Every night between 0330-0430 AM I rush to the bathroom. Of course, I’m careful not to light pulse myself (see here). It’s not baffling that we have an endogenously entrained, circadian rhythm of incontinence given that every other hormonally-regulated behavior like sleeping, waking up, and even sexual desire (see here) is entrained by rhythmic hormone release dictated by the super master circadian clock . Even rats have a circadian rhythm of peeing as shown in this week’s PLoS. Scientifically sexified as urodynamics, of course. In this study, East Coast researchers measured the rate and volume of pee within the entraining dark( active) and light(sleep) periods of a rat. No surprise; the rat peed more during its active period (every 4 minutes!!!!!!!!) than its sleeping time (still every 8 minutes!!!!!!!!). This is amazing considering that as someone who routinely measures drinking rhythms, I can tell you that mice don’t drink every 4 minutes, not even every 8 minutes (except for the early and late portions of their active periods).
In addition to not being impressed by the simplistic research methodologies and conclusions (it very well could be an undergraduate project), I was also shocked that this study didn’t elucidate more of the neurobiological mechanisms of this circadian response, instead of confirming what was done previously. During the 60s, 70s, or 80s, when the field of circadian rhythms was pioneered, the founding fathers and mothers of circadia (Aschoff, Menaker, Hastings, Gillette, and Moore) sought to classify an abundance of circadian phenomena (behavioral and physiological) in a variety of mammalian, reptilian, amphibian, and invertebrate species. Many are documented in the circadian Bible (Biological Rhythms: Handbook of Neurobiology). Secondly, this study failed to discuss how the circadian regulation of anti-diuretic hormone (ADH) could easily drive this urinary rhythm. Though I somewhat sympathize, since everyone is fleeing from the SCN and flocking towards the idea of extra-SCN, circadian oscillators that lie centrally in the nervous system and peripherally in the organs. However, that doesn’t excuse the fact that ADH could have been measured or at least some other physiological marker evident of circadian urination could have been measured, especially given the impact factor of the journal in which the study was published. We already know in humans that ADH is upregulated at night (except when we drink), but what are the circadian-controlled mechanisms???
Gerald M. Herrera1,2, Andrea L. Meredith3* (2010). Diurnal Variation in Urodynamics of Rat
PLoS ONE : 10.1371/journal.pone.0012298