Biomedical subjects

M Clozel

Publications and source records attributed to M Clozel.

At least 73 records · Page 4Linked to original sources

PubMed1993

Relationship between tissue factor expression and deposition of fibrin, platelets, and leukocytes on cultured endothelial cells under venous blood flow conditions.

Endothelial cell-mediated coagulation and leukocyte adhesion are processes that might be connected by the generation of thrombin. To examine the interaction of procoagulant and proadhesive activity, cultures of endothelial cells were stimulated with tumor necrosis factor-alpha, which resulted in the surface expression of tissue factor. Subsequent exposure to human nonanticoagulated blood at a shear rate of 100 s-1 in a parallel plate perfusion device led to the deposition of polymerized fibrin, which covered 63% of the endothelial surface. In addition, numerous platelet aggregates (71 per 10 mm cross-section) and leukocytes (53 +/- 6/mm2) were deposited on stimulated endothelial cells, whereas no fibrin and only a few platelet aggregates (4 +/- 1 per 10 mm cross-section) and leukocytes (6 +/- 1/mm2) were detected on control cells. A significant portion of the adherent leukocytes bound to fibrin and platelets. However, when the deposition of fibrin and platelet aggregates was inhibited with the anti-tissue factor antibody HTFI-7B8 by 100% and 86%, respectively, leukocyte adherence remained unchanged (68 +/- 6/mm2). This indicated that leukocytes could efficiently adhere to endothelial cells through direct cell-cell contact independent of both thrombin and deposited fibrin. Moreover, this direct adhesion of leukocytes to the endothelial surface was reduced twofold to threefold when fibrin deposition occurred. These data suggest a relationship between endothelial procoagulant and proadhesive properties in that tissue factor-initiated coagulation may contribute to leukocyte adhesion through the formation of an adhesive fibrin/platelet meshwork but concurrently prevents the adhesive endothelial surface to bind leukocytes at its full capacity.

Antigens, CD↗

PubMed1993

Influence of congestive heart failure on endothelin levels and receptors in rabbits.

Congestive heart failure, both in man and in animals is associated with an increased plasma level of endothelin. To investigate further the potential role of the endothelin system, we designed a study to determine the effect of experimental congestive heart failure (CHF) on plasma and tissue immunoreactive-endothelin (irET) and on the density and affinity of endothelin-1 receptors in the heart and kidney. For this purpose, CHF was induced in rabbits by combined aortic valvular insufficiency and stenosis. When CHF was established, plasma and tissue irET levels were measured by radioimmunoassay and density and affinity of endothelin-1 receptors were measured by binding assay on tissue homogenates. Compared to control rabbits, plasma irET was significantly elevated in rabbits with CHF [1.04 +/- 0.15 vs. 0.04 +/- 0.01 fmol/ml, P < 0.001]. Tissue irET concentrations in ventricles and kidney were roughly 4 orders of magnitude higher than plasma concentrations. CHF decreased the tissue irET levels in left ventricle and kidney by 32 and 46%, respectively (P < 0.01), whereas CHF increased it by 58% in the right ventricle (P < 0.005). The density of ET-1 receptors was decreased in the right and left ventricles and in kidneys by 26, 36, and 61%, respectively (P < 0.05). Receptor affinity remained unchanged in response to CHF in both ventricles, whereas it increased in kidney [Kd (pM); 154 +/- 17 vs. 99 +/- 9, P < 0.01]. Thus, this study demonstrates that experimental CHF is not only characterized by elevated plasma irET levels but also by a decrease in tissue irET concentrations in the left ventricle and kidney, and by a down-regulation of ET-1 receptors both in the heart and kidney. Functional consequences of these changes need to be determined.

Animals↗

PubMed1993

BQ-123, a peptidic endothelin ETA receptor antagonist, prevents the early cerebral vasospasm following subarachnoid hemorrhage after intracisternal but not intravenous injection.

The aim of this study was to evaluate the role of endothelin and endothelin ETA receptor in the early cerebral vasoconstriction following subarachnoid hemorrhage (SAH) in the rat. SAH induced by injection of autologous blood in the cisterna magna reduced by 22 to 38% cerebral blood flow (CBF) measured with radioactive microspheres at 30, 60 and 120 min after SAH. The cyclic pentapeptide BQ-123, a selective antagonist of the ETA receptor, injected intravenously (3 mg/kg) had no effect on this decrease in CBF. However, intracisternal BQ-123 (10 nmol) completely prevented the decrease in CBF at 60 and 120 min after SAH. These results suggest that BQ-123 does not cross the blood-brain barrier, but demonstrate that endothelin acting on ETA receptor plays a role in the pathogenesis of cerebral vasoconstriction in this rat model of SAH.

Animals↗

PubMed1993

Temporal evolution of endothelial dysfunction in a rat model of chronic heart failure.

OBJECTIVES: The goal of this study was to investigate the evolution of endothelial dysfunction and plasma renin activity in a rat model of heart failure. BACKGROUND: Endothelial dysfunction has been demonstrated in heart failure and may play a significant role in this pathophysiologic process. Studies have also suggested a physiologic interaction between the renin-angiotensin system and endothelium-derived relaxing factor. However, the evolution of endothelial dysfunction and plasma renin activity in heart failure has not been studied to date. METHODS: Endothelium-dependent and -independent relaxations were studied at 1, 4 and 16 weeks after coronary artery ligation in a rat model of heart failure. Thoracic aortic rings were placed in isolated organ baths and acetylcholine and sodium nitroprusside concentration response curves were generated. Plasma renin activity was assessed at each time point. RESULTS: Aortic rings from rats with heart failure demonstrated no evidence of endothelial dysfunction at week 1, although progressive rightward shifts in the acetylcholine curves and decreasing maximal relaxation over time compared with findings in sham-operated control rats were evident at weeks 4 and 16. The sodium nitroprusside curves were not different between rats with heart failure and sham-operated rats. Plasma renin activity was elevated at week 1 and progressively increased through week 16, even though it correlated poorly with endothelial dysfunction. CONCLUSIONS: This study suggests that endothelial dysfunction in heart failure is a progressive time-dependent process that probably plays a minor role early in heart failure. Although plasma renin activity increased significantly in rats with heart failure, it was poorly predictive of endothelial dysfunction.

Acetylcholine↗

PubMed1993

ACE inhibition and the vascular intima in hypertension.

Both the function and the morphology of the vascular intima are altered during hypertension. In spontaneously hypertensive rats, endothelium-dependent relaxation is decreased, and the subendothelium becomes infiltrated with monocyte macrophages. It is not known if these two features are secondary to high blood pressure and what their consequences are; however, both can be reversed by angiotensin-converting enzyme (ACE) inhibition. The present paper summarizes the effects of a chronic treatment with the ACE inhibitor cilazapril on endothelial function and subendothelial morphology in spontaneously hypertensive rats.

Animals↗

PubMed1993

In vivo pharmacology of Ro 46-2005, the first synthetic nonpeptide endothelin receptor antagonist: implications for endothelin physiology.

Ro 46-2005 is a small-molecular-weight nonpeptide antagonist of the endothelin (ET), ETA and ETB receptors, chemically derived from a class of compounds identified by systematic screening of chemicals. In vivo, Ro 46-2005 inhibited the depressor and, only at high doses (100 mg/kg i.v.) the pressor effect of ET-1. However, much lower doses (1 to 10 mg/kg i.v.) were sufficient to inhibit the pressor effect of the precursor big ET-1. As intravenous big ET-1 injection potentially reproduces better than ET-1 injection the physiological pattern of release of ET-1, we propose that intravenous big ET-1 should be used to evaluate the effects of antagonists on the constricting endothelin receptors.

Anesthesia↗

PubMed1993

Downregulation of endothelin receptors by autocrine production of endothelin-1.

The potent vasoconstrictor endothelin-1 (ET-1) is a paracrine, but also autocrine, factor for some types of cells. The goal of our study was to evaluate whether the receptor population in cells expressing endothelin receptor subtype A (rat mesangial cells) or endothelin receptor subtype B (human and rat endothelial cells) was affected by the autocrine production of ET-1. We therefore studied maximal binding capacity of 125I-labeled ET-1 in the presence or absence of the metalloprotease inhibitors phosphoramidon, which blocks the intracellular processing of Big ET-1 to ET-1, and thiorphan, which does not block this conversion. Phosphoramidon inhibited the release of ET-1 by human umbilical vein endothelial cells, rat aortic endothelial cells, and rat mesangial cells, and increased 1.4- to 17-fold the maximal binding capacity in the three types of cells. Thiorphan affected neither ET-1 release nor binding. The increase in receptor binding by phosphoramidon was associated with an increase in the functional effect of ET-1, as measured by arachidonic acid release in rat mesangial cells. We conclude that autocrine production of ET-1 decreases, either by binding or by downregulation, the number of binding sites available for ET-1 of paracrine or systemic sources. This aspect of modulation of the vasoconstrictor effect of endothelin should be considered in pathological situations or after endothelin-converting-enzyme inhibition.

Animals↗

PubMed1993

Effects of calcium channel blockade on the aortic intima in spontaneously hypertensive rats.

Hypertension is associated with an intimal dysfunction characterized by endothelium-dependent constriction to serotonin, decreased endothelium-dependent relaxation to acetylcholine, and a subendothelial infiltration of monocyte-macrophages. The goal of our study was to evaluate the effect of long-term calcium channel blockade with Ro 40-5967, a new long-acting calcium channel blocker, on these alterations in aortas of spontaneously hypertensive rats (SHR). Arterial blood pressure was decreased by Ro 40-5967. In aortas from Ro 40-5967-treated SHR, the serotonin ratio (maximal contraction to serotonin on rings with endothelium over maximal contraction on paired rings without endothelium) was reduced (1.14 +/- 0.10) compared with control SHR (1.72 +/- 0.12, P < .01) because of inhibition of maximal contraction in rings with endothelium. This effect of Ro 40-5967 was partially reversed by an inhibitor of nitric oxide (NO) synthase, NG-nitro-L-arginine-methyl ester, and partially inhibited in the presence of the thromboxane/prostaglandin H2 receptor antagonist AH 23848. Maximal relaxation to acetylcholine in rings with endothelium was increased by Ro 40-5967. In rings without endothelium, Ro 40-5967 treatment enhanced the sensitivity to sodium nitroprusside-induced relaxation. Cyclic GMP content, an indicator of NO release, was not increased in aortas from Ro 40-5967-treated SHR. Thus, improvement of endothelial function was probably achieved by facilitating the action of NO at the level of the smooth muscle cells and by reducing prostaglandin H2-induced constriction. Finally, the number of monocyte-macrophages in the subendothelium was decreased by Ro 40-5967. 40-5967.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1993

Protective effect of cilazapril on the cerebral circulation.

The goal of an antihypertensive treatment is to prevent "end-organ" damage. Cerebral vascular complications are among the most important because they are life threatening and can occur even at an early stage of the disease. Recently, it has been shown that cilazapril can decrease the mortality of stroke-prone rats, suggesting a decrease in the incidence of strokes, which occur spontaneously in these animals. The present article reviews the different functional and morphological changes that may explain the cerebral protective effects of cilazapril, such as the normalization of cerebral vascular reserve, decrease in the media, increase in the external diameter, and normalization of the mechanics and endothelial function of cerebral arterioles. In addition, the inhibition by cilazapril of injury-induced proliferation of smooth muscle cells and the infiltration of the endothelium by macrophages could prevent the development of atherosclerosis.

Animals↗

PubMed1992

The endothelin ETB receptor mediates both vasodilation and vasoconstriction in vivo.

It has been suggested that the endothelin (ET) ETB receptor could mediate endothelium-dependent vasodilation to ET-1 or ET-3, but its in vivo role is still largely unknown. We used sarafotoxin S6C, a selective agonist of the ETB receptor, to study the in vivo effects of ETB stimulation. SRTX S6C induced a transient decrease in blood pressure, followed by a long-lasting pressor response accompanied by a marked renal and mesenteric vasoconstriction. No constriction was observed in isolated mesenteric arteries in vitro, indicating that the in vivo vasoconstrictor effect is most likely indirect. The pressor effect of SRTX S6C was not dependent on central stimulation of ETB receptors and was not mediated by catecholamines from the adrenal medulla, prostanoids or ET-1.

Animals↗

PubMed1992

Protective effect of cilazapril on the cerebral circulation.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1991

Relative preservation of the responsiveness to endothelin-1 during reperfusion following renal ischemia in the rat.

Reperfusion after renal ischemia is characterized by a preglomerular vasoconstriction. As endothelin-1 (ET-1) is a potent preglomerular vasoconstrictor, we designed a study to investigate the role of ET-1 in postischemic renal vasoconstriction. Renal ischemia was induced by 45 min of left renal artery clamping in anesthetized rats. After ischemia, renal blood flow was restored to only 61 +/- 4% of its preischemic value. The sensitivity to exogenous ET-1 after renal ischemia was decreased, but much less than the sensitivity to angiotensin II, which almost lost its vasoconstrictor effect, and to norepinephrine, which became a vasodilator. In addition, the binding affinity of [125I]ET-1 in the kidney increased significantly after renal ischemia, despite no change in the density of binding sites. These findings may be in favor of a role of endogenous ET-1 in postischemic renal vasoconstriction.

Angiotensin II↗

PubMed1991

Endothelial dysfunction and subendothelial monocyte macrophages in hypertension. Effect of angiotensin converting enzyme inhibition.

Hypertension is associated with an impairment of endothelium-dependent relaxation. The angiotensin converting enzyme inhibitors captopril and cilazapril can prevent this endothelial dysfunction. We recently observed that long-term treatment with cilazapril could also prevent subendothelial infiltration by mononuclear cells in spontaneously hypertensive rats. This prompted us to examine whether, in spontaneously hypertensive rats, endothelial dysfunction and subendothelial infiltration by mononuclear cells are associated. These cells were characterized as monocyte macrophages. Infiltration by monocyte macrophages was quantified by morphometry. Endothelial function was estimated by calculating serotonin ratio (maximal contraction to serotonin on isolated arterial rings with endothelium over maximal contraction on paired rings without endothelium). The regional distribution of endothelial dysfunction and subendothelial monocyte macrophages was similar. Both were maximal in the carotid artery, less in the aorta, and nonexistent in the renal artery. A 2-week treatment with cilazapril decreased both endothelial dysfunction (serotonin ratio decreased by 32%) and the number of subendothelial monocyte macrophages in the aorta, which decreased by 38%. We conclude that in spontaneously hypertensive rats, endothelial dysfunction and subendothelial monocyte macrophage infiltration are associated and that cilazapril can decrease both. The observation that angiotensin converting enzyme inhibitors affect subendothelial accumulation of monocyte macrophage may lead to a better understanding of the mechanism of action of this class of drugs.

Acetylcholine↗

PubMed1991

Mechanism of action of angiotensin converting enzyme inhibitors on endothelial function in hypertension.

Hypertension is associated with an endothelial dysfunction characterized by an increased endothelium-dependent contraction and a decreased endothelium-dependent relaxation. Angiotensin converting enzyme (ACE) inhibition with cilazapril or captopril can remarkably improve the endothelial function in spontaneously hypertensive rats (SHRs). The goal of the present study was to investigate whether ACE inhibitors were acting by decreasing endothelium-dependent contraction or by increasing endothelium-dependent relaxation. Endothelial function was estimated by calculating the ratio of maximal contraction to serotonin on isolated aortic rings with endothelium to maximal contraction on paired rings without endothelium, termed the serotonin ratio. The serotonin ratio was greater than 1 in SHRs, indicating the release of a vasoconstrictor substance by the endothelium. This substance was identified as prostaglandin (PG) H2, because the serotonin ratio was significantly decreased by thromboxane (TX) A2/PGH2 receptor antagonists but not by TXA2 synthetase inhibitors. Two weeks of treatment of SHRs with cilazapril led to a marked decrease in the serotonin ratio, although acute administration of cilazaprilat was without any effect. However, after 2 weeks of treatment, the serotonin ratio still could be lowered further by TXA2/PGH2 receptor antagonists, indicating that cilazapril did not act by inhibition of PGH2 synthesis. In contrast, the effect of a 4-week treatment with cilazapril could be completely reversed by inhibiting the action of endothelium-derived relaxing factor with methylene blue. The same result was found after treatment with captopril. We speculate that ACE inhibitors improve endothelial function in SHRs not by inhibiting the synthesis of PGH2 but by increasing the release or the action of endothelium-derived relaxing factor.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1990

Effects of angiotensin converting enzyme inhibitors and of hydralazine on endothelial function in hypertensive rats.

The function of the endothelium is impaired in hypertension. In spontaneously hypertensive rats (SHR), acetylcholine-induced relaxation is decreased and serotonin-induced constriction is increased. The goal of our study was to evaluate the effect of a long-term treatment with cilazapril, a new angiotensin converting enzyme inhibitor, or hydralazine, a vasodilator, on the endothelium-dependent responses in aorta of SHR. Wistar-Kyoto rats were used as normotensive reference. Isolated aortic rings with or without endothelium were suspended in organ chambers. The rings with intact endothelium were contracted with norepinephrine. Acetylcholine-induced relaxation was markedly enhanced by cilazapril treatment. The tension achieved at maximal relaxation was 8 +/- 4% of norepinephrine contraction in the cilazapril-treated SHR versus 55 +/- 5% in the untreated SHR (p less than 0.001). Hydralazine had no significant effect. The effect of serotonin was also markedly modified by cilazapril. In untreated SHR, serotonin induced the release of a vasoconstrictor substance by the endothelium as assessed by the ratio of maximal tension induced by serotonin in rings with endothelium over maximal tension in rings without endothelium, which was greater than 1. This ratio was reversed in cilazapril-treated SHR but not in hydralazine-treated SHR. Captopril had effects similar to cilazapril. Finally, evaluation of carotid arteries showed that cilazapril also prevented morphological changes of the intima in SHR (i.e., infiltration by mononuclear cells). We conclude that angiotensin converting enzyme inhibitors prevent the functional and morphological alterations in endothelium that are found in hypertension and speculate that this action might participate in their antihypertensive effect.

Acetylcholine↗

PubMed1989

Procoagulant activity of endotoxin-treated human endothelial cells exposed to native human flowing blood.

It has been reported that cultured endothelial cells become procoagulant when exposed to endotoxin. This prompted us to investigate whether human endothelial cells treated with endotoxin could promote the generation of fibrin when exposed to human flowing blood. For this purpose we used a parallel-plate perfusion chamber in which confluent cultured endothelial cells from human umbilical veins were exposed for five minutes to directly drawn human nonanticoagulated blood, at wall shear rates of 100, 650, and 2600 sec-1. Fibrin deposition was assessed by morphometry. No fibrin deposition occurred on normal endothelial cells. In contrast, cells incubated with endotoxin for 4 or 18 hours induced fibrin deposition, but only at a shear rate of 100 sec-1. Since some extracellular matrix was exposed between the cells, we investigated whether extracellular matrix played a role in fibrin formation. When the endothelial cells incubated or not with endotoxin were removed by EDTA, the exposed extracellular matrix perfused with blood at 100 sec-1 supported platelet and fibrin deposition in both cases. This suggests that the effect of endotoxin on endothelial cells was not due to extracellular matrix alteration but only to cellular activation or secretion of procoagulant substances. We conclude that human endothelial cells treated with endotoxin can trigger fibrin formation and deposition at their surface when exposed to flowing blood at low shear rate.

Blood Coagulation↗

PubMed1989

Specific receptors for endothelin on membranes from human placenta. Characterization and use in a binding assay.

High-affinity binding sites for endothelin have been found in a human placenta membrane preparation. 125I-endothelin bound to placenta membranes at 20 degrees C with an association half-time of 30 min, whereas the binding was only slowly reversed with a dissociation half-time of 250 min. In saturation experiments, a single class of high-affinity binding sites was identified with an apparent dissociation constant (KD) of 24 pM and a maximal density of 240 fmol per mg of protein. The binding of 125I-endothelin was half-maximally inhibited by cold endothelin at a concentration (IC50) of 140 pM. In contrast, no inhibition was found at 10(-4) M for a variety of vasoactive peptides such as angiotensin II, vasopressin, neuropeptide Y, substance P, CGRP, bradykinin, leucine enkephalin or dynorphin A. Similarly, the binding was modulated neither by the calcium channel blockers nifedipine, verapamil or diltiazem, nor by the calcium channel agonist Bay k 8644. There was also no effect with the structurally-related bee venom apamin. Using this membrane preparation, endothelin-like activity could be measured in the medium of cultured human endothelial cells by competition binding technique.

Binding, Competitive↗

PubMed1989

Endothelin sensitivity and receptor binding in the aorta of spontaneously hypertensive rats.

Endothelin is a very potent vasoconstrictor peptide secreted by endothelial cells. The aim of this study was to determine whether sensitivity to endothelin was greater in isolated aortic rings of spontaneously hypertensive rats (SHR) than in those of normotensive Wistar-Kyoto rats (WKY) and, if so, whether this was due to an increased binding affinity. Adult SHR were more sensitive to endothelin than age-matched WKY, but the maximal tension developed in response to endothelin was significantly lower in SHR than in WKY. The binding affinity of 125I-endothelin was similar in SHR [apparent dissociation constant (Kd) = 76 +/- 11 pmol/l, n = 5] and WKY (Kd = 60 +/- 10 pmol/l, n = 5). However, the density of endothelin binding sites in aortic smooth muscle cells in culture was significantly higher in WKY (2976 +/- 374 receptors per cell) than in SHR (1278 +/- 299 receptors per cell, P less than 0.01). The hyper-responsiveness of a large capacitance vessel in SHR seems relatively specific for endothelin, since the effects of norepinephrine were not significantly different between adult SHR and WKY. This hyper-responsiveness cannot be explained by an alteration in the affinity of endothelin for its receptor. However, a down-regulation of the number of binding sites could explain the lower maximal response to endothelin in SHR.

Animals↗