insulin

A polypeptide hormone, secreted by beta cells in the islets of Langerhans, that promotes glucose utilization, protein synthesis, and the formation and storage of neutral lipids; available in a variety of preparations including genetically engineered human i., which is presently favored, i. is used parenterally in the treatment of diabetes mellitus. [L. insula, island, + -in]

- biphasic i. the specific antidiabetic principle of the pancreas of the ox in a solution of that from the pancreas of the pig.

- globin i. SYN: regular i..

- globin zinc i. a sterile solution of i. modified by the addition of zinc chloride and globin; it contains 100 units per ml; duration of action is about 18 hours.

- human i. a protein that has the normal structure of i. produced by the human pancreas, prepared by recombinant DNA techniques and by semisynthetic processes.

- immunoreactive i. that portion of i. in blood measured by immunochemical methods for the hormone; presumed to represent the free (unbound) and biologically active fraction of total blood i..

- isophane i. a modified form of i. composed of i., protamine, and zinc; an intermediately acting preparation used for the treatment of diabetes mellitus. SYN: NPH i..

- lente i. SYN: i. zinc suspension.

- lispro i. a modified version of natural human i., synthesized by a genetically programmed strain of nonpathogenic Escherichia coli, in which the amino acid s lysine (Lys) and proline (Pro) near the end of the B chain are transposed. This chemical alteration yields an i. with a much faster onset of action, which reaches its peak effect earlier than regular i.. [Lys + Pro] Lispro i., introduced in 1996, has the same molecular weight and the same biochemical functions as the natural hormone, and when administered intravenously its effects are virtually indistinguishable from those of regular i.. However, when it is injected subcutaneously it reaches its peak serum level in 30–90 minutes, as compared to 50–120 minutes for regular i., and it also has a shorter half-life. While the original indication for lispro i. was for use as a rapid-acting premeal i., clinical experience has shown that this agent improves postprandial glucose levels, reduces the incidence of severe hypoglycemia and nighttime hypoglycemia, and improves glucose control as measured by glycosylated hemoglobin, when appropriate adjustments are made to basal i., snacking, and exercise level. Unlike other insulins, lispro i. is not available without a prescription. It is not recommended for use in pregnancy because its effects on the fetus have not been assessed.

- NPH i. SYN: isophane i.. [Neutral Protamine Hagedorn]

- protamine zinc i. i. modified by the addition of protamine and zinc chloride; it contains 100 units per ml.

- regular i. a rapidly acting form of i. which is a clear solution and may be administered intravenously as well as subcutaneously; may be mixed with longer acting forms of i. to extend the duration of effect. Onset of effect occurs in 12 to 1 hour, peak effects are observed in 2 to 3 hours, and the duration of effect is about 5 to 7 hours. SYN: globin i..

- semilente i. SYN: prompt i. zinc suspension.

- ultralente i. a form of zinc precipitated i. in suspension in which the particle size is large, and thus release into the bloodstream after subcutaneous injection is slow; it can be mixed with other insulins having different particle sizes to achieve different durations of activity. Can be derived from porcine, bovine, or genetically engineered human type.

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in·su·lin 'in(t)-s(ə-)lən n a protein hormone that is synthesized in the pancreas from proinsulin and secreted by the beta cells of the islets of Langerhans, that is essential for the metabolism of carbohydrates, lipids, and proteins, that regulates blood sugar levels by facilitating the uptake of glucose into tissues, by promoting its conversion into glycogen, fatty acids, and triglycerides, and by reducing the release of glucose from the liver, and that when produced in insufficient quantities results in diabetes mellitus see ILETIN

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n.

a protein hormone, produced in the pancreas by the beta cells of the islets of Langerhans, that is important for regulating the amount of sugar (glucose) in the blood. Insulin secretion is stimulated by a high concentration of blood sugar. Lack of this hormone gives rise to diabetes mellitus, in which large amounts of sugar are present in the blood and urine. This condition may be treated successfully by insulin injections (see analogue insulins, isophane insulins, insulin pen, continuous insulin infusion pump).

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in·su·lin (inґsə-lin) [L. insula island + -in] 1. a protein hormone secreted by the beta cells of the pancreatic islets, serving as a hormonal signal of the fed state; it is secreted in response to elevated blood levels of glucose and amino acids and promotes efficient storage and use of these fuel molecules by controlling transport of metabolites and ions across cell membranes and regulating intracellular biosynthetic pathways. It promotes entry of glucose, fatty acids, and amino acids into cells; promotes glycogen, protein, and lipid synthesis; and inhibits gluconeogenesis, glycogen degradation, protein degradation, and lipolysis. Its secretion is also influenced by gastrointestinal hormones and by autonomic nervous activity. It is formed from a single polypeptide chain (proinsulin) that is cleaved by proteases at two points; the end pieces (A and B chains), held together by disulfide bridges, make up insulin; the connecting C peptide is also secreted but has no physiologic activity. Relative insulin deficiency is the cause of most cases of diabetes mellitus. 2. a preparation of the hormone, used in the treatment of diabetes mellitus; it may be bovine or porcine in origin or a recombinant human type, although insulin preparations of bovine origin are no longer available in the United States. Types vary in rapidity of onset, duration of action, and degree of purification (most containing some proinsulin and other antigenic components). 3. [USP] a rapid-acting, unmodified form of the hormone with an approximate time of onset of 30 minutes to 1 hour and duration of action of 6 to 8 hours, prepared from crystalline bovine or porcine insulin, or both. Administered subcutaneously, intramuscularly, intravenously, or by continuous infusion pump. Called also regular i.

Primary structure of insulin. The amino acid sequences of the A and B chains of human insulin are shown and the inter- and intrachain disulfide bridges are indicated. Residues in beef and pork insulin and in several modified insulins that differ from those of unmodified human insulin are shown above or below the A and B chains. For the key to the letter codes for individual amino acids, see the illustration at amino acid.