Discussion
We observed clear diurnal differences in Qmax in healthy young men under both dim and bright daylight. Morning Qmax values were significantly lower than the bright daylight evening and the daytime, evening, and pre-sleep timepoints in dim daylight. The pre-sleep Qmax values in dim daylight were significantly higher than bright daylight, while late-night Qmax values in the fixed-time urination period were significantly lower than mDay under both the bright and dim daylight conditions.Diurnal differences in Qmax values were observed in young, healthy men in a light-controlled environment, suggestive of a physiological phenomenon under control of the endogenous central clock system as well as local regulation by bladder-specific timing. The central clock, influenced by light exposure, is located in the supurachiasmatic nucleus and tunes peripheral clocks in organs such as the bladder to coordinate circadian rhythms of intraorgan activities [In addition, we found that bright daylight significantly decreased before sleep Qmax versus dim daylight. This suggests that the pre-sleep bladder may have shifted to “storage” mode under bright daylight conditions, but “voiding” mode might have persisted under dim daylight conditions. In other words, bright daylight could regulate a phase-advancing shift in Qmax diurnal variation, similar to shifts of urinary NaPsychological influence from the dim daylight condition may have also influenced our results [In clinical settings, complaints about difficult nighttime urination are common. As a result, one of our objectives was to compare the Qmax at 4 a.m., a time in the middle of the sleep period that is unassociated with urination on demand, with daytime urination. This comparison was a subsidiary study to a previous experiment that focused on measuring urinary components [Diurnal rhythms of urination typically show a decrease in urinary frequency and an increase in volume voided per micturition upon waking or during nighttime [The present study has several limitations. First, the origin of diurnal Qmax differences in healthy young men is unreported. While bladder and urethral tension studies in healthy volunteers are possible, invasive catheter insertion is difficult to accomplish [