Mouse livers nearly double in size at night
In addition to being able to regenerate and work even when it's cut in half, the liver apparently has another trick up its sleeve: it also doubles in size on a daily basis, at least in mice. Scientists have just discovered that this inflation trick is strongly tied to the rodents' circadian rhythms and hope that if a similar process is at play in humans, we can gain valuable insight into how disrupting those rhythms might be impacting such a valuable organ.
Inside cells are tiny structures, or organelles, known as ribosomes which are like construction workers assembling proteins. Because mice feed at night, it makes sense that the size of the protein-manufacturing crew would increase to help the rodents process the incoming food. And that's exactly what happens. As the number of ribosomes in each liver cell goes up, the cells stretch to accommodate them, and the liver expands by up to 40 percent in size, found researchers at the Université de Genève in Switzerland.
After the night buffet is over, the liver begins to disassemble and eliminate the ribosomes and it returns to its normal size before dawn.
Perhaps most significantly, the researchers found that this process only works in conjunction with the circadian rhythms of the mice. That is, the increased liver size was dependent on the time of day more than it was on the volume of food the rodents ate. When the researchers tried to flip the process by feeding the mice during the day instead of at night, the liver did not increase in size.
This indicates that this vital organ, at least in mice, is finely tuned to cycles of light and darkness and wakefulness and sleep. If the same process is shown to be active in humans, we could gain deeper insight into how activities like working at night or insomnia could be damaging our livers.
Indeed, one previous study from 1986 did show that our livers can fluctuate in size – but only by about 20 percent. That study didn't tie such fluctuations to circadian rhythms, though, as the measurements were only taken during the day. In that study, the increased size was tied to more water and glycogen (a type of stored sugar used for energy) in the organ. Further studies are needed to see if ribosomes influenced by our circadian rhythms are a factor as well.
The study has been published in the journal Cell.