Description
Amylin, or Islet Amyloid Polypeptide (IAPP), is a 37-residue peptide hormone. It is cosecreted with insulin from the pancreatic beta-cells. Amylin plays a role in glycemic regulation by slowing gastric emptying and promoting satiety, thereby preventing post-prandial spikes in blood glucose levels. IAPP is processed from an 89-residue coding sequence. Proislet Amyloid Polypeptide is produced in the pancreatic beta cells (beta-cells) as a 67 amino acid, 7404 Dalton pro-peptide and undergoes post-translational modifications including protease cleavage to produce amylin.
Insulin and IAPP are regulated by similar factors since they share a common regulatory promoter motif. The IAPP promoter is also activated by stimuli which do not affect insulin, such as tumor necrosis factor alpha and fatty acids. One of the defining features of Type 2 diabetes is insulin resistance. This is a condition wherein the body is unable to utilize insulin effectively, resulting in increased insulin production; since proinsulin and proIAPP are cosecreted, this results in an increase in the production of proIAPP as well.
Amylin's metabolic function is well-characterized as an inhibitor of the appearance of nutrient in the plasma. It thus functions as a synergistic partner to insulin, with which it is cosecreted from pancreatic beta cells in response to meals. The overall effect is to slow the rate of appearance of glucose in the blood after eating; this is accomplished via coordinate slowing down gastric emptying, inhibition of digestive secretion [gastric acid, pancreatic enzymes, and bile ejection, and a resulting reduction in food intake. Appearance of new glucose in the blood is reduced by inhibiting secretion of the gluconeogenic hormone glucagon. These actions, which are mostly carried out via a glucose-sensitive part of the brain stem, the area postrema, may be over-ridden during hypoglycemia. They collectively reduce the total insulin demand