Circadian changes in serum corticosterone levels affect hearing in mice exposed to noise.

We assessed the relationship between changes in corticosterone concentrations and hearing in mice exposed to noise during the light (inactive) and dark (active) phases. Serum corticosterone concentrations and hearing levels were measured before, and 1, 3, 5, 7, and 10 days after, noise exposure between 8:00-11:00 h and 15:00-18:00 h. Serum corticosterone concentrations were significantly lower at 8:00-11:00 h than at 15:00-18:00 h and were significantly lower before than after noise exposure. In addition, serum corticosterone concentrations were significantly lower at 11:00 h after noise exposure than at 18:00 h before noise exposure. Mice exposed to noise at 8:00-11:00 h showed significantly elevated threshold shifts after noise exposure than did mice exposed to noise at 15:00-18:00 h. Endogenous serum corticosterone concentration has a significant effect on hearing after noise exposure. Noise exposure during the inactive phase of the hypothalamic-pituitary-adrenal axis may be more harmful to the auditory system than noise exposure during the active phase of the hypothalamic-pituitary-adrenal axis.