Insulin: A natural hormone made by the pancreas that controls the level of the sugar glucose in the blood. Insulin permits cells to use glucose for energy. Cells cannot utilize glucose without insulin.
Diabetes: The failure to make insulin or to respond to it constitutes diabetes mellitus. Insulin is made specifically by the beta cells in the islets of Langerhans in the pancreas. If the beta cells degenerate so the body cannot make enough insulin on its own, type I diabetes results. A person with this type of diabetes must inject exogenous insulin (insulin from sources outside the body).
In type II diabetes, the beta cells produce insulin, but cells throughout the body do not respond normally to it. Nevertheless, insulin also may be used in type II diabetes to help overcome the resistance of cells to insulin.
By reducing the concentration of glucose in the blood, insulin is thought to prevent or reduce the long-term complications of diabetes, including damage to the blood vessels, eyes, kidneys, and nerves.
History of Insulin: In 1921, Frederick Grant Banting and Charles H. Best discovered insulin while they were working in the laboratory of John J.R. Macleod at the University of Toronto. Banting and Best extracted material from the pancreas of dogs. They first used this material to keep diabetic dogs alive and in 1922 they used it successfully on a 14-year-old boy with diabetes. In 1923, James B. Collip, a biochemist, discovered that purifying the extract prevented many of the side effects.
In 1923, Banting and Macleod were awarded the Nobel Prize. Best and Collip were overlooked but Banting and Macleod shared the prize money with them. The US Food and Drug Administration (FDA) first approved insulin in 1939.
Insulin was the first hormone to be synthesized completely in the laboratory, a feat accomplished in 1966 by the American worker Michael Katsoyannis and scientists in China. The first recombinant human insulin was approved by the FDA in 1982.
Types of Insulin: Currently, insulin is available from bovine (beef), porcine (pork), and recombinant (human) sources. Regular (rapid onset, short-acting) and NPH (slower onset, longer duration) human insulin are the most commonly-used preparations. An ultrarapid-acting insulin analog, insulin lispro injection (Humalog®) is a chemically-modified, natural insulin. It was approved by the FDA in June, 1996.
Insulin is administered by injection via the subcutaneous (under the skin) route. Regular insulin acts within 30 minutes, and its effects last 6 to 8 hours. The maximal effect occurs 1 to 3 hours following the injection.
As compared to regular insulin, insulin lispro acts more rapidly, has an earlier maximal effect, and a shorter duration action. Therefore, insulin lispro should be given within 15 minutes of a meal, compared to regular insulin, which is given 30-60 minutes before meals.
NPH insulin is an insulin with an intermediate-duration of action. It has an onset of action about 2 hours following administration and a duration of action of 18 to 26 hours. Its maximal effect is 4 to 12 hours after administration.
Lente insulin also is an intermediate-acting insulin. It has an onset of action after 2 to 4 hours and a duration of action of 18 to 26 hours. The peak activity of lente insulin occurs 6 to 12 hours following administration.