Intermedin elicits a negative inotropic effect in rat papillary muscles mediated by endothelial-derived nitric oxide

Abstract

Pires AL, Pinho M, Sena CM, Seica R, Leite-Moreira AF. Intermedin elicits a negative inotropic effect in rat papillary muscles mediated by endothelial-derived nitric oxide. Am J Physiol Heart Circ Physiol 302: H1131-H1137, 2012. First published January 6, 2011; doi:10.1152/ajpheart.00877.2011.-Intermedin (IMD) is a novel vasoactive peptide from the calcitonin gene-related peptide (CGRP) implicated in cardiac regulation, yet the contractile effects of IMD remain controversial, since previous studies in vivo and isolated cardiomyocytes documented contradictory results. We hypothesized cardiac endothelial cells involvement in IMD modulation of cardiac function as an explanation for these opposing observations. With this in mind, we investigated the direct action of increasing concentrations of IMD (10 Ϫ8 to 10 Ϫ6 M) on myocardial performance parameters in rat left ventricular (LV) papillary muscles with and without endocardial endothelium (EE) and in presence of receptor antagonists and intracellular pathways inhibitors. In LV papillary muscles with intact EE, IMD induced a concentration-dependent negative inotropic action (%decrease relative to baseline, at IMD concentration of 10 Ϫ6 M, active tension of 14 Ϯ 4%, and maximum velocity of tension rise of 10 Ϯ 4%). These effects were blunted by EE removal, AM receptor antagonist (AM22-52), and CGRP receptor antagonist (CGRP8-37). Additionally, nitric oxide (NO) synthase inhibition with N G -nitro-Larginine (L-NAME) in muscles with and without EE and guanylyl cyclase inhibition with {1H-[1,2,4]oxadiazole-[4,4-a]-quinoxalin-1-one} not only blunted the negative inotropic action of IMD but also unmasked IMD-positive inotropic effect dependent on CGRP receptor PKA activation. Western blot quantification of phosphorylated cardiac troponin I (P-cTnI) in IMD-treated papillary muscles revealed a significant increase in P-cTnI when compared with untreated muscles, while in L-NAME-pretreated papillary muscles IMD failed to increase P-cTnI. Finally, we found that stimulation of both EE and microvascular endothelial cells with IMD significantly increased NO production by 40 Ϯ 3 and 38 Ϯ 3%, respectively, suggesting the role of cardiac endothelial cells in NO production upon IMD stimulation. Our findings establish IMD negative inotropic effect in isolated myocardium due to NO/cGMP pathway activation with concomitant thin myofilament desensitization by increase in cTnI phosphorylation and provide a coherent explanation for the previously reported contradictory results.neurohormones; contractile effect; nitric oxide synthase; cardiac endothelial cells; myofilament desensitization; adrenomedullin-2 OVERWHELMING DATA SUPPORT the role of neurohumoral regulation in the cardiovascular system, as illustrated by the fact that some neurohumoral agents due to their pathophysiological function in cardiac disease have become important therapeutic targets (22). In this context, numerous studies have continued to search for new neurohormones. Among the targeted peptide families is the calcitonin...

Reverse myocardial effects of intermedin in pressure‐overloaded hearts: role of endothelial nitric oxide synthase activity

“…Papillary muscles treated with increasing concentrations of IMD 1−47 from Sham rats and analysed by immunoblots presented, in accordance with previous reports (Pires et al . 2012), a 3‐fold increase in p‐cTnI, when compared with untreated muscles (Fig.…”

“…2008). Such NO release was previously shown by us to play a critical role in mediating the myocardial effects of IMD 1−47 in healthy animals (Pires et al . 2012).…”

“…2004; Munzel et al . 2011; Pires et al . 2012) the myocardial effects of IMD in the diseased heart remain unexplored.…”

Intermedin/adrenomedullin2: an autocrine/paracrine factor in vascular homeostasis and disease

“…IMD-stimulated endothelial CRLR is coupled to release of NO, activation of GCs, and promotion of hyperpolarization through large-conductance calcium-activated K(+) channels in the rat main pulmonary artery. IMD had a negative inotropic effect on the isolated myocardium because of NO-cGMP pathway activation with concomitant thin myofilament desensitization by increased cTnI phosphorylation [25], which provides a coherent explanation for the previously reported contradictory results (positive or negative inotropic effect). In conscious rat models, the regional haemodynamic profile of IMD resembled that of ADM [30], and some of the vasodilator effects of IMD were mediated by ADM receptors and NO but not by K(ATP) channels.…”

Intermedin in rat uterus: changes in gene expression and peptide levels across the estrous cycle and its effects on uterine contraction

“…The L-NAME inhibition may be mediated by PKG, which is activated by cGMP in the NO pathway leading to the dephosphorylation of myosin light chain to relax the uterine smooth muscle [43] . Another NO-mediated IMD effect on contraction has been reported in the rat papillary muscle [45]. The PI3K pathway for inhibiting smooth muscle contraction has also been reported in gastrointestinal smooth muscles [46] and an involvement of PI3K pathway for an IMD effect can be found in endoplasmic reticulum stress [21].…”