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Jet Lag of the Liver
19 January 2001 7:00 pm
Adjusting meal times may help travelers avoid the stomach upset sometimes associated with jet lag, suggests new research on circadian rhythms. The bane of globe-trotters, jet lag occurs when a person's sleep schedule is at odds with local time. Sunlight helps adjust the body clock, and now there may be another way to help get the system acquainted to a new time zone. In today's Science, researchers report that the timing of meals can reset a biological clock in the liver, which might help it rev up enzyme production at the right time for digestion. The finding may one day help doctors optimize the timing of treatments for liver diseases.
The body is full of clocks. These circadian rhythms--such as waxing and waning levels of the expression of certain genes--tick in organs from the lungs to the liver. Normally, these rhythms are in step with a master clock in the brain that is controlled by the cycle of daylight and darkness. However, it's not known if the brain synchronizes the other clocks directly (through the timed release of hormones, for example) or if external stimuli play a role in setting them.
To test the possibility that food might set the liver's clock, biologist Michael Menaker of the University of Virginia in Charlottesville and his colleagues looked at the effect of meal timing on one of the cogs of the biological clock, a gene called Per1. The team used rats in which the gene that regulates Per1 expression has been linked to a gene for luciferase, the enzyme that gives fireflies their light. The rats' tissues glow more brightly as Per1 expression increases. By monitoring this glow, the team found that by limiting the hours during which rats could eat, they could shift the peak of Per1 expression in the liver by up to 10 hours. In contrast, the Per1 expression in the brain was unaffected by the altered meal schedule.
"It makes sense that the liver's activity should be tied to feeding--it has to have the right enzymes at the right time," says biologist Craig Heller of Stanford University. But he notes that even though the liver clock responds directly to changes in meal time, the brain may still be in charge: By controlling the sleep-wake cycle, the brain clock determines when an animal is active and searching for food.
Menaker's home page at the University of Virginia