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I've noticed a peculiar phenomenon. A subject drinks 400 ml of water, then observes time until the urge to urinate is felt. The time is 15 minutes. The subject releases water. 14 minutes later another urge to urinate is felt. The subject releases water again.

I'm particularly interested in what kinds of biological systems are involved in timing of such events. Does the time depend on how full the subject's stomach is? Does caffeine and other diuretics play a part? Is it time of day (circadian rhythm) sensitive? Does that predict anything about the suppression/release of diuretic hormones?

What I'm trying to understand is if the timing between human urges to urinate after water consumption can be used to make predictions about the human biological clock and the state of various systems within the body (for example the digestive system).

I will be conducting this experiment at different times of the day. My hypothesis is that at night, when diuretic hormones are suppressed, the timing would be longer for the same amount of water consumed. This is based on my limited research in the area. Update: I did perform the same experiment at night, the time was 75 minutes for the same amount of water. The experiment was performed at the end of one of sleep cycles, which makes me think that 75 minutes was the duration of the subsequent sleep cycle.

I appreciate your input on the subject, along with any keywords that can help me advance my research in this area. Thank you!

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up vote 8 down vote accepted

The fact that urine output (enuresis) and other kidney functions are circadian is well known, just search on pubmed 'circadian urine kidney'. This can be due both to the fact that liquid consumption is less during the night and to the fact that hormones regulating kidney function like aldosterone and plasma angiotensin II are circadian.

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Thanks for a great answer! I got a glimpse that this may be circadian from a general scholarly paper, now I know precise keywords that I can search for. – Alex Stone Apr 26 '12 at 15:14

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