements. Noise exposure resulted in significant elevations of CAP thresholds in both the ADX and non-ADX animals, but had no effect on either EP or endolym phatic K-e(+) Recovery was noted during all post-exposure measurement periods and was significantly faster for ADX animals. EP and K-e(+) di d not change during or after noise exposure. ADX animals showed a non- significant reduction of EP and a statistically significant increase o f K-e(+) during all measurement periods as compared to non-ADX animals .