Rapid fall in plasma threonine followed by increased intermeal interval inresponse 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 pres ent study, we measured plasma amino acid levels and food intake after the f irst exposure to either a threonine-devoid (THR-DEV) or corrected (COR) die t in 16 rats bearing a chronic jugular catheter for blood sampling. Food in take was reduced 165 min (p<0.05) after presentation of the THR-DEV diet. A nalysis of the feeding pattern showed that intake was reduced via a four-fo ld lengthening of the second intermeal interval. plasma threonine levels st arted 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 modi fication of the plasma amino acid pattern in relation to the decrease in fe eding of a diet that is EAA deficient. (C) 1999 Academic Press.