Influence of the oral cavity on insulin release in the rat

Blood glucose and insulin levels were measured in undisturbed and free-moving rats. The insulin level rose in the 1st min after the start of food intake; the glucose level began to increase only in the 3rd min if a fluid carbohydrate-rich food was eaten. The insulin release followed a biphasic pattern. If the same quantity of food ingested orally was injected into the stomach in the same time as the animals needed to complete oral ingestion, delayed insulin release could be seen and the second phase of insulin release was exaggerated. The glucose level, which started to rise in the 3rd min, increased much more than during oral ingestion. With respect to insulin release the same phenomena could be observed if carbohydrate-free fluid food was used instead of carbohydrate-rich fluid food. It is argued that the oral cavity plays a major role in the first phase of insulin release, which in its turn seems to be important in the homeostasis of the blood glucose and insulin levels.