FREE AMINO-ACID LEVELS IN SERUM AND SMALL-INTESTINE DURING THE POSTNATAL-DEVELOPMENT OF NORMAL AND SPARSE-FUR MUTANT MICE

Ornithine transcarbamylase (OTC) is a mitochondrial enzyme which catal yzes the conversion of ornithine into citrulline. In sparse-fur (spf) mutant mice, in which both hepatic and small intestinal OTC are defici ent, only small amounts of citrulline are released into the blood. To evaluate the fate of ornithine as well as the levels of substrates and products of these metabolic pathways in normal and OTC-deficient mice , we measured the concentration of free amino acids in small intestina l mucosa and serum during post-natal development. In control animals, ornithine, alanine and citrulline concentrations in intestinal mucosa increased as a function of age, while glutamine, leucine, valine and m ethionine levels decreased around the weaning period. In contrast, the serum concentration of these amino acids remained fairly constant. Ma jor changes were observed in spf mice: the ornithine level remained lo w in intestinal tissue, citrulline concentration was significantly dec reased in both intestinal tissue and blood, circulating levels of argi nine and essential amino acids were drastically reduced in sucklings w hile plasma glutamine increased after weaning. These data confirm the validity of spf mice as a model for the study of nutritional requireme nts in OTC-deficient animals.