Disorder of the saliva melatonin circadian rhythm in patients with Meniere's disease

Endolymphatic hydrops of inner ear is the mor-phologic entity of Meniere’s disease (MD), how-ever little is known about the generatingmechanism. Stress is involved in the developmentof symptoms of MD and environmental stimuli arewell known to trigger Meniere’s attack (1). Stressinduces a discharge of stress hormone vasopressin(VP) and catecholamine, which may be concernedwith the development of endolymphatic hydrops(2, 3). Under normal conditions, the lymph com-position of the inner ear is maintained by a varietyof subtle regulatory mechanisms. When exposed tostress, however, several substances have beenfound to penetrate into the inner ear fluids andthus induce functional changes (4).Stress-related hormone such as VP is involved inthe circadian rhythm (5), therefore, the home-ostasis of the inner fluids may also be maintainedwith the circadian rhythm. Melatonin (MEL),which is one of the hormones regulating thecircadian rhythm, has been reported to inhibit thesecretion activity of VP and the increase of cyclicadenosine monophosphate concentration in cul-tured suprachiasmatic nuclei cells (6). The vestib-ular function has been reported to have a circadianrhythm similar to the rhythmic activity in theauditory system which has been already demon-strated (7). These results lead to the hypothesis thata disturbance in the circadian rhythm of MEL or adeficiency of MEL may influence the regulation ofthe inner ear composition and thereby inducefunctional changes. However, little information isknown about the association of MEL with MD.Some reports have demonstrated that stress-relateddiseases such as stress ulcers and depression maybe associated with MEL (8, 9). We thereforeinvestigated the MEL concentration in the salivaof MD patients.The MEL concentration in saliva also shows arhythm with a period close to 24 h which iscorrelated with the serum MEL concentration(P < 0.01, r