[Distribution of water between the extracellular and intracellular space in rats]

In anesthetized rats the renal pedicules were clamped and the solution with THO, antipyrine, thyocyanate, inulin, 22Na, 36Cl, 82Br was injected into the tail artery. The space of distribution of THO was 65.1% body weight, antipyrine--81.9%. The volumes of distribution of 22Na (27.4%) and thyocyanate (26.9%) were higher than the 36Cl (24.8%) and 82Br (25.6%) spaces. Inulin space was 13.8%. There was no difference between the volume of distribution of the substances in female and male rats. The same spaces of the substances (except inulin) were determined in rats with intact kidneys. After i.a. administration of 5 ml/100 g body weight of Ringer's solution the recovery of all the substances was about 100%. The data obtained indicate that antipyrine cannot be used for estimation of the total body water in rats. For the measurement of extracellular fluid it is better to use radioisotopes 82Br, 36Cl or 22Na; more variable data were observed with thyocyanate and inulin.