Role of vascular nitric oxide in physiological and pathological conditions.

This review describes the ability of certain diseases, such as essential hypertension, atherosclerosis, angina, and vasospasm, to reduce vascular nitric oxide (NO) formation or to increase its metabolism. In contrast, others, such as hypotension, sepsis, stroke, myocardial depression, and inflammatory responses, increase NO synthesis. The mechanism implicated in the changes in the formation and metabolism of NO are described. To prevent or treat these pathological processes, in which a deficiency in vascular NO formation plays a causative role, NO may be provided through methods such as direct NO administration or indirect NO supply through either NO donors or L-arginine, which facilitates NO formation.

Role of Ca(2+) and vitamin D in the prevention and treatment of osteoporosis.

Osteoporosis is defined as a progressive systemic skeletal disease characterised by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture. The clinical relevance of osteoporosis derives from the fractures that it produces. More than one-third of the adult women will suffer one or more osteoporotic fractures in their lifetime. The lifetime risk in men is approximately one-half that in women. The decrease of the bone mineral density is the most important cause of risk fracture. Among other factors, Ca(2+) and vitamin D deficiencies are important risk factors for a decrease in bone mineral density, consequently inducing osteoporosis. The high prevalence of vitamin D deficiency in healthy elderly people living mainly in southern European countries increase the risk of osteoporotic fractures in these populations above those anticipated for the general elderly population of the European community. In addition, the ageing of the European population will double the number of osteoporotic fractures over the next 50 years, unless adequate preventative measures are undertaken. The efficacy and safety of Ca(2+) and vitamin D supplements at preventing bone loss and reducing the risk of hip and other fractures have been assessed in different clinical trials, which are extensively discussed in this review.

Mechanisms involved in the hemodynamic alterations in congestive heart failure as a basis for a rational pharmacological treatment.

Congestive heart failure is a complex syndrome and one of the major cardiological problems of our time. It is characterized by an important neurohumoral activation to compensate for the reduction of cardiac output and blood pressure, that worsens the prognosis with time. The aim of the treatment is focused on how to improve the quality of life and how to prolong survival. Usually, treatment, either symptomatic or directed to control the neuroendocrine compensatory changes, is necessary. The drugs currently used are angiotensin-converting enzyme inhibitors, diuretics, digoxin, and beta-adrenoceptor agonists. In addition, new drugs, such as angiotensin II receptor antagonists, beta-adrenoceptor antagonists, ibopamine, Ca(2+) antagonists, neutral endopeptidase inhibitors, vasopressin antagonists, Ca(2+)-sensitizers with cyclic AMP-dependent or -independent mechanisms, and endothelin antagonists, are also being used.

[Doxazosine associated to renin-angiotensin blockers and calcioantagonists in chronic renal failure patients]. / Doxazosina asociada a la combinación bloqueante del eje-renina-angiotensina y calcioantagonista en pacientes con insuficiencia renal crónica.

OBJECTIVE: To evaluate the safety and effectiveness of the alfa-blocker doxazosin GITS in CRF patients. DESIGN AND METHODS: The study recruited 203 CRF patients (creatinine > 1,4 mg/dl for males, creatinine > 1,2 mg/dl for females, or creatinine clearance < 80 ml/min). All patients were receiving ACE inhibitores (63.4%) or angiotensin II antagonist (36.6%) therapy but they had higher blood pressure than recommended for CRF (130/85 mmHg). Patients were clinically evaluated 1, 3 and 6 moths after starting treatment with lercanidipine (10 mg once daily). Patients with high blood pressure in spite of combined therapy with two drugs added doxazosin GITS 4-8 mg once daily to treatment. RESULT: 57 patients rendered evaluable for the study (age 64.8 +/- 12.7 years, 47.4% males and 52.6 females). BP significantly decrease from 164 +/- 17/92 +/- 9 mmHg to 135 +/- 13/78 +/- 8 mmHg. 67.6% patients showed a significant BP reduction and 32.4% gets optimal BP control (< 130/85 mmHg). Two patients (3.6%) showed untoward effects. No biochemical changes were detected. CONCLUSIONS: Doxazosin showed a good antihypertensive effect in CRF patients when used as third drug in resistant severe hypertension. It has a good tolerability profile and showed a neutral profile on biochemical parameters.

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.

Homeostasis between lipid peroxidation and antioxidant enzyme activities in healthy human aging.

In healthy people the plasma malondialdehyde increases with age, however there is a simultaneous rise in the activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase in red blood cells, although both enzymes show a biphasic behaviour, that is, reaching the lowest values at 40-50 years of age to rise remarkably later on. No significant changes were found in the case of glutathione peroxidase but the age-dependent behaviour is similar to the other enzymes mentioned above. The activity of glutathione reductase shows a clear increase depending on age, up to middle age, with or without flavin adenine dinucleotide. We conclude that the increase in the activities of the anti-oxidant enzymes of the red blood cells during aging, could be interpreted as a positive feedback mechanism in response to rising lipid peroxidation. Consequently, from the point of view of the parameters used the homeostasis between the production of free radicals and anti-oxidant systems seems to be maintained in the common, normal aging pattern.

Endothelium stimulates the vascular smooth muscle cell Na/K pump of normotensive and hypertensive rats by a protein kinase C pathway.

OBJECTIVE: To investigate the mechanisms involved in the endothelial stimulation of the vascular smooth muscle cell Na/K pump and their possible alteration by hypertension. METHODS: The Na/K pump activity of vascular smooth muscle cells (VSMC) from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) was studied using the radioactive analogue of K+ 86Rb+. Conditioned medium of bovine endothelial aortic cells was used to investigate the endothelial modulation of VSMC Na/K pump activity. RESULTS: Conditioned medium enhanced VSMC Na/K pump activity (ouabain-sensitive 86Rb+ uptake), this effect being higher in SHR cells. This stimulatory effect was neither modified in Na(+)-loaded cells from both rat strains nor inhibited by the Na/H exchange blocker amiloride. Permeable analogues of cyclic adenosine and guanosine monophosphates did not modify the baseline VSMC Na/K pump activity of WKY rats and SHR, and subsequently the guanylate cyclase inhibitor methylene blue did not alter the conditioned medium-induced stimulation of the pump. However, the Ca(2+)-channel inhibitor nifedipine reduced the Na/K pump stimulation by conditioned medium, this decrease being higher in WKY rat than in SHR VSMC. Moreover, treatment with phorbol 12,13-dibutyrate for 24 h or with the protein kinase C inhibitor staurosporine for 15 min reduced the conditioned medium-induced Na/K pump activation in both VSMC cultures. CONCLUSIONS: Na/K pump stimulation by conditioned medium of endothelial cells is mediated mainly via activation of protein kinase C in VSMC from either WKY or SHR VSMC. However, SHR VSMC show some alterations in their intracellular signalling pathways.

Nitric oxide synthase induction by ouabain in vascular smooth muscle cells from normotensive and hypertensive rats.

OBJECTIVE: To investigate the effect of ouabain on inducible nitric oxide synthase (iNOS) activity and expression in cytokine-stimulated vascular smooth muscle cells (VSMC) from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). METHODS: VSMC were treated for 24 h and afterwards, nitric oxide (NO) release was determined by the production of nitrite, a stable metabolite of NO. Activity of iNOS was measured by the conversion of [3H]-L-arginine to [3H]-L-citrulline and iNOS protein expression by Western blotting. RESULTS: Ouabain (0.01-1 mmol/l) further enhanced interleukin-1beta (II-1beta)-induced nitrite production by WKY and SHR VSMC, although a more pronounced effect was observed in SHR cells (maximum response 52.1 +/- 5.2 and 71.2 +/- 6.4% of 11-1beta effect in WKY and SHR cells, respectively). Such response on NO release was mimicked by the calcium ionophore A 23187 (0.01-1 micromol/l) and abolished by the voltage-operated calcium channels (VOCC) nifedipine (0.1 micromol/l). Expression of iNOS showed that ouabain increased the synthesis of the enzyme in WKY and SHR VSMC stimulated with II-1beta, and this effect was higher in SHR cells. The increased iNOS expression was significantly reduced by nifedipine. CONCLUSIONS: Ouabain stimulation of iNOS expression and activity in II-1beta-stimulated VSMCs from WKY rats and SHR seems to be related to increased intracellular calcium influx through VOCC. The more pronounced effect observed in SHR VSMC could be explained by an altered calcium entry in the hypertensive strain.

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.

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.

Age-related changes in vascular responses.

Aging causes changes in the structure and function of the vessels that leads to an increase in the incidence of certain cardiovascular diseases, such as hypertension, coronary artery disease, heart failure, and postural hypotension with enhancement of both morbidity and mortality. When aging is associated with hypertension, these changes are increased. Aging alters endothelial cells, and so the vascular tone regulation, reducing the endothelium-dependent relaxations, probably by a decrease in endothelial synthesis or release of nitric oxide. In addition, endothelium-independent relaxations are essentially unaltered, those elicited by beta-adrenoceptor agonists being usually reduced. Aging scarcely modifies the contractions induced by different agents, such as 5-hydroxytryptamine, histamine, high potassium, and angiotensin, whereas reduces those elicited by noradrenaline or endothelin. Vascular Ca(2+) homeostasis appears to be altered in aging. The extracellular Ca(2+) dependence of contractile responses elicited by agonists is enhanced, which explains the increased sensitivity to Ca(2+) antagonists in elderly. Finally, Na(+) pump activity, that controls cellular ionic homeostasis, seems to be reduced in aging. The contractions elicited by Na(+) pump inhibition with ouabain are negatively modulated by the release of a diffusible endothelial factor, an effect lost in aging, being replaced by an endothelium-dependent contracting factor that facilitates ouabain responses.

Changes in plasma oxidative state with age and their influence on contractions elicited by noradrenaline in the rat tail artery.

The present study analyzes the changes in plasma oxidative state with age and their influence on the contractions induced by noradrenaline (NA) in endothelium-denuded segments from the tail artery of 6- (young), 24- (old) and 30- (very old) month-old Sprague Dawley rats. The sensitivity (-log EC50) to NA increased with age, this increase being higher in old than in very old animals. Moreover, the maximum response (Emax) to NA did not change in old rats, whereas decreased in very old animals. We also found a progressive increase in the plasma oxidative state with age, measured as malondialdehyde (MDA) levels, that was accompanied by a decrease in the plasma antioxidative state, measured as glutathione peroxidase activity. In addition, MDA (0.5, 1 and 10 microM) potentiated the NA responses in 6-, 24- and 30-month-old rats, respectively, without affecting Emax. In young animals, catalase (1000 U/ml) or dimethylsulfoxide (7 mM), scavengers of hydrogen peroxide or hydroxyl radicals, respectively, did not modify either the contractions induced by NA in control situation or the potentiation of these responses caused by MDA. However, the superoxide anion scavenger, superoxide dismutase (SOD, 150 U/ml), completely reversed the increase in sensitivity to NA caused by MDA, without affecting NA responses in control situation. These results suggest that the increase in NA sensitivity with age could be due, at least in part, to the enhancement of plasma oxidative state during aging. In addition, in this alteration of the responses to NA caused by MDA, the generation of superoxide anions appears to be involved. This study supports the hypothesis that the enhancement of plasma oxidative state could play an important role in the increase of vascular resistance with age.

Vasodilator effect and tolerance induced by the nitrocompound SIN-1 in rabbit femoral artery.

The aim of this study was to investigate vascular actions of SIN-1 in comparison with those of other nitrovasodilators in rabbit femoral arteries. SIN-1 induced relaxations that were unaltered by endothelium removal, inhibition of nitric oxide (NO) synthase and inhibition of the formation of oxygen reactive species such as anion superoxide, hydrogen peroxide and hydroxyl radical. Oxyhemoglobin reduced the relaxation caused by SIN-1 and exogenous NO. Exogenous NO and nitroglycerin relaxations were endothelium-independent. However, those produced by sodium nitroprusside were increased in endothelium denuded segments. Preincubation of segments with nitroglycerin (100 mM) produced a marked tolerance, whereas this effect did not occur when preincubation was done with SIN-1 (100 mM). To analyze the in vivo tolerance, rabbits were chronically treated with SIN-1 or nitroglycerin (15 mg/kg every 8 h, s.c.). Chronic treatment with SIN-1 for 5 days did not reduce relaxation response. However, 3 days of treatment with nitroglycerin induced a marked reduction of relaxations. Chronic treatment with nitroglycerin did not modify the relaxation caused by SIN-1, i.e., there was no cross-tolerance between the two drugs. These results suggest that the endothelium-independent relaxation elicited by SIN-1 is not modulated by endothelial NO or free radicals, and does not produce tolerance after its prolonged administration as occurs with nitroglycerin.

[Lercanidipine in diabetic patients with renal failure]. / Lercanidipino en pacientes diabéticos it con insuficiencia renal.

OBJECTIVE: To evaluate the safe use of a new calcium channel blocker, lercanidipine, in diabetic chronic renal failure (CRF) patients. DESIGN AND METHODS: The study recruited 42 diabetic CRF patients (creatinine > 1.4 mg/dl for males, creatinine > 1.2 mg/dl for females, or creatinine clearance < 70 ml/min). Mean age was 68.2 +/- 9.1 years. 53.8% were males and 46.2% females. Three patients were type 1 diabetics and 39 ones were type II. All patients were receiving ACE inhibitors (67.4%) or angiotensin II antagonist (32.6%) therapy but they had higher blood pressure than recommended for CRF patients (130/85 mmHg). No patients were under diuretic treatment. Patients were clinically evaluated 1, 3 and 6 months after starting treatment with lercanidipine. Samples for urine and blood examination were taken during the examination. When needed, a third drug was added to treatment, excluding diuretics. Creatinine clearance was measured using 24 h urine collection. RESULTS: BP significantly decrease from 163 +/- 18/90 +/- 8 mmHg to 134 +/- 12/77 +/- 9 mmHg. One half of patients showed significant reduction of blood pressure, 26.7% reached the target blood pressure (< 130/85 mmHg) and 20.0% gets optimal BP control (< 130/85 mmHg). No one patient showed untoward effects. No edema was detected nor adverse effects related to vasodilatation were found. Plasmatic creatinine did not change (1.9 +/- 0.5 baseline vs 1.8 +/- 0.5 mg/dl) and creatinine clearance increased at the end visit (40.1 +/- 14.5 baseline vs 45.4 +/- 18.2 ml/min) but the difference was not significant. Proteinuria was unchanged. CONCLUSIONS: Lercanidipine showed a good antihypertensive effect in diabetics CRF patients. It has a good tolerability profile and showed neutral effect on plasmatic lipids. Neither impairment of renal function nor increment in proteinuria were detected.

Impairment of acetylcholine relaxations by malondialdehyde, a marker of lipid peroxidation.

The effect of malondialdehyde (MDA), a lipid peroxidation marker, on the relaxations evoked by acetylcholine (ACh) was analyzed in tail arteries of Sprague-Dawley rats, which have MDA plasma levels of 0.43 +/- 0.10 microM. MDA (0.5-30 microM) produced an inhibition of ACh relaxations that persisted after repeated washing periods, and was independent of the incubation time. MDA did not modify the vasodilator responses to either exogenous nitric oxide (NO) or sodium nitroprusside, a NO donor. L-Arginine (the NO synthase substrate) did not prevent the impairment of relaxations to ACh caused by MDA. The association of N omega-nitro-L-arginine methyl ester (a NO synthase inhibitor) and MDA produced an additive inhibition of the ACh-induced relaxations. Superoxide dismutase (a superoxide anion scavenger) completely reversed the inhibitory effect of MDA. These results suggest: (1) MDA is not only a marker of lipid peroxidation but also an agent that can impair endothelium-dependent relaxations; (2) this impairment does not seem to be due to an interference with guanylate cyclase activation by NO or with NO synthase pathway; (3) the effect of MDA appears to be mediated by superoxide anion, and (4) MDA could propagate lipid peroxidation chain reactions in endothelial membranes, that could alter the function of muscarinic receptors.

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.

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.

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.

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.

Oxidative stress induced by tert-butyl hydroperoxide causes vasoconstriction in the aorta from hypertensive and aged rats: role of cyclooxygenase-2 isoform.

We analyzed the mechanisms involved in the effect of tert-butyl hydroperoxide (t-BOOH) in isolated aortic rings with and without endothelium from normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) at 6, 18, and 24 months of age. t-BOOH (1 microM-10 mM) induced concentration-dependent contractions that were scarcely modified by aging and potentiated in SHR and by endothelium removal. The nitric oxide synthase and prostacyclin synthase inhibitors N(G)-nitro-L-arginine methyl ester (100 microM) and tranylcypromine (100 microM), respectively, increased both basal tone and the t-BOOH-induced contractions in intact segments from WKY, with these effects not observed in SHR. Indomethacin (10 microM), a nonspecific cyclooxygenase inhibitor, and SQ 29,548 (10 microM), a prostaglandin H(2)/thromboxane A(2) receptor blocker, abolished the t-BOOH-induced vasoconstriction, independent of age and hypertension. In both strains, these contractile responses were unaltered by the thromboxane synthase inhibitor imidazole (10 microM). The cyclooxygenase-2 inhibitor NS-398 (10 microM) abolished or markedly reduced the t-BOOH-induced contractions in segments with or without endothelium, respectively. In addition, expression of cyclooxygenase-2 protein was detected in aorta from WKY and SHR in either basal condition or after stimulation with t-BOOH. These results suggest that (1) t-BOOH-induced vasoconstriction in the aorta from WKY and SHR is essentially mediated by cyclooxygenase-2 metabolites, different from thromboxane-A(2), probably prostaglandin-H(2), and/or isoprostanes; (2) aging scarcely modifies, whereas endothelium negatively modulates, these contractions in both strains; and (3) nitric oxide and prostacyclin exert a negative modulator role on the t-BOOH-induced vasoconstriction in WKY, with this modulator role lost in SHR.