Proteins are chains of amino acids. So no net gain of water. Blood volume decreases. Replacement water pulled by osmosis from interstitial fluid and cells. This increases the water permeability of the distal tubule and collecting duct.
More water leaves the tubule and reenters the blood stream, so less water leaves the body.
Balanced salt solution put into abdominal cavity, suctioned out half an hour later. Key points Terrestrial animals must conserve water while excreting nitrogenous wastes. To conserve water, the nephron employs both active and passive mechanisms. Urine-altering drugs affect different parts of the nephron.