50 | DO: a op ro? 4 f- PRIVACY AGT MATERIAL REMOVED ft Joven g I Chiniceh Fon Gr L Beaed (6/95) Lnweshgahan'V. 31, Apr. } (1952) STUDIES OF TOTAL BODY WATER WITH TRITIUM?:? yw 20a C. PRENTICE, W. SIRI, N. I. BERLIN, G. M. HYDE, R. J. PARSONS, ie E. E. JOINER, arp J. H. LAWRENCE jou" 401891 (From the Section on Experimental Medicine, Donner Laboratory, University of California, Berkeley, and the Highland Alameda Cownty Hospital, Oskland, Cal.) (Submitted for publication November 5, 1951; accepted February 11, 1952) The precise measurement of total body water in man by fs vive methods is becoming increasingly important as more is learned of the significance of electrolyte and water metabolism in normal and pathologic states. While there is as yet insuffi- cient evidence to suggest that body water determi- nations per se will prove of significant value in diagnosis and therapy, the investigation of body water appears essential to a fuller understanding of disease states in which electrolyte and water balance is altered. Thus far, such measurements remain largely laboratory experiments with the bulk of the data obtained from norma! subjects. However, with the present improvements in the methods for assaying tritium, either with the ionization chamber (1) or the proportional counter effect as well as to evaluate by more direct methods, the magnitude of the error introduced by exchange of tritium with the solid constituents of the body. Total body water has been measured by many investigators using four principal methods: J) post-mortem desiccation of cadavers (3), 2) bal- ance studies of electrolytes and water (4), 3) determination of the specific gravity ofthe whole body in vivo (5,6) and 4) the dilution of various sub- stances presumed to be limited to and uniformly mixed within the body water. Well documented reviews of the literature have recently appeared (5,7). Method 7) has no practical significance in clini- cal investigation. Method 2) requires painstaking (2), the study of total body water and water me- balance experiments and no claim is made for tabolism by tracer methods will doubtless be greatly quantitative accuracy. Method 3), the measureaccelerated. ment of whole body specific gravity, has received The present study was undertaken to develop considerable recent attention. It is based on the further the use of tritium for routine body water premise that the body can be divided into two pormeasurement and to extend the investigation of _ tions, namely, the fat-free portion, called the lean total body water to a variety of disease states. A body mass, and adipose tissue. The lean body rapid method for routine assay of tritium had al- mass purportedly maintains a relatively constant ready been developed in this laboratory, but there gross composition, thus contributing a constant still remained several factors which, a priors, could knowneffect to whole body specific gravity. The influence the accuracy of total body water determi- fat content, on the contrary, varies widely from innations with tritium labeled water. The time re- dividual to individual and is normally the largest quired for complete mixing throughout the body factor responsible for the variation of body den- water following intravenous administration of tri- sity. This basic premise has been substantiated _ tum labeled water was considered particularly im- by careful work in guinea pigs and rats (5,8). In ples could be taken to determine the amount of dilution. It was also of special interest to investigate the possible existence of a significant isotope gravity was measured and thereafter total body fat portant in selecting the time at which blood sam- ‘This work was supported by the Life Insurance Medical Research Fund and the U. S. Atomic Energy Comunission. * Weare grateful to Dr. Leo Stanley, of the California Laut J0 ot el State Prison at San Quentin, and to volunteers from the prison who served as subjects for the normal, middle-aged male group. a5) 50 large groups of these animals, whole body specific determined gravimetrically. A hyperbolic rela- tionship between specific gravity and body fat was found which agreed closely with the curve pre- dicted from theoretical considerations (9). The equation for this curve in humans, % fat = 100 x (248 — 5.044), provides a reasonably accurate Sp. gr. estimate of total body fat when the specific gravity 412 BEST COPY AVAILABLE PRIVACY ACT MATERIAL REMOVED