Vasodilator responses of coronary resistance arteries of exercise-trained pigs

BACKGROUND: The purpose of this study was to test the hypothesis that vasodilator responses of porcine coronary resistance arteries are increased by exercise training. METHODS AND RESULTS: Yucatan miniature swine were randomly divided into groups of exercise-trained (ET) and sedentary (SED) control pigs. ET pigs were placed on a progressive treadmill training program lasting 16 to 20 weeks, and SED pigs remained inactive during the same time period. Coronary resistance arteries 64 to 157 microns in diameter were isolated for in vitro evaluation of relaxation responses to the endothelium-independent dilators sodium nitroprusside (1 x 10(-10) to 1 x 10(-4) mol/L) and adenosine (1 x 10(-10) to 1 x 10(-5) mol/L) and to bradykinin (1 x 10(-13) to 3 x 10(-7) mol/L), an endothelium-dependent agent. Relaxation responses to adenosine and sodium nitroprusside were not altered by exercise training. Endothelium-dependent relaxation to bradykinin was enhanced in coronary resistance arteries from ET pigs (IC50: ET, 0.07 +/- 0.02 nmol/L; SED, 1.59 +/- 0.09 nmol/L). To determine whether prostanoids and/or the nitric oxide synthase pathway were involved in the ET-induced changes in bradykinin-induced vasodilation, responses to bradykinin were examined in coronary resistance arteries from both ET and SED pigs in the presence of indomethacin and in the presence of nitro-monomethyl L-arginine (L-NMMA). Both indomethacin and L-NMMA produced significant inhibition of the bradykinin-induced relaxation in vessels from both groups. Despite decreased bradykinin-induced relaxation after indomethacin, bradykinin-induced vasodilation was still enhanced in vessels from the ET group. L-NMMA caused greater inhibition of the bradykinin-induced relaxation in coronary resistance arteries from ET pigs relative to arteries from SED pigs and eliminated the training-induced enhancement of the bradykinin responses. CONCLUSIONS: These results suggest that exercise training enhances bradykinin-induced vasodilation through increased endothelium-derived relaxing factor/nitric oxide production by the L-arginine/nitric oxide synthase pathway.     

Endothelial-dependent dynamic and antithrombotic properties of porcine aortic and pulmonary valves

BACKGROUND: In the present study, the endothelium-dependent antithrombotic and dynamic properties of porcine aortic (AoV) and pulmonary valves (PuV) were investigated. METHODS: Fifteen fresh AoV and 15 fresh PuV were obtained from 25 9-month-old swines. The valves were examined for endothelial function by pharmacologic evaluation (with and without endothelium) of both the endothelial-releasing capacity of prostacyclin and the endothelial-dependent dynamic response to relaxing (acetylcholine from 10[-10] mol/L to 10[-4] mol/L in AoV and PuV segments precontracted with norepinephrine [3 x 10(-6) mol/L]) and contracting (endothelin-1, from 10[-11] mol/L to 10[-5] mol/L; and NG-monomethyl-L-arginine, 10[-4] mol/L) drugs. The ultrastructural integrity of the endothelial valve layer was also examined with transmission electron microscopy. RESULTS: Acetylcholine caused potent relaxation in both AoV and PuV specimens with, but not in those without, endothelium. Endothelin-1 produced a concentration-dependent tension increase in AoV and PuV with and without endothelium. However, the intrinsic activity of the peptide significantly increased in tissues without endothelium. NG-monomethyl-L-arginine evoked a progressive increase in resting tension of the preparations, but the AoV and PuV without endothelium were less sensitive to the inhibition of the nitric oxide generation. Aortic and pulmonary valves with an intact endothelium showed a spontaneous ability to release prostacyclin. The basal release of this lipidic autacoid significantly decreased in cardiac valves without endothelium. This phenomenon was observed in both basal conditions, and under stimulation with the aforementioned drugs. Transmission electron microscopy showed the perfect preservation of endothelial cells in all the preparations examined. CONCLUSIONS: Valvular endothelium of AoV and PuV seems to have similar antithrombotic and dynamic functions of vascular endothelium, actively participating in valvular homeostasis.     

Development of endothelium-dependent relaxation in canine coronary collateral arteries

BACKGROUND: Little information exists regarding development of vasomotor control mechanisms during coronary collateral artery maturation. Therefore, we studied endothelium-dependent relaxation of canine collateral arteries isolated 2, 4, and 9 months after placement of an ameroid occluder around the proximal left circumflex coronary artery. RESULTS: Collateral arteries isolated after 2 months exhibited markedly reduced endothelium-dependent relaxation in response to acetylcholine (ACh; 10(-10) to 10(-4) mol/L) and bradykinin (BK; 10(-11) to 10(-6) mol/L) compared with relaxation of noncollateral coronary arteries (P<0.01). In contrast, endothelium-independent relaxation of collateral arteries to nitroprusside was only slightly reduced compared with relaxation of noncollateral arteries (P<0.05). Endothelium-dependent relaxation of collateral arteries isolated after 4 and 9 months was increased significantly, to the extent that relaxation to ACh and BK was not significantly different between collateral and noncollateral arteries at these periods. Inhibition of nitric oxide synthesis with NT-nitro-L-arginine methyl ester (L-NAME; 100 micromol/L) markedly inhibited ACh-induced relaxation in all noncollateral arteries and in collateral arteries isolated after 9 months. However, neither L-NAME nor indomethacin (5 micromol/L) alone inhibited ACh-mediated relaxation of collateral arteries isolated after 4 months. ACh-induced relaxation of these collateral arteries was only inhibited when arteries were preconstricted with 30 mmol/L K+ and pretreated with L-NAME and indomethacin (ie, when synthesis/effects of nitric oxide, prostaglandins, and endothelium-derived hyperpolarizing factor were inhibited). CONCLUSIONS: Development of endothelium-dependent relaxation in canine coronary collateral arteries is not complete after 2 months. After 4 months, endothelium-dependent relaxation of collateral arteries is similar to relaxation of noncollateral arteries, but the relaxation exhibits decreased dependence on synthesis of nitric oxide and increased involvement of prostaglandins and endothelium-derived hyperpolarizing factor(s). After 9 months of development, collateral arteries exhibit normal nitric oxide-dependent relaxation, similar to noncollateral arteries.     

Chronic alcohol intake reduces retinoic acid concentration and enhances AP-1 (c-Jun and c-Fos) expression in rat liver

OBJECTIVES: In vivo studies of the human coronary resistance circulation cannot control for indirect effects of myocardial metabolism, compression, and neurohumoral influences. This study directly examined the vasodilator responses of the human coronary microcirculation to both receptor-dependent and -independent agonists. METHODS: Atrial arterioles were dissected from human right atrial appendage (103 +/- 2 microns diameter, n = 185 vessels from 145 patients) obtained at the time of cardiopulmonary bypass and left ventricular vessels from explanted human hearts (148 +/- 10 microns diameter, n = 57 vessels from 18 patients). After dissection, vessels were mounted onto pipettes in Kreb's buffer under conditions of zero flow and at a constant distending pressure of 60 mmHg. Drugs were applied extraluminally and steady state changes in diameter measured with videomicroscopy. RESULTS: After contraction by endothelin or spontaneous tone, increasing concentrations of adenosine diphosphate (ADP) produced a similar dose-dependent dilation in vessels from atria (maximum 89 +/- 4%, n = 76) and ventricles (maximum 74 +/- 9%, n = 10). The dilation to ADP was abolished by mechanical removal of the endothelium. Similar dilator responses were found to bradykinin, substance P, arachidonic acid, and the calcium ionophore A23187 in both atria and ventricle. In contrast, acetylcholine (ACh) constricted all atrial vessels (-58 +/- 3%, n = 63) regardless of patient age or underlying disease. This constriction was attenuated by denudation, but not affected by inhibition of nitric oxide synthase or cyclo-oxygenase. Microvessels isolated from human ventricle exhibited a heterogeneous response to ACh with dilation being the predominant response. CONCLUSIONS: We conclude that isolated human coronary arterioles demonstrate endothelium-dependent dilation. However, the response to acetylcholine is unique with vasoconstriction in atrial vessels and dilation in ventricular arterioles.     

Increased production of nitric oxide in coronary arteries during congestive heart failure

Experiments were designed to determine whether a heterogeneity of endothelium-dependent relaxations in arteries from different vascular beds exists in experimental congestive heart failure (CHF) and to determine the mediators of those responses. CHF was produced in dogs by rapid ventricular pacing for 15 d. Rings of coronary, femoral, and renal arteries with and without endothelium from control and CHF dogs were suspended in organ chambers for measurement of isometric force. In arteries contracted with prostaglandin F2 alpha, endothelium-dependent relaxations to BHT 920 (an alpha 2-adrenergic agonist) were increased in coronary arteries from dogs with CHF (maximal relaxation: control -15 +/- 9% vs CHF -92 +/- 5%; n = 5-6; P < 0.05), with a modest enhancement in renal arteries. Relaxations to adenosine diphosphate and the calcium ionophore were unchanged. Relaxations to BHT 920 in CHF were reduced by NG monomethyl-L-arginine (L-NMMA) and pertussis toxin but not by indomethacin. These data suggest that endothelium-dependent relaxations are affected heterogeneously in CHF. The enhanced response to alpha 2-adrenergic agonists in the coronary artery is mediated by nitric oxide through a mechanism sensitive to inhibition by pertussis toxin. This selective increase in endothelium-dependent relaxations in the coronary artery may contribute to preserving coronary blood flow during CHF.     

Vascular hyporesponsiveness in aortic rings from cirrhotic rats: role of nitric oxide and endothelium

1. The role of nitric oxide as mediator of the vascular alterations present in different models of experimental liver cirrhosis is controversial. In the present study, we evaluated the role of nitric oxide and that of the endothelium in the response to phenylephrine and acetylcholine of isolated aortic rings from chronic bile duct-ligated (29 days) rats and their corresponding controls. Experiments were performed in rings with or without endothelium, in rings pretreated with N-omega-nitro-L-arginine methyl ester (10(-4) mol/l) to inhibit nitric oxide synthesis and in rings pretreated with aminoguanidine (10(-4) mol/l) to inhibit inducible nitric oxide synthesis. 2. Under basal conditions, the maximum absolute tension developed in response to cumulative addition of phenylephrine was significantly decreased in rings from bile duct-ligated animals (1.62 +/- 0.06 g) compared with the control rings (2.15 +/- 0.099). This hyporesponsiveness to phenylephrine of rings from bile duct-ligated animals was corrected after treatment with N-omega-nitro-L-arginine methyl ester and reduced, but not completely eliminated, in rings without endothelium. In contrast, aminoguanidine did not modify the lower response to phenylephrine rings from bile duct-ligated animals. ED50 values were not different between groups under any experimental conditions. 3. The endothelium-dependent vasodilatation to acetylcholine in phenylephrine-constricted rings was similar in both groups of animals, control and bile duct ligated, under all experimental conditions. N-omega-nitro-L-arginine methyl ester pretreatment and removal of the endothelium completely abolished the response to acetylcholine in cirrhotic and control rings. 4. These results demonstrate that in aortic rings from cirrhotic, bile duct-ligated rats, increased production of nitric oxide, mainly of endothelial origin, is responsible for the lower contractile response to phenylephrine. Our data, however, do not support the involvement of the inducible nitric oxide synthase isoform in this alteration. In contrast, endothelial vasodilatory response to acetylcholine is not altered in this model of cirrhosis, which indicates that not all mechanisms of nitric oxide release are abnormal.     

EndothelinA receptor blockade improves nitric oxide-mediated vasodilation in monocrotaline-induced pulmonary hypertension

BACKGROUND: Nitric oxide (NO) and endothelin (ET) have been implicated in the pathogenesis of pulmonary hypertension (PH). Chronic ETA antagonist therapy reduces PH in monocrotaline (MCT)-treated rats. Interactions between the L-arginine-NO pathway and the ET system have been described. We therefore studied the effect of long-term treatment with an oral ETA antagonist (LU 135252) on NO-related vasodilation in isolated lungs from control rats and rats with MCT-induced PH. METHODS AND RESULTS: Three weeks after MCT injection, PH was associated with an increase in right ventricular pressure (from 27.4 +/- 0.9 to 66.6 +/- 4.1 mm Hg) and a decrease in endothelium-independent vasodilation in response to sodium nitroprusside (10(-10) to 10(-5) mol/L; delta Emax, from 11.1 +/- 0.9 to 2.7 +/- 0.3 mm Hg). Endothelium-dependent vasodilation in response to acetylcholine (10(-9) to 10(-4) mol/L) and the calcium ionophore A23187 (10(-9) to 10(-7) mol/L) remained unaffected. Treatment with LU 135252 did not significantly affect the endothelium-dependent and -independent vasodilations in control rats. However, in MCT-treated rats, LU 135252 therapy significantly reduced right ventricular pressure (39.7 +/- 2.1 mm Hg), potentiated acetylcholine-induced vasodilatation (delta Emax, from 1.6 +/- 0.2 to 3.7 +/- 0.4 mm Hg), and improved the responses to sodium nitroprusside (delta Emax, from 2.7 +/- 0.3 to 5.6 +/- 0.6 mm Hg). LU 135252 did not significantly alter the non-receptor-mediated endothelium-dependent vasodilation to A23187 or pulmonary constitutive NO synthase activity. CONCLUSIONS: MCT PH is associated with a reduced smooth muscle responsiveness to NO but a maintained endothelium-dependent vasodilatory potency. Long-term ETA antagonist therapy not only restores smooth muscle responsiveness to NO but also increases endothelium-dependent dilation in response to acetylcholine. This mechanism may contribute to the therapeutic benefit of ETA antagonists in PH.     

Stellate neurones innervating the rat heart express N, L and P/Q calcium channels

BACKGROUND: Distension of the saphenous vein before and after coronary artery bypass grafting results in damage to mechanisms that regulate vascular tone. We have investigated the relationship between the magnitude of distending pressure and the degree of structural, biochemical and functional damage to the vessel wall. METHODS: Vessel segments that had been distended to either 100 or 300 mmHg were set up in isolated organ baths and the function of the smooth muscle and endothelial cells examined. All segments examined were then fixed for assessment of structural damage by scanning electron microscopy and for immunocytochemical localisation of endothelial nitric oxide synthase. RESULTS: Segments of saphenous vein distended to 100 mmHg retained their responsiveness to KCl (90 mmol/l) and phenylephrine (10(-6) mol/l), but those pressurised to 300 mmHg had significantly reduced responses to both agents. There was also a significant reduction in response to the endothelium-dependent dilators, acetylcholine (10(-10)-10(-6) mol/l) and bradykinin (10(-10)-10(-6) mol/l) in those segments distended to 300 mmHg. Quantitative studies of structural endothelial damage showed a significant loss of endothelium at 300 mmHg distension pressure. Remaining endothelial cells retained strong positive staining for endothelial nitric oxide synthase. By electron microscopic examination, those vessels distended to 100 mmHg showed lifting and rounding of individual cells, whereas segments distended to 300 mmHg revealed major areas of denuded endothelium. CONCLUSIONS: Distension of saphenous veins to pressures equivalent to those in the systemic circulation result in structural and biochemical changes in the endothelium that are not paralleled by immediate functional vasomotor changes.     

TRP trapped in fly signaling web

BACKGROUND: Recent reports indicate that myocarditis can be associated with acute myocardial ischemia and even myocardial infarction in patients with normal arteriograms. We therefore tested the hypothesis that patients with biopsy-proven myocarditis have endothelial dysfunction despite angiographically smooth epicardial coronary arteries. METHODS AND RESULTS: Graded concentrations of the endothelium-dependent vasodilator acetylcholine (10(-6) to 10(-4) mol/L) and for comparison, the non-endothelium-dependent vasodilator nitroglycerin (0.3 mg intracoronary), were infused into the left coronary arteries of 18 patients (mean age 47+/-9 years, 8 women and 10 men) with biopsy-proven myocarditis but without angiographically demonstrable coronary artery disease. Vascular responses were analyzed by quantitative coronary angiography. Three patients had an intact vasodilator response to acetylcholine concentrations of up to 10(-4) mol/L in all segments of the left coronary artery, with a mean dilatation of +9.9%+/-2%. In contrast, paradoxical constriction by acetylcholine occurred in 9 patients, who showed a mean change in coronary artery diameter of - 11%+/-3%. Six patients had no significant change in any segments in response to acetylcholine (-2.5%+/-4%). There was a significant inverse correlation between the number of T-lymphocytes in the myocardium and the response of the epicardial coronary arteries to acetylcholine (Pearson correlation coefficient -0.49, P=.03). CONCLUSIONS: It can be assumed that the process of myocarditis is associated with impairment of endothelium-dependent vasodilation in response to acetylcholine in most patients. Vasoconstriction in the presence of acetylcholine in myocarditis is likely to reflect an abnormality of endothelial function. Endothelial dysfunction of coronary arteries may explain the occurrence of myocardial ischemia in patients with myocarditis.     

Acute and chronic effects of dexfenfluramine on the porcine coronary artery

Experiments were designed to verify whether or not acute or chronic exposure to dexfenfluramine favors the occurrence of coronary vasospasm in vivo or in vitro. Rings of left anterior and left circumflex porcine coronary artery, with and without endothelium, were studied in conventional organ chambers for the measurement of isometric force. The donor pigs were divided into two groups: controls and animals fed for 4 weeks with dexfenfluramine. In each group, one-half of the animals underwent balloon denudation of the left anterior descending coronary artery at the beginning of the study. Coronary angiography was performed at the time of denudation and, in all animals, during the 3rd week of the study. Acutely, dexfenfluramine at concentrations higher than 10(-5) M caused contractions which were blunted by the presence of the endothelium and inhibited by indomethacin (an inhibitor of cyclooxygenase). Chronic treatment with dexfenfluramine did not affect coronary diameter and did not alter the response to intracoronary infusion of serotonin. Chronic treatment with dexfenfluramine reduced the contractions of rings without endothelium to serotonin, but not those to norepinephrine or endothelin. It did not affect endothelium-dependent relaxations in the absence or presence of pertussis toxin to serotonin, UK14304 (alpha-2 adrenergic agonist), adenosine diphosphate or aggregating platelets. Chronic treatment with dexfenfluramine did not modify relaxations of rings without endothelium to SIN-1 (nitric oxide donor; the active metabolite of molsidomine) or adenosine diphosphate. These findings do not support the hypothesis that acute or chronic exposure to dexfenfluramine favors the occurrence of coronary vasospasm.     

Paradoxic pulmonary vasoconstriction in response to acetylcholine in patients with primary pulmonary hypertension

Pulmonary vascular reactivity was assessed during diagnostic heart catheterization in two patients with pulmonary hypertension unexplained by pulmonary or cardiac disease and in five patients with atypical chest pain and normal coronary arteriograms. Acetylcholine, an endothelium-dependent vasodilator that also has a direct contracting effect on vascular smooth muscle cells, was infused in the right atrium in a step-wise increasing dose in order to obtain final blood concentrations in the pulmonary circulation ranging from 10(-6) mol/L to 10(-4) mol/L. In the five control patients, acetylcholine induced a dose-related decrease of pulmonary vascular resistance (-52 percent +/- 9 percent). In the patients with primary pulmonary arterial hypertension, however, acetylcholine caused a paradoxic increase of pulmonary arterial pressure and of pulmonary vascular resistance. Thus, it appears that endothelium-dependent vasodilation is impaired in the pulmonary circulation of patients with primary pulmonary arterial hypertension. Endothelial dysfunction in the pulmonary circulation may play a role in the pathophysiology of this disease.     

Volatile anesthetics affect calcium mobilization in bovine endothelial cells

BACKGROUND: The site where volatile anesthetics inhibit endothelium-dependent, nitric oxide-mediated vasodilation is unclear. To determine whether anesthetics could limit endothelium-dependent nitric oxide production by inhibiting receptor-mediated increases in cytosolic Ca2+, experiments were performed to see if the inhalational anesthetics halothane, isoflurane, and enflurane affect intracellular Ca2+ ([Ca2+]i) transients induced by the agonists bradykinin and adenosine triphosphate in cultured bovine aortic endothelial cells. METHODS: Bovine aortic endothelial cells, which had been loaded with the fluorescent Ca2+ indicator Fura-2, were added to medium preequilibrated with volatile anesthetic (1.25% and 2.5% for isoflurane, 1.755 and 3.5% for enflurane, and 0.75% and 1.5% for halothane). In Ca(2+)-containing medium, intracellular Ca2+ transients were elicited in response to bradykinin (10 nM and 1 microM) or adenosine triphosphate (1 microM and 100 microM). RESULTS: Both bradykinin and adenosine triphosphate triggered a rapid rise to peak [Ca2+]i followed by a gradual decline to a plateau above the resting level. Although basal [Ca2+]i was unaltered by the anesthetics, both halothane and enflurane, in a dose-dependent manner, depressed the peak and plateau of the [Ca2+]i transient elicited by 10 nM bradykinin, whereas isoflurane had no effect. When [Ca2+]i transients were elicited by 1 microM bradykinin, halothane (1% and 5%) did not alter peak and plateau levels. Halothane and enflurane also decreased [Ca2+]i transients evoked by 1 microM and 100 microM adenosine triphosphate, whereas isoflurane also had no effect in this setting. CONCLUSIONS: Halothane and enflurane, but not isoflurane, inhibit bradykinin- and adenosine triphosphate-stimulated Ca2+ transients in endothelial cells. Limitations of Ca2+ availability to activate constitutive endothelial nitric oxide synthase could allow for part, but not all, of the inhibition of endothelium-dependent nitric oxide-mediated vasodilation by inhalational anesthetics.     

Does acute improvement of endothelial dysfunction in coronary artery disease improve myocardial ischemia? A double-blind comparison of parenteral D- and L-arginine

OBJECTIVES: Parenteral L-arginine will improve myocardial ischemia in patients with obstructive coronary artery disease. BACKGROUND: Endothelial dysfunction causes coronary arterial constriction during stress, and L-arginine improves endothelial dysfunction. METHODS: Twenty-two patients with stable coronary artery disease and exercise-induced ST-segment depression underwent assessment of forearm endothelial function with acetylcholine and symptom-limited treadmill exercise testing during dextrose 5% infusion and after double-blind intravenous administration of L- and D-arginine (5 mg/kg/min) for 20 min. RESULTS: Forearm blood flow increased with both L- and D-arginine (33%+/-6% and 38%+/-7%, respectively, p < 0.001). Acetylcholine-mediated forearm vasodilation also improved with both L- and D-arginine (p < 0.0001). The magnitude of improvement was similar with both enantiomers and was observed in patients throughout the range of acetylcholine responses and cholesterol levels. Heart rate and blood pressure at rest and during each stage of exercise and exercise duration remained unchanged with L- and D-arginine compared to control. Ischemic threshold, measured either as the rate-pressure product or the duration of exercise at the onset of 1-mm ST-segment depression during exercise, also remained unchanged. Serum arginine, insulin and prolactin levels (p < 0.01) increased with both enantiomers. CONCLUSIONS: Parenteral arginine produces non-stereo-specific peripheral vasodilation and improves endothelium-dependent vasodilation in patients with stable coronary artery disease by stimulation of insulin-dependent nitric oxide release or by nonenzymatic nitric oxide generation. Despite enhanced endothelial function, there was no improvement in myocardial ischemia during stress with either enantiomer. Whether parenteral arginine will be of therapeutic benefit in acute coronary syndromes and oral arginine in myocardial ischemia needs to be studied further.     

The role of endothelium and nitric oxide in rat pial arteriolar dilatory responses to CO2 in vivo

Using a closed cranial window system and intravital microscopy/videometry, we studied the rat pial arteriolar (30-60 microns) responses to CO2 before and following a light/dye (L/D) endothelial injury or topical application of the nitric oxide synthase (NOS) inhibitor, nitro-L-arginine (L-NA) or its inactive form, D-NA. L/D treatment consisted of intravenous injection of sodium fluorescein and the illumination (for 90 s) of arteriolar discrete segments on the cortical surface with light from a mercury lamp. Functional changes in pial arteriolar endothelium were characterized by evaluating responses to topical application of acetylcholine (Ach, 5 x 10(-4) M) and to intravenous (i.v.) oxotremorine (OXO, a stable blood-brain barrier permeant muscarinic agonist, 1 microgram kg-1 min-1). After the L/D injury, dilation to Ach was absent whereas dilations to the NO donor, S-nitrosoacetyl-penicillamine (SNAP, 10(-5) M) and to CO2 (5%) were unchanged (PaCO2 = 70 mm Hg). Loss of Ach response but intact SNAP response confirmed functional endothelial injury and intact smooth-muscle function. The global endothelium-dependent vasodilation induced by i.v. OXO was markedly attenuated when expanding the L/D injury field from 300 microns to 6 mm in diameter. However, the global vasodilation induced by inhalation of CO2 was still unaffected by this increase in the area of light exposure. This provides evidence that the expanded exposure was capable of impairing global vasodilation resulting from endothelium-dependent stimuli but not from inhalation of CO2. The intact CO2 response despite an endothelial dysfunction suggests that the reported NO dependence of hypercapnia-induced cerebral hyperemia in rats cannot be attributed to an endothelial NO source.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of cardiopulmonary bypass and circulatory arrest on endothelium-dependent vasodilation in the lung

Endothelial injury with failure of pulmonary endothelium-dependent vasodilatation has been proposed as a possible cause for the increased pulmonary vascular resistance observed after cardiopulmonary bypass, but the mechanisms underlying this response are not understood. An in vivo piglet model was used to investigate the role of endothelium-dependent vasodilatation in postbypass pulmonary hypertension. The pulmonary vascular responses to acetylcholine, a receptor-mediated endothelium-dependent vasodilator, and nitric oxide, an endothelium-independent vasodilator, were studied in one group of animals after preconstriction with the thromboxane A2 analog U46619 (n = 6); a second group was studied after bypass with 30 minutes of deep hypothermic circulatory arrest (n = 6). After preconstriction with U46619, both acetylcholine and nitric oxide caused significant decreases in pulmonary vascular resistance (34% +/- 6% decrease, p = 0.007, and 39% +/- 4% decrease, p = 0.001). After cardiopulmonary bypass with circulatory arrest, acetylcholine did not significantly change pulmonary vascular resistance (0% +/- 8% decrease, p = 1.0), whereas nitric oxide produced a 32% +/- 4% decrease in pulmonary vascular resistance (p = 0.007). These results demonstrate a loss of receptor-mediated endothelium-dependent vasodilatation with normal vascular smooth muscle function after circulatory arrest. Administration of the nitric oxide synthase blocker Ngamma-nitro-L-arginine-methyl-ester after circulatory arrest significantly increased pulmonary vascular resistance; thus, although endothelial cell production of nitric oxide may be diminished, it continues to be a major contributor to pulmonary vasomotor tone after cardiopulmonary bypass with deep hypothermic circulatory arrest. In summary, cardiopulmonary bypass with deep hypothermic circulatory arrest results in selective pulmonary endothelial cell dysfunction with loss of receptor-mediated endothelium-dependent vasodilatation despite preserved ability of the endothelium to produce nitric oxide and intact vascular smooth muscle function.     

Effects of timolol and betaxolol on choroidal blood flow in the rabbit

Endothelium-dependent hyperpolarization of vascular smooth muscle cells (VSMCs) plays a crucial role in regulating vascular tone, especially in resistance vessels. It has been proposed that metabolites of arachidonic acid (AA), formed by cytochrome P-450 monooxygenase (P450), are endothelium-derived hyperpolarizing factors (EDHFs). These metabolites have been reported to mediate dilation to endogenous vasoactive compounds, such as bradykinin and acetylcholine. However, it is not known whether these metabolites of AA contribute to dilation of human resistance vessels. This is important since it has been proposed that EDHF serves as a compensatory mechanism to maintain dilation in disease states. Therefore, we studied the effect of AA on vessel diameter and VSMC membrane potential in isolated human coronary microvessels. Arterioles (81+/-5 microm, n=70) were dissected from right atrial appendages at the time of cardiac surgery and cannulated at a distending pressure of 60 mm Hg and zero flow. Changes in internal diameter were recorded with videomicroscopy. Some vessels were impaled with glass microelectrodes to measure membrane potential of VSMCs while internal diameters were simultaneously recorded. After constriction (47+/-2%) with endothelin-1, AA (10(-10)to 10(-5)mol/L) induced substantial dilation of human coronary microvessels, which was abolished by removal of the endothelium. Treatment with 17-octadecynoic acid (17-ODYA, 10(-5) mol/L; a P450 inhibitor) attenuated maximal dilation to AA (49+/-9% versus 91+/-4% [control]; P<0.05 versus control), whereas indomethacin (INDO, 10(-5) mol/L; a cyclooxygenase inhibitor) and N omega-nitro-L-arginine methyl ester (L-NAME, 10(-4) mol/L; a NO synthase inhibitor) were without effect. Both 17-ODYA and miconazole (10(-5) mol/L, a chemically distinct P450 inhibitor) further reduced the dilation to AA in the presence of INDO. The presence of 40 mmol/L KCl or charybdotoxin (10(-8) mol/L, a blocker of large-conductance Ca2+-activated K+ channels) impaired dilation to AA (19+/-9% [KCI] versus 76+/-5% [control] and 47+/-6% [charybdotoxin] versus 91+/-3% [control]; P<0.05 for both). After depolarization with endothelin-1 (-26+/-1 mV from -48+/-3 mV [before endothelin]), AA (10(-5)mol/L) in the presence of INDO and L-NAME induced hyperpolarization of VSMCs (-57+/-5 mV). In the presence of 17-ODYA together with INDO and L-NAME, endothelin produced similar depolarization (-26+/-2 mV from - 48+/- 3 mV), but hyperpolarization to AA was reduced (-33+/-2 mV; P<0.05 versus absence of 17-ODYA). AA metabolites formed primarily by P450 produce potent endothelium-dependent dilation of human coronary arterioles via opening of Ca2+-activated K+ channels and hyperpolarization of VSMCs. These findings support an important role for P450 metabolites in the regulation of human coronary arteriolar tone.     

Defective L-arginine-nitric oxide pathway in offspring of essential hypertensive patients

BACKGROUND: Essential hypertension is characterized by impaired endothelium-dependent vasodilation. The present study was designed to investigate whether this abnormality is a primary defect or a consequence of blood pressure increases. METHODS AND RESULTS: In offspring of essential hypertensive patients (n = 34) and normotensive subjects (n = 30), we evaluated forearm blood flow (strain-gauge plethysmography) modifications induced by intrabrachial acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 micrograms.100 mL-1.min-1), an endothelium-dependent vasodilator, and sodium nitroprusside (1, 2, and 4 micrograms.100 mL-1.min-1), an endothelium-independent vasodilator. Minimal forearm vascular resistances also were calculated as the ratio between mean intra-arterial pressure and maximal forearm blood flow induced by forearm ischemia and hand exercise. Vasodilation to acetylcholine was significantly (P < .01) blunted in offspring of hypertensive patients compared with offspring of normotensive subjects, whereas the responses to sodium nitroprusside and minimal forearm vascular resistances were similar. In two subgroups of 14 offspring of essential hypertensive patients but not in 10 offspring of normotensive subjects, vasodilation to acetylcholine was increased by intra-brachial L-arginine (1 mumol.100 mL-1.min-1), the substrate for nitric oxide synthesis, whereas in the other 10 and 8 offspring of essential hypertensive patients and normotensive subjects, respectively, cyclooxygenase blockade by intra-brachial indomethacin (50 micrograms.100 mL-1.min-1) was ineffective. CONCLUSIONS: Offspring of essential hypertensive patients are characterized by a reduced response to acetylcholine linked to a defect in the nitric oxide pathway, suggesting that an impairment in nitric oxide production precedes the onset of essential hypertension.     

Adventitial expression of recombinant eNOS gene restores NO production in arteries without endothelium

The current study was designed to determine the effect of recombinant endothelial nitric oxide synthase (eNOS) gene expression on endothelium-dependent relaxations to bradykinin in isolated canine basilar, coronary, or femoral arteries. Arterial rings were exposed ex vivo (30 minutes at 37 degrees C) to an adenoviral vector encoding either the eNOS gene (AdCMVeNOS) or the beta-galactosidase reporter gene (AdCMVbeta-Gal). Twenty-four hours after transduction, transgene expression was evident mainly in the adventitia. Expression of recombinant proteins was much higher in basilar arteries than in coronary or femoral arteries. Rings of control, AdCMVbeta-Gal, and AdCMVeNOS arteries with and without endothelium were suspended for isometric tension recording. Levels of cGMP were measured by radioimmunoassay. In AdCMVeNOS basilar arteries with endothelium, relaxations to low concentrations of bradykinin (3 x 10(-11) to 10(-9) mol/L) were significantly augmented. In contrast, in coronary and femoral arteries with endothelium, AdCMVeNOS transduction did not affect relaxations to bradykinin. Removal of the endothelium abolished bradykinin-induced relaxations in control and AdCMVbeta-Gal basilar arteries. However, in basilar arteries transduced with AdCMVeNOS even when the endothelium was removed, stimulation with bradykinin (3 x 10(-11) to 10(-9) mol/L) caused relaxations as well as increases in cGMP production. The relaxations to bradykinin were completely blocked by an NOS inhibitor, NG-nitro-L-arginine methyl ester. Electron microscopic analysis revealed that recombinant eNOS protein was expressed in fibroblasts of the basilar artery adventitia. These results suggest that genetically modified adventitial fibroblasts may restore production of NO in cerebral arteries without endothelium. Our findings support a novel concept in vascular biology that fibroblasts in the adventitia may play a role in the regulation of vascular tone after successful transfer and expression of recombinant eNOS gene.     

Different populations of progesterone receptor-steroid complexes in binding to specific DNA sequences: effects of salts on kinetics and specificity

The endothelium plays an obligatory role in a number of relaxations of isolated arteries. These endothelium-dependent relaxations are due to the release by the endothelial cells of potent vasodilator substances [endothelium-derived relaxing factors (EDRF)]. The best characterized EDRF is nitric oxide (NO). Nitric oxide is formed by the metabolism of L-arginine by the constitutive NO synthase of endothelial cells. In arterial smooth muscle, the relaxations evoked by EDRF are explained best by the stimulation by NO of soluble guanylate cyclase that leads to the accumulation of cyclic GMP. The endothelial cells also release an unidentified substance that causes hyperpolarization of the cell membrane (endothelium-derived hyperpolarizing factor, EDHF). The release of EDRF from the endothelium can be mediated by both pertussis toxin-sensitive (alpha2-adrenergic activation, serotonin, thrombin, aggregating platelets) and insensitive (adenosine diphosphate, bradykinin) G-proteins. In blood vessels from animals with regenerated endothelium, and/or atherosclerosis, there is a selective loss of the pertussis-toxin sensitive mechanism of EDRF-release which favors the occurrence of vasospasm, thrombosis and cellular growth.     

The endothelium-dependent response of human hepatic artery after preservation with the UW solution

The University of Wisconsin's (UW) solution has been used commonly for current liver transplantation. However, its effect on the vascular endothelium remains unclear. Experiments were designed to study the effects. Human hepatic arteries harvested from patients with hepatocellular carcinoma undergoing liver resection were preserved in 4 degree C physiological solution (group 1, the content showed on the text) and UW solution (group 2) for 1 hr. Segments of preserved and control (group 3) hepatic arteries were suspended in organ chamber to measure the isometric force. The relaxations to acetylcholine (ACH) and adenosine diphosphate in segments of hepatic artery with endothelium were significantly greater than those segments without endothelium. The maximal relaxation to ACH in arterial segments with endothelium of group 2 was significantly different from those of group 1 and 3 (group 1 to group 3, 82 +/- 2%, 57 +/- 6%, and 83 +/- 4% of the initial tension contracted by neoepinephrine (3 X 10-7 mole/l, P < 0.05). The maximal relaxation to adenosine diphosphate was similar to the response to ACH. Perfusate hypoxia (oxygen tension 30 +/- 5 mmHG) caused endothelium-dependent contraction of the arterial segments (group 1 to group 3, 233 +/- 32%, 276 +/- 35%, and 251 +/- 40% of the initial tension, P < 0.05). Endothelium-independent relaxation and contraction of human hepatic artery to sodium nitroprusside and norepinephrine were not altered by UW solution. In summary, the impaired endothelium-dependent relaxation by UW solution and prominent endothelium-dependent contraction to hypoxia of human hepatic artery would favor vasospasm and thrombus formation after liver transplantation.