Chronomics reveal and quantify circadian rhythmic melatonin in duodenum of rats

Abstract

A circadian rhythm is documented in duodenal melatonin in rats, peaking 16.8 hours after light onset. This component is more readily detected after logl0-transformation of the data. It differs between male and female rats, females having a larger circadian amplitude and an earlier acrophase. The circadian rhythm in duodenal melatonin is also found to lead that of pineal melatonin. The results are qualified by the presence at the start of mapping of the second extremum of a double magnetic storm. KeywordsChronomics; Duodenum; Rats; Circadian; Melatonin AimTo examine in rats, as a widely used model, whether the mammalian gut is characterized by a variation for which the zero circadian amplitude assumption can be rejected. If by this objective time-microscopic cosinor approach, a rhythm can be validated, we can also examine the timing of a duodenal rhythm in the light of circadian acrophases in other tissues obtained concomitantly. Data from the same rats on other tissues were also analyzed to assess their time structure by chronomics, in international cooperative studies along the scale of the day and the week.*Corresponding author. E-mail address: halbe00l @ umn.edu (F. Halberg). NIH Public Access BackgroundAs a rule, in health [1][2][3][4][5] in many species, a prominent time-macroscopic human, murine and avian circadian melatonin rhythm characterizes not only the circulation but also the pineal. Melatonin is found to peak during the daily dark span, with but few exceptions in humans [6] and other organisms [7][8][9], when time-microscopy is used. The variation is obvious to the naked eye and quantifiable with its parameters by time-microscopy [7]. Chronomics, the study of chronomes (time structures) in data of the stroke-prone spontaneously hypertensive Okamoto rat, has revealed phase differences among circadian melatonin rhythms in the hypothalamus and the pituitary vs. that in the pineal [8]. This study was designed to explore any circadian variation of melatonin in the duodenum, in the context of that in other different tissues of the same group of rats, sampled around the clock for 7 days, even though each rat could only be sampled once. Duodenal tissue was only available from a fraction of the animals used for measurement of melatonin in plasma, pineal gland and hypothalamus [9]. An additional meta-analysis on data from Bratislava on the quail [10] is beyond our scope herein, even if, as originally stated, it represents an important qualification of any generalization. Materials and methodsOne hundred and three Wistar (Amsterdam) rats (52 males and 51 females) had been randomly assigned to two rooms kept for a standardization span of 1 month on opposite LD12:12 regimens, to be sampled for 7 days only during working hours at 4-h intervals at six circadian stages should the adjustment to the antiphase regimen be complete. This adjustment was validated by the agreement of data on plasma and pineal with those reported earlier. After bleeding, the animals were killed by cervical dislocation; the tissue...

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