Glucocorticoids Reset the Nasal Circadian Clock in Mice

The symptoms of allergic rhinitis show marked day-night changes that are likely to be under the control of the circadian clock, but the mechanism of this control is poorly understood. Because most peripheral tissues have endogenous circadian clocks, we examined the circadian rhythm of the clock gene product PERIOD2 (PER2) in the nasal mucosa of male mice using a luciferase reporter and demonstrated for the first time the phase-dependent effects of dexamethasone (DEX) on nasal PER2 rhythm in vivo and ex vivo. The phase shifts in PER2 rhythm caused by DEX were observed around the peak phase of serum glucocorticoids, suggesting that the circadian rhythm of endogenous glucocorticoids regulates the peripheral clock of the mouse nasal mucosa. From the viewpoint of circadian physiology, the best time to administer intranasal steroid treatment for allergic rhinitis would be when no phase shift is caused by DEX: in the early evening in diurnal humans.