EFFECTS OF MONOSODIUM GLUTAMATE (UMAMI TASTE) WITH AND WITHOUT GUANOSINE 5'-MONOPHOSPHATE ON RAT AUTONOMIC RESPONSES TO MEALS

Monosodium glutamate (MSG) is used as a food additive to improve the t aste of food. The effect of MSG on sweet taste is enhanced by guanosin e 5'-monophosphate (GMP). Because increased palatability is known to i ncrease the vagally mediated preabsorptive insulin response (PIR), we hypothesized that MSG and GMP will enhance the PIR. To study this, mal e Wistar rats were provided with permanent cannulas for venous blood s ampling and intragastric drug administration. The MSG and GMP were eit her added to a test meal or infused into the stomach during a test mea l. Blood samples were taken to measure concentrations of glucose, insu lin, epinephrine (E), and norepinephrine (NE). Addition of 56 mg MSG t o a control meal markedly reduced both phases of the meal-induced incr ease in plasma insulin and had no effects on blood glucose and plasma E and NE responses. Infusion of 56 mg MSG into the stomach at the onse t of food intake reduced the PIR with no effect on glucose, E, NE, or the second phase insulin release. Addition of 2 mg MSG in combination with GMP to the test meal or gastric administration of these drugs did not affect the changes in any of the blood components measured. It is concluded that addition of a high dose of MSG to a test meal leads to a reduction in the vagal response to food.