Insulin Release

Insulin is released by various stimuli initiated by the organism. Probably the most important stimulus for the release of the tissue hormone is an increase in the blood sugar level. From a glucose level of approximately 5 mmol/l, the beta cells of the pancreas begin to secrete insulin.

In addition, various amino acids, free fatty acids and some other hormones induce insulin release. Especially the hormones gastrin, secretin, GIP and GLP-1 have a strong stimulating effect on the cells of the pancreas. The actual release of the hormone into the bloodstream follows a certain cycle, even when blood sugar levels are high.

Insulin is released about every three to six minutes. Immediately after food intake, insulin secretion follows a biphasic (2 phase) pattern. Approximately three to five minutes after food intake, the secretion of a first hormone portion takes place.

The first secretory phase lasts about 10 minutes. This is followed by a pause in which the blood sugar level is detected again. If the glucose level in the blood is still too high, a second secretion phase follows, which lasts until the sugar concentration has reached a normal value.

During the first phase, mainly stored insulin is released, while in the second interval newly formed amounts of the hormone are released. The actual release mechanism is triggered by the penetration of a sugar molecule into the beta cells. After the glucose has entered the cell via a special transporter (so-called GLUT-2 transporter), it is split into its individual parts.

During this metabolic process, probably the most important energy carrier, ATP, is produced. By binding to a specific ATP receptor, the outflow of potassium ions is then reduced. The result is a change in the charge of the respective cell membranes (technical term: depolarization).

This in turn leads to an opening of voltage-dependent calcium channels, and the calcium content inside the cell rises sharply. This increased calcium concentration is the actual signal for the release of the insulin-filled vesicles.The body’s own hormone insulin is an important component of the blood sugar regulating system. The regulation of the glucose (sugar) dissolved in the blood is carried out by two messenger substances, which are released depending on the blood sugar concentration currently present.

Besides insulin, glucagon, another hormone produced in the pancreas, also contributes to this regulation. While insulin is able to lower the blood glucose level via various mechanisms, glucagon is able to increase it. Glucagon is therefore the antagonist of insulin.

In addition to these two main regulators, the hormones adrenaline and cortisol, among others, have an influence on blood sugar. The blood sugar-lowering effect of the proteohormone is primarily based on an increase in the passage of glucose from the blood plasma and tissue fluid into the interior of various tissues (for example, into muscle cells or the liver). Within the tissues, sugar can be stored in the form of so-called glycogen or can be immediately converted into energy via a metabolic pathway known as glycolysis.

In addition to regulating blood sugar, the hormone insulin influences fat and amino acid metabolism and is involved in maintaining the potassium balance. Problems in the area of insulin secretion or its formation to specific receptors can therefore have considerable effects on the entire organism. Diseases such as diabetes mellitus, hyperinsulinism, insulinomas, insulin resistance and the so-called metabolic syndrome are all based on a defective regulation of the insulin balance.

Diabetics suffer from an insulin deficiency, so that glucose (sugar) is difficult to introduce into the cells. This transport is only possible when the blood sugar level is increased. Due to the lack of glucose in the fat cells, ketone bodies are built up which can cause metabolic disorders (ketoacidotic coma). Inuslin is secreted from the pancreas in order to maintain the basic metabolism and also during food intake.