Insulin

Insulin is synthesized from its precursors, preproinsulin and proinsulin in the beta cells of the islets of Langerhans and serves as a regulator for the storage and production of carbohydrates. Secretion of insulin is stimulated by an increased glucose concentration in circulation. This leads to higher insulin concentrations and more rapid tissue assimilation of glucose followed by a decline in insulin concentrations as the glucose concentration reduces. The relationship between glucose and insulin must be strictly balanced. When this balance is disturbed, insulin is either under- or over-excreted. Insulin concentrations are severely reduced in insulin-dependent diabetes mellitus (IDDM) and hypopituitarism. Insulin concentrations are raised in non-insulin dependent diabetes mellitus (NIDDM), obesity, insulinoma and certain endocrine conditions such as Cushing syndrome and acromegaly.