Adrenomedullin Peptides

Definition
Adrenomedullin (AM) is a pluripotent peptide and a hypotensive substance extracted from human adrenal tumour. Due to its origin of discovery, i.e. the medulla of the adrenal gland, the peptide is named adrenomedullin.

Discovery
AM was initially isolated from phaechromcytoma cells in 1993 by Kitmura K and his associates1.

Classification
AM is a member of the calcitonin family of peptides. In teleost fish, AM forms an independent subfamily consisting of five members viz. (AM1–AM5). This teleost AM family comprises three groups, AM1/AM4, AM2/AM3, and AM5 2,3.

Structural Characteristics
The peptide consists of 52 amino acids with a 6-member ring structure linked by a disulfide bond between amino acid 16 and 21 and amidated-COOH terminal4. It has 27 % homology with the calcitonin gene-related peptide (CGRP).

Mechanism of action
AM peptides act through specific receptors in the plasma membrane to activate adenylate cyclase activity and modulate Ca2+ flux in the target cells. The intracellular free Ca2+ increases on the activation of phospholipase C and formation of inositol 1, 4, 5-trisphosphate in the endothelial cells. The intracellular increase of Ca2+ activates endothelial nitric oxide synthase which leads to vascular relaxation5.

Function
AM is the most potent endogenous vasodilatory peptide found in the body6. They increase the tolerance of cells to oxidative stress, hypoxic injury and angiogenesis. It plays an important role in neurotransmission and ovarian function and in kidney, it acts as a diuretic and natriuretic7. AM is considered to play an important endocrine role in various tissues in maintaining electrolyte and fluid homeostasis8. It is used in the diagnosis and treatment of preeclampsia, type II diabetic patients and to promote fetal growth. They also play an important role in the regulation of insulin secretion and blood glucose metabolism.

References

1. Kitamura K, Kangawa K, Kawamoto M, Ichiki Y, Nakamura S, Matsuo H, Eto T (1993). Adrenomedullin: a novel hypotensive peptide isolated from human pheochromocytoma. Biochem Biophys Res Commun., 192 (2):553-560.
2. Ogoshi M, Nobata S, and Takei Y (2008). Potent osmoregulatory actions of homologous adrenomedullins administered peripherally and centrally in eels. Am J Physiol Regul Integr Comp Physiol, 295: 2075-2083.
3. Ogoshi M, Inoue K, Naruse K, Takei Y (2006). Evolutionary history of the calcitonin gene-related peptide family in vertebrates revealed by comparative genomic analyses. Peptides, 27 (12):3154-3164.
4. Cockcroft JR, Noon JP, Gardner-Medwin J, Bennett T (1997). Haemodynamic effects of adrenomedullin in human resistance and capacitance vessels. Br J Clin Pharmacol, 44(1):57-60.
5. Shimekake Y, Nagata K, Ohta S, Kambayashi Y, Teraoka H, Kitamura K, Eto T, Kangawa K, Matsuo H (1995). Adrenomedullin stimulates two signal transduction pathways, cAMP accumulation and Ca2+ mobilization, in bovine aortic endothelial cells. J Biol Chem, 270: 4412-4417.
6. Yanagawa B, Nagaya N (2007). Adrenomedullin: molecular mechanisms and its role in cardiac disease. Amino Acids, 32 (1):157-164.
7. Vesely DL (2003). Natriuretic peptides and acute renal failure. Am J Physiol Renal Physiol, 285 (2):167-177.
8. Ruzicska E, Toth M, Tulassay Z, Somogyi A (2001). Adrenomedullin and diabetes mellitus. Diabetes Metab Res Rev, 17 (5):321-329.