Changes of Serum Aldosterone Concentration after Noise Exposure in Mice

다국어 초록 (Multilingual Abstract)

Introduction



Aldosterone is a mineralocorticoid (MC) that is released from the zona glomerulosa of the adrenal cortex. Several recent studies have shown the stria vascularis has numerous MC and glucocorticoid receptors.1,2) The MC receptor of the inner ear controls the homeostasis of the endolymph by means of ion channels and transporters that exist in the cochlear duct cells.3,4) Deprivation or imbalance of such activities affects the morphological functions of the related cells, which leads to hearing loss.5,6,7)Even though little animal research is available on the relevance of hearing loss and aldosterone, it has been reported that injection of aldosterone to mrl/mpj-fas (lpr) autoimmune mice that have stria vascularis and no hair cell pathology facilitates the regeneration of the stria vascularis to its normal form.8) Since stria vascularis abnormality causes abnormal sodium ion (Na+) and potassium ion (K+) transport, it can be suggested that the enhancement of such transport is necessary to fully recover normal hearing level.8) Recently, it has also been reported that the difference in serum aldosterone concentration between normal hearing and presbycusic groups is highly significant.9) Although there are no explanations available, the decreased serum aldosterone concentration, which affects the expression of Na, K-ATPase and Na-K-Cl cotransporter (NKCC1) on the cell membranes of the inner ear cells, is related to the disrupted homeostasis of endolymph due to abnormal K+ regeneration in the cochlea.9)Aldosterone plays a critical role in maintaining the homeostasis of the inner ear. However, previous studies have tended to focus on noise-induced hearing loss and steroid injection.10,11) Not much is known about the protein changes related to K+ regeneration and the role(s) of aldosterone in noise-induced hearing loss. The aim of this study was to determine whether serum aldosterone is influenced by noise exposure by comparing aldosterone levels of BALB/c mouse before and after noise exposure.


Materials and Methods

Experimental animals Nine, 6-week-old, male BALB/c mice (Orient Co., Seongnam, Korea) weighing 21-24 g with normal Preyer's reflexes and normal hearing at auditory brain stem response were used. The mice were randomly divided into three groups (n=3 per group; see below), weighed, and bred in a cage. All mice were allowed unrestricted access to food and water.


Organization of experimental groups Serum aldosterone was measured in each of the three groups. In the control group, mice were not exposed to noise. Another group was noise-exposed for 3 consecutive days prior to measurement of serum aldosterone immediately after termination of the exposure (0 day after noise group). The last group was also noise-exposed for 3 days but serum aldosterone was measured 3 days after termination of the exposure (3 days after group).


Instruments for noise exposure For noise exposure, a sound-proof noise booth was used. Noise was generated by a speaker with input/output resistance of 8 Ω (290-8L; Altec Lansing, Oklahoma City, OK, USA) that was directly amplified through a model R-399 amplifier (INTER M, Seoul, Korea). The amplifier was placed in the left corner of the room and the speaker was placed above the amplifier, with the speaker horn at a 45° angle.


Noise-induced hearing loss Noise-exposed mice were rounded up in a cage, placed inside a noise booth, and exposed to white noise of 120 dB peak equivalent SPL for 3 hours per day for 3 days to induce permanent threshold shift (PTS). Noise was generated through Cool Edit 1.52 PC software, and the amplitude of the noise was measured over 120 dB SPL using a sound level meter (B&K, Nærum, Denmark) in the center and each corner of the soundproof room. The amount of noise exposure used in this study to cause PTS has been previously demonstrated to induce continuous threshold change in a study that used the same equipment and conditions.12)

Measurement of hearing...

다국어 초록 (Multilingual Abstract)

Background and Objectives: The study was designed to measure the change of serum aldosterone concentration after noise exposure in BALB/c mice.


Materials and Methods: BALB/c hybrid mice with ≤25 dB nHL in auditory brainstem responses (ABR) were used. Six mice were exposed to 120 dB SPL broad white band noise for 3 hours per day for 3 consecutive days. ABRs in all mice were examined after noise exposure. Serum aldosterone concentration was checked by radioimmunoassay in three mice without noise exposure, in three mice immediately after noise exposure (0 day after noise group), and in three mice 3 days after noise exposure (3 days after noise group).


Results: Permanent noise exposure-related threshold shift was induced in mice of 0 day after noise group and 3 days after noise group (83.3±2.9 and 88.3±2.9 dB nHL, respectively). The serum aldosterone concentration of the mice after noise exposure was significantly lower than control mice (p=0.046). The changes of aldosterone concentration were 879±137.5 pg/mL without noise exposure, 623±75.9 pg/mL immediately after noise exposure, and 683±49.2 pg/mL 3 days after noise exposure.


Conclusions: In BALB/c mice, serum aldosterone concentration is decreased significantly after noise exposure

참고문헌 (Reference)

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