Water Losses and Gains in Fasting and Nephrectomized Rats

¹ From the Department of Physiology, Washington University School of Medicine, Saint Louis, Missouri

Fasting rats lose solids as fast as or faster than they lose water. After nephrectomy they gain water while losing solids. Calculated insensible water loss agrees with directly determined. Fall in plasma Na 24 hours after nephrectomy is accounted for by dilution effects (water gain plus exchanges with gastrointestinal contents, GIC), but fall in plasma Cl is greater, indicating cell entry of Cl. After 48 hours some cell entry of Na is indicated, with greater entry of Cl. A 1-kg normal nonfasted rat gains 705 – 678 = 27 gm water in 24 hours after nephrectomy. Of this retained water, 6 gm is in skin, none in liver or GIC, and 21 in remainder of carcass, largely in skeletal muscle. There is no change in grams water per kilogram fresh tissue after fasting or nephrectomy in heart ventricles or cerebral hemispheres, but there are significant increases in skin, muscle and liver, greater in nephrectomized than in fasting.