atrial-natriuretic-factor and acetovanillone

Reactive oxygen species (ROS) are formed as a natural by-product of the normal metabolism of oxygen and have important roles in cell signaling. The aim of this study was to investigate direct effects of ROS on atrial hemodynamics and ANP secretion in isolated perfused beating rat atria with antioxidants. When atria were paced at 1.2 Hz, N-acetyl cystein (antioxidant, NAC), α-lipoic acid (antioxidant), tempol (superoxide dismutase mimic), and apocynin (NADPH oxidase inhibitor; NOX inhibitor) did not affect ANP secretion and atrial contractility. When pacing frequency was increased from 1.2 Hz to 4 Hz, the ANP secretion increased and atrial contractility decreased. H(2)O(2) level was increased in perfusate obtained from atria stimulated by high pacing frequency. NAC, α-lipoic acid and tempol attenuated high pacing frequency-induced ANP secretion but apocynin did not. In contrast, pyrogallol (a superoxide generator) augmented high pacing frequency-induced ANP secretion. NOX-4 protein was increased by high pacing stimulation and in diabetic rat atria. In diabetic rat atria, high pacing frequency caused an increased ANP secretion and a decreased atrial contractility, that were markedly attenuated as compared to control rats. NAC and apocynin reduced high pacing frequency-induced ANP secretion in diabetic rat atria. These results suggest that intracellular ROS formation partly through an increasing NOX activity in response to high pacing frequency is associated with an increased ANP secretion in rat atria.

Topics: Acetophenones; Acetylcysteine; Animals; Antioxidants; Atrial Function; Atrial Natriuretic Factor; Blood Pressure; Cardiac Pacing, Artificial; Cyclic N-Oxides; Diabetes Mellitus, Experimental; Electric Stimulation; Enzyme Activation; Extracellular Fluid; Heart Atria; Hemodynamics; Hydrogen Peroxide; In Vitro Techniques; Male; Myocardial Contraction; NADPH Oxidase 4; NADPH Oxidases; Pyrogallol; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; Spin Labels; Thioctic Acid

It has been shown that angiotensin II (Ang II) is involved in cardiac remodeling mediated by NADPH oxidase-dependent reactive oxygen species (ROS). Accordingly, NADPH oxidase-dependent ROS may play a role in cardiac hypertrophy induced by pressure overload. In the present study, we sought to determine whether inhibition of NADPH oxidase prevents cardiac hypertrophy. After abdominal aorta banding to induce cardiac hypertrophy, rats were treated for 8 weeks with apocynin (Apo) or captopril (Cap). Measures of cardiac hypertrophy were evaluated. Treatment with Cap or Apo reduced the left ventricle/body weight ratio (LV/BW), LV transnuclear myocyte diameter, and atrial natriuretic factor (ANF) mRNA expression relative to those of untreated rats subjected to aorta banding. The activity of NADPH oxidase and the ROS levels were decreased in treated animals. Cap, but not Apo, decreased Ang II levels and inhibited expression of p22phox and p67phox in LVs. In conclusion, local expression of Ang II appears to contribute to pressure overload-induced cardiac hypertrophy by upregulating NADPH oxidase expression and promoting ROS synthesis. Inhibition of NADPH oxidase and elimination of ROS may prevent or repair damage due to cardiac hypertrophy.

Topics: Acetophenones; Angiotensin II; Animals; Antioxidants; Atrial Natriuretic Factor; Base Sequence; Captopril; Cardiomegaly; DNA Primers; Enzyme Inhibitors; Male; NADPH Oxidases; Phosphoproteins; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; RNA, Messenger

The cardiovascular hormone atrial natriuretic peptide (ANP) exerts anti-inflammatory effects on tumor necrosis factor-alpha-activated endothelial cells by inducing mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1). The underlying mechanisms are as yet unknown. We aimed to elucidate the signaling pathways leading to an induction of MKP-1 by ANP in primary human endothelial cells. By using antioxidants, generation of reactive oxygen species (ROS) was shown to be crucially involved in MKP-1 upregulation. ANP was found to increase ROS formation in cultured cells as well as in the endothelium of intact rat lung vessels. We applied NAD(P)H oxidase (Nox) inhibitors (apocynin and gp91ds-tat) and revealed this enzyme complex to be crucial for superoxide generation and MKP-1 expression. Moreover, by performing Nox2/4 antisense experiments, we identified Nox2 as the critically involved Nox homologue. Pull-down assays and confocal microscopy showed that ANP activates the small Rho-GTPase Rac1. Transfection of a dominant-negative (RacN17) and constitutively active Rac1 mutant (RacV12) indicated that ANP-induced superoxide generation and MKP-1 expression are mediated via Rac1 activation. ANP-evoked production of superoxide was found to activate c-Jun N-terminal kinase (JNK). Using specific inhibitors, we linked ANP-induced JNK activation to MKP-1 expression and excluded an involvement of protein kinase C, extracellular signal-regulated kinase, and p38 MAPK. MKP-1 induction was shown to depend on activation of the transcription factor activator protein-1 (AP-1) by using electrophoretic mobility shift assay and AP-1 decoys. In summary, our work provides insights into the mechanisms by which ANP induces MKP-1 and shows that ANP is a novel endogenous activator of endothelial Rac1 and Nox/Nox2.

Topics: Acetophenones; Animals; Atrial Natriuretic Factor; Capillaries; Cell Cycle Proteins; Cells, Cultured; Cyclic GMP; Cycloheximide; DNA, Antisense; Dual Specificity Phosphatase 1; Endothelial Cells; Endothelium, Vascular; Enzyme Induction; Glycoproteins; Guanylate Cyclase; Humans; Immediate-Early Proteins; JNK Mitogen-Activated Protein Kinases; Lung; MAP Kinase Kinase 4; MAP Kinase Signaling System; Membrane Glycoproteins; Membrane Proteins; Mitogen-Activated Protein Kinase Kinases; NADPH Oxidase 1; NADPH Oxidase 2; NADPH Oxidase 4; NADPH Oxidase 5; NADPH Oxidases; Oligonucleotides, Antisense; Phosphoprotein Phosphatases; Protein Phosphatase 1; Protein Tyrosine Phosphatases; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; Receptors, Atrial Natriuretic Factor; Recombinant Fusion Proteins; RNA, Messenger; Transcription Factor AP-1; Transfection; Umbilical Veins