Induced alterations in metabolism of dl-norleucine-2-C¹⁴ in the intact cow

¹ School of Veterinary Medicine and Department of Animal Husbandry, University of California, Davis, California

The metabolism of dl-norleucine-2-C¹⁴ was compared in intact cows before and after prolonged injections of unlabeled norleucine. The appearance of C¹⁴ in respired CO₂, milk, and urinary acetone indicated that the cow readily metabolizes norleucine. The distribution of C¹⁴ in the urinary acetone was found to be compatible with a pathway involving deamination, decarboxylation and subsequent ß-oxidation. Injections of unlabeled norleucine resulted in accumulation of a pool of unlabeled norleucine in the cow's tissues. Relative increases were noted in the specific activities of the respired CO₂ and in milk constituents, and absolute decreases were noted in the specific activities of urinary acetone—nearly to zero. These findings suggest that oxidative and synthetic mechanisms had been stimulated by the prolonged injections of unlabeled norleucine.