Commissural nucleus of the solitary tract regulates the antihypertensive effects elicited by moxonidine

The rostral ventrolateral medulla (RVLM) contains the presympathetic neurons involved in cardiovascular regulation that has been implicated as one of the most important central sites for the antihypertensive action of moxonidine (an α2-adrenergic and imidazoline agonist). Here, we sought to evaluate the cardiovascular effects produced by moxonidine injected into another important brainstem site, the commissural nucleus of the solitary tract (commNTS). Mean arterial pressure (MAP), heart rate (HR), splanchnic sympathetic nerve activity (sSNA) and activity of putative sympathoexcitatory vasomotor neurons of the RVLM were recorded in conscious or urethane-anesthetized, and artificial ventilated male Wistar rats. In conscious or anesthetized rats, moxonidine (2.5 and 5 nmol/50 nl) injected into the commNTS reduced MAP, HR and sSNA. The injection of moxonidine into the commNTS also elicited a reduction of 28% in the activity of sympathoexcitatory vasomotor neurons of the RVLM. To further assess the notion that moxonidine could act in another brainstem area to elicit the antihypertensive effects, a group with electrolytic lesions of the commNTS or sham and with stainless steel guide-cannulas implanted into the 4th V were used. In the sham group, moxonidine (20 nmol/1 μl) injected into 4th V decreased MAP and HR. The hypotension but not the bradycardia produced by moxonidine into the 4th V was reduced in acute (1 day) commNTS-lesioned rats. These data suggest that moxonidine can certainly act in other brainstem regions, such as commNTS to produce its beneficial therapeutic effects, such as hypotension and reduction in sympathetic nerve activity.

Central autonomic control in spontaneously hypertensive rats: a study on phasic phenomena during rapid-eye-movement sleep

The cardiovascular regulation undergoes wide changes in the different states of sleepwake cycle. In particular, the relationship between spontaneous fluctuations in heart period and arterial pressure clearly shows differences between the two sleep states. In non rapid-eye-movement sleep, heart rhythm is under prevalent baroreflex control, whereas in rapid-eye-movement sleep central autonomic commands prevail (Zoccoli et al., 2001). Moreover, during rapid-eye-movement sleep the cardiovascular variables show wide fluctuations around their mean value. In particular, during rapid-eyemovement sleep, the arterial pressure shows phasic hypertensive events which are superimposed upon the tonic level of arterial pressure. These phasic increases in arterial pressure are accompanied by an increase in heart rate (Sei & Morita, 1996; Silvani et al., 2005). Thus, rapid-eye-movement sleep may represent an “autonomic stress test” for the cardiovascular system, able to unmask pathological patterns of cardiovascular regulation (Verrier et al. 2005), but this hypothesis has never been tested experimentally. The aim of this study was to investigate whether rapid-eye-movement sleep may reveal derangements in central autonomic cardiovascular control in an experimental model of essential hypertension. The study was performed in Spontaneously Hypertensive Rats, which represent the most widely used model of essential hypertension, and allow full control of genetic and environmental confounding factors. In particular, we analyzed the cardiovascular, electroencephalogram, and electromyogram changes associated with phasic hypertensive events during rapid-eyemovement sleep in Spontaneously Hypertensive Rats and in their genetic Wistar Kyoto control strain. Moreover, we studied also a group of Spontaneously Hypertensive Rats made phenotypically normotensive by means of a chronic treatment with an angiotensin converting enzyme inhibitor, the Enalapril maleate, from the age of four weeks to the end of the experiment. All rats were implanted with electrodes for electroencephalographic and electromyographic recordings and with an arterial catheter for arterial pressure measurement. After six days for postoperative recovery, the rats were studied for five days, at an age of ten weeks.The study indicated that the peak of mean arterial pressure increase during the phasic hypertensive events in rapid-eye-movement sleep did not differ significantly between Spontaneously Hypertensive Rats and Wistar Kyoto rats, while on the other hand Spontaneously Hypertensive Rats showed a reduced increase in the frequency of theta rhythm and a reduced tachicardia with respect to Wistar Kyoto rats. The same pattern of changes in mean arterial pressure, heart period, and theta frequency was observed between Spontaneously Hypertensive Rats and Spontaneously Hypertensive Rats treated with Enalapril maleate. Spontaneously Hypertensive Rats do not differ from Wistar Kyoto rats only in terms of arterial hypertension, but also due to multiple unknown genetic differences. Spontaneously Hypertensive Rats were developed by selective breeding of Wistar Kyoto rats based only on the level of arterial pressure. However, in this process, multiple genes possibly unrelated to hypertension may have been selected together with the genetic determinants of hypertension (Carley et al., 2000). This study indicated that Spontaneously Hypertensive Rats differ from Wistar Kyoto rats, but not from Spontaneously Hypertensive Rats treated with Enalapril maleate, in terms of arterial pH and theta frequency. This feature may be due to genetic determinants unrelated to hypertension. In sharp contrast, the persistence of differences in the peak of heart period decrease and the peak of theta frequency increase during phasic hypertensive events between Spontaneously Hypertensive Rats and Spontaneously Hypertensive Rats treated with Enalapril maleate demonstrates that the observed reduction in central autonomic control of the cardiovascular system in Spontaneously Hypertensive Rats is not an irreversible consequence of inherited genetic determinants. Rather, the comparison between Spontaneously Hypertensive Rats and Spontaneously Hypertensive Rats treated with Enalapril maleate indicates that the observed differences in central autonomic control are the result of the hypertension per se. This work supports the view that the study of cardiovascular regulation in sleep provides fundamental insight on the pathophysiology of hypertension, and may thus contribute to the understanding of this disease, which is a major health problem in European countries (Wolf-Maier et al., 2003) with its burden of cardiac, vascular, and renal complications.

The role of nitric oxide in regulation of the cardiovascular system in reptiles

The roles that nitric oxide (NO) plays in the cardiovascular system of reptiles are reviewed, with particular emphasis on its effects on central vascular blood flows in the systemic and pulmonary circulations. New data is presented that describes the effects on hemodynamic variables in varanid lizards of exogenously administered NO via the nitric oxide donor sodium nitroprusside (SNP) and, preliminary data on the effects of SNP inhibition of nitric oxide synthase (NOS) by L-nitroarginine methyl ester (L-NAME). Furthermore. on hemodynamic variables in the tegu lizard are presented. The findings are compared with previously published data from Our laboratory on three other species of reptiles: pythons (Skovgaard, N., Galli, G., Taylor, E.W., Conlon, J.M., Wang.. T., 2005. Hemodynamic effects of python neuropeptide gamma in the anesthetized python, Python regius. Regul. Pept. 18, 15-26), rattlesnakes (Galli, G., Skovgaard, N., Abe, A.S., Taylor, E.W., Wang, T., 2005. The role of nitric oxide in the regulation of the systemic and the pulmonary vasculature of the rattlesnake, Crotalus durissus terrificus. J. Comp. Physiol. 175B, 201-208) and turtles (Crossley, D.A., Wang, T., Altimiras, J., 2000. Role of nitric oxide in the systemic and pulmonary circulation of anesthetized turtles (Trachemys scripta). J. Exp. Zool. 286, 683-689). These five species of reptiles possess different combinations of division of the heart and structural complexity of the lungs. Comparison of their responses to NO donors and NOS inhibitors may reveal whether the potential contribution of NO to vascular tone correlates with pulmonary complexity and/or with blood pressure. All existing studies oil reptiles have clearly established a potential role for NO in regulating vascular tone in the systemic circulation and NO may be important for maintaining basal systemic vascular tone in varanid lizards, pythons and turtles, through a continuous release of NO. In contrast., the pulmonary circulation is less responsive to NO donors or NOS inhibitors, and it was only in pythons and varanid lizards that the lungs responded to SNP. Both species have a functionally separated heart, so it is possible that NO may exert a larger role in species with low pulmonary blood pressures, irrespective of lung complexity. (C) 2005 Elsevier B.V. All rights reserved.

Role of membrane lipids in the regulation of erythrocytic oxygen-transport function in cardiovascular diseases

The composition and condition of membrane lipids, the morphology of erythrocytes, and hemoglobin distribution were explored with the help of laser interference microscopy (LIM) and Raman spectroscopy. It is shown that patients with cardiovascular diseases (CVD) have significant changes in the composition of their phospholipids and the fatty acids of membrane lipids. Furthermore, the microviscosity of the membranes and morphology of the erythrocytes are altered causing disordered oxygen transport by hemoglobin. Basic therapy carried out with the use of antiaggregants, statins, antianginals, beta-blockers, and calcium antagonists does not help to recover themorphofunctional properties of erythrocytes. Based on the results the authors assume that, for the relief of the ischemic crisis and further therapeutic treatment, it is necessary to include, in addition to cardiovascular disease medicines, medication that increases the ability of erythrocytes’ hemoglobin to transport oxygen to the tissues. We assume that the use of LIM and Raman spectroscopy is advisable for early diagnosis of changes in the structure and functional state of erythrocytes when cardiovascular diseases develop.

Expression, regulation and putative nutrient-sensing function of taste GPCRs in the heart

G protein-coupled receptors (GPCRs) are critical for cardiovascular physiology. Cardiac cells express >100 nonchemosensory GPCRs, indicating that important physiological and potential therapeutic targets remain to be discovered. Moreover, there is a growing appreciation that members of the large, distinct taste and odorant GPCR families have specific functions in tissues beyond the oronasal cavity, including in the brain, gastrointestinal tract and respiratory system. To date, these chemosensory GPCRs have not been systematically studied in the heart. We performed RT-qPCR taste receptor screens in rodent and human heart tissues that revealed discrete subsets of type 2 taste receptors (TAS2/Tas2) as well as Tas1r1 and Tas1r3 (comprising the umami receptor) are expressed. These taste GPCRs are present in cultured cardiac myocytes and fibroblasts, and are enriched in myocytes, which we corroborated using in situ hybridization. Tas1r1 gene-targeted mice (Tas1r1Cre/Rosa26tdRFP) strikingly recapitulated these data. In vivo taste receptor expression levels were developmentally regulated in the postnatal period. Intriguingly, several Tas2rs were upregulated in cultured rat myocytes and in mouse heart in vivo following starvation. The discovery of taste GPCRs in the heart opens an exciting new field of cardiac research. We predict that these taste receptors may function as nutrient sensors in the heart.

GABAB receptors expressed in human aortic endothelial cells mediate intracellular calcium concentration regulation and endothelial nitric oxide synthase translocation

GABAB receptors regulate the intracellular Ca2+ concentration ([Ca2+]i) in a number of cells (e.g., retina, airway epithelium and smooth muscle), but whether they are expressed in vascular endothelial cells and similarly regulate the [Ca2+]i is not known. The purpose of this study was to investigate the expression of GABAB receptors, a subclass of receptors to the inhibitory neurotransmitter γ-aminobutyric acid (GABA), in cultured human aortic endothelial cells (HAECs), and to explore if altering receptor activation modified [Ca2+]i and endothelial nitric oxide synthase (eNOS) translocation. Real-time PCR, western blots and immunofluorescence were used to determine the expression of GABAB1 and GABAB2 in cultured HAECs. The effects of GABAB receptors on [Ca2+]i in cultured HAECs were demonstrated using fluo-3. The influence of GABAB receptors on eNOS translocation was assessed by immunocytochemistry. Both GABAB1 and GABAB2 mRNA and protein were expressed in cultured HAECs, and the GABAB1 and GABAB2 proteins were colocated in the cell membrane and cytoplasm. One hundred μM baclofen caused a transient increase of [Ca2+]i and eNOS translocation in cultured HAECs, and the effects were attenuated by pretreatment with the selective GABAB receptor antagonists CGP46381 and CGP55845. GABAB receptors are expressed in HAECs and regulate the [Ca2+]i and eNOS translocation. Cultures of HAECs may be a useful in vitro model for the study of GABAB receptors and vascular biology.

The role of catechol-O-methyltransferase (COMT) and the effects of COMT inhibition in brain and in cardiovascular and renal pathophysiology

Catechol-O-methyltransferase (COMT) metabolizes catecholamines such as dopamine (DA), noradrenaline (NA) and adrenaline, which are vital neurotransmitters and hormones that play important roles in the regulation of physiological processes. COMT enzyme has a functional Val158Met polymorphism in humans, which affects the subjects COMT activity. Increasing evidence suggests that this functional polymorphism may play a role in the etiology of various diseases from schizophrenia to cancers. The aim of this project was to provide novel biochemical information on the physiological and especially pathophysiological roles of COMT enzyme as well as the effects of COMT inhibition in the brain and in the cardiovascular and renal system. To assess the roles of COMT and COMT inhibition in pathophysiology, we used four different study designs. The possible beneficial effects of COMT inhibition were studied in double-transgenic rats (dTGRs) harbouring human angiotensinogen and renin genes. Due to angiotensin II (Ang II) overexpression, these animals exhibit severe hypetension, cardiovascular and renal end-organ damage and mortality of approximately 25-40% at the age of 7-weeks. The dTGRs and their Sprague-Dawley controls tissue samples were assessed with light microscopy, immunohistochemistry, reverse transcriptase-polymerase chain reaction (RT-PCR) and high-pressure liquid chromatography (HPLC) to evaluate the tissue damages and the possible protective effects pharmacological intervention with COMT inhibitors. In a second study, the consequence of genetic and pharmacological COMT blockade in blood pressure regulation during normal and high-sodium was elucidated using COMT-deficient mice. The blood pressure and the heart rate were measured using direct radiotelemetric blood pressure surveillance. In a third study, the effects of acute and subchronic COMT inhibition during combined levodopa (L-DOPA) + dopa decarboxylase inhibitor treatment in homocysteine formation was evaluated. Finally, we assessed the COMT enzyme expression, activity and cellular localization in the CNS during inflammation-induced neurodegeneration using Western blotting, HPLC and various enzymatic assays. The effects of pharmacological COMT inhibition on neurodegeneration were also studied. The COMT inhibitor entacapone protected against the Ang II-induced perivascular inflammation, renal damage and cardiovascular mortality in dTGRs. COMT inhibitors reduced the albuminuria by 85% and prevented the cardiovascular mortality completely. Entacapone treatment was shown to ameliorate oxidative stress and inflammation. Furthermore, we established that the genetic and pharmacological COMT enzyme blockade protects against the blood pressure-elevating effects of high sodium intake in mice. These effects were mediated via enhanced renal dopaminergic tone and suggest an important role of COMT enzyme, especially in salt-sensitive hypertension. Entacapone also ameliorated the L-DOPA-induced hyperhomocysteinemia in rats. This is important, since decreased homocysteine levels may decrease the risk of cardiovascular diseases in Parkinson´s disease (PD) patients using L-DOPA. The Lipopolysaccharide (LPS)-induced inflammation and subsequent delayed dopaminergic neurodegeneration were accompanied by up-regulation of COMT expression and activity in microglial cells as well as in perivascular cells. Interestingly, similar perivascular up-regulation of COMT expression in inflamed renal tissue was previously noted in dTGRs. These results suggest that inflammation reactions may up-regulate COMT expression. Furthermore, this increased glial and perivascular COMT activity in the central nervous system (CNS) may decrease the bioavailability of L-DOPA and be related to the motor fluctuation noted during L-DOPA therapy in PD patients.

Regulation of Kinin receptor Expression in Heart Failure with a Focus on Vascular Endothelium

Accumulating evidence show that kinins, notably bradykinin (BK) and kallidin, have cardioprotective effects. To these include reduction of left ventricular hypertrophy (LVH) and progression of heart failure. The effects are mediated through two G protein-coupled receptors- bradykinin type-2 receptor (BK-2R) and bradykinin type -1 receptor (BK-1R). The widely accepted cardioprotective effects of BK-receptors relate to triggering the production and release of vasodilating nitric oxide (NO) by endothelial cells. They also exert anti-proliferative effects on fibroblasts and anti-hypertrophic effects on myocytes, and thus may play an essential role in the cardioprotective response to myocardial injury. The role for BK-1Rs in HF is based on experimental animal models, where the receptors have been linked to cardioprotective- but also to cardiotoxic -effects. The BK-1Rs are induced under inflammatory and ischemic conditions, shown in animal models; no previous reports, concerning BK-1Rs in human heart failure, have been presented. The expression of BK-2Rs is down-regulated in human end-stage heart failure. Present results showed that, in these patients, the BK-1Rs were up-regulated, suggesting that also BK-1Rs are involved in the pathogenesis of human heart failure. The receptors were localized mainly in the endothelium of intramyocardial coronary vessels, and correlated with the increased TNF-α expression in the myocardial coronary vessels. Moreover, in cultured endothelial cells, TNF-α was a potent trigger of BK-1Rs. These results suggest that cytokines may be responsible for the up-regulation of BK-1Rs in human heart failure. A linear relationship between BK-2R mRNA and protein expression in normal and failing human left ventricles implies that the BK-2Rs are regulated on the transcriptional level, at least in human myocardium. The expression of BK-2Rs correlated positively with age in normal and dilated hearts (IDC). The results suggest that human hearts adapts to age-related changes, by up-regulating the expression of cardioprotective BK-2Rs. Also, in the BK-2R promoter polymorphism -58 T/C, the C-allele was accumulated in cardiomyopathy patients which may partially explain the reduced number of BK-2Rs. Statins reduce the level of plasma cholesterol, but also exert several non-cholesterol-dependent effects. These effects were studied in human coronary arterial endothelial cells (hCAEC) and incubation with lovastatin induced both BK-1 and BK-2Rs in a time and concentration-dependent way. The induced BK-2Rs were functionally active, thus NO production and cGMP signaling was increased. Induction was abrogated by mevalonate, a direct HMG-CoA metabolite. Lovastatin is known to inhibit Rho activation, and by a selective RhoA kinase inhibitor (Y27632), a similar induction of BK-2R expression as with lovastatin. Interestingly a COX-2-inhibitor (NS398) inhibited this lovastatin-induction of BK-2Rs, suggesting that COX-2 inhibitors may affect the endothelial BK-2Rs, in a negative fashion. Hypoxia is a common denominator in HF but also in other cardiovascular diseases. An induction of BK-2Rs in mild hypoxic conditions was shown in cultured hCAECs, which was abolished by a specific BK-2R inhibitor Icatibant. These receptors were functionally active, thus BK increased and Icatibant inhibited the production of NO. In rat myocardium the expression of BK-2R was increased in the endothelium of vessels, forming at the border zone, between the scar tissue and the healthy myocardium. Moreover, in in vitro wound-healing assay, endothelial cells were cultured under hypoxic conditions and BK significantly increased the migration of these cells and as Icatibant inhibited it. These results show, that mild hypoxia triggers a temporal expression of functionally active BK-2Rs in human and rat endothelial cells, supporting a role for BK-2Rs, in hypoxia induced angiogenesis. Our and previous results show, that BK-Rs have an impact on the cardiovascular diseases. In humans, at the end stage of heart failure, the BK-2Rs are down-regulated and BK-1Rs induced. Whether the up-regulation of BK-1Rs, is a compensatory mechanism against the down-regulation of BK-2Rs, or merely reflects the end point of heart failure, remains to bee seen. In a clinical point of view, the up-regulation of BK-2Rs, under hypoxic conditions or statin treatment, suggests that, the induction of BK-2Rs is protective in cardiovascular pathologies and those treatments activating BK-2Rs, might give additional tools in treating heart failure.

Cyclin dependent protein kinases as drug targets – potential in cardiovascular diseases

Complications of atherosclerosis such as myocardial infarction and stroke are the primary cause of death in Western societies. The development of atherosclerotic lesions is a complex process, including endothelial cell dysfunction, inflammation, extracellular matrix alteration and vascular smooth muscle cell (VSMC) proliferation and migration. Various cell cycle regulatory proteins control VSMC proliferation. Protein kinases called cyclin dependent kinases (CDKs) play a major role in regulation of cell cycle progression. At specific phases of the cell cycle, CDKs pair with cyclins to become catalytically active and phosphorylate numerous substrates contributing to cell cycle progression. CDKs are also regulated by cyclin dependent kinase inhibitors, activating and inhibitory phosphorylation, proteolysis and transcription factors. This tight regulation of cell cycle is essential; thus its deregulation is connected to the development of cancer and other proliferative disorders such as atherosclerosis and restenosis as well as neurodegenerative diseases. Proteins of the cell cycle provide potential and attractive targets for drug development. Consequently, various low molecular weight CDK inhibitors have been identified and are in clinical development. Tylophorine is a phenanthroindolizidine alkaloid, which has been shown to inhibit the growth of several human cancer cell lines. It was used in Ayurvedic medicine to treat inflammatory disorders. The aim of this study was to investigate the effect of tylophorine on human umbilical vein smooth muscle cell (HUVSMC) proliferation, cell cycle progression and the expression of various cell cycle regulatory proteins in order to confirm the findings made with tylophorine in rat cells. We used several methods to determine our hypothesis, including cell proliferation assay, western blot and flow cytometric cell cycle distribution analysis. We demonstrated by cell proliferation assay that tylophorine inhibits HUVSMC proliferation dose-dependently with an IC50 value of 164 nM ± 50. Western blot analysis was used to determine the effect of tylophorine on expression of cell cycle regulatory proteins. Tylophorine downregulates cyclin D1 and p21 expression levels. The results of tylophorine’s effect on phosphorylation sites of p53 were not consistent. More sensitive methods are required in order to completely determine this effect. We used flow cytometric cell cycle analysis to investigate whether tylophorine interferes with cell cycle progression and arrests cells in a specific cell cycle phase. Tylophorine was shown to induce the accumulation of asynchronized HUVSMCs in S phase. Tylophorine has a significant effect on cell cycle, but its role as cell cycle regulator in treatment of vascular proliferative diseases and cancer requires more experiments in vitro and in vivo.

Novel mechanisms for regulation of cell survival and migration by ceramide 1-phosphate

201 p. : gráf.

Suppression of zebrafish VEGF gene by cytomegalovirus promoter-driven short hairpin constructs induces vascular development defects and down regulation NRP1 expression

The usage of RNA interference for gene knockdown in zebrafish through expression of the small interfering RNA mediators from DNA vectors has created a lot of excitement in the research community. In this work, the ability of human cytomegalovirus immediate early promoter (CMV promoter)-driven short hairpin RNA (shRNA) expression vector to induce shRNA against vascular endothelial growth factor (VEGF) gene in zebrafish was tested, and its effects on VEGF-mediated vasculogenesis and angiogenesis were evaluated. Altogether four vectors targeting various locations of VEGF gene were constructed, and pSI-V4 was proven to be the most effective one. Microinjection of pSI-V4 into the zebrafish embryos resulted in defective vascular formation and down regulation of VEGF expression. In situ hybridization analysis indicated that silencing VEGF gene expression by pSI-V4 resulted in down regulation of neuropilin-1 (NRP1), a potent VEGF receptor. Knockdown of VEGF expression by morpholino gave the same result. This provided evidence that the VEGF-mediated angiogenesis in zebrafish was in part dependent on NRP1 expression. The results contributed to a better understanding of molecular mechanisms of cardiovascular development and provided a potential promoter for making inducible knockdown in zebrafish.

Regulation of G protein-coupled receptor signaling by scaffold proteins.

The actions of many hormones and neurotransmitters are mediated through stimulation of G protein-coupled receptors. A primary mechanism by which these receptors exert effects inside the cell is by association with heterotrimeric G proteins, which can activate a wide variety of cellular enzymes and ion channels. G protein-coupled receptors can also interact with a number of cytoplasmic scaffold proteins, which can link the receptors to various signaling intermediates and intracellular effectors. The multicomponent nature of G protein-coupled receptor signaling pathways makes them ideally suited for regulation by scaffold proteins. This review focuses on several specific examples of G protein-coupled receptor-associated scaffolds and the roles they may play in organizing receptor-initiated signaling pathways in the cardiovascular system and other tissues.

Transient receptor potential melastatin 8 (TRPM8) channel involvement in the regulation of vascular tone

The transient receptor potential melastatin 8 (TRPM8) channel has been characterized as a cold and menthol receptor expressed in a subpopulation of sensory neurons but was recently identified in other tissues, including the respiratory tract, urinary system, and vasculature. Thus TRPM8 may play multiple functional roles, likely to be in a tissue- and activation state-dependent manner. We examined the TRPM8 channel presence in large arteries from rats and the functional consequences of their activation. We also aimed to examine whether these channels contribute to control of conscious human skin blood flow. TRPM8 mRNA and protein were detected in rat tail, femoral and mesenteric arteries, and thoracic aorta. This was confirmed in single isolated vascular myocytes by immunocytochemistry. Isometric contraction studies on endothelium-denuded relaxed rat vessels found small contractions on application of the TRPM8-specific agonist menthol (300 microM). However, both menthol and another agonist icilin (50 microM) caused relaxation of vessels precontracted with KCl (60 mM) or the alpha-adrenoceptor agonist phenylephrine (2 microM) and a reduction in sympathetic nerve-mediated contraction. These effects were antagonized by bromoenol lactone treatment, suggesting the involvement of Ca(2+)-independent phospholipase A(2) activation in TRPM8-mediated vasodilatation. In thoracic aorta with intact endothelium, menthol-induced inhibition of KCl-induced contraction was enhanced. This was unaltered by preincubation with either N(omega)-nitro-l-arginine methyl ester (l-NAME; 100 nM), a nitric oxide synthase inhibitor, or the ACh receptor antagonist atropine (1 microM). Application of menthol (3% solution, topical application) to skin caused increased blood flow in conscious humans, as measured by laser Doppler fluximetry. Vasodilatation was markedly reduced or abolished by prior application of l-NAME (passive application, 10 mM) or atropine (iontophoretic application, 100 nM, 30 s at 70 microA). We conclude that TRPM8 channels are present in rat artery vascular smooth muscle and on activation cause vasoconstriction or vasodilatation, dependent on previous vasomotor tone. TRPM8 channels may also contribute to human cutaneous vasculature control, likely with the involvement of additional neuronal mechanisms.

Significance of peroxisome proliferator-activated receptors in the cardiovascular system in health and disease.

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated nuclear transcription factors that belong to the nuclear receptor superfamily. Three isoforms of PPAR have been identified, alpha, delta and gamma, which play distinct roles in the regulation of key metabolic processes, such as glucose and lipid redistribution. PPARalpha is expressed predominantly in the liver, kidney and heart, and is primarily involved in fatty acid oxidation. PPARgamma is mainly associated with adipose tissue, where it controls adipocyte differentiation and insulin sensitivity. PPARdelta is abundantly and ubiquitously expressed, but as yet its function has not been clearly defined. Activators of PPARalpha (fibrates) and gamma (thiazolidinediones) have been used clinically for a number of years in the treatment of hyperlipidaemia and to improve insulin sensitivity in diabetes. More recently, PPAR activation has been found to confer additional benefits on endothelial function, inflammation and thrombosis, suggesting that PPAR agonists may be good candidates for the treatment of cardiovascular disease. In this regard, it has been demonstrated that PPAR activators are capable of reducing blood pressure and attenuating the development of atherosclerosis and cardiac hypertrophy. This review will provide a detailed discussion of the current understanding of basic PPAR physiology, with particular reference to the cardiovascular system. It will also examine the evidence supporting the involvement of the different PPAR isoforms in cardiovascular disease and discuss the current and potential future clinical applications of PPAR activators.