Light-dark and feeding regimens affect circadian phasing of blood-ethanol decay rates.

Rats maintained on a 12 hour:12 hour light-dark cycle, with food continuously available, exhibited a prominent and reproducible circadian rhythm in the slope of the linear blood-ethanol clearance curve. Peak values fell near the end of the dark period and trough values late in the light period. These phase relationships persisted with 4, 8 and 12 hours phase shifts of the illumination schedule. However, when food availability was restricted to 4 hours per day the feeding regimen became the dominant synchronizer for the rhythms in blood-ethanol decay rate and body core temperature. With resumption of the ad lib feeding regimen, the L-D cycle again entrained these rhythms. Ethanol injections (1.5 g/kg, IP) did not alter the expected excursion of the circadian temperature curve, as measured 4 hours after dosing.