A number of observations suggest that amino acid metabolism may have something to do with the regulation of hunger. If amino acid solutions are infused too rapidly, anorexia or nausea may appear (I, 2), and gastric peristalsis has been found to cease during the intravenous administration of amino acids (3). In this laboratory measurements of the serum amino acid and blood sugar concentrations have been made under a variety of circumstances (4, 5). Simultaneously, crude estimations of appetite have been attempted. MethodJust before each blood sample was taken the subject was asked whether or not he was 'hungry.' An attempt was made to interpret his response according to the following scale: nauseated, minus I; no desire for food, 0; might eat if offered food, but not very hungry, I plus; ravenous, 4 plus; and 2 plus and 3 plus graded between I plus and 4 plus.In all of the experiments reported here the subjects were either normal volunteers or patients with no disease known to affect protein or carbohydrate metabolism. In experiment I nine subjects ate a standard breakfast containing approximately 20 gm of protein: two eggs, a glass of milk and a piece of toast. Venous blood was collected in the fasting state and at hourly intervals after the breakfast for 4 hours. The serum amino acid nitrogen concentration of each blood sample was determined in duplicate by the method of Albanese and Irby as previously described (4). The standard deviation in 230 such pairs was 0.16 mg%.In experiment II, with I1 subjects, 500 cc of 5% amino acids and 5% glucose2 were infused in 45 minutes. BloodCopyright 0 1997 NAASO. specimens were obtained in the fasting state and at hourly intervals for a period of 4 hours after the beginning of the infusion. In five instances blood samples were also obtained '/2 hour after the start of the infusion. Serum amino acid nitrogen was determined as described above, and the blood sugar concentration of each sample was determined by the Mattice modification of the Fohn-Wu method (6). For 286 such paired determinations the standard deviation was 2.7 mg%.In experiment III, with 13 subjects, 250 cc of a 10% aqueous solution of enzymatically digested casein' were infused in 45 minutes. Blood specimens were obtained immediately preceding the infusion and after the beginning of the infusion at the following intervals: 10 minutes, 30 minutes, 1 hour, 2 hours, 3 hours and 4 hours. Blood sugar concentration of each specimen was determined as described above, and serum amino acid concentration of each specimen, except those drawn at 10 and 30 minutes, was estimated as described above.In experiment IV each of 13 subjects drank 250 cc of the same 10% amino acid mixture used in experiment III. Both serum amino acid nitrogen and blood sugar were estimated in the fasting state and at %-hour intervals for 2 hours and for another 2 hours at 1-hour intervals. ResultsFor a long time we were unable to decide how these data could best be analyzed. In fact, it seemed unlikely that such crude estimations of the desire to ...

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