Eosinophil Rhythm in Mice: Range of Occurrence; Effects of Illumination, Feeding and Adrenalectomy

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Abstract
Mice (Mus musculus) of 9 inbred strains as well as hybrids on a regimen of (a) ad libitum feeding, (b) single housing (c) controlled environmental temp. and (d) light during daytime and darkness during the night, show a morning "high" and a night "low" in number of tail-blood eosinophils. Cyclic eosinopenia occurs in the absence of all recognizable extraordinary stimulation in mice of both sexes, ranging in age from 6 weeks to 25 months. The temporal placement of cyclic eosinopenia within the 24-hr. period in ad libitum-fed mice depends on the lighting regimen. For mice severely restricted in calories, the time of feeding assumes a more critical role than lighting. The eosinophil rhythm is not detected at the usual sampling times after exposure to continuous light for 9 days. Mice returned from continuous light to a standard alternating light-dark regimen for 9 days reveal the eosinophil rhythm with its usual temporal placement within the 24-hr. period. Mice kept in continuous darkness up to 13 days continued to show cyclic eosinopenia. The study supports the assumption of an intrinsic mechanism through which environmental effects are mediated and modified. The adrenal gland is probably part of this intrinsic mechanism.