DETERMINATION OF OROTIC-ACID IN URINE

Orotic acid was separated from other urinary constituents by ion-pair formation with tetrabutylammonium, and isocratic elution from a revers ed-phase column. Absorbance at 280 nm was recorded for quantitation. O wing to the better column characteristics the separations are somewhat faster, and the sensitivity of the method is higher than those of ana logous methods using anion-exchange columns. The method was used for t he determination of orotic acid in human urine, in urine of rats with portacaval shunts and in small (30 mul) urine samples from sparse fur mice. Shunted rats excreted ca. 100% more orotic acid per 24 h than sh am-operated controls, in spite of their considerably lower body weight . Excessive orotic acid in urine indicates a conditional deficiency of ornithine. Sparse fur mice are congenitally hyperammonemic because of a defective hepatic ornithine carbamoyltransferase. Determination of orotic acid in the urine is a suitable method to identify those animal s among litter mates which have the hereditary enzyme defect.