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Systematic Oscillations in the Metabolism of Orotic Acid in the Rat Adapted to a Controlled Feeding Schedule¹

McArdle Laboratory, Medical Center, University of Wisconsin, Madison, Wisconsin

Orotic acid labeled with ¹⁴C in the 7-, 2- or 6-position has been used to obtain information on its metabolism in the rat adapted to a 48-hour cycle of 8 hours of feeding and 40 hours of fasting. The conversion of orotic acid to uridine monophosphate (UMP) did not vary with the nutritional state of the rat throughout the cycle. However, the further metabolism of UMP derived from injected ring-labeled orotic acid, as determined by its incorporation into liver RNA and degradation to CO₂, did show cyclic variations, corresponding with a cyclic variation of the total liver RNA content. The increase in degradation to CO₂ of UMP derived from injected orotic acid in the fasting period of the cycle suggests an increase in catabolic enzymic activity. A simple and efficient method for collecting and determining expired ¹⁴CO₂ is described.

² Fellow of the Jane Coffin Childs Memorial Fund for Medical Research, 1965–1966. Present address: Paterson Laboratories, Christie Hospital and Holt Radium Institute, Manchester 20, England.

Manuscript received 15 December 1967.