Question

Rats were fasted overnight and then given a single meal that was low in carbohydrate and high in protein content. The meal contained all amino acids except arginine, which is an essential amino acid. Within 2 hours, blood ammonia levels rose by 800%. A control group of rats were fasted and then fed the same low carb and high protein meal but with arginine included. This latter group showed no change in blood ammonia levels.

Fasting was required to obtain this difference in blood ammonia levels. Why?

What caused the ammonia level to rise in the experimental group compared to the control group?

Answer 1

1. Fasting will result in lowering of blood glucose levels.

2.On feeding arginine free diet, there will be a rapid catabolism of all the ingested amino acids, especially the glucogenic ones. This catabolism was exacerbated by the lack of an essential amino acid, which prevented protein synthesis.

3. Oxidative deamination of amino acids caused the elevation of ammonia levels. '

4. Arginine (an intermediate in the urea cycle) in its absence will slow the conversion of ammonia to urea. Arginine (or ornithine) synthesis in the cat is not sufficient to meet the needs imposed by the stress of this experiment, suggesting that arginine is an essential amino acid.
5. Ornithine (or citrulline) can be included instead of arginine because it also is an intermediate in the urea cycle.