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Urine volume The urine volume is a measurement of the amount of urine excreted during a controlled period of time and can be affected by the level of hydration of the subject being tested.(1) I was in a dehydrated state during this test period due to inadequate fluid intake. According to the graph of my results for urine volume, my lag period was one hour before my urine volume increased to eliminate the test load. According to our lab manual for Urinalysis, this increase in volume is indicative of ADH and aldosterone inhibition. During normal hydration, ADH can directly regulate reabsorption of water through water channels (aquaporins) present in the lumen of the distal tubule and collecting duct (2/150). Aldosterone indirectly affects water reabsorption by coupling the water to sodium reabsorption, called “obligatory water reabsorption since water is obliged to follow sodium by osmosis” (2/151). This allows the diffusion of urea out of the medullary collecting duct into the interstitial fluid through an osmotic gradient created in the medullary collecting duct. This allows passive diffusion of urea out to the interstitial fluid where it plays a major role in the counter current exchange with the vasa recta. The u