Diurnal fluctuation of blood ammonia levels in adult-type citrullinemia.

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Abstract
A 48-yr-old man, who was diagnosed as adult-type citrullinemia by quantitative estimation of urea cycle enzymes in the liver, showed a regular nocturnal rise of blood ammonia level. To elucidate the mechanism of diurnal fluctuation of blood ammonia level, the patient was fasted for 4 days. The blood ammonia level rose at the night of the first fasting day even though no food was taken, then it decreased gradually and reached the lowest level in the morning of the third fasting day. Intravenous administration of an amino acid mixture under the same starved condition gave rise to a significant elevation of blood ammonia level. Hyperammonemia of adult-type citrullinemia could result from the accumulation of free ammonia which was produced from the catabolism of amino acids absorbed from the small intestine and surpassed the urea synthesis of defective urea cycle to flood into the blood. Furthermore, the rise of blood ammonia level at the night of the first fasting day suggested that trhe circadian rhythm of amino acid-carbohydrate metabolism might superimpose on the process mentioned above.