Angiotensin II Triggers NLRP3 Inflammasome Activation by a Ca2+ Signaling-Dependent Pathway in Rat Cardiac Fibroblast Ang-II by a Ca2+-Dependent Mechanism Triggers NLRP3 Inflammasome in CF

Angiotensin II (Ang-II) is a widely studied hypertensive, profibrotic, and pro-inflammatory peptide. In the heart, cardiac fibroblasts (CF) express type 1 angiotensin II receptors (AT1R), Toll-like receptor-4 (TLR4), and the NLRP3 inflammasome complex, which play important roles in pro-inflammatory processes. When activated, the NLRP3 inflammasome triggers proteolytic cleavage of pro-IL-1, resulting in its activation. However, in CF the mechanism by which Ang-II assembles and activates the NLRP3 inflammasome remains not fully known. To elucidate this important point, we stimulated TLR4 receptors in CF and evaluated the signaling pathways by which Ang-II triggers the assembly and activity. In cultured rat CF, pro-IL-1β levels, NLRP3, ASC, and caspase-1 expression levels were determined by Western blot. NLRP3 inflammasome complex assembly was analyzed by immunocytochemistry, whereas by ELISA, we analyzed NLRP3 inflammasome activity and [Formula: see text] release. In CF, Ang-II triggered NLRP3 inflammasome assembly and caspase-1 activity; and in LPS-pretreated CF, Ang-II also triggered [Formula: see text] secretion. These effects were blocked by losartan (AT1R antagonist), U73221 (PLC inhibitor), 2-APB (IP3R antagonist), and BAPTA-AM (Ca²⁺ chelator) indicating that the AT1R/PLC/IP3R/Ca²⁺ pathway is involved. Finally, bafilomycin A1 prevented Ang-II-induced [Formula: see text] secretion, indicating that a non-classical protein secretion mechanism is involved. These findings suggest that in CF, Ang-II by a Ca²⁺-dependent mechanism triggers NLRP3 inflammasome assembly and activation leading to [Formula: see text] secretion through a non-conventional protein secretion mechanism.

Angiotensin-(1-7), a protective peptide against vascular aging

Vascular aging is a complex and multifaceted process that provokes profound molecular, structural, and functional changes in the vasculature. Eventually, these profound aging alterations make arteries more prone to vascular disease, including hypertension, atherosclerosis and other arterial complications that impact the organism beyond the cardiovascular system and accelerate frailty. For these reasons, preventing or delaying the hallmarks of vascular aging is nowadays a major health goal, especially in our aged societies. In this context, angiotensin(Ang)-(1-7), a major player of the protective branch of the renin-angiotensin system, has gained relevance over recent years as growing knowledge on its anti-aging properties is being unveiled. Here, we briefly review the main actions of Ang-(1-7) against vascular aging. These include protection against vascular cell senescence, anti-inflammatory and antioxidant effects together with the induction of cytoprotective systems. Ang-(1-7) further ameliorates endothelial dysfunction, a hallmark of vascular aging and disease, attenuates fibrosis and calcification and promotes protective angiogenesis and repair. Although further research is needed to better understand the anti-aging properties of Ang-(1-7) on the vasculature, this heptapeptide arises as a promising pharmacological tool for preventing vascular aging and frailty.

Pathways responsible for apoptosis resulting from amadori-induced oxidative and nitrosative stress in human mesothelial cells

BACKGROUND

Apoptosis and inflammatory/oxidative stress have been associated with hyperglycemia in human peritoneal mesothelial cells (HPMCs) and other cell types. We and others have highlighted the role of early products of non-enzymatic protein glycation in inducing proinflammatory conditions and increasing apoptotic rates in HPMCs. Loss of HPMCs seems to be a hallmark of complications associated with peritoneal membrane dysfunction. The aim of this work is to elucidate the mechanisms by which Amadori adducts may act upon HPMC apoptosis.

METHODS

HPMCs isolated from different patients were exposed to different Amadori adducts, i.e. highly glycated hemoglobin (10 nM) and glycated bovine serum albumin (250 μg/ml), to study cell death and several proapoptotic markers by different experimental approaches.

RESULTS

Amadori adducts, but not their respective controls, impaired cell proliferation and cell viability by means of apoptosis in a time-dependent manner. They regulated the intrinsic mitochondrial cell death signaling pathway and modulated activation of caspases, Bax, iNOS, p53, NF-κB, and mitogen-activated protein kinases (p38 and JNK) through different reactive oxygen and nitrosative species.

CONCLUSIONS

Our data strongly support the idea that long-term hyperglycemia could act as an inducer of apoptosis in HPMCs through Amadori adducts, involving different oxidative and nitrosative reactive species.

Extracellular PBEF/NAMPT/visfatin activates pro-inflammatory signalling in human vascular smooth muscle cells through nicotinamide phosphoribosyltransferase activity

AIMS/HYPOTHESIS

Extracellular pre-B cell colony-enhancing factor/nicotinamide phosphoribosyltransferase/visfatin (ePBEF/NAMPT/visfatin) is an adipocytokine, whose circulating levels are enhanced in metabolic disorders, such as diabetes mellitus and obesity. Here, we explored the ability of ePBEF/NAMPT/visfatin to promote vascular inflammation, as a condition closely related to atherothrombotic diseases. We specifically studied the ability of PBEF/NAMPT/visfatin to directly activate pathways leading to inducible nitric oxide synthase (iNOS) induction in cultured human aortic smooth muscle cells, as well as the mechanisms involved.

METHODS

iNOS levels and extracellular signal-regulated kinase (ERK) 1/2 activity were determined by western blotting. Nuclear factor (NF)-kappaB activity was assessed by electrophoretic mobility shift assay.

RESULTS

ePBEF/NAMPT/visfatin (10-250 ng/ml) induced iNOS in a concentration-dependent manner. At a submaximal concentration (100 ng/ml), ePBEF/NAMPT/visfatin time-dependently enhanced iNOS levels up to 18 h after stimulation. Over this time period, ePBEF/NAMPT/visfatin elicited a sustained activation of NF-kappaB and triggered a biphasic ERK 1/2 activation. By using the respective ERK 1/2 and NF-kappaB inhibitors, PD98059 and pyrrolidine dithiocarbamate, we established that iNOS induction by ePBEF/NAMPT/visfatin required the consecutive upstream activation of ERK 1/2 and NF-kappaB. The pro-inflammatory action of ePBEF/NAMPT/visfatin was not prevented by insulin receptor blockade. However, exogenous nicotinamide mononucleotide, the product of NAMPT activity, mimicked NF-kappaB activation and iNOS induction by ePBEF/NAMPT/visfatin, while the NAMPT inhibitor APO866 prevented the effects of ePBEF/NAMPT/visfatin on iNOS and NF-kappaB.

CONCLUSIONS/INTERPRETATION

Through its intrinsic NAMPT activity, ePBEF/NAMPT/visfatin appears to be a direct contributor to vascular inflammation, a key feature of atherothrombotic diseases linked to metabolic disorders.

Pro-inflammatory effects of early non-enzymatic glycated proteins in human mesothelial cells vary with cell donor's age

BACKGROUND AND PURPOSE

Diabetes mellitus is prevalent in the elderly population. It is also a disease causing tissue damage through several different mechanisms. Some of these mechanisms are also activated by ageing and this overlap raises questions about how diabetes induces damage in the elderly. Early products of non-enzymatic glycation of proteins (Amadori adducts), and the ageing process share the capacity to induce oxidative stress and inflammation in human peritoneal mesothelial cells (HPMCs). We have evaluated the interactions between the age of the donor of the HPMCs and the pro-inflammatory effects of Amadori adducts in those cells.

EXPERIMENTAL APPROACH

HPMCs were isolated from 20 individuals (age range 21-81 years) and grown in culture. Using different experimental approaches we determined NF-kappaB dependent transcriptional activity and different NF-kappaB-related pro-inflammatory gene and protein expressions in basal (or non-stimulated) conditions and after stimulation with two Amadori adducts; highly-glycated haemoglobin and glycated bovine serum albumin.

KEY RESULTS

Amadori-induced effects on NF-kappaB dependent-transcription and on the activity of NOS, COX and several NF-kappaB-related pro-inflammatory genes (iNOS, COX-2, TNF-alpha, IL-1beta, and IL6) diminished as the donor's age increased, being practically absent in cells from donors more than 65 years old. Such decreased effects were inversely correlated with an increased basal expression and activity of these pro-inflammatory markers with age.

CONCLUSIONS AND IMPLICATIONS

Pro-inflammatory effects of Amadori-adducts in HPMCs were strongly dependent on cell donor's age. This may have significant implications for the mechanisms underlying diabetes-induced tissue damage in patients of different ages.

Changes in the human peritoneal mesothelial cells during aging

The number of older patients admitted to peritoneal dialysis (PD) programmes is growing. At the same time, there is increasing data about the role of mesothelial cells in determining the functional alteration of the peritoneum during PD. However, little is known about the functional changes accompanying the ageing process in mesothelial cells. We aimed to evaluate whether the aging process is accompanied by changes in some functional characteristic of the human peritoneal mesothelial cells (HPMC), which could account for the poor prognosis observed in old patients with PD. HPMCs were isolated from patients undergoing a nonurgent, nonseptic abdominal surgical procedure, without renal, vascular or inflammatory disease. Cytokine levels (by enzyme-linked immunosorbent assay (ELISA)), nitrates+nitrites, and cyclooxygenase (COX) activity (by a chemiluminescence assay), cytokines, COX, nitric oxide synthase (NOS), and nuclear factor (NF)-kappaB1, two messenger ribonucleic acid (mRNA) gene expressions (by reverse transcriptase (RT)-Multiplex PCR), COX, and NOS promoter gene activities, and NF-kappaB-dependent transcription (by transient transfection assays) were determined. Our data show a significant increase in cytokines, COX, and NOS activities, and mRNA expression of cytokines, COX-2, inducible nitric oxide synthase (iNOS) and precursors of NF-kappaB in HPMCs from old people. This was also the case for COX-2 and iNOS promoter gene activities and NF-kappaB-dependent transcription. There was a positive correlation between the age of the donor's cell and the proinflammatory profile of the HPMCs. Such age-dependent increase (around two-three times) is partially abolished by different antioxidant or free-radical scavengers. Thus, aging is accompanied by the presence of an inflammatory state in HPMCs, which involves the participation of different reactive oxygen species.

Early and intermediate Amadori glycosylation adducts, oxidative stress, and endothelial dysfunction in the streptozotocin-induced diabetic rats vasculature

AIMS/HYPOTHESIS

In a model of streptozotocin-induced Type 1 diabetes mellitus in rats of 9 weeks duration, we analysed time associations between the development of hyperglycaemia, early and intermediate glycosylation Amadori adducts, or AGE compared with enhancement of oxidative stress and endothelial dysfunction.

METHODS

Endothelial function was tested at several stages of streptozotocin-induced diabetes and after treatment with insulin, resulting in different concentrations of blood glucose, glycosylated haemoglobin (an Amadori adduct), and AGE. Other animals were studied antagonising the formation of AGE with aminoguanidine.

RESULTS

Relaxation in response to acetylcholine (1 nmol/l to 10 micro mol/l) was tested in isolated segments from aorta or mesenteric microvessels. Impairment of endothelium-dependent relaxations occurred after 2 weeks of untreated diabetes. Preincubation of vessels affected with 100 U/ml superoxide dismutase improved the relaxations to acetylcholine, along the time-course of the endothelial impairment. This indicates the participation of reactive oxygen species on diabetic endothelial dysfunction. The impairment of endothelium-dependent relaxations was recovered after 3 more weeks of insulin treatment. Aminoguanidine treatment did not modify this pattern of development. The time course of the rise and disappearance of endothelial dysfunction showed a higher correlation with glycosylated haemoglobin concentrations than with blood glucose or serum AGE.

CONCLUSION/INTERPRETATION

Enhancement of early and intermediate Amadori adducts of protein glycosylation was the factor showing a better relation with the development of endothelium impairment. These results are consistent with a role for these products in the development of diabetic vasculopathy.

High glucose induces cell death of cultured human aortic smooth muscle cells through the formation of hydrogen peroxide

Alterations of the vessel structure, which is mainly determined by smooth muscle cells through cell growth and/or cell death mechanisms, are characteristic of diabetes complications. We analysed the influence of high glucose (22 mM) on cultured human aortic smooth muscle cell growth and death, as hyperglycaemia is considered one of the main factors involved in diabetic vasculopathy. Growth curves were performed over 96 h in medium containing 0.5% foetal calf serum. Cell number increased by 2 - 4 fold over the culture period in the presence of 5.5 mM (low) glucose, while a 20% reduction in final cell number was observed with high glucose. Under serum-free conditions, cell number remained constant in low glucose cultures, but a 40% decrease was observed in high glucose cultures, suggesting that high glucose may induce increased cell death rather than reduced proliferation. Reduced final cell number induced by high glucose was also observed after stimulation with 5 or 10% foetal calf serum. The possible participation of oxidative stress was investigated by co-incubating high glucose with different reactive oxygen species scavengers. Only catalase reversed the effect of high glucose. Intracellular H(2)O(2) content, visualized with 2',7'-dichlorofluorescein and quantified by flow cytometry, was increased after high glucose treatment. To investigate the cell death mechanism induced by high glucose, apoptosis and necrosis were quantified. No differences were observed regarding the apoptotic index between low and high glucose cultures, but lactate dehydrogenase activity was increased in high glucose cultures. In conclusion, high glucose promotes necrotic cell death through H(2)O(2) formation, which may participate in the development of diabetic vasculopathy.

Thapsigargin induces apoptosis in cultured human aortic smooth muscle cells

Vascular remodeling is a key feature of many pathologic states, including atherosclerosis, or hypertension. Vascular smooth muscle cells participate in determining the vessel structure by several mechanisms such as cell migration, cell growth, or cell death (necrosis or apoptosis). Here we report that thapsigargin, an inhibitor of endoplasmic reticulum Ca2+ -adenosine triphosphatase (ATPase), is able to induce apoptosis in human vascular smooth muscle cells (HVSMCs). Apoptosis was assessed by three different methods: differential chromatin binding dye staining. cytoplasmic histone-associated DNA fragments detection by enzyme-linked immunosorbent assay (ELISA) and terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). When HVSMCs were treated for 1 h with thapsigargin (100 nM-10 microM), there was a concentration-dependent increase in both parameters 24 h after the thapsigargin pulse. When a time-course experiment was performed, both parameters were significantly enhanced from 3 to 6 h after the exposure to thapsigargin. We conclude that thapsigargin promotes apoptosis in HVSMCs, providing a useful tool for the study of programmed cell death in human vascular smooth muscle.

Endogenous angiotensin II and cell hypertrophy in vascular smooth muscle cultures from hypertensive Ren-2 transgenic rats

We investigated the possible role of a tissular renin-angiotensin system in promoting the growth of vascular smooth muscle cells (VSMCs) from hypertensive transgenic rats (TGRs) with the mouse renin gene Ren-2. Mean arterial pressure values were 99.4 +/- 2.8 and 186.7 +/- 5.0 mm Hg for control Sprague-Dawley rats (SDs) and TGRs, respectively (p < 0.05). The tunica media of femoral arteries obtained from hypertensive TGRs was found to be thickened compared to that of age-matched normotensive SDs. Angiotensin II could be detected by dot blot and immunocytochemistry and quantified by radioimmunoassay in transgenic VSMCs, but not in control SD ones. Under serum-free conditions, VSMCs derived from TGRs showed a higher protein content than those derived from SDs (337 +/- 19 vs. 269 +/- 14 pg/cell, p < 0.05, n = 3). Under the same basal conditions, the mean planar cell surface area was significantly higher in TGR VSMCs than in SD ones (4,764 +/- 204 vs. 4,074 +/- 238 micron 2, p < 0.05). In addition, TGR VSMCs showed an enhanced [14C]-leucine uptake but SD VSMCs did not (13,188 +/- 663 vs. 7,633 +/- 713 dpm/well, p < 0.05). VSMCs showed a concentration-dependent proliferative response to fetal calf serum (FCS) that was more marked in TGRs than in SDs. In the absence of FCS, c-fos and c-jun mRNAs were expressed only in transgenic cultures. From the present results, we can hypothesize that cultured TGR VSMCs are able to synthesize angiotensin II that, being almost exclusive into the cells, contributes to produce VSMC growth in the absence of FCS stimulation.

Treatment with acarbose may improve endothelial dysfunction in streptozotocin-induced diabetic rats

We sought to determine whether a single reduction of hyperglycemia and those derivatives from nonenzymatic protein glycosylation may be effective in reducing the development of diabetic endothelial dysfunction. Therefore, we investigated how acarbose, an inhibitor of intestinal alpha-glucosidase that reduce hyperglycemia by lowering glucose absorption, may prevent the impairment of acetylcholine (ACh)-induced endothelium-dependent relaxations observed in isolated vascular segments from untreated streptozotocin-induced diabetic rats. When administered after diabetes induction, 10 mg/kg acarbose decreased modestly the enhancement of blood glucose and glycosylated hemoglobin (HbA1c) levels, but not those of advanced glycosylation end products (AGEs). This effect was linked to a partial improvement of ACh-induced responses both in conductance vessels, such as aortic segments, and resistance vasculature, like mesenteric microvessels. When acarbose was introduced after 6 weeks of untreated diabetes, blood glucose, HbA1c, and AGE levels were not affected and endothelial dysfunction remained unchanged in mesenteric microvessels, whereas a small improvement was observed in aortic segments. The addition of 100 U/ml superoxide dismutase enhanced the impaired relaxations to values similar to vessels from nondiabetic rats, indicating a main role for superoxide anions in diabetes-induced endothelial dysfunction. We conclude that hyperglycemia itself or elevated HbA1c, but not plasma AGEs, are related to enhanced oxidative stress and to the impairment of endothelium function associated to diabetes. This process can be partially prevented by reducing glucose absorption with acarbose.

Correction of glycosylated oxyhemoglobin-induced impairment of endothelium-dependent vasodilatation by gliclazide

We have investigated whether gliclazide, a second-generation sulfonylurea hypoglycemic agent, interferes with the impairment of endothelium-dependent nitric-oxide-mediated relaxation produced by 14%-glycosylated human oxyhemoglobin (GHHb). For comparative purposes, other agents, like glibenclamide, aminoguanidine, ascorbic acid or superoxide dismutase (SOD), were also tested. GHHb (10 nM) caused a reduction in endothelium-dependent relaxation induced by acetylcholine (1 nM to 10 microM) in both isolated aortic segments and mesenteric microvessels from normoglycemic nondiabetic rats. Preincubation of the vessels with gliclazide (100 nM to 10 microM) prevented the impairment of endothelial relaxation, the threshold concentration of gliclazide being 300 nM. In addition, 10 microM gliclazide also prevented the reduction by 10 nM GHHb of the relaxation induced by exogenous nitric oxide (NO, 10 nM to 100 microM). Determination of superoxide anion release measured by the reduction in ferricytochrome c indicated that GHHb produced significant amounts of these free radicals that were concentration-dependently inhibited by gliclazide. The impairment of endothelium-mediated responses was also prevented by 100 U/ml SOD or 10 microM ascorbic acid, but not by 10 microM glibenclamide or 100 microM aminoguanidine. We conclude that gliclazide can reduce the impairment of nitric-oxide-mediated endothelium-dependent relaxation produced by GHHb. This reduction is likely related to the antioxidant properties of the drug, a mechanism suggested by these studies which demonstrate the inactivation of superoxide anions produced by the glycosylated protein by gliclazide.

Prevention of endothelial dysfunction in streptozotocin-induced diabetic rats by gliclazide treatment

The aim of the present work was to analyze whether the oral hypoglycemic drug gliclazide affects diabetic endothelial dysfunction in streptozotocin-induced diabetic rats. Gliclazide was compared with glibenclamide, ascorbic acid, and aminoguanidine. An insulin-dependent model of diabetes was selected to exclude insulin-releasing effects of the drugs. Both in isolated aortic segments and mesenteric microvessels, endothelium-dependent relaxation evoked by acetylcholine (ACh, 1 nM to 10 microM) was significantly reduced in vessels from diabetic animals. This impairment was reversed when the segments were previously incubated with 100 U/ml superoxide dismutase. When streptozotocin-induced diabetic rats were orally treated from the time of diabetes induction with gliclazide (10 mg/kg) or ascorbic acid (250 mg/kg), ACh-induced endothelium-dependent relaxation was well preserved both in aortic segments and mesenteric microvessels. In addition, the impaired vasodilatation to exogenous nitric oxide (NO) in aortic segments was also improved in gliclazide-treated diabetic rats. On the other hand, oral treatment with glibenclamide (1 and 10 mg/kg) or aminoguanidine (250 mg/kg) did not produce significant improvements in diabetic endothelial dysfunction. We conclude that gliclazide reverses the endothelial dysfunction associated with diabetes. This effect appears to be due not to the metabolic actions of the drug but rather to its antioxidant properties, as it can be mimicked by other antioxidants. We propose that the mechanism involved is the inactivation of reactive oxygen species, which are increased in diabetes probably as a result of increased early protein glycosylation products, such as glycosylated hemoglobin (HbA(1c)). These effects of gliclazide are not shared by other oral hypoglycemic agent such as glibenclamide, or by blockade of advanced glycosylation end product (AGE) generation with aminoguanidine.

Enhancement of S-nitrosylation in glycosylated hemoglobin

In this study, we report a novel differential nitric oxide interaction with nonglycosylated and glycosylated hemoglobin. After in vitro incubation of hemoglobin with S-nitroso N-acetyl penicillamine (SNAP), S-nitrosoglutathione, or S-nitrosocysteine, S-nitrosylation was significantly higher in human glycosylated hemoglobin purified from diabetic subjects compared to nondiabetic controls. Inversely, spontaneous decomposition was significantly lower for S-nitrosohemoglobin obtained from glycosylated hemoglobin. Bidimensional isoelectric focusing of hemoglobins incubated in vitro with SNAP also revealed a greater interaction of nitric oxide with glycosylated hemoglobin. In addition, a significantly higher level of S-nitrosohemoglobin was found in erythrocyte lysates from streptozotocin-induced diabetic rats compared to control rats. We suggest that highly glycosylated hemoglobin in diabetic subjects may favor S-nitrosylation, which may in turn impair vascular function, and participate in diabetic microangiopathy.

Highly glycated oxyhaemoglobin impairs nitric oxide relaxations in human mesenteric microvessels

AIMS/HYPOTHESIS

It has been recently shown that glycated human haemoglobin induces endothelial dysfunction in rat vessels by generating superoxide anions that interfere with nitric oxide mediated responses. Our study analysed the effect of glycated human haemoglobin on the endothelium-dependent relaxations of human vessels.

METHODS

Omental microvessels were obtained from patients (without diabetes, hypertension or vascular disease) during surgery and mounted in a small vessel myograph to study their vasoactive responses (vessels from 3-7 patients for each set of experiments).

RESULTS

Cumulative vasodilatory responses to bradykinin (10 nmol/l to 3 mumol/l) were induced in vessels precontracted with 35-50 mmol/l potassium chloride. Addition of 100 mumol/l NG-nitro-L-arginine methyl ester reduced the relaxation evoked by bradykinin, but preincubation with both NG-nitro-L-arginine methyl ester and 10 mumol/l indomethacin was needed to abolish it. Bradykinin-induced responses were inhibited by 1 mumol/l non-glycated oxyhaemoglobin whereas no effect was obtained with 10 nmol/l oxyhaemoglobin. At these low concentrations (10 nmol/l), glycated human oxyhaemoglobin caused an impairment of bradykinin-induced relaxation when the percentage of glycation was 10% or higher. This effect was prevented by preincubating the vessels with ascorbic acid (10 mumol/l), superoxide dismutase (100 U/ml) and gliclazide (1 and 10 mumol/l), but not with indomethacin (10 mumol/l), catalase (400-600 U/ml), dimethylthiourea (1 mmol/l) or glibenclamide (10 mumol/l). In vessels preincubated with NG-nitro-L-arginine methyl ester (100 mumol/l), glycohaemoglobin did not add any additional effect.

CONCLUSION/INTERPRETATION

Highly glycated human oxyhaemoglobin, at physiological plasmatic concentrations, impairs nitric oxide-mediated responses by a mechanism involving superoxide anions but not cyclooxygenase derivatives.

Pharmacological interference of vascular smooth muscle cell hypertrophy induced by glycosylated human oxyhaemoglobin

Nonenzymatically glycosylated human oxyhaemoglobin induces vascular smooth muscle cell hypertrophy by releasing reactive oxygen species. We analysed the ability of drugs with antihypertrophic properties for the vascular wall and/or antioxidant activity, such as captopril, losartan, and nifedipine, or gliclazide, carvedilol, and ascorbic acid, to interfere with 10 nM glycosylated human oxyhaemoglobin-induced increase in vascular smooth muscle cell size (118+/-0.5% of basal). Vascular smooth muscle cell hypertrophy was abolished concentration-dependently, with pD(2) values over a 100-fold interval: 6.4+/-0.3, 7.7+/-0.4, 7.3+/-0.4, 7.4+/-0.6, 8. 8+/-0.2, and 9.0+/-0.2 for captopril, losartan, nifedipine, ascorbic acid, carvedilol and gliclazide, respectively. Drugs with powerful antioxidant properties, especially carvedilol and gliclazide, are particularly effective in preventing glycosylated human oxyhaemoglobin-induced vascular smooth muscle cell hypertrophy.

Impairment of nitric oxide-mediated relaxations in anaesthetized autoperfused streptozotocin-induced diabetic rats

This work was designed to determine in vivo the influence of the metabolic control of streptozotocin-induced diabetic rats, measured by the levels of haemoglobin glycosylation in blood (HbA1c), on developing vascular endothelial dysfunction. For this, the vasoactive responses to basal and stimulated endothelial nitric oxide (NO) were studied using the technique of the anaesthetized autoperfused rat, analyzing the responses to acetylcholine (ACh) and N(G)-nitro-L-arginine methyl ester (L-NAME) in non-diabetic and diabetic rats with different degrees of metabolic control (four groups with HbA1c levels of 5.5-7.4%, 7.5-9.4%, 9.5-12%, and >12%, respectively). When administered over a noradrenaline-induced vasopressor tone, ACh (0.25, 0.75, 2.5, 7.5 and 25 microg kg(-1)) induced dose-dependent vasodilatatory responses in all rat groups, reducing both mean arterial pressure and perfusion pressure of the left hindlimb. These responses were similar in non-diabetic and in diabetic rats with good metabolic control (HbA1c 5.5-7.4%), while diabetic rats with levels of HbA1c higher than 7.5% showed significantly lower vasodilatatory responses to ACh. In untreated diabetic rats, the relaxant responses evoked by the NO donor sodium nitroprusside were also impaired. On the other hand, increasing doses of L-NAME (0.1 to 10 mg kg(-1)) enhanced both mean arterial pressure and left hindlimb perfusion pressure in diabetic and non-diabetic rats. As with ACh, the responses to L-NAME were significantly reduced in diabetic rats with HbA1c levels higher than 7.5%. To determine the mechanism underlying the NO-mediated endothelial dysfunction, the responses to ACh in untreated diabetic rats (HbA1c >12%) were studied in the presence of the NO substrate L-arginine, in the presence of the oxygen-derived free radical scavenger superoxide dismutase (SOD), or in the presence of both compounds. Both L-arginine and SOD produced a partial improvement of the ACh-induced vasodilatatory responses, but the effects of these agents were not additive. In this group of animals, SOD also induced a partial recovery of the L-NAME-evoked vasoconstrictions. In non-diabetic and untreated diabetic rats, the plasma levels of NO derivatives and arginine were measured. No significant differences were obtained in the amount of nitrites plus nitrates, while plasma levels of arginine were markedly reduced in the untreated diabetic animals. The results indicate that the endothelial dysfunction associated to diabetes is closely related to the level of metabolic control of the disease. Therefore, it is possible to establish a threshold for developing endothelium impairment from percentages of HbA1c higher than 7.5%. As the responses to the NO synthase blocker L-NAME were analogously impaired, it is reasonable to suggest that diabetic endothelial dysfunction is related to the interference with mechanisms linked both to stimulated and basal production of NO. We suggest that this interference is partially due to a deficit in the substrate availability for NO and to an increased generation of superoxide anions.

Vascular smooth muscle cell hypertrophy induced by glycosylated human oxyhaemoglobin

1. Nonenzymatic protein glycosylation is a possible mechanism contributing to oxidative stress and vascular disease in diabetes. In this work, the influence of 14%-glycosylated human oxyhaemoglobin (GHHb), compared to the non-glycosylated protein (HHb), was studied on several growth parameters of rat cultured vascular smooth muscle cells (VSMC). A role for reactive oxygen species was also analysed. 2. Treatment of VSMC for 48 h with GHHb, but not with HHb, increased planar cell surface area in a concentration dependent manner. The threshold concentration was 10 nM, which increased cell size from 7965+/-176 to 9411+/-392 microm2. Similarly, only GHHb enhanced protein content per well in VSMC cultures. 3. The planar surface area increase induced by 10 nM GHHb was abolished by superoxide dismutase (SOD; 50 200 u ml(-1)), deferoxamine (100 nM-100 microM), or dimethylthiourea (1 mM), while catalase (50 200 u ml(-1)) or mannitol (1 mM) resulted in a partial inhibition of cell size enhancement. 4. When a known source of oxygen free radicals was administered to VSMC, the xanthine/xanthine oxidase system, the results were analogous to those produced by GHHb. Indeed, enhancements of cell size were observed, which were inhibited by SOD, deferoxamine, or catalase. 5. These results indicate that, at low concentrations, GHHb induces hypertrophy in VSMC, this effect being mediated by superoxide anions, hydrogen peroxide, and/or hydroxyl radicals. Therefore, glycosylated proteins can have a role in the development of the structural vascular alterations associated to diabetes by enhancing oxidative stress.

Endothelial factors and autoregulation during pressure changes in isolated newborn piglet cerebral arteries

To analyze newborn cerebrovascular autoregulation, middle cerebral arteries from 3-4-d-old piglets were cannulated, and diameter changes after transmural pressure variation were measured. After an equilibration period at 30 mm Hg, pressure was modified from 10 to 70 mm Hg in 20-mm Hg steps. Segments with endothelium showed vasodilation during pressure decrease and vasoconstriction during pressure increase. In each case the maximum response was about 5% that of the resting diameter. Segments without endothelium responded passively to pressure change. Vasodilation during pressure decrease was reduced by the preferential calcium-activated potassium (KCa) channel blocker, tetraethylammonium (1 mM), and was absent with the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methylester (L-NAME, 10 microM). The NO synthase substrate, L-arginine (10 microM), counteracted the dilation blockade caused by L-NAME. The cyclooxygenase inhibitor indomethacin (10 microM) and the endothelin A receptor antagonist BQ-123 (10O microM) eliminated the pressure increase-induced vasoconstriction. The ATP-sensitive potassium channel blocker, glibenclamide (1 microM), and the endothelin B receptor antagonist, BQ-788 (10 nM), did not modify the autoregulatory response. None of these drugs modified the passive changes produced by pressure variations in segments without endothelium. These results suggest that: 1) piglet middle cerebral artery autoregulation is endothelium-dependent; 2) NO and KCa channels are involved in vasodilation during transmural pressure decrease, and 3) endothelin-1, through endothelin A receptors, and prostanoids mediate vasoconstriction during pressure increase.

Endothelial dysfunction and metabolic control in streptozotocin-induced diabetic rats

1. The aim of this work was to study the influence of the metabolic control, estimated by the levels of glycosylated haemoglobin in total blood samples (HbA1c), in developing vascular endothelial dysfunction in streptozotocin-induced diabetic rats. Four groups of animals with different levels of insulin treatment were established, by determining HbA1c values in 5.5 to 7.4%, 7.5 to 9.4%, 9.5 to 12% and > 12%, respectively. 2. The parameters analysed were: (1) the endothelium-dependent relaxations to acetylcholine (ACh) in isolated aorta and mesenteric microvessels; (2) the vasodilator responses to exogenous nitric oxide (NO) in aorta: and (3) the existence of oxidative stress by studying the influence of the free radical scavenger superoxide dismutase (SOD) on the vasodilator responses to both ACh and NO. 3. In both isolated aortic segments and mesenteric microvessels, the endothelium-mediated concentration-dependent relaxant responses elicited by ACh were significantly decreased when the vessels were obtained from diabetic animals but only with HbA1c values higher than 7.5%. There was a high correlation between HbA1c levels and the impairment of ACh-induced relaxations, measured by pD2 values. 4. The concentration-dependent vasorelaxant responses to NO in endothelium-denuded aortic segments were significantly reduced only in vessels from diabetic animals with HbA1c values higher than 7.5%. Again, a very high correlation was found between the HbA1c values and pD2 for NO-evoked responses. 5. In the presence of SOD, the responses to ACh or NO were only increased in the segments from diabetic rats with HbA1c levels higher than 7.5%, but not in those from non-diabetic or diabetic rats with a good metabolic control (HbA1c levels <7.5%). 6. These results suggest the existence of: (1) a close relation between the degree of endothelial dysfunction and the metabolic control of diabetes, estimated by the levels of HbA1c; and (2) an increased production of superoxide anions in the vascular wall of the diabetic rats, which is also related to the metabolic control of the disease.

Angiotensin II mediates cell hypertrophy in vascular smooth muscle cultures from hypertensive Ren-2 transgenic rats by an amiloride- and furosemide-sensitive mechanism

We have reported that cultured vascular smooth muscle cells (VSMC) from hypertensive Ren-2 transgenic rats (TGR) are constitutively hypertrophic when compared to matched cells from normotensive Sprague-Dawley rats (SD), by a mechanism involving the endogenous production of angiotensin II (AII). In the present work, we analyzed the possible involvement of two Na+ transport mechanisms in TGR-VSMC hypertrophy. In both SD- and TGR-VSMC, AII increased both cell size, by a furosemide- and amiloride-sensitive mechanism, and Na+/K+/2Cl- cotransport activity, by an amiloride-sensitive mechanism. Under basal unstimulated conditions, TGR-VSMC showed higher cell size and Na+/K+/2Cl- cotransport activity than SD-VSMC. Under these same conditions, losartan, furosemide, or amiloride reduced cell size only in TGR-VSMC. Similarly, basal cotransport activity was reduced by losartan and amiloride to levels similar to those observed in SD-VSMC. We conclude that hypertrophy of TGR-VSMC is dependent on the endogenous production of AII and mediated by increased Na(+)-H+ exchange and Na+/K+/2Cl- cotransport activities.

Effects of captopril, losartan, and nifedipine on cell hypertrophy of cultured vascular smooth muscle from hypertensive Ren-2 transgenic rats

1. We hypothesized that tissular renin-angotensin system (RAS) induces vascular hypertrophy in hypertensive Ren-2 transgenic rats (TGR; strain name TGR(mRen2)L27). This assumption was tested in cell cultures of vascular smooth muscle (VSMC) from both hypertensive TGR and control normotensive Sprague-Dawley (SD) rats. Planar cell surface area, protein synthesis, and protein content per cell were studied, the role for locally produced angiotensin II (AII) was evaluated and the possible pharmacological interference by different drugs was analysed. 2. By use of radioimmunoassay techniques, AII could be determined in TGR cultures (10.25 +/- 0.12 pg per 10(7) cells) while it could not be detected in SD ones. 3. Under serum-free conditions, VSMC from hypertensive TGR were hypertrophic when compared to SD VSMC, as they presented a higher protein content per cell (335 +/-18 and 288 +/- 7 pg per cell respectively; P<0.05) and increased mean planar cell surface area, as determined by image analysis (4,074 +/- 238 and 4,764 +/- 204 microm2, respectively; P < 0.05). 4. When exogenously added to cultured SD and TGR VSMC, AII (100 pM to 1 microM) promoted protein synthesis and protein content in a concentration-dependent manner without affecting DNA synthesis. Maximal effects were observed at 100 nM. At this concentration, AII effectively increased planar cell surface area in both SD and TGR cultures by approximately 20%. 5. Treatment of TGR cultures, in the absence of exogenous AII, with the angiotensin-converting enzyme inhibitor captopril or the angiotensin AT1 receptors antagonist losartan (100 nM to 10 microM) reduced planar cell surface area in a concentration-dependent manner. In addition, both captopril and losartan (10 microM), decreased protein synthesis by approximately 15%. 6. Treatment of SD VSMC, in the absence of exogenous AII, with both captopril and losartan had no effect either on planar cell surface area or protein synthesis. 7. Treatment with the Ca2+ antagonist nifedipine (100 nM to 10 microM) reduced cell size in both SD and TGR cultures. Maximal cell reduction reached by nifedipine averaged 906 +/- 58 and 1,292 +/- 57 microm2, in SD and TGR, respectively (P<0.05). In addition, nifedipine, nitrendipine and nisoldipine (all at 10 microM) decreased protein synthesis in both cell types by 15-25%. 8. We concluded that cultured VSMC from TGR are hypertrophic in comparison with those from SD. This cell hypertrophy can be the consequence of the expression of the transgene Ren-2 that activates a tissular RAS and locally produces AII, which acts in a paracrine, autocrine, or intracrine manner. Cell hypertrophy in TGR cultures could be selectively reduced by RAS blockade, while nifedipine decreased cell size and protein synthesis in both hypertrophic and non hypertrophic cells.

Nifedipine, losartan and captopril effects on hyperplasia of vascular smooth muscle from Ren-2 transgenic rats

Vascular smooth muscle cells from hypertensive transgenic rats for the mouse Ren-2 gene exhibited radioimmunoassayable angiotensin II and hyperplasia in comparison with cells from Sprague-Dawley rats. However, neither captopril, losartan, saralasin, nor PD123319 (all at 10 microM) modified DNA synthesis or cell number observed in 4-day growth curves with 10% fetal calf serum. Nifedipine reduced DNA synthesis in both cell types, the concentration required being significantly higher in Sprague-Dawley- (1 microM) than in transgenic-derived cultures (100 nM). The EC50 values were of 2.43 +/- 0.32 and 1.0 +/- 0.17 microM, respectively (P < 0.05). In both cell types, only 10 microM nifedipine reduced serum-induced cell proliferation, but inhibition percentage was higher in transgenic-derived cultures. In conclusion, hyperplasia of transgenic-derived vascular smooth muscle cells is not blocked by angiotensin-converting enzyme inhibitors or angiotensin receptor antagonists, but these cells are more sensitive to the antiproliferative effects of nifedipine.

Effects of indomethacin and iloprost on contraction of the afferent arterioles by endothelin-1 in juxtamedullary nephron preparations from normotensive Wistar-Kyoto and spontaneously hypertensive rats

The contractile effects of endothelin-1 on the afferent arterioles of normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) and the modulation of these responses by cyclooxygenase blockade or by the prostacyclin analog iloprost were investigated. For this, the preglomerular vasculature was visualized by using the juxtamedullary nephron preparation. Endothelin-1 (100 pM-1 microM) induced concentration-dependent reduction of afferent diameters either in WKY and SHR kidneys, which were inhibited by 1 microM nifedipine, indicating its dependence on extracellular calcium. After incubation with 20 microM indomethacin, the endothelin-1-induced contractions were potentiated in WKY but abolished in SHR vessels. These results could be explained if endothelin-1 is releasing vasodilator prostanoids in WKY, whereas in SHR preparations, vasoconstrictor prostanoids predominate. The prostacyclin analog iloprost (1 nM-1 microM) did not modify basal diameters of the WKY afferent arterioles, whereas a weak vasodilatatory effect was observed in the SHR afferent vasculature. Both in WKY and SHR preparations, iloprost (10 nM-1 microM) abolished the afferent contractility by endothelin-1, this effect being more prominent in SHR. We conclude that a defective production of vasodilator prostanoids or an enhanced release of vasoconstrictor cyclooxygenase derivatives may determine the renovascular effects of endothelins in SHR kidneys.

Impairment of endothelium-dependent relaxation by increasing percentages of glycosylated human hemoglobin. Possible mechanisms involved

High levels of glycosylated human hemoglobin impair nitric oxide-mediated responses. However, the percentage of glycosylation for which this effect is observed and the mechanisms involved are unknown. We tested endothelium-dependent relaxations caused by acetylcholine in rat aortic segments either in control conditions or after preincubation with increasing percentages of glycosylated human hemoglobin. Human hemoglobin (1 and 10 nmol/L) inhibited endothelium-dependent relaxations only when glycosylated at 9% or higher. We evaluated the effect of 14% glycosylated human hemoglobin on acetylcholine-evoked responses in vessels preincubated with scavengers of superoxide anions, hydroxyl radical, or hydrogen peroxide (superoxide dismutase, deferoxamine, and catalase, respectively); with inhibitors of xanthine oxidase, cyclooxygenase, or thromboxane synthase (allopurinol, indomethacin, and dazoxiben, respectively); with blockers of thromboxane A2/prostaglandin H2 or endothelin receptors (SQ 30741 and BQ-123); and with the precursor of nitric oxide synthesis L-arginine. Superoxide dismutase abolished the effect of glycosylated hemoglobin, and the other substances did not have any effect. Glycosylated hemoglobin at 14% did not modify either the vasoconstrictions induced by the blocker of nitric oxide synthase NG-nitro-L-arginine methyl ester or the relaxations evoked in deendothelialized vessels by sodium nitroprusside and 8-bromo-cGMP. However, it inhibited the vasodilations evoked by exogenous nitric oxide. Superoxide dismutase abolished this latter effect. We conclude that the threshold for glycosylated human hemoglobin (Hb A1) to inhibit endothelium-dependent relaxation is 9%. This effect is due to interference with endothelial nitric oxide by means of superoxide anion production.

Effect of ageing and hypertension on endothelial modulation of ouabain-induced contraction and sodium pump activity in the rat aorta

OBJECTIVE

To investigate the endothelial modulation of the rat thoracic aorta sodium-potassium ATPase activity and its possible alteration by ageing and hypertension.

METHODS

Male spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) aged 5 weeks, 3, 6, 12 and 18 months were anaesthetized. Their aortae were dissected and divided into cylindrical segments and vasomotor responses obtained in segments with or without endothelium were recorded on a polygraph.

RESULTS

Endothelium removal increased ouabain responses in young (aged 3 and 6 months) WKY rat aortic segments, but reduced those obtained in old (aged 18 months) WKY rat segments and in segments from SHR aged 3, 6 and 12 months. An enhancement of contractions in response to ouabain with age was observed in both strains, but it occurred at earlier ages in vessels from SHR. At ages 3 and 6 months, responses to ouabain were higher in intact vessels from SHR than they were in those from WKY, but were lower in endothelium-denuded vessels. In aortic segments from 6-month-old WKY rats and SHR, ouabain reduced or abolished potassium-induced relaxations in segments with or without endothelium, respectively. In vessels from SHR and WKY rats aged 18 months, ouabain abolished potassium-induced relaxations both in intact and in endothelium-denuded vessels.

CONCLUSIONS

Endothelium of WKY rat aorta might release a factor in response to ouabain that modulates its contraction negatively. Endothelium of SHR and old WKY rat aorta releases a contracting factor that modulates ouabain contractions positively. Thus, the inhibitory effect of endothelium on contractions induced by ouabain might be lost as a consequence both of hypertension and of age, being replaced by an endothelium-dependent contracting factor that facilitates ouabain responses.

Noradrenergic transmission in the tail artery of hypertensive rats transgenic for the mouse renin gene Ren-2

1. The aim of the present study was to analyse the noradrenergic transmission in the tail artery of hypertensive rats transgenic for the mouse renin gene Ren-2 (TGR) in comparison with its control, the Sprague-Dawley (SD) rat. 2. Electrical field stimulation (EFS) of vascular segments produced frequency-dependent vasoconstrictions that were significantly greater in TGR arteries. 3. These contractions were abolished by tetrodotoxin (0.1 microM). Phentolamine (50 nM) and prazosin (1 - 10 nM) produced an inhibition of these responses that was significantly greater in SD arteries, whereas that produced by yohimbine (0.5-1 microM) was higher in TGR arteries. In both strains, propranolol (1 microM) potentiated the responses to EFS, and this increase was observed at lower frequencies in TGR arteries. 4. The EFS-evoked [3H]-noradrenaline (NA) release was significantly greater in TGR than in SD rats. However, NA (10 nM-10 microM) reduced and yohimbine and phentolamine (10 nM-10 microM) increased the tritium outflow to a similar degree in both strains. 5. Exogenous NA also induced greater vasoconstriction in TGR arteries. 6. These results suggest the existence in TGR tail artery of an increase in: (a) NA-release and alpha 2-adrenoceptor-mediated contractions, which could contribute to the elevated blood pressure in these rats; and (b) beta-adrenoceptor-mediated vasodilatations, which may be a mechanism to counteract high blood pressure.

Endothelial modulation of ouabain-induced contraction and sodium pump activity in aortas of normotensive Wistar-Kyoto and spontaneously hypertensive rats

The influence of vascular endothelium on ouabain-induced contractions and sodium pump activity in aortic segments of Wistar-Kyoto (WKY) and spontaneously hypertensive rat (SHR) was analyzed. De-endothelialization increased and reduced ouabain-induced contractions in WKY and SHR segments, respectively. The effects of de-endothelialization were not reproduced by pretreatment of the segments with NG-nitro-L-arginine methyl ester, indomethacin, or 5, 8, 11, 14-eicosatetraenoic acid, acetyl salicylic acid, dazoxiben, phosphoramidon, BQ-123, or superoxide dismutase. Bioassay experiments suggest that ouabain releases a diffusible factor from endothelial cells that inhibits or facilitates digitalis-induced contractions in WKY and SHR segments, respectively. In a potassium-free solution, potassium-induced relaxation in segments of both strains was abolished by ouabain in de-endothelialized aortas and reduced in intact ones. Ouabain-sensitive 86Rb+ uptake was significantly reduced by de-endothelialization both in WKY and in SHR. These results suggest that the vascular endothelium of WKY and SHR aortas releases a diffusible factor that stimulates the sodium pump and/or protects it from ouabain blockade. Ouabain also releases a diffusible endothelium-derived factor in SHR aortas that facilitates ouabain-induced contractions.

Influence of age on the relaxation induced by nifedipine in aorta from spontaneously hypertensive and Wistar Kyoto rats

1. Nifedipine induces relaxation in aortic segments from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) of 5-week-, 3-month-, 6-month- and 1.5-year-old precontracted with 50 mM K+ or 0.1 microM noradrenaline (NA). 2. In WKY rat segments precontracted with K+, nifedipine relaxation was reduced at 1.5 years. However, in SHR segments, the greatest relaxation was observed at 1.5 years. The relaxation elicited by nifedipine in segments from WKY of 6-month and 1.5-year-old precontracted with NA was higher than that reached at 5-week- and 3-month-old. However, the relaxation induced in SHR of 6-month and 1.5-year-old was only higher than that obtained at 5-week-old. 3. Relaxations elicited by nifedipine in segments from WKY precontracted with K+ were smaller than those observed in age-matched SHR segments. 4. The endothelium positively and negatively modulates the relaxation to nifedipine in segments from SHR and WKY rats of different ages precontracted with K+, respectively. However, in segments of both strain precontracted with NA, endothelium removal did not alter the relaxations obtained at different ages. 5. These results suggest that the relaxation elicited by nifedipine: (1) depends on the strain, with a tendency to be greater in the hypertensive strain; (2) is negatively and positively modulated by endothelium in WKY and SHR, respectively, and (3) is influenced by age, and this influence depends on both the contractile agent and the strain.

Effects of Bay K 8644 in aorta from spontaneously hypertensive and Wistar Kyoto rats of different ages

1. The Ca(2+)-channel agonist, Bay K 8644, induced small contractions in aortae from Wistar-Kyoto (WKY) rats of 5-week-, 3-month-, 1-year- and 1.5-year-old, which were unaltered with age. These contractions were increased by partial depolarization with 15 mM K+. 2. In segments from spontaneously hypertensive rats (SHR), the contractions obtained in both situations were similar and equivalent to those observed in segments from normotensive animals partially depolarized. Responses to Bay K 8644 were modified by age only in tissues from the SHR, the responses to this agent in basal conditions being increased in tissues from 3-month- and 1-year-old animals and depressed in those from 1.5-year SHR. 3. A reduction of the response to Bay K 8644 was observed in partial depolarized endothelium denuded segments from WKY of all ages, and no modification in basal situation. However, the direct contractions induced by Bay K 8644 in aortae from 3-month- and 1.5-year-old SHR were reduced by endothelium removal. 4. These results suggest that: (a) in the hypertensive strain the voltage-gated Ca2+ channels seem to be partially activated; (b) the direct contractions induced by Bay K 8644 were unaltered by age in aortae from WKY but increased in tissues from SHR of 3-month-and-1-year old and depressed in those from 1.5 years, and (c) the contractions evoked by Bay K 8644 seem to involve an endothelium-derived contracting factor in aortae from both strains, or the endothelium produces a partial depolarization of vascular smooth muscle that increases the responsiveness to Bay K 8644.

Endothelial stimulation of sodium pump in cultured vascular smooth muscle

We studied vascular sodium pump activity and its regulation by vasoactive agents and endothelium in cultured aortic vascular smooth muscle cells from normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Baseline sodium pump activity (ouabain-inhibitable 86Rb+ uptake) was similar in cells from both rat strains. Angiotensin II and endothelin-1 increased ouabain-inhibitable 86Rb+ uptake more in SHR than WKY cells, whereas no effects were obtained with sodium nitroprusside, 8-bromo-cGMP, or iloprost. We examined the influence of endothelium on vascular sodium pump activity either by coculturing smooth muscle and endothelial cells or by using conditioned medium. Both coculture for 24 hours with endothelial cells and treatment with conditioned medium increased smooth muscle cell sodium pump activity, this effect being higher in SHR cells. These results suggest that the endothelium may modulate sodium pump activity in the underlying smooth muscle by releasing a diffusible compound, which is more active on SHR smooth muscle. The conditioned medium obtained in the presence of inhibitors of angiotensin-converting enzyme, endothelin-1-converting enzyme, cyclooxygenase, lipoxygenase, and nitric oxide synthase had no effect on the ability of conditioned medium to increase sodium pump activity, suggesting that angiotensin II, endothelin-1, eicosanoids, and nitric oxide are not involved in this stimulatory effect. The nature of the possible endothelial factor involved is still unknown, but it possesses a molecular weight between 25 and 50 kD, is heat stable, and is sensitive to trypsin treatment. We propose it could be a growth factor.

Influence of endothelium on cultured vascular smooth muscle cell proliferation

The endothelium exerts a large influence on the underlying vascular smooth muscle, not only by the release of both contracting and relaxing factors but also by its ability to synthesize a large number of molecules that influence vascular smooth muscle growth. In addition to well-characterized growth promoters or growth inhibitors, some endothelium-derived factors, originally described as vasoactive compounds, seem to possess growth-regulatory properties. The vasoconstrictor endothelin-1 elicited a dose-dependent increase of cultured vascular smooth muscle cell DNA synthesis with a maximal effect of 57 +/- 14% over basal levels, whereas vasodilators such as prostacyclin, sodium nitroprusside, and 8-bromoguanosine 3':5'-cyclic monophosphate reduced DNA synthesis by 19 +/- 5%, 22 +/- 2%, and 31 +/- 3%, respectively. Medium conditioned by cultured bovine aortic endothelial cells markedly stimulated both DNA synthesis and proliferation of smooth muscle cells. When medium was conditioned in the presence of the endothelin-converting enzyme inhibitor phosphoramidon, the mitogenic effect was significantly reduced, thus indicating a role for endothelin in the stimulation of smooth muscle cell growth by endothelial cells. However, when both cell types were maintained in a coculture system, a 13 +/- 2% decrease of DNA synthesis was observed in smooth muscle cultures. The addition of the nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester, the cyclooxygenase inhibitor indomethacin, or both during the coculture period did not revert the antiproliferative effect of endothelial cells in coculture, thereby indicating it is not likely due to these unstable endothelium-derived vasorelaxant molecules.

Functional vascular renin-angiotensin system in hypertensive transgenic rats for the mouse renin gene Ren-2

1. Isolated aortic segments from transgenic rats for the mouse renin gene Ren-2 were more sensitive than those from control Sprague-Dawley ones to the vasoconstrictions induced by angiotensin II and to the potentiation of norepinephrine contractions by this peptide. 2. In transgenic, but not in control aorta, pretreatment with angiotensinogen potentiated norepinephrine-induced vasoconstrictions, this effect being abolished by captopril. 3. These results suggest that in the aorta of transgenic rats there is a higher functional tissue renin-angiotensin system that potentiates the vascular reactivity to norepinephrine.

Role of nitric oxide on the endothelium-dependent vasodilation in newborn piglet cerebral arteries

1. The present study was undertaken to determine whether endothelial nitric oxide (NO) is involved in the endothelium-dependent vasodilation elicited by bradykinin (BK) in rings of newborn (1-7-day-old) piglet cerebral arteries precontracted with KCl (25 mM). 2. In these rings, BK (10(-10)-10(-6) M) induced concentration-dependent relaxation. The preincubation with the precursor of NO synthesis, L-arginine (10(-4) M), reduced KCl-induced contraction and increased the BK relaxation. However, preincubation with the NO synthase inhibitor, NG-nitro-L-arginine-methyl ester (L-NAME; 3 x 10(-5) M), increased KCl contraction and basal tone, and inhibited BK relaxation. 3. These results suggest that the endothelium of these arteries possesses the ability to produce NO, either basal or stimulated by agents like BK.

Pressure-induced contraction of the juxtamedullary afferent arterioles in spontaneously hypertensive rats

1. In the SHR juxtamedullary nephron preparation, the increase of the perfusion pressure from 80 to 160 mmHg increased the diameters of arcuate arteries but produced a pressure-dependent contraction of the afferent arterioles, a response that can account for renal autoregulation. 2. The pressure-induced contractions of the afferent arterioles were abolished by 1 microM nifedipine and by 10 microM furosemide, suggesting that the autoregulatory responses are mainly mediated by tubuloglomerular mechanisms and can be abolished by calcium antagonists.

Neurogenic component of ouabain-evoked contractions is modulated by the endothelium

The influence of endothelium on the neurogenic component of ouabain-induced contractions in isolated perfused guinea pig carotid arteries was analyzed. Ouabain (0.1 mumol/L to 0.1 mmol/L) evoked concentration-dependent increases of perfusion pressure. Phentolamine (0.3 to 10 mumol/L) and prazosin (30 nmol/L to 10 mumol/L) (nonselective antagonist of alpha-adrenergic receptors and selective antagonist of alpha 1-adrenergic receptors, respectively) induced a concentration-dependent relaxation in segments precontracted with ouabain (0.1 mmol/L). When the arteries were preincubated with those blockers (both at 3 mumol/L) or the animals were pretreated with reserpine, the contractions to the glycoside were diminished, indicating that they are partially mediated by norepinephrine release from adrenergic nerve endings. De-endothelialization abolished the effect of adrenergic blockade on ouabain-induced contractions. On the other hand, de-endothelialization did not modify significantly the effect of the adrenergic blockade on norepinephrine-induced contractions. The nitric oxide blocker oxyhemoglobin, at concentrations (10 mumol/L) that abolished endothelium-dependent relaxations induced by 3 mumol/L acetylcholine; or the cyclooxygenase blocker indomethacin (10 mumol/L) did not modify the relaxation caused by phentolamine. In bioassay experiments, 30 mumol/L phentolamine induced a relaxation on the ouabain-elicited contraction only when the glycoside was added through a donor segment with endothelium. Ouabain-induced tritiated norepinephrine release was significantly reduced by the removal of endothelium but not by 1 mumol/L oxyhemoglobin or 1 mumol/L indomethacin. These results suggest that the endothelium modulates the neurogenic component involved in contractions evoked by the glycoside by a diffusible factor (or factors) whose nature is unknown; however, the factor is neither nitric oxide nor a cyclooxygenase-related compound.

Nitric-oxide-related and non-related mechanisms in the acetylcholine-evoked relaxations in cat femoral arteries

The possible contribution of nitric oxide (NO) and other endothelial factors to the vasodilatation induced by acetylcholine (ACh) was analyzed in cat femoral arteries. For this purpose, the modifications by different treatments of ACh-induced relaxations were compared with those of exogenous NO-induced relaxations. Although the ACh-induced endothelium-dependent relaxation was not affected by the cyclooxygenase inhibitor indomethacin, it was partially inhibited by the lipoxygenase blocker 5,8,11,14-eicosatetraenoic acid, and by the NO inactivators phenidone, hydroquinone and oxyhemoglobin (OxHb). Additionally, this type of relaxation was reduced by the NO-synthase inhibitor NG-monomethyl-L-arginine (L-NMMA) and abolished by NG-nitro-L-arginine methyl ester; these later effects were selectively antagonized by L-arginine. Exogenous NO-induced vasodilatations were abolished by OxHb and unmodified by L-NMMA. Blocking sodium pump activity decreased vasodilatations to ACh, NO, sodium nitroprusside and 8-bromoguanosine 3',5'-cyclic monophosphate. 4-Aminopyridine, a K+ channel antagonist, reduced the relaxation induced by ACh but not that induced by exogenous NO. These results suggest: (1) ACh-induced relaxation in these vessels is mainly due to endothelial cell NO release; (2) NO does not act on 4-AP-sensitive K+ channels, although these channels may be involved in NO release from the endothelium, and (3) one of the relaxant mechanisms of NO could be the activation of the vascular sodium pump.

Interference of glycosylated human hemoglobin with endothelium-dependent responses

BACKGROUND

Hypertension and other vascular diseases are more prevalent in diabetic patients than in the general population. In humans and in several animal models of diabetes, a disturbance of endothelium-dependent responses has been shown. Oxyhemoglobin is one of the most known modulators of these endothelium-dependent responses. We postulate that high levels of plasmatic glycosylated hemoglobin, a frequent profile in diabetic patients, may be the cause of the disturbance in endothelium-dependent relaxation and/or contraction.

METHODS AND RESULTS

Endothelium-dependent responses to acetylcholine and several alpha-adrenergic agonists (norepinephrine, methoxamine, and clonidine) were tested in segments of rat aorta. Experiments were carried out in control segments and in those preincubated with several concentrations of nonglycosylated, low-glycosylated (7.3%), and high-glycosylated (14%) human hemoglobin. Low concentrations of high-glycosylated human hemoglobin (1 to 100 nmol/L) but not of low- or nonglycosylated hemoglobin, inhibited endothelium-dependent relaxation caused by acetylcholine in intact vessels. The same effect was observed on relaxations caused by nitric oxide in denuded ones. High-glycosylated human hemoglobin (10 nmol/L) induced an increase in norepinephrine-evoked contraction in intact vessels; this latter effect was also shown in vessels contracted with methoxamine but not with clonidine. De-endothelialization of the vascular segments blunted these effects of high-glycosylated human hemoglobin.

CONCLUSIONS

High glycosylation of human hemoglobin impairs endothelium-mediated vasoactive responses and may play a pathophysiological role in producing hypertension and vascular diseases in diabetic patients.

Endothelial role in ouabain-induced contractions in guinea pig carotid arteries

The influence of endothelium on the direct contractile effects of ouabain in vascular smooth muscle was analyzed in isolated perfused guinea pig carotid arteries. After blocking the neurogenic component of the glycoside contraction with alpha-adrenergic receptor blocking drugs or treating the animals with reserpine, ouabain-induced contractions were markedly reduced in vessels with intact endothelium. However, removal of the vascular endothelium from reserpinized carotid arteries resulted in ouabain-induced contractions similar to those observed in control arteries. These effects were not mimicked by the inhibitor of nitric oxide NG-monomethyl L-arginine or by the cyclooxygenase blocker indomethacin. Bioassay experiments suggested that these endothelial effects are mediated by diffusible factors. Uptake of 86Rb to measure sodium pump activity was significantly reduced by removal of the endothelium. These results suggest the existence of an inhibitory modulation by the endothelium of contractions induced by ouabain, likely mediated by a diffusible factor (or factors) released from these cells. The nature of this substance is unknown, but it is neither related to prostaglandins nor a nitric oxide-related compound. Its mechanism of action could be the stimulation of vascular sodium pump activity, the antagonism of the pump's inhibition by ouabain, or both.

Sodium pump activation by 5-hydroxytryptamine in human placental veins

The aim of the present study was to determine the influence of the sodium pump on the responses elicited by 5-hydroxytryptamine (5-HT) in segments of human placental veins. 5-HT (10(-9)-3 x 10(-7) M) elicited potent concentration-dependent vasoconstrictor responses, but a fall in tone was observed at higher concentrations. In the presence of 10(-7) M ouabain, this fall in tension was abolished. A single concentration of 5-HT (10(-6) M) produced a biphasic response, consisting in a fast early contraction followed by a slow relaxation. This relaxant phase was concentration dependently inhibited by ouabain (10(-7) and 10(-6) M), and abolished by preincubating the vessels in a K(+)-free solution and reducing bath temperature to 28 degrees C, methods usually employed to inhibit the sodium pump. After adding 7.5 mM K+ or returning the temperature to 37 degrees C, marked relaxation was observed. On the other hand, the relaxant phase with the amine remained unchanged by pretreatment with phenidone, oxyhemoglobin, indomethacin (all at 10(-5) M) and endothelium removal. 5-HT (10(-7) and 10(-6) M) elicited increases in ouabain-sensitive 86Rb+ uptake. These results suggest that: (1) 5-HT activates Na+,K(+)-ATPase, likely by an indirect mechanism that involves an increase of intracellular sodium concentration; and (2) the relaxant phase of 5-HT-evoked vasoactive responses is not mediated by the release of nitric oxide or prostacyclin from the endothelium.

Endothelial modulation of the ouabain-induced contraction in human placental vessels

Ouabain (1 x 10(-7)-3 x 10(-5) M) elicited concentration-dependent vasoconstriction in human placental arteries and veins. These responses, but not those produced by 10(-6) M 5-hydroxytryptamine, were increased after the removal of vascular endothelium. In placental arteries, the respective blockade of cyclooxygenase or lipoxygenase with indomethacin of 5,8,11,15-eicosatetraynoic acid as well as the inactivation of nitric oxide with phenidone or oxyhemoglobin and the inhibition of nitric oxide synthesis with NG-monomethyl L-arginine (all at 10(-5) M) did not mimic the effects of endothelial denudation on ouabain-evoked contractions. Bioassay experiments suggested that the above-mentioned endothelial effects are mediated by diffusible factors. 86Rb+ uptake, a method to measure sodium pump activity, was significantly reduced by the removal of endothelium. These results suggest the existence of an inhibitory modulation by the endothelium of the contractions induced by ouabain, likely mediated by a diffusible factor(s) released from these cells. The nature of this substance is unknown but is not related to prostaglandins or leukotrienes, and neither is it a nitric oxide-related compound. Its mechanism of action could be stimulating the activity of vascular sodium pump and/or antagonizing its inhibition by ouabain.

Na+/Ca2+ exchange mediation in the ouabain-induced contraction in human placental vessels

1. Ouabain induced concentration-dependent contractions in segments of human placental arteries and veins, which were practically abolished in a Ca(2+)-free medium and not modified by the calcium antagonist nifedipine or the calcium agonist Bay K 8644. 2. Ouabain (10(-4) M) elicited a time-dependent enhancement of the 45Ca2+ uptake, which remained equal in presence of nifedipine or Bay K 8644. 3. The Na+/Ca2+ exchange blocker amiloride reduced both the contractions and the 45Ca2+ uptake induced by ouabain, whereas the Na ionophore monensin produced a parallel shift to the left of the concentration-response curve to ouabain. 4. These results suggest that ouabain-induced contractions in these vessels are dependent on the extracellular Ca2+, which mainly enters into the cell through the Na+/Ca2+ exchange system.

Vascular smooth muscle proliferation in hypertensive transgenic rats

In vascular smooth muscle cell (VSMC) cultures from Sprague-Dawley (SD) and hypertensive transgenic rats for the mouse renin gene Ren-2 (TGR), the DNA synthesis, which was analyzed by the uptake of [3H]thymidine, was higher in TGR than SD VSMCs (2.5- to 8-fold, mean of 5.6-fold) under basal conditions. DNA synthesis was increased by fetal calf serum (10%) in SD cells more than in TGR VSMCs, and was decreased by heparin (400 micrograms/ml) and by phorbol-12,13-dibutyrate (10(-7) M) in TGR VSMCs to a higher degree than in SD cells. Neither endothelin (10(-7) M), angiotensinogen (10(-8) M), the renin inhibitor CGP 29,287 (10(-4) M), angiotensin I (10(-7) M), captopril (10(-5) M), angiotensin II (10(-7) M), nor saralasin (10(-6) M) modified DNA synthesis in either type of VSMCs. Sodium nitroprusside (10(-4) and 10(-3) M) increased DNA synthesis in both kinds of VSMCs but in TGR cultures it became toxic at 10(-3) M. 8-Bromocyclic GMP (10(-7) to 10(-5) M) reduced DNA synthesis in SD cells more than in TGR VSMCs. These results suggest that (a) cellular mechanisms of proliferation appear to be more activated in TGR VSMCs, likely involving a protein kinase C-dependent pathway but not the renin-angiotensin system, and (b) in both type of cells, sodium nitroprusside possesses proliferative properties whereas 8-bromocyclic GMP has antiproliferative properties.

Functional role of sodium pump in human placental arteries

Ouabain (10(-7) to 10(-4) M) elicited concentration-dependent contractile responses in human placental arteries. The contractions were reduced by 10(-4) M amiloride and Ca(2+)-free medium, but not affected by 10(-6) M nifedipine or 10(-6) M Bay-K-8644, which markedly reduced or potentiated 75 nM K(+)-induced contractions, respectively. After contracting the vessels with 10(-6) M prostaglandin F2 alpha in a K(+)-free medium, the subsequent addition of 7.5 mM K+ induced a marked relaxation, which was blocked by 10(-6) M ouabain. This glycoside (10(-8) to 10(-4) M) also produced a concentration-dependent reduction of 86Rb+ uptake. Scatchard analysis of the [3H]-ouabain binding to membrane fractions from human placental arteries suggests a single class of binding sites with a KD of 88.3 nM and a Bmax of 345 fmol/mg. 5-Hydroxytryptamine (5-HT; 10(-9) to 10(-5) M) caused concentration-dependent contractions. Single concentrations produced transient responses composed of an initial contraction, followed by a slow fall in tension. Ouabain (10(-8) to 10(-6) M), K(+)-free medium or the reduction of bath temperature (28 degrees C) did not modify contractions but inhibited the relaxant phase of the response. 5-HT (10(-8) to 10(-6) M) increased both total and ouabain-insensitive 86Rb+ uptake, but the difference between them was not modified. These data indicate that: (1) human placental arteries possess an important sodium pump activity, inhibition or stimulation of which markedly alters vascular tone, (2) ouabain-evoked contractions are produced by Ca2+ entry mainly through Na(+)-Ca2+ exchange, secondary to intracellular Na+ accumulation, (3) the relaxant component of 5-HT response is dependent on the activity of the sodium pump, (4) the activation of Na+,K(+)-ATPase activity by this amine is not apparently due to direct effect, and (5) the inhibition of the sodium pump can cause long lasting increases of placental vascular resistance in the presence of physiological concentrations of 5-HT.

Sodium pump activity and contractile effect of ouabain in human placental veins

The aim of the present study was to determine the number and affinity of [3H]ouabain binding sites, the sodium pump activity and the mechanisms involved in the contractile effects of ouabain in human placental veins. Scatchard analysis suggested the existence of a single population of binding sites with a KD of 196.7 nM and a Bmax of 1606 fmol/mg protein. The sodium pump activity was determined from the 86Rb+ uptake, which was reduced concentration dependently by ouabain (10(-8)-10(-4) M), and from the K+ (7.5 mM)-induced relaxation in veins preincubated in a K(+)-free medium and precontracted with PGF2 alpha (10(-6) M), which was also blocked by the glycoside (10(-6) M). Ouabain (10(-7)-10(-4) M) induced concentration-dependent contractions, which were not modified by either nifedipine or Bay K 8644 (10(-7) and 10(-6) M). Ca2+ omission from the medium or amiloride (10(-4) M) inhibited these contractions, whereas monensin (10(-6) M) potentiated them. These data indicate that human placental veins possess sodium pump activity and that its inhibition by ouabain induces potent contractions mainly mediated by Ca2+ entry through the Na(+)-Ca2+ exchange system.

Role of endothelium-formed nitric oxide on vascular responses

1. Endothelial cells of blood vessels generate factors which can modulate underlying smooth muscle tone, inducing vasorelaxation, (endothelium-derived relaxing factor, EDRF, and endothelium-derived hyperpolarizing factor) and/or vasoconstriction (endothelium-derived contracting factors, EDCFs, including the peptide endothelin). 2. EDRF is nitric oxide (NO) or a RNO compound from which this oxide is released. Its half-life is very short (6-50 sec), and it produces rapid vasodilations and inhibits platelet aggregation. 3. NO is formed from the terminal guanidino of L-arginine, but not of D-arginine. NO effects and NO formation are inhibited by NG-monomethyl-L-arginine (L-NMMA), but not by D-NMMA. These inhibitory effects are blocked by L-arginine. 4. Removal of endothelium or pathological situations that can induce endothelial dysfunction (atherosclerosis, diabetes, hypertension or subarachnoid hemorrhage) cause increases on the vascular contractility elicited by agonists (noradrenaline, serotonin, EDCFs, etc.). These findings suggest that EDRF produces a physiological inhibitory modulation of vascular smooth muscle tone and its alteration produces or facilitates the development of diseases such as hypertension or coronary and cerebral vasospasm.

Endothelium-derived contractile factors

1. Vascular endothelium releases different substances (endothelium-derived contractile factors, EDCFs), which mediate vasoconstrictor responses induced by several agents. 2. Clear differences have been reported in endothelium-dependent contractions, which suggest at least three distinct EDCFs, named EDCF1, EDCF2 and EDCF3, respectively. 3. EDCF1 is a cyclooxygenase metabolite(s) of arachidonic acid. EDCF2 is a polypeptide released from cultured endothelial cells. It has been isolated and identified as a 21-amino acid peptide called endothelin, which is described as the most potent vasoconstrictor agent known to date. EDCF3 is an unidentified contractile factor(s), which is neither EDCF1 nor EDCF2. 4. The physiological role of these endothelial contractile factors is not yet clear. However, they have been implicated in the local mechanisms involved in blood flow regulation, as well as in some pathological conditions, such as hypertension or cerebral vasospasm.

Ultrastructural changes induced by experimental subarachnoid haemorrhage and 6-hydroxydopamine in cat cerebral arteries

Transmission electron microscopy of the middle cerebral artery from cats exposed to subarachnoid injection of blood 3 and 7 days before, showed several damage of the vascular ultrastructure. The intima was thickened with swelling and vacuolization of endothelial cells, with a plump appearance and disruption of tight junctions. The cellular surface was corrugated and the subendothelial space contained proliferating and vacuolated smooth muscle cells capped by elastin and collagen fibres. The internal elastic lamina was also corrugated and disrupted. The adventitial changes were axonic cytoplasmic and mitochondrial swelling, virtual absence of synaptic vesicles, and disruption of the outer axonal membrane, suggesting denervation of cerebral vessels. With administration of 6-hydroxy-dopamine (6-OHDA), similar ultrastructural changes were observed in the adventitia. These observations indicate that denervation induced by subarachnoid bleeding could be involved in the pathophysiology of cerebrovascular spasm. Subarachnoid haemorrhage, but not 6-OHDA, affects also intima and tunica media, suggesting other mechanisms, in addition to denervation, can participate in the vasospasm.

Effects of the Ca2+ agonists, Bay K 8644 and CGP 28392, on isolated cat cerebral and peripheral arteries

Ca2+-agonists, Bay K 8644 and CGP 28392, produced concentration-dependent contractions in cat middle cerebral arteries. Only Bay K 8644 induced contractile responses in femoral arteries when they were partly depolarized with 15 mM K+. Nifedipine (0.3 microM) caused a reduction of the contractions elicited by low concentrations of both Ca2+ agonists. In femoral arteries, Bay K 8644 (0.1 microM) increased the contractions elicited by K+ concentrations from 25 to 120 mM, whereas CGP 28392 (0.1 microM) only potentiated the response caused by 25 mM K+. The increase of K+-responses induced by Bay K 8644 was blocked by nifedipine (0.1 microM), whereas that produced by CGP 28392 was not only antagonized but the remaining contractions were less than those obtained in the control situation. In both kinds of arteries preincubated with [3H]noradrenaline, nifedipine (50 microM), CGP 28392 (1 microM and 10 microM) and Bay K 8644 (1 microM) neither modified the spontaneous tritium release nor the stimulated tritium secretion elicited by K+ (25, 50 and 75 mM) or electrical stimulation. These data suggest that CGP 28392 and, mainly, Bay K 8644 facilitate the Ca2+ entry into smooth muscle cells, through voltage-dependent Ca2+ channels (that appear to be preactivated in cerebral arteries), whereas those present in the perivascular adrenergic nerve terminals are unaffected. This fact indicates that the channels existent in both vascular structures seem to have different properties.