Discovery of adrenomedullin in rat ischemic cortex and evidence for its role in exacerbating focal brain ischemic damage.

Abstract

Focal brain ischemia is the most common event leading to stroke in humans. To understand the molecular mechanisms associated with brain ischemia, we applied the technique of mRNA differential display and isolated a gene that encodes a recently discovered peptide, adrenomedullin (AM), which is a member of the calcitonin gene-related peptide (CGRP) family. Using the rat focal stroke model of middle cerebral artery occlusion (MCAO), we determined that AM mRNA expression was significantly increased in the ischemic cortex up to 17.4-fold at 3 h post-MCAO (P < 0.05) and 21.7-fold at 6 h post-MCAO (P < 0.05) and remained elevated for up to 15 days (9.6-fold increase; P < 0.05). Immunohistochemical studies localized AM to ischemic neuronal processes, and radioligand (12II-labeled CGRP) displacement revealed high-affinity (IC50 = 80.3 nmol) binding of AM to CGRP receptors in brain cortex. The cerebrovascular function of AM was studied using synthetic AM microinjected onto rat pial vessels using a cranial window or applied to canine basilar arteries in vitro. AM, applied abluminally, produced dosedependent relaxation of preconstricted pial vessels (P < 0.05). Intracerebroventricular (but not systemic) AM administration at a high dose (8 nmol), prior to and after MCAO, increased the degree of focal ischemic injury (P < 0.05). The ischemia-induced expression of both AM mRNA and peptide in ischemic cortical neurons, the demonstration of the direct vasodilating effects of the peptide on cerebral vessels, and the ability of AM to exacerbate ischemic brain damage suggests that AM plays a significant role in focal ischemic brain injury.Adrenomedullin (AM) is a recently discovered peptide that was initially identified from human pheochromocytoma (1). Biologically active AM consists of 52 amino acids in humans and 50 amino acids in rats (1, 2), and both AMs exhibit potent vasodilator activity in vitro and in vivo (3-6). AM bears homology to a family of peptides that includes calcitonin gene-related peptide (CGRP) (7-10) and amylin (11,12). CGRP is a widely distributed neuropeptide best known for its potent vasodilator actions (13-15) and its effect on insulin functions (16). Amylin is the major protein found in islet amyloid (11, 16) in humans with non-insulin-dependent diabetes mellitus. CGRP and amylin have been found to have a wide range of biological activities, including energy metabolism, central nervous system and cardiovascular functions, and calcium metabolism (for review see refs. 16 and 17). In contrast, little is known of the biological function of AM beyond vasodilation. In contrast to CGRP, AM mRNA and peptide have not been detected in normal brain (1, 2). Very recently, AM has been associated with congestive heart failure, since elevated levels of AM were found in cardiac tissue of the failing hearts (18).In the present report, we used a recently developed mRNA differential display technique (19) to identify genes expressedThe publication costs of this article were defrayed in part by page charge payment. Th...

Involvement of adrenomedullin induced by hypoxia in angiogenesis in human renal cell carcinoma

“…demonstrated that brain ischemia increased AM mRNA expression in rat brain cortex. 8 Hypoxia also induced an increase in AM mRNA expression and protein production in a human colorectal carcinoma cell line. 9 Furthermore, the induction of AM mRNA by hypoxia depends on the transcription factor hypoxia-inducible factor-1 (HIF-1) in human tumor cells.…”

Phenylephrine Infusion Prevents Impairment of ATP- and Calcium-Sensitive Potassium Channel-Mediated Cerebrovasodilation after Brain Injury in Female, but Aggravates Impairment in Male, Piglets through Modulation of ERK MAPK Upregulation

“…Adrenomedullin is a 52-amino-acid peptide belonging to the CGRP family. In rats, adrenomedullin mRNA expression is upregulated after ischemia and may be cerebroprotective, particularly after stroke (Miyashita et al, 2006;Wang et al, 1995). Adrenomedullin increases CBF and prevents ischemia after middle cerebral artery occlusion (Dogan et al, 1997).…”

Adrenomedullin expression in the mouse mammary gland: evidence for the mature form in milk

“…It is synthesized as a 185 amino acid precursor which is processed by consecutive enzymatic steps into a 6000 molecular mass bioactive peptide (Kitamura et al 1993b, Sugo et al 1994. AM production has been characterized in a wide spectrum of tissues, including the cardiovascular (Sakata et al 1993), nervous (Ueta et al 1995, Wang et al 1995, Satoh et al 1996, respiratory (Martínez et al 1995b), endocrine , Satoh et al 1996, renal (Jougaski et al 1994), and digestive systems (Washimine et al 1995). AM mRNA expression is enhanced by inflammatory response elements (interleukin-1 and tumor necrosis factor) and the peptide is markedly up-regulated in the circulation following endotoxin (lipopolysaccharide) challenge or bacterial sepsis (Sugo et al 1995, Hirata et al 1996.…”