Journal of Applied Physiology, Vol 76, Issue 1 391-396, Copyright © 1994 by American Physiological Society
Application of conservation principle in estimating body volume in rats
K. L. Huang, P. S. Chien, Y. Kishi and Y. C. Lin
Department of Physiology, University of Hawaii, John A. Burns School of Medicine, Honolulu 96822.
Obesity is a risk factor in diving and aviation during acute reduction of
pressure, because N2 is five times more soluble in fat than in water. In
addition to concerns of decompression applications, body fat content (BFC)
bears importance in the disposition of drugs, the evaluation of dietary
regimens and exercise programs, and in long-term health status. Most of the
currently available methods for quantifying BFC are impractical for small
animals. We devised a method that does not require the cooperation of the
animal. Our method uses a simple gas-dilution technique to measure the body
volume. The body density was determined as the ratio of body weight (g) to
body volume (ml). After the whole body density was determined, the fraction
of body fat was calculated according to established formulas. Calibration
with aluminum blocks showed a high correlation (r = 0.99) between measured
volumes and the known block volumes. Furthermore, comparing body volumes of
shaved and unshaved rats showed that the volume of air between hairs did
not affect the measurement of body volume with the dilution method. In four
groups, each consisting of 10 male Wistar rats [body wt 81 +/- 1 (SE), 152
+/- 3,297 +/- 5, and 496 +/- 4 g], BFC was 7.0 +/- 2.8, 14.6 +/- 1.9, 22.0
+/- 1.8, and 32.3 +/- 1.3%, respectively. These values compared favorably
with chemically determined BFC values for rats in the literature. Our
results suggest that the gas-dilution technique is a feasible and simple
method for the determination of BFC in small animals.
