In a study conducted some years ago, cats were fasted overnight then given a sin
ID: 70877 • Letter: I
Question
In a study conducted some years ago, cats were fasted overnight then given a single meal complete in all amino acids except arginine. Within 2 hours, blood ammonia levels increased from a normal level of 18 mg/L to 140 mg/L, and the cats showed the clinical symptoms of ammonia toxicity. A control group fed a complete amino acid diet or an amino acid diet in which arginine was replaced by ornithine showed no unusual clinical symptoms. What was the role of fasting in the experiment? What caused the ammonia levels to rise in the experimental group? Why did the absence of arginine lead to ammonia toxicity?Explanation / Answer
6a. Fasting lowers blood glucose levels. In such a condition, gluconeogenesis occurs, i.e. the body starts using amino acids as energy sources. And it starts converting amino acids to glucose.
b. Arginine is an essential amino acid. The human body is unable to prepare it. Lack of arginine in diet will disallow protein synthesis. Ammonia levels are increased because of oxidative deamination of amino acids. Arginine is an intermediate of urea cycle. Lack of arginine disallows conversion of ammonia to urea. So, lot of ammonia collects in the body.