Alain Berdeaux

Beta 3‐adrenoceptor stimulation induces vasorelaxation mediated essentially by endothelium‐derived nitric oxide in rat thoracic aorta

The relaxant effects of isoprenaline may result from activation of another β‐adrenoceptor subtype in addition to β1 and β2. This study evaluated the role of a third β‐adrenoceptor subtype, β3, in β‐adrenoceptor‐induced relaxation of rat thoracic aorta by isoprenaline. Isoprenaline produced a concentration‐dependent relaxation of phenylephrine pre‐contracted rings of the thoracic aorta (pD2=7.46±0.15; Emax=85.9±3.4%), which was partially attenuated by endothelium removal (Emax=66.5±6.3%) and administration of the nitric oxide (NO) synthase inhibitor, L‐NG‐monomethyl arginine (L‐NMMA) (Emax=61.3±7.9%). In the presence of nadolol, a β1‐ and β2‐adrenoceptor antagonist, isoprenaline‐induced relaxation persisted (Emax=55.6±5.3%), but occurred at higher concentrations (pD2=6.71±0.10) than in the absence of nadolol and lasted longer. Similar relaxant effects were obtained with two β3‐adrenoceptor agonists: SR 58611 (a preferential β3‐adrenoceptor agonist), and CGP 12177 (a partial β3‐adrenoceptor with β1‐ and β2‐adrenoceptor antagonistic properties). SR 58611 caused concentration‐dependent relaxation (pD2=5.24±0.07; Emax=59.5±3.7%), which was not modified by pre‐treatment with nadolol but antagonized by SR 59230A, a β3‐adrenoceptor antagonist. The relaxation induced by SR 58611 was associated with a 1.7 fold increase in tissue cyclic GMP content. Both relaxation and the cyclic GMP increase induced by SR 58611 were greatly reduced by endothelium removal and in the presence of L‐NMMA. We conclude that in the rat thoracic aorta, β3‐adrenoceptors are mainly located on endothelial cells, and act in conjuction with β1‐ and β2‐adrenoceptors to mediate relaxation through activation of an NO synthase pathway and subsequent increase in cyclic GMP levels.

Stimulation of Bradykinin B1 Receptors Induces Vasodilation in Conductance and Resistance Coronary Vessels in Conscious Dogs Comparison With B2 Receptor Stimulation

Background—Constitutive bradykinin B1 receptors have been identified in dogs; however, their physiological implications involving the coronary circulation remain to be determined. This study examined, in conscious dogs, the coronary response to des-Arg9-bradykinin (a B1 receptor agonist) and the mechanisms involved. Methods and Results—Eleven dogs were instrumented with a left ventricular micromanometer, a circumflex coronary catheter, a cuff occluder, a Doppler flow probe, and ultrasonic crystals to measure coronary blood flow velocity (CBFv) and coronary diameter (CD). Intracoronary des-Arg9-bradykinin (3 to 100 ng/kg) and bradykinin (0.1 to 10 ng/kg) did not modify systemic hemodynamics but dose-dependently increased CBFv and CD. Des-Arg9-bradykinin was less potent than bradykinin. Hoe 140 (a B2 antagonist, 10 μg/kg) abolished the effects of bradykinin but did not influence the effects of des-Arg9-bradykinin. When CBFv increase was prevented by the cuff occluder, CD responses to bradykinin and des-Arg9...

Structure and pharmacology of swelling‐sensitive chloride channels, ICl,swell

Since several years, the interest for chloride channels and more particularly for the enigmatic swelling‐activated chloride channel (ICl,swell) is increasing. Despite its well‐characterized electrophysiological properties, the ICl,swell structure and pharmacology are not totally elucidated. These channels are involved in a variety of cell functions, such as cardiac rhythm, cell proliferation and differentiation, cell volume regulation and cell death through apoptosis. This review will consider different aspects regarding structure, electrophysiological properties, pharmacology, modulation and functions of these swelling‐activated chloride channels.

Chronic Infusion of Bradykinin Delays the Progression of Heart Failure and Preserves Vascular Endothelium-Mediated Vasodilation in Conscious Dogs

Background—This study examined the effects of chronic bradykinin infusion on hemodynamics and myocardial and endothelial functions during the development of heart failure. Methods and Results—Sixteen instrumented dogs were randomized to receive through the left atria either vehicle or bradykinin (1 &mgr;g/min) during ventricular pacing (250 bpm, 5 weeks). Hemodynamic and left ventricular (LV) parameters and the vasodilator responses to intravenous acetylcholine (0.3 to 3 &mgr;g/kg) and nitroglycerin (1 to 10 &mgr;g/kg) were examined in the control and after 3 and 5 weeks of pacing. The expression of endothelial NOS in femoral, carotid, and renal arteries was determined by Western blot analysis. After 3 weeks of pacing, changes in LV diastolic and systolic parameters were significantly lower in bradykinin-treated than vehicle-treated dogs (LV end-diastolic pressure, +10±3 versus +19±2 mm Hg; time constant of LV isovolumic relaxation, +11±2 versus +17±1 ms; LV wall thickening, −33±18% versus −75±9%; and cardiac output, −16±6% versus −32±6%; all P <0.05). Compared with vehicle-treated dogs, bradykinin-treated dogs had a reduced rightward shift of the diastolic LV pressure-diameter relation and a reduced diastolic LV wall stress. Similar trends were observed after 5 weeks. The vasodilator response to nitroglycerin was preserved in both groups. The response to acetylcholine was blunted in vehicle-treated but preserved in bradykinin-treated dogs. Vascular endothelial NOS expression decreased in vehicle-treated but was preserved in bradykinin-treated dogs. Conclusions—In conscious dogs, chronic bradykinin infusion delays the heart failure progression by preserving LV diastolic and systolic functions and by preserving vascular endothelial function.

Vascular and angiogenic activities of CORM-401, an oxidant-sensitive CO-releasing molecule.

Carbon monoxide (CO) is generated by heme oxygenase-1 (HO-1) and displays important signaling, anti-apoptotic and anti-inflammatory activities, indicating that pharmacological agents mimicking its action may have therapeutic benefit. This study examined the biochemical and pharmacological properties of CORM-401, a recently described CO-releasing molecule containing manganese as a metal center. We used in vitro approaches, ex-vivo rat aortic rings and the EA.hy926 endothelial cell line in culture to address how CORM-401 releases CO and whether the compound modulates vascular tone and pro-angiogenic activities, respectively. We found that CORM-401 released up to three CO/mole of compound depending on the concentration of the acceptor myoglobin. Oxidants such as H2O2, tert-butyl hydroperoxide or hypochlorous acid increased the CO liberated by CORM-401. CORM-401 also relaxed pre-contracted aortic rings and vasorelaxation was enhanced in combination with H2O2. Consistent with the release of multiple CO molecules, CORM-401-induced vasodilation was three times higher than that elicited by CORM-A1, which exhibits a similar half-life to CORM-401 but liberates only one CO/mole of compound. Furthermore, endothelial cells exposed to CORM-401 accumulated CO intracellularly, accelerated migration in vitro and increased VEGF and IL-8 levels. Studies using pharmacological inhibitors revealed HO-1 and p38 MAP kinase as two independent and parallel mechanisms involved in stimulating migration. We conclude that the ability of CORM-401 to release multiple CO, its sensitivity to oxidants which increase CO release, and its vascular and pro-angiogenic properties highlight new advances in the design of CO-releasing molecules that can be tailored for the treatment of inflammatory and oxidative stress-mediated pathologies.

Endothelial Modulation of β-Adrenergic Dilation of Large Coronary Arteries in Conscious Dogs

BACKGROUNDnEndothelium-derived relaxing factors have been described as important intermediates in beta-adrenergic vasodilation of resistance coronary vessels, but their involvement at the level of large epicardial coronary arteries remains controversial. Therefore, we examined the role of vascular endothelium in the beta-adrenergic-mediated vasodilation of large epicardial coronary arteries in conscious dogs.nnnMETHODS AND RESULTSnNine dogs were instrumented for measurement of left circumflex coronary artery diameter (CD) by sonomicrometry and coronary blood flow velocity (CBFv) with a Doppler technique in response to graded doses of isoproterenol (0.001 to 0.1 microgram/kg IV bolus). Under control conditions, isoproterenol induced dose-dependent increases in CD and CBFv. When CBFv was kept constant at its baseline value by inflation of a cuff occluder, isoproterenol still induced dose-dependent increases in CD, but the latter were of lesser magnitude than those observed under normal CBFv conditions (110 +/- 20 versus 170 +/- 30 microns, respectively, ie, a reduction of 33% of the dilatory response at 0.1 microgram/kg, P < .01). In the same dogs, the coronary endothelium was then mechanically removed at the site of CD measurement by a balloon angioplasty technique. After this procedure, the dose-dependent increases in CD induced by isoproterenol under either normal or controlled CBFv conditions were overimposable, and their magnitude was similar to that of the increases observed in the presence of an intact endothelium when CBFv was kept constant. After beta 1-adrenergic receptor blockade by atenolol (1 mg/kg), isoproterenol-induced increases in CD were abolished either when CBFv was kept constant or after endothelium removal.nnnCONCLUSIONSnIn conscious dogs, the direct stimulating effect of isoproterenol on beta 1-adrenergic receptors is endothelium-independent at the level of large coronary arteries. The endothelium reinforces the dilatory response to isoproterenol through an indirect, flow-dependent mechanism.

Comparisons of the effects of nicorandil, pinacidil, nicardipine and nitroglycerin on coronary vessels in the conscious dog: role of the endothelium

1 The vasodilator properties of nicorandil on large and small coronary arteries were compared to those of nicardipine, pinacidil, nitroglycerin and acetylcholine in six conscious dogs. 2 Intravenous bolus injections of acetylcholine (0.1 μg kg−1), nitroglycerin (0.3–3 μg kg−1), pinacidil (10–100 μg kg−1), nicardipine (3–30 μg kg−1) and nicorandil (10–100 μg kg−1) dose‐dependently increased circumflex coronary artery diameter and decreased coronary vascular resistance, indicating vasodilator effects on both conduit and resistance coronary arteries. 3 Three days after removal of the endothelium of the circumflex coronary artery (balloon angioplasty), pinacidil‐ and nicardipine‐induced dilatation of large coronary arteries was greatly reduced (both − 76%, P<0.01) whereas that produced by nitroglycerin and nicorandil was decreased only slightly and to a similar extent for both drugs (− 19%, P<0.01 and −28%, P<0.05, respectively). 4 Thus in conscious dogs, nicardipine‐ and pinacidil‐induced dilatation of large coronary arteries is endothelium‐dependent. In contrast, the vasodilator effects of nitroglycerin and nicorandil on conduit vessels are endothelium‐independent. 5 Finally, our results demonstrate that nicorandil dilates the large coronary arteries through its nitrate‐like action and that the ATP‐potassium channel opening properties of the drug are not involved in this effect in the conscious dog.

Clearance of atrial natriuretic peptide in patients with cirrhosis. Role of liver failure.

In non-cirrhotic patients, splanchnic, renal and pulmonary vascular beds are involved in the plasma clearance for atrial natriuretic peptide (ANP). In patients with cirrhosis, endogenous plasma ANP clearance by these vascular beds has not been systematically studied. In addition, the influence of the severity of liver failure on plasma ANP clearance is not known. Thus, in this study we determined plasma ANP clearance by splanchnic, renal and pulmonary circulations using both arteriovenous differences in plasma ANP concentrations and organ plasma flow in 11 patients with cirrhosis. The role of forearm circulation in plasma ANP extraction was also studied. Splanchnic plasma ANP extraction was 29 +/- 7% (mean +/- S.E.) and splanchnic plasma ANP clearance was 404 +/- 130 ml/min (n = 7). Renal plasma ANP extraction and clearance were 32 +/- 8% and 191 +/- 57 ml/min, respectively. Forearm plasma ANP extraction was 11 +/- 4%. Pulmonary plasma ANP extraction and clearance were 8 +/- 5% and 312 +/- 272 ml/min, respectively. A significant negative correlation was found between logarithm of serum bilirubin concentration, on one hand, and splanchnic and forearm plasma ANP extraction, on the other. A significant negative correlation was found between Pughs score, on one hand, and renal plasma ANP extraction and clearance, on the other. No significant correlation was found between the severity of liver failure and pulmonary plasma ANP extraction and clearance. As a result, we conclude that in cirrhotic patients splanchnic, renal, forearm and pulmonary vascular beds are involved in plasma ANP extraction and clearance. Plasma ANP extraction and/or clearance may be attenuated in the splanchnic, renal and forearm circulations due to liver failure.

Inhibitors of swelling-activated chloride channels increase infarct size and apoptosis in rabbit myocardium.

Apoptosis is a significant contributor to myocardial cell death during ischemia‐reperfusion and swelling‐activated chloride channels (ICl,swell) contribute to apoptosis. However, the relationship between ICl,swell, ischemia‐reperfusion and apoptosis remains unknown. To further investigate this, New Zealand rabbits underwent a 20‐min coronary artery occlusion (CAO) followed by 72u2003h of coronary artery reperfusion (CAR). Two ICl,swell blockers, 5‐nitro‐2‐[3‐phenylpropylamino]benzoic acid (NPPB) and indanyloxyacetic acid 94 (IAA‐94) (both 1u2003mg/kg), were administered prior to CAO and throughout the 72u2003h CAR. Infarct size (IS) was increased with NPPB and IAA‐94 compared with control (vehicle) rabbits (51u2003±u20032% and 48u2003±u20033% and vs. 35u2003±u20032%, respectively, Pu2003<u20030.05). Similar results were found when NPPB was administered only during the reperfusion period. The percentage of TUNEL‐positive nuclei in the border zone of the infarct was increased with NPPB compared with control (37u2003±u20032% vs. 25u2003±u20033%, Pu2003<u20030.05) as well as the number of cytoplasmic histone‐associated DNA fragments (0.45u2003±u20030.06 vs. 0.33u2003±u20030.04 absorbance units, Pu2003<u20030.05). These findings support the concept that ICl,swell channels play an important role in the determination of myocardial infarct size and apoptosis during ischemia‐reperfusion.

Comparative effects of frovatriptan and sumatriptan on coronary and internal carotid vascular haemodynamics in conscious dogs

The effects of frovatriptan and sumatriptan on internal carotid and coronary vascular haemodynamics were investigated and compared in conscious dogs. Frovatriptan and sumatriptan (0.1–100u2003μgu2003kg−1) induced a transient increase in external coronary artery diameter (eCOD) of up to 2.9±1.2 and 1.8±0.6%, respectively (both P<0.05). This was followed by a prolonged and dose‐dependent decrease in eCOD of up to −5.2±1.2 and −5.3±0.9% (both P<0.05), with ED50 values of 86±21 and 489±113u2003μmolu2003kg−1, respectively. In contrast, only a decrease in the external diameter of the internal carotid artery was observed (−6.0±0.6 and −6.2±1.4%, both P<0.05, and ED50 values of 86±41 and 493±162u2003μmolu2003kg−1, respectively). Frovatriptan was thus 5.7 fold more potent than sumatriptan at the level of both large coronary and internal carotid arteries. After endothelium removal by balloon angioplasty in coronary arteries, the initial dilatation induced by the triptans was abolished and delayed constriction enhanced. The selective antagonist for the 5‐HT1B receptors SB224289 dose‐dependently blocked the effects of sumatriptan on large coronary and internal carotid arteries whereas the selective antagonist for the 5‐HT1D receptors BRL15572 did not affect any of these effects. In conclusion, frovatriptan and sumatriptan initially dilate and subsequently constrict large coronary arteries in the conscious dog, whereas they directly constrict the internal carotid artery. The vascular endothelium modulates the effects of these triptans on large coronary arteries. Finally, 5‐HT1B but not 5‐HT1D receptors are primarily involved in canine coronary and internal carotid vasomotor responses to sumatriptan.