Effects of taste stimulation on the behavior of serum amino acid concentrations and amylase and trypsin activities in fasting rats.

The effect of taste stimulation on serum free-amino acid concentrations and amylase and trypsin activities in fasting rats was studied. Following an acclimation period of 5 d, male Sprague-Dawley rats were fasted for 4 d and sacrificed after taste stimulation with a palatable sodium saccharin or unpalatable quinine sulfate flavored diet. Blood was collected from the portal vein and inferior vena cava at 0, 5, 10, 20 and 30 min after taste stimulation. Intestinal contents were also collected at the same time intervals as the blood collections. Total amino acid concentrations in the saccharin stimulated group increased significantly at 5 and 20 min following taste stimulation in comparison with the control of 0 time in the portal vein, and a significant difference between the saccharin and quinine stimulated groups was also observed at 5 min. No difference was found in the inferior vena cava. A high level of alanine and low level of glutamine were depicted in the portal vein as compared to that of the inferior vena cava. The elevation of alanine that is gluconeogenic amino acid was remarkable in the saccharin group at 20 min in the portal vein. Moreover, amylase and trypsin activities in the saccharin group reached peak values promptly and kept constant throughout the experiment as compared to the quinine group. The results suggest that taste stimulation originates changes in the cephalic phase amino acid concentrations in the portal vein and that taste information, overcoming a hunger, plays an important role in amino acid metabolism and digestive enzyme activities. Therefore, eating with gusto is significant for the maintenance of body functions even under starvation conditions.