Water Absorption from Urine by the Urinary Bladder

      Overnight measurements of human urinary bladder capacity during sleep were performed using transabdominal realtime 3-D ultrasound in healthy volunteers of various ages. Two types of patterns were observed in the increasing curve of capacity; namely, gradual elevation pattern (GEP) when overnight urine production was less than functional bladder capacity (FBC) and steep-flat pattern (SFP) when it was more than FBC. During SFP, bladder capacity reached levels of the FBC quickly, then maintained steadily at that level till morning without awakening. Intravesical urine vanishment (IVUV) phenomenon occurred occasionally, when the volumes of urine reached FBC. Thus, a considerable amount of water may be absorbed from urine in the bladder during sleep to maintain a good level of sleep. This is the first report which exhibits water absorption from urine within the human urinary bladder in the fully physiological situation without any invasive techniques. Possible physiological mechanism for bladder absorption will be discussed.