Water distribution in rabbits undergoing hypothermia. Experimental study using radio-sodium and tritiated water

The simultaneous distributions of labelled water (HTO) and sodium (Na 24) have been studied in rabbits undergoing experimental hypothermia (internal temperature 19-20 deg. C) and compared with those observed under the same conditions in rabbits at normal temperature. The speed of distribution of water or of sodium within the body was found to be unaffected by hypothermia; the apparent distribution volume of the tracer as a function of time was, on the other hand, always smaller in the chilled rabbits than in the normal, both for HTO and radiosodium. The diminution of the diffusion space was relatively greater for radiosodium (45 per cent of the control value) than for HTO (18 percent). Kinetic study indicated that this diminution during hypothermia was not due to a reduced rate of diffusion of the indicators into unmodified compartments but rather to a normal diffusion rate into available compartments of smaller volume. The following interpretation is advanced. The diminution of accessible HTO space is the result of the circulatory exclusion of certain vascular territories including both extracellular and cellular spaces (18 per cent). In addition to this, some extracellular water (27 per cent) would shift into the cells during chilling: this would explain the greater reduction of available sodium space than water space. Reprint from the 'Revue francaise d'etudes cliniques et biologiques', 1957, Volume Ii, Number 8, Pages 782-788 (authors)