Abstract-The peripheral apelin system plays a significant role in cardiovascular homeostasis and in the pathophysiology of cardiovascular diseases. However, the central effect of this neurohormonal system in neural control of cardiovascular function remains poorly understood. Thus, this study was undertaken to evaluate the effect of apelin in the rostral ventrolateral medulla (RVLM) on blood pressure, cardiac function, and sympathetic nerve activity. Apelin mRNA and protein levels were detected with real-time RT-PCR and Western blots, respectively. Expression of apelin was significantly enhanced in the RVLM of spontaneously hypertensive rat (SHR) compared with normotensive Wistar-Kyoto (WKY) rats. To study the functional consequence of upregulated apelin expression, apelin was overexpressed by bilateral microinjection of the AAV2-apelin viral vector into the RVLM of WKY rats. Immunofluorescence staining and Western blots demonstrated that microinjection of AAV2-apelin into the RVLM resulted in a significant increase in apelin expression, which was associated with a chronic elevation in blood pressure and cardiac hypertrophy. In addition, direct microinjection of exogenous apelin-13 (200 pmol in 50 nL) into the RVLM caused a 20 mm Hg elevation in blood pressure and a 24% increase in sympathetic nerve activity. The present study is the first to show that apelin expression is enhanced in the RVLM of SHR versus WKY rats and that overexpression of this gene in the RVLM results in chronic blood pressure elevation and cardiac hypertrophy in normotensive rats. Thus, the apelin system in the RVLM may play a very important role in central blood pressure regulation and in the pathogenesis of hypertension. Key Words: blood pressure Ⅲ hypertension Ⅲ hypertrophy Ⅲ brain Ⅲ sympathetic A pelin is a peptide recently isolated from bovine stomach extracts. 1 It has been identified as the endogenous ligand for the orphan G protein-coupled receptor APJ, 1,2 which is comprised of 7 transmembrane domains and shares a 31% amino acid sequence identity to the angiotensin II type 1 receptor. 3 Despite the degree of homology between these receptors, angiotensin (Ang) II does not bind the APJ receptor, and apelin is the only known ligand for the APJ receptor. 3 Multiple apelin peptides appear to be derived from a 77-aa precursor peptide, including preproapelin apelin-36 (42-77), apelin-17 (61-77), and apelin-13 (65-77). Apelin and APJ are widely distributed in various tissues and are thought to be involved in cardiovascular regulation, 4,5 heart contractility, body fluid homeostasis, 6 control of appetite, and, possibly, immune functions. 7 The role of apelin and APJ in the cardiovascular system is currently the best documented. The accumulated evidence indicates that apelin and its APJ receptor are expressed throughout the cardiovascular system. Both pressor and depressor responses have been described in response to peripheral administration of apelin. 1,5,8 -10 Genetic studies in humans also demonstrate that disruption of the endogenous ...

Sun C. 20-HETE increases NADPH oxidase-derived ROS production and stimulates the L-type Ca 2ϩ channel via a PKCdependent mechanism in cardiomyocytes. Am J Physiol Heart Circ Physiol 299: H1109 -H1117, 2010. First published July 30, 2010; doi:10.1152/ajpheart.00067.2010.-The production of 20-hydroxyeicosatetraenoic acid (20-HETE) is increased during ischemia-reperfusion, and inhibition of 20-HETE production has been shown to reduce infarct size caused by ischemia. This study was aimed to discover the molecular mechanism underlying the action of 20-HETE in cardiac myocytes. The effect of 20-HETE on L-type Ca 2ϩ currents (ICa,L) was examined in rat isolated cardiomyocytes by patch-clamp recording in the whole cell mode. Superfusion of cardiomyocytes with 20-HETE (10 -100 nM) resulted in a concentration-dependent increase in I Ca,L, and this action of 20-HETE was attenuated by a specific NADPH oxidase inhibitor, gp91ds-tat (5 M), or a superoxide scavenger, polyethylene glycol-superoxide dismutase (25 U/ml), suggesting that NADPH-oxidase-derived superoxide is involved in the stimulatory action of 20-HETE on ICa,L. Treatment of cardiomyocytes with 20-HETE (100 nM) increased both NADPH oxidase activity and superoxide production by approximately twofold. To study the molecular mechanism mediating the 20-HETE-induced increase in NADPH oxidase activity, PKC activity was measured in cardiomyocytes. Incubation of the cells with 20-HETE (100 nM) significantly increased PKC activity, and pretreatment of cardiomyocytes with a selective PKC inhibitor, GF-109203 (1 M), attenuated the 20-HETE-induced increases in I Ca,L and in NADPH oxidase activity. In summary, 20-HETE stimulates NADPH oxidase-derived superoxide production, which activates L-type Ca 2ϩ channels via a PKC-dependent mechanism in cardiomyocytes. 20-HETE and 20-HETE-producing enzymes could be novel targets for the treatment of cardiac ischemic diseases.20-hydroxyeicosatetraenoic acid; L-type calcium channel; protein kinase C; cardiac myocytes; reactive oxygen species 20-HYDROXYEICOSATETRAENOIC ACID (20-HETE) is a lipid metabolite of arachidonic acid that is produced by -hydroxylase enzymes of the cytochrome P-450 (CYP)4A and CYP4F families, which are relatively abundant and exert regulatory functions dependent on the tissue (18). For example, in the kidney, 20-HETE regulates renal functions, such as renal vascular tone, tubuloglomerular feedback, autoregulation of renal blood flow, tubular transport, and mitogenesis (20). In blood vessels, 20-HETE is a potent vasoconstrictor that activates L-type Ca 2ϩ channels and inhibits Ca 2ϩ -sensitive K ϩ channels in vascular smooth muscle cells (28,29). In pulmonary arteries, 20-HETE enhances NADPH oxidase-dependent production of ROS in endothelial cells (21). Thus, it was proposed that 20-HETE plays an important role in the control of apoptosis and angiogensis in vascular endothelial cells in the pulmonary microcirculation (13). Recently, 20-HETE and CYP -hydroxylase were also identified in hearts from the rat and dog (13,26...

It has been shown that reactive oxygen species (ROS) are involved in the intracellular signaling response to G-protein coupled receptor stimuli in vascular smooth muscle cells and in neurons. In the present study, we tested the hypothesis that NAD(P)H oxidasederived ROS are involved endothelin-1 (ET-1)-induced L-type calcium channel activation in isolated cardiac myocytes. ET-1 (10 nM) induced a 2-fold increase in L-type calcium channel openstate probability (NPo). This effect of ET-1 was abolished by. Pretreatment of cells with the ROS scavenger tempol (100 M), polyethylene glycol-superoxide dismutase (SOD, 25 U/ml), or the NAD(P)H-oxidase inhibitor gp91ds-tat ([H]RKKRRQRRR-CSTRIR-RQL[NH 3 ]) (5 M) significantly attenuated ET-1-induced increases in calcium channel NPo. Tempol, SOD, and gp91ds-tat alone had no effect on basal calcium channel activity. In addition, ET-1 significantly increased NAD(P)H oxidase activity and elevated intracellular superoxide levels in cultured cardiac myocytes. The superoxide generator, xanthine-xanthine oxidase (10 mM, 20 mU/ ml), also increased calcium channel NPo in cardiac myocytes, mimicking the effect of ET-1. These observations provide the first evidence that ET-1 induces the activation of L-type Ca 2ϩ channels via stimulation of NAD(P)H-derived superoxide production in cardiac myocytes.

Angiotensin II (ANG II) increases GABA(B) receptor expression in neuronal cultures from the nucleus tractus solitarii (NTS). In the present study, the chronic effects of ANG II on GABA(B) receptor expression and activity were examined in the NTS of Sprague-Dawley rats. Intracerebroventricular infusion of ANG II caused a significant elevation in blood pressure (BP) and an increase in GABA(B) receptor expression in the NTS. Conversely, chronic N(G)-nitro-l-arginine methyl ester (l-NAME) treatment also increased BP, but had no effect on GABA(B) receptor expression in the NTS. Next, we examined the BP response to the GABA(B) receptor agonist baclofen microinjected into the NTS of ANG II- or artificial cerebrospinal fluid (aCSF)-infused rats. NTS microinjection of baclofen increased BP in both groups of rats. However, the pressor response to baclofen was enhanced in ANG II-infused rats compared with aCSF-infused rats. In addition, bilateral microinjection of the GABA(B) receptor antagonist CGP-35348 into the NTS evoked a decrease in BP in both group of rats, and the depressor responses to CGP-35348 were enhanced in the ANG II-infused rats. In contrast, the pressor responses to the GABA(A) receptor agonist muscimol and the depressor responses to the GABA(A) receptor antagonist bicuculline were comparable between aCSF- and ANG II-infused rats. These results indicate that chronic ANG II infusion stimulates GABA(B) receptor expression and augments GABA(B) receptor-mediated responses in the NTS. This effect could contribute to the central nervous system actions of ANG II that result in dampening of baroreflexes and elevation in arterial BP.