Metabolism cage for carbon dioxide trapping studies.

This report describes the design and construction of a metabolism cage that allows for separation of urine and feces and for trapping expired CO2. Such a cage could find use in pharmacokinetic studies of drug excretion rates where potential metabolism to CO2 should be considered. To demonstrate the separation qualities of this cage design, the radioactivity appearing in the urine, feces, and exhaust gases was determined daily for 14 days after the single oral administration of 26-[14C]cholesterol. Less than 1% of the administered radioactivity appeared in the urine, whereas 61% appeared in the feces and 19% in the expired CO2.