Rapid Fall in Plasma Threonine followed by Increased Intermeal Interval in Response to First Ingestion of a Threonine-devoid Diet in Rats

In most animals, ingestion of a diet lacking an essential amino acid (EAA) gives rise to anorexia within a few hours. The first signal in this feeding response may be the fall in plasma levels of the limiting EAA. In the present study, we measured plasma amino acid levels and food intake after the first exposure to either a threonine-devoid (THR-DEV) or corrected (COR) diet in 16 rats bearing a chronic jugular catheter for blood sampling. Food intake was reduced 165 min (p<0·05) after presentation of the THR-DEV diet. Analysis of the feeding pattern showed that intake was reduced via a four-fold lengthening of the second inter-meal interval. Plasma threonine levels started to fall between 30 and 60 min after onset of the meal (p<0·05). These results, observed in the same rats, lend further support for an early modification of the plasma amino acid pattern in relation to the decrease in feeding of a diet that is EAA deficient.