ESTIMATION OF WATER CONTENT BY TRITIUM DILUTION OF ANIMALS SUBJECTED TO RAPID LIVE-WEIGHT CHANGES

The use of tritiated water to estimate total body-water content of animals experiencing recovery from under-nutrition was studied. The time for equilibration of tritiated water (TOH), given intraperitoneally, with total body water (TBW) was determined in rabbits and in rats. As judged by the specific activity of blood water, equilibration had occurred by 76-125 min in the rabbit and did not appear to be affected by the plane of nutrition. However, between slaughter groups the specific activity of water obtained from the liver 180 min after injection of TOH was significantly different from the specific activity of water simultaneously obtained from the blood plasma. It is concluded that the liver is not a suitable tissue to use for testing achievement of equilibration. As judged by the specific activity of blood water compared to that of water from the whole body macerate, equilibration in mature rats either in stable body condition or undergoing rapid compensatory growth occurred in less than 60 min. A trial comparing TOH-space (corrected by 3% body weight) and actual TBW (by desiccation) was conducted on thirty rabbits which experienced under-nutrition followed by compensatory growth. Prior to under-nutrition the agreement between actual and estimated TBW was satisfactory and within 2.3%. During compensatory growth the agreement was poor- the TOH values over-estimating actual TBW by about 12%. A trial with mature rats confirmed the findings with rabbits. For rats in stable body weight the mean estimated TOH-space for fourteen animals was within 1.2% of the actual TBW. For fourteen rats undergoing compensatory growth the mean estimated TOH-space (corrected by 3% body weight) overestimated actual TBW by 6.2%. © 1969, Cambridge University Press. All rights reserved.