To what extent is it possible to dissociate the anxiolytic and sedative/hypnotic properties of GABAA receptors modulators?

The relatively common view indicates a possible dissociation between the anxiolytic and sedative/hypnotic properties of benzodiazepines (BZs). Indeed, GABAA receptor (GABAAR) subtypes have specific cerebral distribution in distinct neural circuits. Thus, GABAAR subtype-selective drugs may be expected to perform distinct functions. However, standard behavioral test assays provide limited direction towards highlighting new action mechanisms of ligands targeting GABAARs. Automated behavioral tests, lack sensitivity as some behavioral characteristics or subtle behavioral changes of drug effects or that are not considered in the overall analysis (Ohl et al., 2001) and observation-based analyses are not always performed. In addition, despite the use of genetically engineered mice, any possible dissociation between the anxiolytic and sedative properties of BZs remains controversial. Moreover, the involvement the different subtypes of GABAAR subtypes in the anxious behavior and the mechanism of action of anxiolytic agents remains unclear since there has been little success in the pharmacological investigations so far. This raises the question of the involvement of the different subunits in anxiolytic-like and/or sedative effects; and the actual implication of these subunits, particularly, α-subunits in the modulation of sedation and/or anxiety-related disorders. This present review was prompted by several conflicting studies on the degree of involvement of these subunits in anxiolytic-like and/or sedative effects. To this end, we explored the GABAergic system, particularly, the role of different subunits containing synaptic GABAARs. We report herein the targeting gene encoding the different subunits and their contribution in anxiolytic-like and/or sedative actions, as well as, the mechanism underlying tolerance to BZs.

5-HT2C receptors in psychiatric disorders: A review.

5-HT2Rs have a different genomic organization from other 5-HT2Rs. 5HT2CR undergoes post-transcriptional pre-mRNA editing generating diversity among RNA transcripts. Selective post-transcriptional editing could be involved in the pathophysiology of psychiatric disorders through impairment in G-protein interactions. Moreover, it may influence the therapeutic response to agents such as atypical antipsychotic drugs. Additionally, 5-HT2CR exhibits alternative splicing. Central serotonergic and dopaminergic systems interact to modulate normal and abnormal behaviors. Thus, 5HT2CR plays a crucial role in psychiatric disorders. 5HT2CR could be a relevant pharmacological target in the treatment of neuropsychiatric disorders. The development of drugs that specifically target 5-HT2C receptors will allow for better understanding of their involvement in the pathophysiology of psychiatric disorders including schizophrenia, anxiety, and depression. Among therapeutic means currently available, most drugs used to treat highly morbid psychiatric diseases interact at least partly with 5-HT2CRs. Pharmacologically, 5HT2CRs, have the ability to generate differentially distinct response signal transduction pathways depending on the type of 5HT2CR agonist. Although this receptor property has been clearly demonstrated, in vitro, the eventual beneficial impact of this property opens new perspectives in the development of agonists that could activate signal transduction pathways leading to better therapeutic efficiency with fewer adverse effects.

Immunosuppressant regimen based on sirolimus decreases aortic stiffness in renal transplant recipients in comparison to cyclosporine.

Whether or not a cyclosporine A (CsA)-free immunosuppressant regimen based on sirolimus (SRL) prevents aortic stiffening and improves central hemodynamics in renal recipients remains unknown. Forty-four patients (48 ± 2 years) enrolled in the CONCEPT trial were randomized at week 12 (W12) to continue CsA or switch to SRL, both associated with mycophenolate mofetil. Carotid systolic blood pressure (cSBP), pulse pressure (cPP), central pressure wave reflection (augmentation index, AIx) and carotid-to-femoral pulse-wave velocity (PWV: aortic stiffness) were blindly assessed at W12, W26 and W52 together with plasma endothelin-1 (ET-1), thiobarbituric acid-reactive substances (TBARS) and superoxide dismutase (SOD) and catalase erythrocyte activities. At W12, there was no difference between groups. At follow-up, PWV, cSBP, cPP and AIx were lower in the SRL group. The difference in PWV remained significant after adjustment for blood pressure and eGFR. In parallel, ET-1 decreased in the SRL group, while TBARS, SOD and catalase erythrocyte activities increased in both groups but to a lesser extent in the SRL group. Our results demonstrate that a CsA-free regimen based on SRL reduces aortic stiffness, plasma endothelin-1 and oxidative stress in renal recipients suggesting a protective effect on the arterial wall that may be translated into cardiovascular risk reduction.

[Endothelial dysfunction: role of vasodilating betablockers in hypertension and chronic heart failure]. / Dysfonction endothéliale : le rôle des bêtabloquants vasodilatateurs dans l'hypertension artérielle et l'insuffisance cardiaque chronique.

The beneficial effects of beta blocking drugs in hypertension and heart failure are well known. However, this class of drugs is pharmacologically heterogeneous. In contrast to the non vasodilator betablockers like propranolol, atenolol or metoprolol which, in hypertension do not decrease intima media thinckness both in arterioles and large arteries, do not decrease arterial rigidity and can induce diabetes mellitus, the betablockers with vasodilating properties are beneficial on these parameters. Moreover, in heart failure, they more markedly decrease left ventricular workload than betablockers without any vascular relaxing effect and the results of SENIOR with nebivolol could suggest the beneficial role of NO on left ventricular dysfunction. Finally, the third generation betablockers, represented by celiprolol, carvedilol and nebivolol, have antioxidant properties which are probably implicated in their endothelial protective effects and in their absence of deleterious metabolic effects, effects which are probably of interest in term of protection of target organs during chronic treatment of hypertensive patients.

Antiphospholipid antibodies induce vascular functional changes in mice: a mechanism of vascular lesions in antiphospholipid syndrome?

A premature atherosclerosis has been presumed in patients with antiphospholipid syndrome. The potential role of antiphospholipid antibodies in the development of atheroma is rather controversial. In this study, we tested the hypothesis that antiphospholipid antibodies could induce atherosclerosis via vascular functional changes. CD1 mice received one single injection of antiphospholipid monoclonal antibodies derived from male (BXSB x NZW) F1 mice with a lupus-like disease associated with an antiphospholipid syndrome and coronary artery disease. One week later, first-order mesenteric arteries (diameter 220-260 microm) were isolated and mounted on a small-vessel myograph for the measurement of the relaxation responses to acetylcholine or the NO donor nitroprusside after precontraction by phenylephrine. Five out of eight antiphospholipid monoclonal antibodies reduced the response to acetylcholine compared with control mice, and this effect was especially marked with one of them. No change in the response to nitroprusside was observed. The impairment was maintained after 3 weeks of treatment and appeared related to a moderate decrease in NO-mediated responses and a marked decrease in prostanoid-mediated relaxations. These vascular functional changes could be prevented by chronic treatment with statins or aspirin. These data could constitute additional elements supporting a direct pathogenic role of antiphospholipid antibodies. We suggest that a sub-population of these autoantibodies could be responsible for the endothelial dysfunction observed in antiphospholipid syndrome.

[Role of vascular calcium-activated potassium channels in the regulation of human peripheral conduit artery diameter]. / Rô1e des canaux potassiques calcium-dépendants dans la régulation du diamètre basal des artères de conductance périphériques humaines.

The role of an endothelium-derived hyperpolarizing factor (EDHF), acting through the opening of vascular calcium-activated potassium (K(Ca)) channels, in the regulation of the basal diameter of human peripheral conduit arteries has never been investigated in vivo. We measured in 7 healthy subjects the effect of the local infusion of an inhibitor of K(Ca) channels, tetraethylammonium chloride (TEA, 9 micromol/min, 8 min), on radial artery diameter (echotracking) and flow (Doppler). Endothelium-independent dilatation was assessed before and after TEA using sodium nitroprusside (SNP: 5, 10 and 15 nmol/min, 3 min each). TEA induced a decrease in radial artery diameter (2.65 +/- 0.09 to 2.52 +/- 0.09 mm: p < 0.05) and flow (9.4 +/- 1.2 to 7.4 +/- 1.1 ml/min; p < 0.01) without modification in the radial artery dilatation in response to SNP (NS). The decrease in radial artery diameter was still significant even when the decrease in flow was taken as covariate into analysis (p < 0.05). These results demonstrate the role of vascular K(Ca) channels in the regulation of basal peripheral conduit artery diameter and arteriolar tone in human strongly suggesting the involvement of an EDHF a these two levels.

Targeting endothelial dysfunction in hypertensive subjects.

The endothelium is a favourite early target of cardiovascular risk factors and cardiovascular diseases like hypertension. This key role of the endothelium results from its capacity to respond to numerous autocrine and paracrine stimuli and to mechanical factors like shear stress but also from the pathophysiological consequences of endothelial dysfunction on vasomotor tone, arterial stiffness, arterial remodelling, and inflammation, all of which are factors that play a critical role in atherosclerosis and target-organ damage. In hypertension, endothelial dysfunction has been shown at the level of both resistance and conduit arteries and mainly results from an increase in nitric oxide (NO) degradation by interaction between NO and superoxide anions, while in experimental models of hypertension a decrease in NO production can also be observed. The fact that forearm endothelial dysfunction is a marker of future cardiovascular events in patients with hypertension stresses the importance of the clinical evaluation of endothelial function and of the evaluation of the effects of the different antihypertensive drug classes on this parameter. In this context, many studies have demonstrated that angiotensin-converting enzyme inhibitors, the perindopril-indapamide combination, and angiotensin II type I receptor (AT1) blockers improve endothelium-dependent vasodilatation partly independently of arterial pressure. Both their antioxidant effects and the stimulation of the release of NO are involved in their beneficial effects. For calcium antagonists, only the recent drugs have been shown to improve endothelial function with a simultaneous improvement in several markers of oxidative stress. Finally, beta-blockers classically do not affect endothelial function. Only nebivolol, a beta-blocker with NO donor properties, has been shown to improve endothelial function, but this effect results from the increase in NO and not from the beta-blocking properties of the drug.

[Hand skin heating: a new method for the evaluation of conduit artery endothelial function in insulin-dependent diabetic patients]. / Le chauffa e cutané distal: une nouvelle méthode d'étude de la fonction endothéliale des artères de conductance périphériques chez le diabétique insulinodépendant.

The presence of an altered endothelium-mediated flow-dependent dilatation (FDD) of peripheral conduit arteries in insulin-dependent diabetic patients without microangiopathy is still controversial. We studied 10 normotensive and non atherosclerotic insulin-dependent diabetic patients (D group) without complication (neuropathy, microalbuminuria or neuropathy) and 10 control subjects (C group) matched for age, sex and BMI. Radial artery diameter (RAD, echotracking) and flow (RAF, Doppler) were measured at baseline and during FDD in response to distal hand skin heating (from 34 to 44 degrees C). a method developed to increase RAF by stable steps by decreasing gradually hand skin vascular resistance. Endothelium-independent dilatation was evaluated by administration of glyceryl trinitrate (GTN: 0.3 mg spray). At baseline, there was no difference between group for RAF (C: 18 +/- 5 vs D: 18 +/- 2 mL/min; NS) and RAD (C: 2.51 +/- 0.12 vs D: 2.54 +/- 0.07 mm; NS). Heating induced in the diabetic group a smaller increase in RAF (C: 473 +/- 126% vs D: 262 +/- 63%; p<0.05) and RAD (C: 22.6 +/- 2.6% vs D: 16.1 +/- 1.8%; p<0.01). This last result remains significant when the increase in RAF was included into the analysis of RAD variation during heating (p<0.05). GTN-induced dilatation was similar in the 2 groups. Our results obtained by use of the hand skin heating method demonstrate the presence of an abnormal arteriolar skin reactivity and an altered peripheral conduit artery endothelium-dependent dilatation in uncomplicated insulin-dependent diabetic patients. The early identification of these anomalies, with negative prognostic value, could contribute to the management of these patients.

Chronic decrease in flow contributes to heart failure-induced endothelial dysfunction in rats.

Chronic heart failure (CHF) impairs endothelium-dependent, nitric oxide (NO)-mediated dilation. This decreased dilation may be partly secondary to the chronic decrease in blood flow, but this hypothesis has not yet been tested. Thus, we assessed whether a localized, chronic increase in blood flow in vivo reverses endothelial dysfunction of small arteries in rats with CHF. Two months after coronary artery ligation or sham surgery, second-order side branches of the superior mesenteric artery were ligated in order to obtain persistently elevated blood flow (HF) in the adjacent first-order side branch compared with normal vessels (NF). One month later, responses to acetylcholine and flow-mediated vasodilatation (FMD) were assessed in vitro in an arteriograph. Chronic heart failure induced a decrease in mesenteric blood flow (374 +/- 25 and 305 +/- 27 micro L/min for sham and CHF, respectively; P < 0.05). Neither CHF nor the chronic increase in flow affected the responses to acetylcholine. Chronic heart failure decreased FMD (maximal response in sham and control 34 +/- 6 and 13 +/- 4%, respectively; P < 0.05). Chronic increases in blood flow did not modify FMD in sham, but restored FMD in CHF rats (28 +/- 4%; P < 0.05 vs CHF NF). The restored response was abolished by an inhibitor of NO synthesis (N(G)-nitro-l-arginine). Chronic heart failure did not affect the abundance of mesenteric endothelial NO synthase (eNOS) mRNA. A chronic increase in flow significantly increased the abundance of eNOS mRNA in sham rats, but only moderately and non-significantly in CHF rats. Thus, endothelial dysfunction of small arteries in CHF appears to be largely the consequence of the chronic decrease in flow.

Coronary endothelial cells: a target of ischemia reperfusion and its treatment?

Ischemia/reperfusion injury of the heart is not limited to cardiomyocytes but also extends to coronary vascular cells, and especially coronary endothelium. Indeed, in different animal models, ischemia followed by reperfusion (but not ischemia alone) markedly decreases endothelium-dependent relaxations of coronary arteries, and especially those induced by nitric oxide (NO), while endothelium-independent responses and smooth muscle responsiveness are usually maintained. Such injury to the endothelium appears to depend on the increased production of oxygen-derived free radicals upon reperfusion, leading to an increased degradation of NO and an acute inflammatory response characterized by an increased adhesion of neutrophils to endothelial cells. Indeed, reperfusion injury to the endothelium may be prevented by free radical scavengers, by prevention of adhesion and/or activation of neutrophils, by exogenous NO supply or increased endogenous production of NO, as well as by ischemic preconditioning. Given the essential role of the endothelium and of NO in the regulation of vasomotor tone, as well as platelet and leukocyte function, it is likely that such changes in coronary endothelial function have important adverse consequences in terms of altered perfusion, and increased risk of vasospasm, but also on the long-term risk of thrombosis and atherosclerosis. Although these coronary endothelial alterations have been essentially evaluated in experimental models and are indeed difficult to assess in the human coronary circulation in the context of myocardial infarction, data obtained in healthy volunteers demonstrate that such post-ischemic alterations of endothelial function may be detected in the peripheral circulation, with underlying molecular mechanisms similar to those demonstrated experimentally. A better understanding of the mechanisms responsible for such endothelial injury may lead to the development of new treatments that protect the endothelium during ischemia and reperfusion, but also possibly in other diseases associated with endothelial dysfunction.

Rotating wall vessel as a new in vitro shear stress generation system: application to rat coronary endothelial cell cultures.

In this paper, we describe a simple new design for the application of controlled, top-hat profiled wall shear stress forces in a way that is independent of hydrostatic pressure and oxygen tension, based on a rotating wall vessel system. This system has been applied to the culture of rat coronary endothelial cells obtained with a Langendorff-derived procedure isolation. Endothelial cells are immunopurified on the basis of RECA expression, and conservation of endothelial phenotype has been assessed on the basis of morphology, RECA and von Willebrand factor expressions and diI-Ac-LDL uptake. Shear stress induced by the rotating wall vessel was measured using a mathematical formula specifically designed for this type of model, and its impact on coronary endothelial cells was evaluated. Shear stress produced cell orientation parallel to the flux direction, elevated NO production and decreased monocyte adhesion. Cells were kept viable and functional for at least 4 days under shear. This simple design allows the handling and management of numerous vials in parallel and appears to be suitable for large-scale studies of both the acute and chronic impact of modulation of the physico-chemical environment on endothelial cell physiology and function.

Lack of impairment of nitric oxide-mediated responses in a rat model of high-renin hypertension.

1. Angiotensin (Ang) II triggers the expression of a pro- oxidant phenotype in the vascular wall, suggesting that activation of the renin-angiotensin system (RAS) causes endothelial dysfunction in various pathological situations, such as hypertension. However, this hypothesis has been mostly tested in a setting of exogenous administration of AngII. 2. We tested the hypothesis of a role for endogenous activation of the RAS leading to oxidant stress and endothelial dysfunction in a high-renin model of hypertension (i.e. two-kidney, one-clip hypertension) in rats. One month after clipping or sham surgery, aorta were isolated from untreated rats or rats treated by the angiotensin AT1 receptor antagonist irbesartan (10 mg/kg per day). Mesenteric artery segments were also isolated from normotensive or hypertensive rats. 3. Hypertension reduced the relaxations to acetylcholine but did not affect the ratio of contractions to phenylephrine in the presence compared with the absence of a nitric oxide (NO) synthase inhibitor, used as an index of basal release of NO. 4. The free radical scavenger tempol reduced the contractions to phenylephrine in the absence, but not in the presence, of an inhibitor of NO synthesis. This index of free radical-mediated degradation of NO was not affected by hypertension. In parallel, hypertension did not affect the expression of p22phox, a component of the free radical generating enzyme reduced nicotinamide adenine dinucleotide phosphate oxidase. 5. Chronic treatment with the AT1 receptor antagonist decreased blood pressure, moderately improved the response to acetylcholine, but did not affect basal NO release in hypertensive rats, although it did increase basal NO release in normotensive rats. 6. Thus, this model of hypertension is characterized by an impaired stimulated NO release but not of basal NO release in isolated arteries. Furthermore, there was no functional evidence of an increased oxidative stress-mediated impairment of NO release. This is not in favour of a direct link between activation of the RAS and development of endothelial dysfunction in experimental hypertension.

Induction of heme-oxygenase-1 prevents the systemic responses to hemorrhagic shock.

Oxidant-mediated reperfusion injury of the gut is a major contributor of the systemic inflammatory response in hemorrhagic shock. Recent studies have suggested that heme-oxygenase-1 (HO-1) represents an endogenous protective mechanism against oxidant stress. We assessed whether HO-1 induction modulates the synthesis of tumor necrosis factor-alpha (TNF-alpha) in hemorrhagic shock. In rats submitted to hemorrhagic shock, pretreatment with hemoglobin (Hb) increased HO-1 mRNA expression in macrophages. This increased expression was associated with a decreased expression of TNF-alpha mRNA, as well as decreased plasma concentrations of TNF-alpha. These effects of Hb were reduced by the HO-1 inhibitor tin-protoporphyrin (Sn-PP 20 micromol/kg), while Sn-PP had no effect in the absence of Hb. In parallel, Hb pretreatment reduced pulmonary edema, vascular injury, and increased mesenteric blood flow, and these effects were reduced by Sn-PP. Thus, induction of HO-1 is protective in hemorrhagic shock, possibly through its antioxidant properties. Interventions that induce HO-1 may be beneficial in the treatment of shock states, leading to a reduced systemic inflammatory response.

Chronic ACE inhibition enhances the endothelial control of arterial mechanics and flow-dependent vasodilatation in heart failure.

Reduced conduit arteries flow-dependent dilatation and altered compliance have been described during heart failure. However, the role of shear stress, the relation between endothelial dysfunction and mechanics, and the effect of chronic ACE inhibition on this relationship have not been investigated. The present study was designed to evaluate in heart failure patients the relationship between flow-dependent dilatation and radial artery mechanics at known shear stress levels and to assess the effect of chronic ACE inhibition. Sixteen stable congestive heart failure patients, who had never been treated with ACE inhibitors, participated in the study. Arterial pressure, cardiac output (bioimpedance), radial artery diameter (echo tracking) and flow (Doppler), total blood viscosity, and mean artery wall shear stress were assessed before and during a gradual increase in the forearm blood flow in response to gradual distal hand skin heating. Cross-sectional radial artery compliance and distensibility indexes were calculated at 34 degrees C, 40 degrees C, and 44 degrees C. The endothelium-independent vasodilatation was evaluated by use of glyceryl trinitrate. All parameters were assessed before and 24 hours after the last administration of perindopril (4 mg once daily) or placebo in a 2-month double-blind randomized study. Before treatment, there was no difference between the 2 groups for all parameters. After chronic ACE inhibition, systolic arterial pressure decreased at baseline from 126+/-11 to 118+/-10 mm Hg (P<0.05). During heating, the increase in diameter in response to shear stress was higher after ACE inhibition than after placebo (time/treatment interaction, P<0.05). Moreover, in contrast to placebo, at the same shear stress, there was a significant increase in compliance (3.23+/-0.79 x 10(-7) to 6.82+/-2.47 x 10(-7) m(2)/kPa, P<0.05) and distensibility (5.71+/-1.35 x 10(-3) to 8.87+/-1.88 x 10(-3)/kPa, P<0.05) during heating after ACE inhibition. The effect of glyceryl trinitrate did not change. The present study demonstrates that chronic administration of the ACE inhibitor perindopril increases the magnitude of the flow-dependent dilatation and restores the flow-dependent increase in compliance and distensibility of the radial artery evaluated at stable shear stress. In addition, the decrease in baseline systolic arterial pressure after ACE inhibitor suggests an associated increase in the distensibility of the proximal elastic conduit arteries.

Production and metabolism of serotonin (5-HT) by the human adrenal cortex: paracrine stimulation of aldosterone secretion by 5-HT.

In the human adrenal cortex, serotonin (5-HT) is contained in mast-like cells, and we have shown that 5-HT stimulates aldosterone secretion, suggesting that 5-HT may control glomerulosa cells through a paracrine mechanism. Concurrently, the presence of 5-hydroxyindolacetic acid in human adrenocortical extracts indicates that 5-HT may be metabolized after local release by mast cells. The aim of the present study was to investigate in vitro the production and metabolism of 5-HT by the human adrenal cortex. Perifused adrenal slices released spontaneously detectable amounts of 5-HT (0.74 +/- 0.38 fmol/mg wet tissue.min). The mast cell-depleting drug compound 48/80 induced a burst of 5-HT secretion followed by a gradual increase in aldosterone production. Administration of the specific 5-HT(4) receptor antagonist GR 113808 (10(-6) M) did not affect compound 48/80-induced 5-HT release but abolished the stimulatory effect of compound 48/80 on aldosterone secretion, indicating that 5-HT released locally is responsible for a paracrine control of steroidogenesis. Incubation of cells from the human adrenal cortex with 5-HT (10(-5) M) provoked the formation of the 5-HT metabolite 5-hydroxytryptophol. The type A monoamine oxidase (MAO) inhibitor clorgyline (10(-6) M) suppressed the metabolism of 5-HT into 5-hydroxytryptophol. Immunocytochemical staining of cultured cells revealed the presence of a subpopulation of MAO-A-positive cells. Double labeling with an antiserum against chromogranin A showed that MAO-A was actually contained in chromaffin cells. Similarly, immunohistochemical staining of adrenal slices showed that MAO-A was expressed in chromaffin cells located both in the medulla and in intracortical rays. In conclusion, the present study shows that, in the human adrenal cortex, 5-HT, released by mast-cells, may stimulate aldosterone secretion in a paracrine manner. Our data also indicate that 5-HT is metabolized by MAO-A located in intracortical chromaffin cells.

In vivo regulation of vasomotricity by nitric oxide and prostanoids during gestation.

Pharmacological studies using the Doppler technique revealed that pregnancy decreases the systemic blood pressure and enhances uterine blood velocity in rats. The reactivity of the uterine artery to alpha-adrenoceptor and muscarinic receptor agonists was higher than that of systemic arteries. Sodium nitroprusside increased uterine arterial blood velocity slightly during gestation and markedly in non-pregnant rats. N(G)-L-Arginine methyl ester (L-NAME) decreased the uterine blood velocity mainly in gravid animals. The effect of diclofenac on uterine blood velocity was also more pronounced during pregnancy. The actions of sodium nitroprusside, L-NAME and diclofenac on systemic blood pressure were similar in pregnant and virgin rats. Altogether, these results indicate that pregnancy enhances nitric oxide (NO) and vasodilatory prostanoid production in the uterine vascular muscle which becomes less sensitive to exogenous NO. The uterine vasodilated status appears to be determined by conjugated actions of endothelial NO and vasodilator prostanoids of which the synthesis and the effects are weakly modified in systemic arteries during gestation.

Functional evidence for a role of vascular chymase in the production of angiotensin II in isolated human arteries.

BACKGROUND: In human arteries, angiotensin-converting enzyme (ACE) inhibitors incompletely block the production of angiotensin (Ang) II from Ang I. This ACE-independent production of Ang II appears to be caused by serine proteases, one of which presumably is chymase. However, several serine proteases may produce Ang II, and the exact role of chymase in the vascular production of Ang II has never been directly evaluated using selective chymase inhibitors. METHODS AND RESULTS: Rings of human mammary arteries were subjected to either Ang I or the chymase-selective substrate [pro,(11) D-Ala(12)] Ang I in the absence or the presence of the ACE inhibitor captopril, the serine protease inhibitor chymostatin, or the selective chymase inhibitor C41. Captopril only partially inhibited (by 33%) the response to Ang I. In the absence of captopril, C41 markedly reduced (by 44%) the response to Ang I, and this effect was identical to that of chymostatin. C41 also significantly reduced the response to Ang I in the presence of captopril, although this inhibitory effect was slightly less than that of captopril in combination with chymostatin. [Pro,(11)D-Ala(12)] Ang I induced potent contractions that were not affected by captopril but were abolished by chymostatin and markedly reduced by C41. In addition, we found that prior treatment of the patients with an ACE inhibitor did not affect the in vitro response to Ang I (in the absence or the presence of captopril) or to [Pro,(11)D-Ala(12)] Ang I. CONCLUSIONS: Our results reinforce the hypothesis that chymase is a major serine protease implicated in the ACE-independent production of Ang II in human arteries.

Endothelin antagonism in experimental ischemic heart failure: hemodynamic, structural and neurohumoral effects.

Heart failure is characterized both by an activation of the endothelin system and an increased vasoconstrictor contractile response to the peptide. Given its pharmacological profile, it is likely that endothelin (ET-1) plays a deleterious role in the development of heart failure, and that blockers of the endothelin system are beneficial in this disease. Indeed, in rats with heart failure, ET(A) and dual ET(A)-ET(B) receptor antagonists reduce arterial pressure as well as left ventricular end diastolic pressure. The same antagonists also prevent the degradation of left ventricular function, as evidenced by the increased left ventricular fractional shortening and wall thickening. ET(A) and ET(A)-ET(B) antagonists also reduce LV dilatation and LV fibrosis, but do not affect LV hypertrophy. Moreover, comparison between selective ET(A) and combined ET(A)-ET(B) antagonists reveal no differences in terms of their effects on blood pressure, LV hemodynamics or remodeling. However, only combined ET(A)-ET(B) antagonists significantly decreased heart rate. ET(B) antagonists alone do not affect blood pressure or LV hemodynamics, but reduce LV fibrosis. With regard to survival, we have shown that long term treatment with the dual ET(A)-ET(B) antagonist bosentan increased survival to the same extent as an angiotensin converting enzyme inhibitor. However, the effect of selective ET(A) antagonists on survival is more controversial, since we found that the non-peptide ET(A) antagonists LU 135252 did not affect survival of rats with myocardial infarction, while others have shown that the peptide ET(A) antagonist BQ-123 increased survival in the same model. These conflicting data regarding the efficacy of selective ET(A) vs dual ET(A)-ET(B) blockade points out the need for controlled long term studies comparing the effects of theses two pharmacological approaches on survival.