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J Marín

Publications and source records attributed to J Marín.

At least 73 records · Page 4Linked to original sources
PubMed1999

Changes of cardiac calcium homeostasis in spontaneously hypertensive rats.

The aim of the present study was to assess the alterations in cardiac Ca2+ homeostasis induced by hypertension using electrically paced right ventricular strips from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). 2 Basal contractile force was higher in SHR than in WKY. Similarly, the beta-adrenoceptor agonist isoprenaline (10 nM-10 microM) induced a concentration-dependent positive inotropic effect that was higher in SHR than in WKY, which was in turn inhibited by the beta-adrenoceptor antagonist propranolol (1 microM) in both strains. 3 Preincubation of strips with the L-type Ca2+ channel blockers, nifedipine (1 microM) or verapamil (10 microM), markedly inhibited the isoprenaline response, the inhibition being higher in SHR than in WKY. However, this inhibition was minor by the T-type Ca2+ channel blocker mibefradil (10 microM). 4 Bay K 8644 (10 nM-10 microM), a L-type Ca2+ channel activator induced a concentration-dependent positive inotropic effect, that was greater in SHR than WKY. 5 Nifedipine and verapamil (both 0.1 nM-10 microM) inhibited in a concentration-dependent way the inotropic effect induced by 0.3 microM isoprenaline or 1 microM Bay K 8644. The inhibition was higher in SHR than in WKY. Mibefradil (0.1 nM-10 microM) only clearly inhibited the isoprenaline and Bay K 8644 inotropic effects at 10 microM in both strains. 6 The inhibitor of the sarcoplasmic reticulum Ca2+ release, ryanodine (10 nM-10 microM), was a more effective depressor of isoprenaline-induced response in SHR than in WKY. 7 These results suggest that cardiac Ca2+ homeostasis in SHR ventricular strips is altered compared with those of WKY, showing an increased Ca2+ entry through L-type Ca2+ channels and release from sarcoplasmic reticulum; the participation of T-type Ca2+ channels are irrelevant in this tissue.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1999

Effect of ouabain in pressurized middle cerebral arteries from normotensive and hypertensive rats.

The aim of the present study was to assess the ability of ouabain to induce vasomotor responses and interfere with the myogenic tone in isolated segments of middle cerebral arteries from male Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) subjected to different pressures and no-flow conditions using a pressure myograph. At 60 mmHg, ouabain (1 nM-1 mM) caused relaxations at concentrations of 10 microM and up in segments from WKY while 1 nM ouabain produced a relaxation that was unaltered by the remaining concentrations in SHR segments. The relaxations were higher in SHR than in WKY arteries. Endothelium removal practically abolished the relaxation in arteries from both strains, whereas 10 microM L-NAME (an inhibitor of nitric oxide synthase) had no effect. When arteries were pressurized from 20-120 mmHg, myogenic activity developed in 3 out of 10 WKY arteries while SHR arteries did not show myogenic tone. Endothelium removal did not alter the effects of pressure increase in both strains, and incubation of segments in a Ca(2+)-free medium to abolish myogenic tone, shifted the pressure-response curve of WKY segments to the left; pressure-response curves from SHR were not modified. Although ouabain (0.1 mM) did not alter the pressure-response curve from WKY segments, curves obtained from SHR were shifted to the left. These results suggest that: 1) ouabain produces vasodilation in pressurized middle cerebral arteries of WKY and SHR which is positively modulated by an endothelial factor distinct from nitric oxide; and 2) only WKY arteries develop myogenic activity while the diameter of SHR arteries is passively enhanced with increases in intraluminal pressure. This passive increase is facilitated by ouabain. Therefore, hypertension modifies the mechanical properties of cerebral arteries resulting in a loss in the capacity for autoregulation.

Animals↗
PubMed1999

Mechanisms involved in relaxation induced by exogenous nitric oxide in pig coronary arteries.

The aim of the present study was to analyze the mechanisms involved in the vasodilator responses elicited by nitric oxide (NO) in segments of porcine posterior descending coronary artery. Exogenous NO (0.1-30 microM) induced concentration-dependent relaxations in segments precontracted with a concentration of the thromboxane A2 mimetic, U-46619 (30-300 nM) that produced a contraction 70% (submaximal contraction) of that elicited by 75 mM K+ (maximal contraction). The relaxations were almost abolished by 6-anilinoquinoline-5,8-quinone (LY-83583, 10 microM), an inhibitor of guanylate cyclase, and with precontraction with 40 or 60 mM K+. Relaxations were reduced by 5 mM tetraethylammonium (TEA), a blocker of Ca(2+)-activated K+ channels (Kca channels) and unaltered by ouabain (500 microM), 4-aminopyridine (1 mM), glibenclamide (10 microM), apamin (1 microM) and charybdotoxin (0.3 microM), inhibitors of sodium pump, voltage-sensitive, ATP-sensitive, small-conductance Kca and large-conductance KcaK+ channels, respectively. These results suggest that the relaxation caused by exogenous NO is mediated by guanylate cyclase activation, with only a slight participation of a hyperpolarizing mechanism mediated by activation of Kca channels.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1999

Mechanisms of bradykinin-induced relaxation in pig coronary arteries.

Bradykinin (BK) induced endothelium- and concentration-dependent relaxations in segments of porcine posterior descending coronary arteries submaximally precontracted with the thromboxane A2 mimetic, U-46619. The effects of BK were reduced by L-NG-monomethylarginine (L-NMMA) and 6-anilinoquinoline-5,8-quinone (LY-83583), respective inhibitors of nitric oxide (NO) synthase and guanylate cyclase, but were unaffected by the cytochrome P450 monoxygenase blocker, thiopentone sodium; however, BK effects were slightly reduced by dimethyl sulfoxide (DMSO), an hydroxyl radical scavenger. Relaxant responses were reduced markedly by ouabain, a sodium pump inhibitor but only slightly by tetraethylammonium (TEA) and charybdotoxin, respective blockers of Ca-activated (KCa) and large-conductance (BKCa) K+ channels. However, BK responses were practically abolished by TEA + L-NMMA + ouabain while unaffected by apamin, 4-aminopyridine and glibenclamide, blockers of small-conductance KCa voltage-sensitive and ATP-sensitive K+ channels, respectively. In segments submaximally precontracted with K+, BK-induced relaxation was lower than that of those precontracted with U-46619, and was further reduced by L-NMMA, LY-83583 and especially, ouabain; L-NMMA + ouabain + TEA abolished the effect. Precontraction of segments with higher K+ concentrations almost abolished the relaxation. These results suggest that the relaxation to BK is mediated: 1) by endothelial NO release which activates guanylate cyclase of smooth muscle cells; 2) by hydroxyl radicals; and 3) by an endothelial hyperpolarizing factor, that does not seem to be a metabolite derived from cytochrome P450 monoxygenases and that relaxes activating K+ channels (mainly BKCa), and especially, the sodium pump.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1999

Gender differences in the endothelial regulation of alpha2-adrenoceptor-mediated contraction in the rat aorta.

The aim of this study was to determine the possible influence of sex hormones on the contractile responses induced by clonidine, an agonist of alpha2-adrenoceptors, as well as the endothelial modulation of these responses. For this purpose, thoracic aorta segments from male (control and castrated) and female (in oestrous phase and ovariectomized) rats were used. In intact segments from the four groups of rats, clonidine (0.01-10 micromol/l) induced concentration-dependent contractions, which were increased by the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester (0.1 mmol/l) or by endothelium removal, but were reduced by 1 micromol/l yohimbine (an alpha2-adrenoceptor antagonist) in all animals and by 1 micromol/l indomethacin (a cyclo-oxygenase inhibitor) in control males only. The rank order of the magnitude of the maximal response was: oestrous females>ovariectomized females>control males>castrated males, whereas the sensitivity to clonidine (EC50 value) was similar in all animals. In endothelium-denuded segments, the rank order was: oestrous females=control males>ovariectomized females=castrated males. These results suggest that: (1) the presence of oestrogen or androgen increases the contraction caused by alpha2-adrenoceptor activation with clonidine; (2) endothelium negatively modulates the response to this agonist in the four groups of rats, due to endothelial NO release (entirely in females and in part in males); (3) androgen also seems to modulate the response by stimulating the release of an endothelial contracting factor, probably a prostanoid; and (4) the endothelium of males has a greater capacity than that of comparable females for negative regulation of the tension generated by the underlying vascular smooth muscle.

Adrenergic alpha-Agonists↗
PubMed1999

Androgen deprivation facilitates acetylcholine-induced relaxation by superoxide anion generation.

The aim of the present study was to assess the role of superoxide anions in the relaxation induced by acetylcholine (ACh) in aortic segments from male rats, and to investigate if their production is altered by sex hormone deprivation. In segments precontracted with 10 nmol/l noradrenaline, ACh (0.1 nmol/l-10 micromol/l) induced concentration-dependent relaxation, which was greater in segments from castrated compared with control animals. ACh-induced relaxation was abolished in segments from control rats, and reduced in those from castrated rats, by 0.1 mmol/l N(G)-nitro-L-arginine methyl ester (L-NAME; a nitric oxide synthase inhibitor). Indomethacin (1 micromol/l; a cyclo-oxygenase blocker) decreased the ACh-induced relaxation in arteries from control males only. Incubation of segments with superoxide dismutase (SOD; 100 units/ml; a superoxide anion scavenger) enhanced and reduced relaxation in segments from control and castrated animals respectively. For arteries from castrated animals, the presence of SOD plus L-NAME abolished such responses. In these arteries, incubation with L-NAME abolished the relaxation caused by ACh when the segments were precontracted with 30 mmol/l KCl. In segments obtained from castrated rats and pretreated with L-NAME, 1 mmol/l tetraethylammonium or 0.4 micromol/l charybdotoxin [blockers of Ca(2+)-sensitive and large-conductance Ca(2+)-sensitive (BK(Ca)) K(+) channels respectively] abolished the relaxation induced by ACh. These results suggest that ACh generates endothelial NO and superoxide anions from the arterial wall in both control and castrated animals; these agents negatively modulate ACh-induced relaxation in control rats by destruction of NO, and positively modulate ACh-induced relaxation in castrated rats by activation of BK(Ca) channels.

Acetylcholine↗
PubMed1998

Bacterial sulfate production by biodesulfurization of aromatic hydrocarbons, determined by ion chromatography.

The use of bacteria to remove sulfur from crude oil or petroleum distillates is a novel concept that presents an alternative biotechnology to the current technology of hydrodesulfurization (HDS). Sulfur must be removed from crude oils prior use. The burning of fossil fuels containing sulfur releases sulfur dioxide into the atmosphere causing acid rain. The aim of this work is to determine the sulfate concentration by ion chromatography (IC), and calculate the percentage of transformation of organic bound sulfur, that is converted to sulfate, and estimate the efficiency of bacteria in desulfurization. IC is a suitable method for sulfate concentration determination. However, when chloride concentrations are significantly high, interference of the sulfate signal does occur. In this case, it could be avoided by diluting samples. A Dionex Model 2000i/SP IC system, with an anionic pre-column (Dionex AG4A), an anion separator column (Dionex AS4A), a suppressor column (Dionex AMMS-II), and a conductivity detector was used. The eluent (21 mM NaOH) and regenerant (electrolyzed 18 M omega/cm water) flow-rates were 1.0 and 2.0 ml/min, respectively. The sample loop volume was 10 microliters and the conductivity sensitivity was 30 muS. The diluted samples were filtered through a 0.45-micron filter before injection. The highest sulfate concentration detected was 24.10 mg/l, corresponding to a maximal conversion rate of 10% in a month. Sulfate ions were not detected in control samples. The correlation coefficient for a linear least squares fit was 0.99 (p < 0.001). The minimal concentration that we can read was 0.02 mg/l and this concentration corresponded to the limit of detection obtained under the conditions employed in this study. IC is an economical, sensitive and accurate way to estimate the sulfate concentrations in microbiological samples.

Bacillus↗
PubMed1998

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.

Acetylcholine↗
PubMed1998

Effect of age on the vasorelaxation elicited by cromakalim. Role of K+ channels and cyclic GMP.

The objective of this study was to investigate whether age induces changes on vasodilator response induced by cromakalim, an ATP-sensitive K+ (K(ATP)) channel opener, as well as the underlying mechanism involved in this possible alteration. For this purpose, aortic segments from young (3-5 months) and old (3 years) rabbits were used, which were precontracted with noradrenaline (NA, 1 microM). The vasodilator response induced by cromakalim (0.01-100 microM) was reduced in intact segments from old rabbits, and endothelium removal reduced and did not modify this effect in young and old animals, respectively. In both groups of animals, glibenclamide (10 microM), a blocker of K(ATP) channels, significantly reduced the response elicited by cromakalim, which was not modified by the large conductance Ca2+-activated K+ channel blocker charybdotoxin (ChTX, 0.4 microM). Acetylcholine (ACh, 10 microM) and sodium nitroprusside (SNP, 100 microM) induced a lesser vasodilator effect in aortic segments from old compared with young rabbits. In segments precontracted with NA, 10 microM ACh or 100 microM SNP similarly increased cGMP levels in both groups of animals. However, basal cGMP level was reduced in segments from old rabbits. Incubation with 8-bromo-cGMP (100 microM) increased the response induced by cromakalim in both groups of animals, reaching similar maximum values in young and old rabbits. The response induced by cromakalim plus 8-bromo-cGMP was markedly decreased by glibenclamide and unmodified by ChTx in both types of animals. These results suggest that aging decreases the vasodilator response to cromakalim, mechanism in which appears to be involved the maintained low cGMP levels observed in old rabbits, and that this messenger modulates the degree of K(ATP) channel activation.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1998

Differences in sensitivity, maximal response and position of the concentration-response curve to methacholine between asthmatics, patients with allergic rhinitis and healthy subjects.

The aim of this study was to detect differences in maximal response and position of the concentration-response curves to methacholine between asthmatics and subjects with allergic rhinitis. A total of 228 adults (107 mild asthmatics, 96 allergic rhinitics and 25 healthy control subjects) were challenged with methacholine. The test was interrupted when FEV1 dropped by more than 40% or when the highest concentration of methacholine (200 mg ml-1) had been administered. Concentration-response curves were characterized by their PC20 (concentration of methacholine that produced 20% fall in FEV1 = airway sensitivity), and if possible, by their EC50 (concentration of methacholine that produced 50% of the maximal response = position) and level of plateau. The proportion of subjects with plateau was significantly lower in asthmatics (18.7%) than in either allergic rhinitics (57.3%) or healthy subjects (92%). It was also significantly lower in allergic rhinitics than in healthy subjects. The level of plateau for asthmatics was (means +/- SD) 31.5 +/- 5.5%, compared with 20.8 +/- 8.1% in allergic rhinitics and 13.7 +/- 6.7% in healthy subjects (P < 0.01). It was also higher in allergic rhinitics than in healthy subjects (P < 0.01). The EC50 values were decreased in asthmatics when they were compared with either allergic rhinitics or healthy subjects (geometric mean EC50: asthmatics = 2.7 mg ml-1, allergic rhinitics = 6.2 mg ml-1, healthy subjects = 8.7 mg ml-1; P < 0.01), but no significant differences were detected between allergic rhinitics and healthy subjects. These results demonstrate that in subjects with allergic rhinitis, the prevalence and level of the plateau on the methacholine concentration-response curve is intermediate between that of asthmatics and normals. Furthermore, while the asthmatic curves differ from normal in having both an increased maximal response and a leftward shift, the rhinitic curves differ only in terms of plateau level. These results suggest that airway responsiveness in asthma and allergic rhinitis may be a consequence of mechanisms that are at least partially different.

Adult↗
PubMed1998

Role of lipid peroxidation and the glutathione-dependent antioxidant system in the impairment of endothelium-dependent relaxations with age.

1. Age-related changes in the blood prooxidant-antioxidant state, as well as its influence on the relaxant responses to acetylcholine (ACh) were studied in the tail artery from 6-, 24- and 30-month-old Sprague-Dawley (SD) rats. 2. Malondialdehyde (MDA) plasma levels increased 2 and 3 times in 24- and 30-month-old rats, respectively, when compared with 6-month-old rats (0.43+/-0.09 microM). This increase was accompanied by an induction of 6-phosphogluconate dehydrogenase (6PG-DH) and glutathione reductase (GR) activities in red blood cells from 24-month-old rats. In 30-month-old rats, a further induction of these enzymatic activities, as well as glucose-6-phosphate dehydrogenase (G6P-DH) and glutathione peroxidase (GPx) activities was observed. 3. No differences with age were found in the concentration-response curves to ACh in isolated tail artery segments from 6- and 24-month-old rats precontracted with 0.3 microM noradrenaline (NA). However, a decrease in sensitivity to ACh-induced relaxation was observed in 30-month-old rats; EC30 values were 3.5 (1.3-8.0) x 10(-7) M and 18.1 (8.9-30.1) x 10(-7) M for 6- and 30-month-old rats, respectively. Moreover, a decrease in maximum ACh relaxation (10 microM) was found in 30-month-old rats in comparison with that obtained in 6-month-old rats (58.5+/-3.9% and 42.5+/-3.4% of previous NA contraction, respectively). 4. Incubation of tail artery segments with MDA (0.5, 1 or 10 microM) caused a reduction of ACh-induced relaxations that was different in the three ages. Thus, the reduction of ACh-induced relaxations became significant with 0.5 microM MDA in 6-, with 1 microM MDA in 24-, and with 10 microM MDA in 30-month-old rats. In addition, MDA did not cause a shift in the concentration-response curve to ACh, but a decrease in the maximum response. 5. Superoxide dismutase (SOD; 150 u ml(-1), a superoxide anion scavenger) reversed the inhibitory effect of MDA on ACh-induced relaxations at all ages studied. 6. We conclude that: (1) ageing produces an increase in lipid peroxidation process, as indicated by the increase in MDA plasma levels, that is accompanied by an induction of lipid peroxide detoxification enzymes: (2) the changes in prooxidant-antioxidant equilibrium with age contribute, at least partially, to the impairment of the relaxant responses evoked by ACh; and (3) the effect of MDA appears to be mediated by superoxide anion at all ages studied.

Acetylcholine↗
PubMed1998

Effect of clenbuterol on non-endothelial nitric oxide release in rat mesenteric arteries and the involvement of beta-adrenoceptors.

1. The aim of the present study was to explore the contribution of adrenergic, sensory and nitrergic innervations to the inhibitory effects of the beta2-adrenoceptor agonist clenbuterol on responses to electrical field stimulation (EFS, 200 mA, 0.3 ms, 1-16 Hz, for 30 s, at 1 min interval) in rat mesenteric artery segments without endothelium and the possible involvement of adrenergic, sensory and nitrergic innervations. 2. Clenbuterol (1 microM) reduced EFS-induced contractile responses, and this effect was reversed by the beta-antagonist propranolol (1 microM) (contraction at 16 Hz expressed as % of 75 mM K+-induced contraction was: control, 69+/-9, clenbuterol, 31+/-6, n=13, P<0.001; control, 83+/-5, clenbuterol+propranolol 70+/-7, n=11, P>0.05). 3. In arteries preincubated with [3H]-noradrenaline (NA), clenbuterol did not modify the tritium overflow evoked by EFS (200 mA, 0.3 ms, 4 Hz, for 60 s; ratio between tritium release in the second and first stimuli was: control, 0.80+/-0.05 and clenbuterol added before second stimulus, 0.91+/-0.11, n=5, P>0.05). 4. The nitric oxide (NO) synthase inhibitors NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine methyl ester (L-NAME) (10 and 100 microM), and the guanylate cyclase inhibitor methylene blue (10 microM) increased the contractions caused by EFS (% contraction at 16 Hz, control, 81+/-7, n=26; 10 microM L-NMMA, 109+/-12, n=8, P<0.05; methylene blue, 119+/-6, n=6, P<0.05). However, these contractions were decreased by the NO synthase substrate L-arginine 10 microM (14+/-6%, n=6, P<0.001), but not modified by either the sensory neurones toxin capsaicin (0.5 microM, 75+/-6%, n=6, P>0.05) or the protein synthesis inhibitor cycloheximide (10 microM, 83+/-6%, n=8, P>0.05). None of these drugs altered the concentration-response curves to exogenous NA (n=7). 5. Pretreatment with capsaicin or cycloheximide did not modify the reduction of the EFS-evoked contraction provoked by clenbuterol. However the presence of L-NMMA (or L-NAME) or methylene blue did decrease the effect of clenbuterol (% contraction at 16 Hz, clenbuterol, 31+/-6, n=13; clenbuterol+10 microM L-NMMA, 93+/-11, n=8, P<0.05; clenbuterol+methylene blue, 90+/-7, n=6, P<0.05). 6. These results suggest that the reduction caused by clenbuterol in the contraction induced by EFS in rat mesenteric arteries seems to be mediated by NO release, through the activation of beta2-adrenoceptors probably present on nitrergic nerves.

Adrenergic beta-Agonists↗
PubMed1998

Contractile responses elicited by hydrogen peroxide in aorta from normotensive and hypertensive rats. Endothelial modulation and mechanism involved.

The present study analyses the influence of hypertension and endothelium on the effect induced by hydrogen peroxide (H2O2) on basal tone in aortic segments from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) of 6-month-old, as well as the possible mechanisms involved. Single (1 mM) or cumulative (100 nM-10 mM) concentrations of H2O2 produced a transient contraction or a concentration-dependent increase of basal tone, respectively, in segments from WKY and SHR. In both cases, the contractions were higher in intact segments from hypertensive than from normotensive rats, and increased by endothelium removal in both strains. Catalase (1000 u ml(-1), a H2O2 scavenger) abolished the contraction elicited by 1 mM H2O2 in both strains. Superoxide dismutase (SOD, 150 u ml(-1)) and dimethylsulphoxide (DMSO, 7 mM), scavengers of superoxide anions and hydroxyl radicals, respectively, did not alter H2O2-induced contractions in intact segments from both strains. However, L-NG-nitroarginine methyl ester (L-NAME, 100 microM, a nitric oxide synthase inhibitor) increased the response to H2O2 in normotensive rats, although the increase was less than that produced by endothelium removal. Incubation of segments with 1 mM H2O2 for 15 min and subsequent washout reduced the contractile responses induced by 75 mM KCl in intact segments from SHR and in endothelium-denuded segments from both strains; this effect being prevented by catalase (1000 u ml(-1)). Indomethacin (10 microM, a cyclo-oxygenase inhibitor) and SQ 29,548 (10 microM, a prostaglandin H2/thromboxane A2 receptor antagonist) practically abolished the contractions elicited by H2O2 in normotensive and hypertensive rats. We conclude that: (1) the oxidant stress induced by H2O2 produces contractions mediated by generation of a product of the cyclo-oxygenase pathway, prostaglandin H2 or more probably thromboxane A2, in normotensive and hypertensive rats; (2) oxygen-derived free radicals are not involved in the effect of H2O2; (3) in normotensive rats, endothelium protects against H2O2-mediated injury to contractile machinery, determined by the impairment of KCl-induced contractions; and (4) endothelial nitric oxide has a protective role on the contractile effect induced by H2O2, that is lost in hypertension.

Animals↗
PubMed1998

The L-arginine inhibition of rat middle cerebral artery contractile responses is mediated by inducible nitric oxide synthase.

1. The effect of L-arginine (L-Arg), the nitric oxide synthase (NOS) substrate, on the responses to prostaglandin F2alpha (PGF2alpha, 10 microM) and K+ (120 mM) in rat middle cerebral artery (MCA) segments was analysed. 2. PGF2alpha induced a stable contraction of 0.35+/-0.06 mN mm(-1); the subsequent addition of bradykinin (BK, 1 microM) produced a relaxation of 42+/-9% of the PGF2alpha-induced tone. K+ induced a response consisting of a rapid basal tone increase (1.42+/-0.16 mN mm(-1)) followed by a decrease to a stable phase (1.24+/-0.15 mN mm(-1)). 3. L-Arg (0.1 mM), but not D-Arg, decreased the basal tone and reduced the contraction to PGF2alpha in segments with and without endothelium. The contractile response to K+ was also reduced and not maintained in the presence of L-Arg. 4. The inhibitory effect of L-Arg on the PGF2alpha- and K+-induced contractions was completely reversed by the NOS inhibitor, NG-monomethyl-L-arginine (L-NMMA, 0.1 mM). 5. Pre-incubation of segments with dexamethasone (1 microM), to inhibit inducible NOS (iNOS), or with the antibiotic polymyxin B (10 microg ml(-1)) reduced the L-Arg inhibition, whereas it was increased by lipopolysaccharide (LPS, 100 ng ml(-1)), an inductor of iNOS. L-NMMA antagonized the effects of dexamethasone and LPS. 6. The present results suggest that L-Arg inhibition of the PGF2alpha- and K+-induced contractions in rat MCA is the result of NO synthesis by iNOS stimulation.

Animals↗
PubMed1998

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.

Angiotensin II↗
PubMed1998

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.

Animals↗
PubMed1997

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.

Angiotensin II↗