Circadian rhythms of alcohol dehydrogenase and MEOS in the rat.

The circadian peak in alcohol dehydrogenase (ADH) activity fell near the time of maximal blood ethanol clearance rates both in groups of rats injected with a single ethanol dose (acute group) and in rats continuously exposed to ethanol for 22 weeks (chronic group). However, at all timepoints investigated ADH activity levels were lower and fluctuated less in the chronic group than in either the acute or control (ethanol naive) groups. In contrast, activity levels of the microsomal ethanol oxidizing system (MEOS) revealed a prominent rhythm that was 180 degrees out of phase with the ADH rhythm in the chronic group, while MEOS activity showed very low levels in the acute and control groups and did not vary over the circadian span.