Adrenomedullin Induces Endothelium-Dependent Vasorelaxation via the Phosphatidylinositol 3-Kinase/Akt–Dependent Pathway in Rat Aorta

Abstract

Abstract-To study the mechanisms by which adrenomedullin (AM) induces endothelium-dependent vasorelaxation, we examined whether AM-induced endothelium-dependent vasodilation was mediated by the phosphatidylinositol 3-kinase (PI3K)/Akt-dependent pathway in rat aorta, because it was recently reported that PI3K/Akt was implicated in the activation of endothelial NO synthase. AM-induced vasorelaxation in thoracic aorta with intact endothelium was inhibited by pretreatment with PI3K inhibitors to the same level as that in endothelium-denuded aorta. AM elicited Akt phosphorylation in a time-and dose-dependent manner. AM-induced Akt phosphorylation was inhibited by pretreatment with a calmodulin-dependent protein kinase inhibitor as well as with PI3K inhibitors. When an adenovirus construct expressing a dominant-negative Akt mutant (Ad/dnAkt) was injected into abdominal aortas so that the mutant was expressed predominantly in the endothelium layer, AM-induced vasodilation was diminished to the same level as that in endothelium-denuded aortas. Finally, AM-induced cGMP production, which was used as an indicator for NO production, was suppressed by PI3K inhibition or by Ad/dnAkt infection into the endothelium. These results suggested that AM induced Akt activation in the endothelium via the Ca 2ϩ /calmodulin-dependent pathway and that this was implicated in the production of NO, which in turn induced endothelium-dependent vasodilation in rat aorta. Key Words: adrenomedullin Ⅲ phosphatidylinositol 3-kinase Ⅲ Akt Ⅲ nitric oxide Ⅲ gene transfer V ascular endothelial cells (ECs) are critically implicated in the modulation of vascular tone by producing a variety of vasoactive substances. Among them, endothelin has a vasoconstrictive activity, whereas NO and prostacyclin possess a vasorelaxant activity. The modulation of vascular tone by ECs is known to be perturbed in pathophysiological states such as hypertension, diabetes mellitus, and hyperlipidemia. 1 A novel peptide, which increases the level of cAMP in platelets, was recently isolated from human adrenal medulla and was dubbed adrenomedullin (AM). 2 AM is a 52-amino acid peptide with a potent vasorelaxant activity and natriuretic activity. [3][4][5] Although AM was originally isolated from human pheochromocytoma tissue, it is now well known that AM is also produced by vascular ECs, vascular smooth muscle cells, and macrophages, 6 -8 suggesting its role as a local mediator in normal and/or diseased vessels. Although little is known of the intracellular signaling pathways that are activated by AM, it is reported that AM increases intracellular cAMP and [Ca 2ϩ ] i . 9 AM also activates extracellular signalregulated kinase (ERK), which appears to be involved in AM-induced cell proliferation, 10 -12 although AM seems to inhibit cell proliferation in some cells, 13 depending on cell types. It was originally postulated that AM-induced vasorelaxation might be mediated by its effect on intracellular cAMP. However, we have recently shown that AM induced vasorelaxation, at least p...

Adrenomedullin

“…14 -17 In a further analysis of the mechanism, AM dilated rat aorta by activating phosphatidylinositol 3-kinase (PI3K) and Akt via the Ca 2ϩ /calmodulin-dependent pathway, which leads to increased production of NO through phosphorylation of endothelial NO synthase. 18 On the other hand, endothelium-independent vasodilatation by AM has also been shown ex vivo in experiments with dog arteries or porcine coronary artery. 19,20 The mechanisms so far proposed for endothelium-independent vasodilatation are an increase in the intracellular cyclic AMP (cAMP) level, a decrease in the Ca 2ϩ concentration, and the activation of K ϩ channels in vascular smooth muscle cells (SMCs).…”

A role for adrenomedullin as a pain-related peptide in the rat

“…AM-induced vasodilatation and myocardial protection is mediated through the activation of the phosphatidylinositol 3-kinase (PI3K)͞Akt-dependent pathway (15,16). The phosphorylation of Akt in DRG is involved in the maintenance of inflammatory pain caused by intraplantar injection of capsaicin (17).…”

Responses to human CGRP, ADM, and PAMP in human thymic arteries

“…Although CGRP receptors are present in the human thymus, little if anything is known about the actions of CGRP and related peptides on vascular function in small arteries from the thymus (25). Moreover, there is a paucity of information about the actions and mechanisms of action of CGRP, ADM, and PAMP in small human arteries (9,27,29,30,32,36). The present study was, therefore, undertaken to investigate responses and the role of endothelium-derived nitric oxide in mediating responses to CGRP, ADM, and PAMP in small arteries from the human thymus.…”

“…CGRP is a spliced variant of the calcitonin gene and this neuropeptide is present in perivascular sensory nerves (29). ADM, PAMP, and CGRP have vasodilator activity with different mechanisms of action (4,6,7,16,17,(27)(28)(29)35). ADM has been reported to relax vascular muscle in an endothelium-dependent manner in some vascular beds studied, and those responses are species or vascular bed dependent, whereas PAMP has modest activity and has been reported to inhibit norepinephrine release or decrease vascular resistance by a nitric oxide-independent mechanism (4-6, 17, 27, 28, 33-35).…”