By Andrew Bennett Hellman
The body's internal clock helps to regulate a water-storing hormone so that nightly dehydration or trips to the toilet are not the norm, research suggests.
In an article published in Nature Neuroscience today, neurophysiologists Eric Trudel and Charles Bourque at the Research Institute of the McGill University Health Centre in Montreal, Canada, propose a mechanism by which the body's circadian system, or internal clock, controls water regulation1. By allowing cells that sense water levels to activate cells that release vasopressin, a hormone that instructs the body to store water, the circadian system keeps the body hydrated during sleep.
"We've known for years that there's a rhythm of vasopressin that gets high when you're sleeping. But no one knew how that occurred. And this group identified a very concrete physiological mechanism of how it occurs," says Christopher Colwell, a neuroscientist who studies sleep and circadian rhythms at the David Geffen School of Medicine at the University of California, Los Angeles.
The body regulates its water content mainly by balancing water intake through thirst with water loss through urine production. People don't drink during sleep, so the body has to minimize water loss to remain sufficiently hydrated. Scientists knew that low water levels excite a group of cells called osmosensory neurons, which direct another set of neurons to release vasopressin into the bloodstream. Vasopressin levels increase during sleep; clock neurons, meanwhile, get quieter.
Thirst alert
Trudel and Bourque tested the idea that lower clock-neuron activity might allow osmosensory neurons to more easily activate vasopressin-releasing neurons, which would mean more water retention and less urine production during sleep.
To do this, they isolated thin slices of rat brain containing intact sensory, vasopressin-releasing and clock neurons. Even when removed from the brain, clock neurons continue to mark time.
The duo then stimulated the sensory neurons and recorded any electrical activity in the vasopressin-releasing neurons to monitor communication between the two cell groups. The researchers then moved on to look at the effect of the clock cells on this pathway. When they did not activate the clock cells during the 'sleep' part of their cycle, it was easier for the sensory cells to communicate with vasopressin-releasing cells. Conversely, when they activated the clock cells, this communication decreased markedly.
The results suggest that clock cells function as a dimmer switch for water control. When their activity is high, they prevent sensory cells from instructing secretory cells to release vasopressin. Then, when clock cells are less active, sensory cells can easily instruct secretory cells to release vasopressin, ensuring that the body holds on to its water reserves.
Colwell points out that the study was done in rats, which are nocturnal. Although the vasopressin cycle and clock-neuron activity are similar in rats and humans, the question of whether the same mechanism occurs in animals that sleep at night remains to be answered.
"We show this for this one circuit, but it's possible that clock neurons regulate other circuits in a similar manner and this remains to be studied," says Bourque. He speculates that future studies might reveal whether the same mechanism regulates hunger, sleepiness and other aspects of physiology related to circadian rhythms.
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9 Comments
Add CommentWhy the body isn't thirsty at night? Who says it isn't? That's quite a bit of a generalization. I grew up at sea level in a humid place but since I moved to Wyoming at 6,300 feet elevation with 15% relative humidity I wake up once or twice every night with the need to drink. Most people on the planet I believe live in humid areas and this has an impact on not getting too thirsty they get at night. Anyway, if you're feeling thirsty, day or night, your body is telling you that dehydration already started.
Reply | Report Abuse | Link to thisI'm thirsty all night long.
Reply | Report Abuse | Link to thisI'm thirsty all night long.
Reply | Report Abuse | Link to thisI believe the correct term is hypohydration. Dehydration is the absence of all water.
Reply | Report Abuse | Link to thisAnyway, the body is much less active at night, using less energy and producing less waste. Could this have an effect on the thirst??
Umm...Most people that I have met are thirsty at night... When I was in the military, my one roommate from San Bernadeno, Ca would by habit freeze a plastic 20oz bottle every night so he would have cold water by his bed...
Reply | Report Abuse | Link to thisBoth of my wives over the years had had thirst problems during the night one way or the other at different times..... My first wife would sleep on whatever side of the bed was closest the bathroom so she could use it during the night...
The Varibles alone as suggested with humidity, Central Air, Altitude etc really put this study at a loss... In my own body, I slept on a heated water bed for 10 years, during those times.. I would sweat alot on the bed itself.. finially causes the mattress to have a hard spot in the plastic where I would sleep... My body does very good at adapting to the enviroment, and I would find that it is more this type adaptation that causes someone to be less or more thirsty during the night, how active a lifestyle they have, or if they are obese, not something in your sleeping clock cycle..
Umm...Most people that I have met are thirsty at night... When I was in the military, my one roommate from San Bernadeno, Ca would by habit freeze a plastic 20oz bottle every night so he would have cold water by his bed...
Reply | Report Abuse | Link to thisBoth of my wives over the years had had thirst problems during the night one way or the other at different times..... My first wife would sleep on whatever side of the bed was closest the bathroom so she could use it during the night...
The Varibles alone as suggested with humidity, Central Air, Altitude etc really put this study at a loss... In my own body, I slept on a heated water bed for 10 years, during those times.. I would sweat alot on the bed itself.. finially causes the mattress to have a hard spot in the plastic where I would sleep... My body does very good at adapting to the enviroment, and I would find that it is more this type adaptation that causes someone to be less or more thirsty during the night, how active a lifestyle they have, or if they are obese, not something in your sleeping clock cycle..
I awake several times in the night in need of a drink of water.
Reply | Report Abuse | Link to thisIf you are adequately hydrated when you fall asleep the dimmers (clock cells) keep you body from processing water at the normal rate. So you don't have to drink as much. If you are under-hydrated to begin with then you will still get thirsty. On a physiological level you will still need water. so that is why you can still wake up thirsty. The clock cells put the both into water conservation mode but they don't remove the need for water.
Reply | Report Abuse | Link to thisBart (while walking in a cemetery at midnight): Grampa, do you think the dead get up and walk around at night?
Reply | Report Abuse | Link to thisGrampa Simpson: If they're like me, they have to get up at least twice.
My hydrologic cycle runs round the clock.