Transient hyperammonemia during aging in ornithine transcarbamylase-deficient, sparse-fur mice.

Ornithine transcarbamylase [EC 2.1.3.3] (OTC) deficient, sparse-fur (spf) mice are considered to be a good model of human OTC deficiencies. We measured the blood ammonia concentration in spf mice. It was not always at a high level. It was high only during weaning, then gradually decreased and finally fell to a normal level. A similar phenomenon was observed in the change of hepatic ammonia concentration. Excretion of urinary orotate in spf mice was 15-20 times higher than in control mice just after weaning. It also gradually decreased during aging, but remained at a high level compared with adult control mice. OTC activity at pH 7.7 in the liver of spf mice increased significantly between the weaning period and 30-40 days old, when blood ammonia was falling to a normal level.