Role of the recombinant non-integrin platelet collagen receptor P65 on platelet activation induced by convulxin

Convulxin (Cvx) isolated from Crotalus durissus terrificus venom selectively binds with a high affinity to platelets and induces platelet aggregation by a mechanism that resembles that induced by collagen. Taking advantage that P65 has been recently cloned and expressed as a recombinant soluble protein (rec-P65), we examined the role of this non-integrin collagen receptor in platelet activation induced by Cvx. Rec-P65 blocked platelet adhesion to collagen-coated surfaces and inhibited platelet aggregation and ATP secretion induced by type I collagen. On the other hand, rec-P65 did not inhibit platelet aggregation and ATP secretion induced by Cvx, and it did not affect platelet adhesion to Cvx. In addition, ligand-blotting indicated that the Cvx binding to the collagen receptor GPVI was preserved in the presence of rec-P65. These observations indicate that P65 does not play a significant role in platelet activation by Cvx; in contrast, platelet response to collagen involves multiple receptors.     

Cognac polyphenolic compounds increase bradykinin-induced nitric oxide production in endothelial cells

We recently reported that in vitro Cognac polyphenolic compounds (CPC) induce NO-dependent vasorelaxant effects and stimulate cardiac function. In the present study, we aim to investigate the effect of CPC on both nitric oxide (NO) and superoxide anions (O(2)(-)) production in cultured human endothelial cells. In addition, its effect on the bradykinin (BK)-induced NO production was also tested. The role and sources of O(2)(-) in the concomitant effect of BK plus CPC were pharmacologically determined. NO and O(2)(-) signals were measured using electron paramagnetic resonance technique using specific spin trappings. Both, CPC and BK induced an increase in NO production in human endothelial cells. The combination of both further enhanced NO release. The capacity of CPC plus BK to increase NO signal was blunted by the NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester, and was enhanced in the presence either of superoxide dismutase or catalase. Moreover, CPC plus BK response was greater after inhibition of either NADPH oxidase by apocynin or xanthine oxidase by allopurinol but it was not affected by rotenone. CPC did not affect O(2)(-) level either alone or after its increase upon lipopolysaccharide treatment. Finally, the capacity of BK alone to increase NO was enhanced either by apocynin or allopurinol. Altogether, these data demonstrate that CPC is able to directly increase NO production without affecting O(2)(-) and enhances the BK-induced NO production in human endothelial cells. The data highlight the ability of BK to stimulate not only NADPH oxidase- but also xanthine oxidase-inhibitor sensitive mechanisms that reduce its efficiency in increasing NO either alone or in the presence of CPC. These results bring pharmacological evidence for vascular protection by CPC via its potentiating effect of BK response in terms of endothelial NO release.     

Effects of novel plant antioxidants on platelet superoxide production and aggregation in atherosclerosis.

Superoxide anion is produced in human platelets predominantly by Nox2-dependent NADPH oxidases. In vitro experiments have shown that it might play a role in modulating platelet functions. The relationship between platelet superoxide production and aggregation remains poorly defined. Accordingly, we aimed to study superoxide production and aggregation in platelets from subjects with significant cardiovascular risk factors (hypertension, hypercholesterolemia, smoking and diabetes mellitus) and from control individuals. Moreover, we studied the effects of novel polyphenol-rich extracts of Aronia melanocarpa (chokeberry) berries on platelet function in vitro. Superoxide production was significantly increased in patients with cardiovascular risk profile when compared to controls, while platelet aggregation in response to either collagen or thrombin were borderline higher, and did not reach statistical significance. Interestingly, no relationship was observed between platelet aggregation ex vivo and platelet superoxide production in either of studied groups. No correlation was found between endothelial function (measured by FMD) and platelet aggregation ex vivo either. Polyphenol-rich extracts of A. melanocarpa berries caused a significant concentration dependent decrease in superoxide production only in patients with cardiovascular risk factors, while no effect was observed in the control group. A. melanocarpa extracts abolished the difference in superoxide production between risk factor patients and controls. A. melanocarpa extracts exerted significant concentration dependent anti-aggregatory effects in both studied groups, which indicated that these effects may be independent of it's ability to modulate superoxide production. The anti-aggregatory effects of chokeberry extracts were similar irrespective of aggregation inducing agent (collagen or thrombin). Moreover, they appear to be independent of platelet NO release as NOS inhibition by L-NAME did not lead to their abrogation.     

Platelet aggregation may not be a prerequisite for collagen-stimulated platelet generation of nitric oxide

By determining the sum of the supernatant concentrations of nitrite and nitrate the stimulated generation of nitric oxide (NO) by human washed platelets induced by a range of fibrillar collagen concentrations (0.0156-25 microg ml(-1)) was investigated. Platelet serotonin (5-hydroxytryptamine, 5-HT) efflux and platelet aggregation were also measured. Under resting conditions (0 microg ml(-1) collagen) platelet NO release was equivalent to 1.06+/-0.17 nmol per 10(8) platelets. Maximal NO release, equivalent to 2.1+/-0. 37 nmol per 10(8) platelets, was observed with only 0.0625 microg ml(-1) collagen (P<0.02, stimulated vs. resting release), higher collagen concentrations producing no further increases in platelet NO output. By contrast, maximal platelet aggregation and 5-HT efflux did not occur until collagen concentrations of 2.5 microg ml(-1) and 10-25 microg ml-1), respectively, had been achieved. L-NAME (1 mmol l(-1)) and L-NMMA (1 mmol l(-1)) inhibited stimulated platelet NO generation by 78+/-6% and 72%, respectively. Contrasting with fibrillar collagen, fibrillar beta-amyloid protein had no effect on platelet NO generation, or on 5-HT efflux or aggregation. These data perhaps indicate that NO generation by human platelets is stimulated by concentrations of fibrillar collagen insufficient to elicit an aggregatory response. Such a mechanism could operate in vivo to inhibit platelet aggregation which might otherwise be induced by low concentrations of circulating agonists.     

Reactivation of peroxisome proliferator-activated receptor alpha is associated with contractile dysfunction in hypertrophied rat heart

In pressure overload-induced hypertrophy, the heart increases its reliance on glucose as a fuel while decreasing fatty acid oxidation. A key regulator of this substrate switching in the hypertrophied heart is peroxisome proliferator-activated receptor alpha (PPARalpha). We tested the hypothesis that down-regulation of PPARalpha is an essential component of cardiac hypertrophy at the levels of increased mass, gene expression, and metabolism by pharmacologically reactivating PPARalpha. Pressure overload (induced by constriction of the ascending aorta for 7 days in rats) resulted in cardiac hypertrophy, increased expression of fetal genes (atrial natriuretic factor and skeletal alpha-actin), decreased expression of PPARalpha and PPARalpha-regulated genes (medium chain acyl-CoA dehydrogenase and pyruvate dehydrogenase kinase 4), and caused substrate switching (measured ex vivo in the isolated working heart preparation). Treatment of rats with the specific PPARalpha agonist WY-14,643 (8 days) did not affect the trophic response or atrial natriuretic factor induction to pressure overload. However, PPARalpha activation blocked skeletal alpha-actin induction, reversed the down-regulation of measured PPARalpha-regulated genes in the hypertrophied heart, and prevented substrate switching. This PPARalpha reactivation concomitantly resulted in severe depression of cardiac power and efficiency in the hypertrophied heart (measured ex vivo). Thus, PPARalpha down-regulation is essential for the maintenance of contractile function of the hypertrophied heart.     

Effects of a dammarane-type saponin,ginsenoside Rd,in nicotine-induced vascular endothelial injury

BackgroundPanax notoginseng (Burk.) F.H. Chen is a traditional medicinal plant widely used to prevent and treat cardiovascular diseases. Ginsenoside Rd (GRd) is a major bioactive component of P. notoginseng, but specific effects on cardiovascular disease-related pathogenic processes are rarely studied, especially vascular endothelial injury.PurposeThis study investigated the potential protective efficacy of GRd against nicotine-induced vascular endothelial cell injury, disruption of vascular nitric oxide (NO) signaling, aberrant endothelium–monocyte adhesion, platelet aggregation, and vasoconstriction.Study design/MethodsVascular endothelial injury and functional disruption were investigated in cultured human umbilical vein endothelial cells (HUVECs) by biochemical assays for nitric oxide (NO) and angiotensin II (Ang II), immunofluorescence (IF) and western blotting for expression analyses of apoptosis- related proteins, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), Ang II type receptor 1 (AGTR1), toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88), and nuclear factor-kappa B (NF-κB). In addition, vascular protection by GRd was examined in nicotine-administered Sprague-Dawley (SD) rats by serum NO and Ang II assays, and by hematoxylin-eosin (HE) and immunostaining of aorta. We also examined effects of GRd on monocyte (THP-1 cells) adhesion assays, adenosine diphosphate (ADP)-induced platelet aggregation, and phenylephrine (PE)-induced vasoconstriction of isolated rat aortic rings.ResultsIn HUVECs, nicotine significantly suppressed NO production, enhanced Ang II production, downregulated eNOS expression, and upregulated expression levels of AGTR1, TLR4, MyD88, NF-κB, iNOS, Bax/Bcl-2 ratio, cleaved caspase-3, and cytochrome c (cyt c). All of these changes were significantly reversed by GRd. In rats, oral GRd reversed the reduction NO and enhanced Ang II production in serum induced by nicotine administration, and HE staining revealed protection of aortic endothelial cells. In addition, GRd reversed nicotine-mediated enhancement of HUVECs-monocyte adhesion, inhibited ADP-induced platelet aggregation and PE-induced vasoconstriction.ConclusionGRd may prevent nicotine-induced cardiovascular diseases by preserving normal vascular endothelial NO signaling, suppressing platelet aggregation and vasoconstriction, and by preventing endothelial cell–monocyte adhesion.     

The effects of oxidation products of arachidonic acid and n3 fatty acids on vascular and platelet function

15-F?(t)-isoprostane (15-F?(t)-IsoP), an oxidation product of arachidonic acid (AA), affects vascular and platelet function; however, the bioactivity of other fatty acids oxidation products is unknown. This paper studied rat aortic vascular reactivity and human platelet aggregation in response to 14 oxidation products of AA, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and α-linolenic acid (ALA) compared with 15-F?(t)-IsoP. It also compared the F?(t)-IsoPs profile in human platelets. EPA-derived 15-F?(t)-IsoP constricted rat aorta less than 15-F?(t)-IsoP, but none of the other oxidation products affected vascular reactivity. Only 15-F?(t)-IsoP (10?? M) directly affected platelet aggregation. 15-F?(t)-IsoP, ent-16-F?-phytoprostane (from ALA) and isofurans A and B (from AA) inhibited reversible aggregation to U46619. Unlike plasma, the platelet profile of F?-IsoP showed that 8-F(2t)-IsoP were higher than 15-F?(t)-IsoP. Unlike 15-F?(t)-IsoP, the test compounds derived from fatty acids oxidation did not affect vascular or platelet function. Elevated platelet 8-F?(t)-IsoP could limit 15-F?(t)-IsoP-induced aggregation under conditions of oxidant stress.     

Pannexin1 Single Nucleotide Polymorphism and Platelet Reactivity in a Cohort of Cardiovascular Patients

Pannexin1 (Panx1), a membrane channel-forming protein permitting the passage of small-sized molecules, such as ATP, is expressed in human platelets. Recently, we showed that inhibiting Panx1 affects collagen-induced platelet aggregation but not aggregation triggered by other agonists. We also found that a single nucleotide polymorphism (SNP; rs1138800) in the Panx1 gene encoded for a gain-of-function channel (Panx1-400C) and was associated with enhanced collagen-induced platelet reactivity. Here, we assessed the association of this SNP with platelet reactivity in a cohort of 758 stable cardiovascular patients from the ADRIE study treated with aspirin and/or clopidogrel. We found that presence of the Panx1-400C allele was not associated with platelet reactivity in stable cardiovascular patients, irrespective of the platelet aggregation agonist used (collagen, ADP or arachidonic acid) or the anti-platelet drug regimen. Moreover, the Panx1-400A?>?C SNP did also not affect the re-occurrence of cardiac ischemic events in the same stable cardiovascular patient cohort.     

Small molecular weight heat shock-related protein, HSP20, exhibits an anti-platelet activity by inhibiting receptor-mediated calcium influx

We have shown that Hsp20, one of small molecular weight heat shock protein, which is present at a high concentration both in vascular smooth muscle cells and in circulating blood in patient with vascular disease, strongly inhibits platelet aggregation in vitro and ex vivo. To clarify the mechanism, we investigated the effect of Hsp20 on free calcium concentration in human platelet cytoplasm using fura 2. Hsp20 inhibited thrombin-induced calcium influx without affecting calcium release from intracellular calcium stores. The degree of inhibition is well-correlated with that of suppression of thrombin-induced platelet aggregation by this substance. Hsp20 also inhibited the elevation of cytoplasmic free calcium level triggered by collagen, but not that by A-23187. In contrast, Hsp28, another type of small molecular weight Hsp, failed to affect the cytoplasmic free calcium level. These findings suggest that Hsp20 inhibits the receptor-mediated calcium influx of platelets without affecting calcium release from intracellular calcium stores, leading to its anti-platelet activity.     

Catcholamine and nitric oxide systems as targets of chronic lead exposure in inducing selective functional impairment

Rats were exposed for ten months to 60 ppm of lead (Pb, as acetate) in drinking water to further assess cardiovascular effects of chronic Pb exposure. At the end of the treatment, mean blood Pb was 3.1+/-0.3 microg/dL in the control rats and 22.8+/-1.2 microg/dL in the Pb-exposed rats (means+/-SE, n=12 in each group); these values were not comparable to those of humans. Pb greatly increased plasma levels of noradrenaline (NA) and adrenaline (A), but not those of L-DOPA and dopamine; monoaminoxidase activity was augmented by Pb, mostly in the aorta and in the liver; the aorta, liver, heart and kidney showed discrete histopathological alterations in the Pb-exposed rats, in which plasma levels of nitric oxide (NO, determined as L-citrulline) were reduced. Pb was able to induce blood hypertension, resulting from increase of cardiac inotropism and, mostly, total peripheral resistance. These data were discussed also in relation to those obtained in our previous studies carried out in rats exposed to Pb in drinking water (15-60 ppm) for periods ranging from five to eighteen months. Pb appeared to increase both sympathetic nerve activity by central mechanisms (thus increasing plasma NA and A) and cyclic adenosine monophosphate (cAMP)-dependent availability of calcium ions (Ca++) for contractile mechanisms in the vascular and cardiac myocells (also through an increased vascular alpha2- and myocardial beta1-adrenoreceptor reactivity). The reduction of plasma NO, contributing to increase vascular resistance and cardiac inotropism, was explained as a result of actions of Pb on enzyme activities concerned with the kallikrein-kinin (KK) and renin-angiotensin-aldosterone (RAA) systems. It was concluded that chronic Pb exposure is able to affect selective neuroendocrine (i.e., catecholamine), au- tacoidal (i.e., KK and RAA) and transductional pathways (i.e., cAMP, NO, Ca++) involved in the cardiovascular function.     

Differential effects of nitric oxide on the activity of prostaglandin endoperoxide H synthase-1 and -2 in vascular endothelial cells

A number of studies have demonstrated that prostacyclin and nitric oxide (NO) regulate blood pressure, blood flow and platelet aggregation. In this paper, we have examined the possible relationship between NO and prostaglandin endoperoxide H synthase (PGHS)-1 and -2 activities in cultured bovine aortic endothelial cells. In the non-activated condition endothelial cells expressed PGHS-1 activity alone. When these cells were pretreated with aspirin to inactivate their PGHS-1 and then activated by serum and phorbol ester (TPA) for 6 h, the cells expressed PGHS-2 activity alone. The PGHS activity was assessed by the generation of 6-ketoprostaglandin F1alpha (6-ketoPGF1alpha), a stable metabolite of prostacyclin, after the treatment of these cells with arachidonic acid. The simultaneous addition of NOC-7, a NO donor, with arachidonic acid did not affect the production of 6-ketoPGF1alpha in PGHS-1 expressed cells, but attenuated it in PGHS-2-expressed cells. The inhibitory effect of NOC-7 on PGHS-2 activity was dose dependent, and the different effects of NOC-7 on the activities of PGHS isozymes were also observed in other NO donors. To confirm the different effect of NO on PGHS isozymes demonstrated in the cultured endothelial cells, we carried out an ex vivo perfusion assay in aorta isolated from normal and lipopolysaccharide (LPS)-treated rats. In the aortae isolated from normal rats, where dominant expression of PGHS-1 was expected, the NO donor did not affect the PGHS activity, while in aortae isolated from LPS-treated rats, where PGHS-2 was dominantly expressed, the NO donor dramatically inhibited the PGHS activity, suggesting that NO suppressed PGHS-2 activity alone. The inhibitory effect of NO on PGHS-2 activity was not mediated by cyclic GMP (cGMP), since (a) methylene blue, an inhibitor of soluble guanylate cyclase did not abolish the inhibitory effect of the NO donor on PGHS-2 activity, and (b) 8-Br-cGMP, a permeable cGMP analogue, failed to mimic the effect of NO donors. These data suggest that the effect of NO on prostacyclin production in endothelial cells was dependent on the expression rate of PGHS-1 and PGHS-2 in the cells.     

Hyperinsulinemic rats are normotensive but sensitized to angiotensin II

The effect of insulin on blood pressure (BP) is debated, and an involvement of an activated renin-angiotensin aldosterone system (RAAS) has been suggested. We studied the effect of chronic insulin infusion on telemetry BP and assessed sympathetic activity and dependence of the RAAS. Female Sprague-Dawley rats received insulin (2 units/day, INS group, n = 12) or insulin combined with losartan (30 mg.kg(-1).day(-1), INS+LOS group, n = 10), the angiotensin II receptor antagonist, for 6 wk. Losartan-treated (LOS group, n = 10) and untreated rats served as controls (n = 11). We used telemetry to measure BP and heart rate (HR), and acute ganglion blockade and air-jet stress to investigate possible control of BP by the sympathetic nervous system. In addition, we used myograph technique to study vascular function ex vivo. The INS and INS+LOS groups developed euglycemic hyperinsulinemia. Insulin did not affect BP but increased HR (27 beats/min on average). Ganglion blockade reduced mean arterial pressure (MAP) similarly in all groups. Air-jet stress did not increase sympathetic reactivity but rather revealed possible blunting of the stress response in hyperinsulinemia. Chronic losartan markedly reduced 24-h-MAP in the INS+LOS group (-38 +/- 1 mmHg P < 0.001) compared with the LOS group (-18 +/- 1 mmHg, P 相似文献   

Cedrelopsis grevei induced hypotension and improved endothelial vasodilatation through an increase of Cu/Zn SOD protein expression

This study was designed to investigate the cardiovascular consequences of oral administration of Cedrelopsis grevei (CG) in normotensive rats. Experiments were designed to investigate hemodynamic parameters in vivo as well as the consequences of CG treatment on the vasoconstriction response to norepinephrine and the vasorelaxant response to ACh ex vivo in isolated aortas and small mesenteric arteries (SMA). Treatment of male Wistar rats with 80 mg/kg CG for 4 wk induced a progressive decrease in systolic blood pressure. In the aorta, CG did not significantly alter the response to norepinephrine despite the participation of extraendothelial nitric oxide (NO)-induced hyporeactivity. In the SMA, contraction to norepinephrine was not modified by CG treatment even though it enhanced the participation of endothelial NO. Endothelium-dependent relaxation to ACh was increased in both the aorta and SMA from CG-treated rats. In the aorta from CG-treated rats, the mechanism involved superoxide dismutase (SOD)- and catalase-sensitive free radical production. The latter was associated with enhanced expression of Cu/Zn SOD and endothelial NO synthase. These results suggest that oral administration of CG produces a decrease in blood pressure in normotensive rats. This hemodynamic effect was associated with enhanced endothelium-dependent relaxation and an induction of Cu/Zn SOD and endothelial NO synthase expressions in the vessel wall. They also show subtle mechanisms that compensate for the increased participation of NO to maintain unchanged agonist-induced contractility. These data provide a pharmacological basis for the empirical use of CG against cardiovascular diseases.     

Downregulation of hypoxic vasoconstriction by chronic hypoxia in rabbits: effects of nitric oxide

Hypoxic pulmonary vasoconstriction (HPV) matches lung perfusion to ventilation for optimizing pulmonary gas exchange. Chronic alveolar hypoxia results in vascular remodeling and pulmonary hypertension. Previous studies have reported conflicting results of the effect of chronic alveolar hypoxia on pulmonary vasoreactivity and the contribution of nitric oxide (NO), which may be related to species and strain differences as well as to the duration of chronic hypoxia. Therefore, we investigated the impact of chronic hypoxia on HPV in rabbits, with a focus on lung NO synthesis. After exposure of the animals to normobaric hypoxia (10% O(2)) for 1 day to 10 wk, vascular reactivity was investigated in ex vivo perfused normoxic ventilated lungs. Chronic hypoxia induced right heart hypertrophy and increased normoxic vascular tone within weeks. The vasoconstrictor response to an acute hypoxic challenge was strongly downregulated within 5 days, whereas the vasoconstrictor response to the thromboxane mimetic U-46619 was maintained. The rapid downregulation of HPV was apparently not linked to changes in the lung vascular NO system, detectable in the exhaled gas and by pharmacological blockage of NO synthesis. Treatment of the animals with long-term inhaled NO reduced right heart hypertrophy and partially maintained the reactivity to acute hypoxia, without any impact on the endogenous NO system being noted. We conclude that chronic hypoxia causes rapid downregulation of acute HPV as a specific event, preceding the development of major pulmonary hypertension and being independent of the lung vascular NO system. Long-term NO inhalation partially maintains the strength of the hypoxic vasoconstrictor response.     

Evidence that a collagen derived octapeptide inhibits fibrinogen binding to platelets stimulated by collagen and not by ADP

A synthetic octapeptide derived from type III collagen which specifically inhibits the activation and aggregation of platelets by collagen without affecting their adhesion was assayed on the collagen and ADP dependent fibrinogen binding to platelets. With 20 micrograms/ml collagen, the octapeptide (6 mM) inhibited by 68% the fibrinogen binding: this inhibition was correlated (p less than 0.01) to a decrease in the velocity of aggregation, suggesting that the fibrinogen binding might influence this parameter. The octapeptide did not affect the ADP-induced platelet aggregation and fibrinogen binding. This indicates that the octapeptide does not inhibit the binding of fibrinogen to its receptor directly, but interferes with some step(s) preceding the collagen-induced expression of the fibrinogen receptor.     

Compensatory mechanisms influence hemostasis in setting of eNOS deficiency

The balance between thrombosis and hemorrhage is carefully regulated. Nitric oxide (NO) is an important mediator of these processes, as it prevents platelet adhesion to the endothelium and inhibits platelet recruitment. Although endothelial NO synthase (eNOS)-deficient mice have decreased vascular reactivity and mild hypertension, enhanced thrombosis in vivo has not been demonstrated. To determine the role of endogenous NO in hemostasis, a model of carotid arterial injury and thrombosis was performed using eNOS-deficient and wild-type mice. Paradoxically, the eNOS-deficient animals had a prolongation of time to occlusion compared with the wild-type mice (P < 0.001). Consistent with this finding, plasma markers suggesting enhanced fibrinolysis [tissue plasminogen activator (t-PA) activity and antigen and D-dimer levels] were significantly elevated in eNOS-deficient animals. Vascular tissue expression of t-PA and platelet activity levels were not altered. In endothelial cells, t-PA is stored in Weibel-Palade bodies, and exocytosis of these storage granules is inhibited by NO. Thus in the absence of NO, release of Weibel-Palade body contents (and t-PA) could be enhanced; this observation is also supported by increased von Willebrand factor levels observed in eNOS-deficient animals. In summary, although eNOS deficiency attenuates vascular reactivity and increases platelet recruitment, it is also associated with enhanced fibrinolysis due to lack of NO-dependent inhibition of Weibel-Palade body release. These processes highlight the complexity of NO-dependent regulation of vascular homeostasis. Such compensatory mechanisms may partially explain the lack of spontaneous thrombosis, minimally elevated baseline blood pressure, and normal life span that are seen in animals deficient in a pivotal regulator of vascular patency.     

Effect of salvianolic acids from Radix Salviae miltiorrhizae on regional cerebral blood flow and platelet aggregation in rats.

This study was conducted to observe the effect of salvianolic acids (SA) on regional cerebral blood flow (rCBF) in rats and on platelet aggregation in vitro and in vivo. Cerebral ischemia was produced in rats by occluding of the right middle cerebral artery, together with the right common carotid artery. rCBF was monitored by H2 clearance method with a tissue blood-flow meter. Platelet aggregation induced by collagen, ADP, and AA was measured in vitro and in vivo by platelet aggregometer. Doses of SA at 6 and 10 mg/kg body wt. (i.v.) improved rCBF in rats after ischemia, but had no obvious effect on normal rCBF. In vitro, SA inhibited significantly the platelet aggregation induced by collagen, ADP, and AA with IC50 values of 0.197, 2.22 and 3.29 x 10(3) mg/l, respectively. In vivo, doses of SA at 6 and 10 mg/kg body wt. inhibited significantly the platelet aggregation induced by collagen, and SA at 10 mg/kg body wt. inhibited remarkably platelet aggregation induced by ADP. The results suggest that SA could improve rCBF in the ischemic hemisphere and inhibit platelet aggregation in rats.     

Effects of prostacyclin analogue (carbacyclin) on the interaction of platelets with different collagen substrates. Inhibition of cAMP increase by collagens type I, III, and IV

We investigated the effects of a stable prostacyclin analogue, carbacyclin, on the interaction of platelets with collagen substrates differing in their ability to activate platelets: human collagens type I, III, IV and V (CI, CIII, CIV and CV), and commercial calf skin collagen type I (CSC). The total adhesion was measured using 51Cr-labelled platelets, and quantitative morphometry of adherent platelets was performed by scanning electron microscopy (SEM). Carbacyclin in the concentrations inducing a 10-fold rise in platelet cAMP did not affect the adhesion of platelets to weak substrates, CV and CSC, but reduced the adhesion to strong substrates, CIV (by 49%) and CI/CIII (by 78%), which stimulated massive spreading and formation of surface-bound aggregates respectively. Carbacyclin inhibited all morphological manifestations of platelet activation associated with adhesion: conversion of native discoid platelets to spherical ones on CSC; massive spreading on CIV; and aggregate formation on CI/CIII. Massive spreading and aggregation on a weak substrate (CSC) stimulated by arachidonic acid and thrombin was also inhibited by carbacyclin. Under the same concentration of agonists aggregation of platelets was more sensitive to the action of carbacyclin, than spreading. Strong collagen substrates CI, CIII and CIV, but not CV and gelatin, inhibited the carbacyclin-induced rise in platelet cAMP.     

Chronic intermittent hypoxia increases infarction in the isolated rat heart.

Coronary heart disease is frequently associated with obstructive sleep apnea syndrome and treating obstructive sleep apnea appears to significantly improve the outcome in coronary heart disease. Thus we have developed a rat model of chronic intermittent hypoxia (IH) to study the influence of this condition on myocardial ischemia-reperfusion tolerance and on functional vascular reactivity. Wistar male rats were divided in three experimental groups (n = 12 each) subjected to chronic IH (IH group), normoxia (N group), or control conditions (control group). IH consisted of repetitive cycles of 1 min (40 s with inspired O(2) fraction 5% followed by 20 s normoxia) and was applied for 8 h during daytime, for 35 days. Normoxic cycles were applied in the same conditions, inspired O(2) fraction remaining constant at 21%. On day 36, mean arterial blood pressure (MABP) was measured before isolated hearts were submitted to an ischemia-reperfusion protocol. The thoracic aorta and left carotid artery were also excised for functional reactivity studies. MABP was not significantly different between the three experimental groups. Infarct sizes (in percent of ventricles) were significantly higher in IH group (46.9 +/- 3.6%) compared with N (26.1 +/- 2.8%) and control (21.7 +/- 2.1%) groups. Vascular smooth muscle function was similar in aorta and carotid arteries from all groups. The endothelium-dependent relaxation in response to acetylcholine was also similar in aorta and carotid arteries from all groups. Chronic IH increased heart sensitivity to infarction, independently of a significant increase in MABP, and did not affect vascular reactivity of aorta and carotid arteries.     

内源性一氧化氮在高血压心肌肥厚中的作用

目的和方法：本实验用Ｌ精氨酸和一氧化氮合酶（ＮＯＳ）抑制剂ＬＮＡＭＥ观察内源性一氧化氮（ＮＯ）在高血压性心肌肥厚中的作用。结果：腹主动脉缩窄引起大鼠动脉血压显著升高,左心室重量／体重比值显著增加,左心室ＮＯ含量显著下降;Ｌ精氨酸不影响主动脉缩窄大鼠动脉血压,但减轻左心室重量／体重比值,明显升高左心室ＮＯ含量,加入ＬＮＡＭＥ可消除Ｌ精氨酸的上述作用;主动脉缩窄大鼠给予ＬＮＡＭＥ,动脉血压和左心室／体重比值并没有进一步增加;假手术大鼠给予ＬＮＡＭＥ,血压明显升高,左心室重量／体重比值轻度增加;主动脉缩窄大鼠不论是服用Ｌ精氨酸还是ＬＮＡＭＥ,左心室ｃＧＭＰ含量都明显增加。结论：口服Ｌ精氨酸可减轻主动脉缩窄大鼠心肌肥厚但不影响动脉血压,此作用可能是通过Ｌ精氨酸ＮＯ途径实现的,与ｃＧＭＰ机制无关。