AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 1 174-R177, Copyright © 1988 by American Physiological Society
Measurement of 2H2O by IR absorbance in doubly labeled H2O studies of energy expenditure
W. H. Karasov, L. R. Han and J. C. Munger
Department of Wildlife Ecology, University of Wisconsin, Madison 53706.
The energy expenditure of animals in their natural surroundings can be
determined by measuring the turnover in body water of isotopes of oxygen
and hydrogen. We evaluated the use of infrared spectrophotometry for
measuring 2H2O in small (20-microliters) water samples also labeled with
18O. For 2H2O over the enrichment range of 0.1-1 atom%, there was a linear
relationship between infrared absorbance and 2H2O enrichment. 2H2O
enrichments could be measured with a precision and accuracy of less than or
equal to 1%, using this relationship. The presence of 18O in water samples
in enrichments of up to 1 atom% had no significant effect on measurement of
2H2O by infrared absorbance. We measured the simultaneous turnover rates of
2H2O and 3H in mice and turtles also labeled with 18O. Our results
validated the use of infrared absorbance in doubly labeled water measures
of energy expenditure and indicated that the fractionation factors in vivo
for 2H2O and 3H do not differ.
