The accuracy of doubly-labeled water measurements of CO/sub 2/ production in lizards of the genus Sceloporus was assessed by comparison of CO/sub 2/ production rates determined simultaneously by labeled water and gas chromatography. Five lizards were weighed and given intraperitoneal injections of 55 ..mu..l of water containing 10 microcuries of tritium as HTO and 50 atom % oxygen-18 as H/sub 2/ /sup 18/O. Initial blood samples were taken from the infraorbital sinus ten hours later, and the lizards were placed in sealed metabolism chambers kept at 28 C. After 179 h the lizards were weighed and blood samples taken. Blood samples were microdistilled, assayed for tritium activity and for oxygen-18 content. Isotope measurements were used to calculate rates of CO/sub 2/ production. Gas samples were withdrawn from each chamber after 18, 63, 109, and 179 h and measured against 0.5 and 1.0% CO/sub 2/ standards with a Beckman GC-55 gas chromatograph fitted with silica gel 42-60 mesh column. These results were used to calculate rates of CO/sub 2/ production. Results supported the conclusion that the doubly-labeled water method accurately measured rates of CO/sub 2/ production in Sceloporus lizards, and could therefore be a valuable technique in field studies of lizardmore » energetics.« less
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Congdon et al. (1978) studied this question.