In vivo role of heme oxygenase in ischemic coronary vasodilation

The heart constitutively expresses heme oxygenase (HO)-2, which catabolizes heme-containing proteins to produce biliverdin and carbon monoxide (CO). The heart also contains many possible substrates for HO-2 such as heme groups of myoglobin and cytochrome P-450s, which potentially could be metabolized into CO. As a result of observations that CO activates guanylyl cyclase and induces vascular relaxation and that HO appears to confer protection from ischemic injury, we hypothesized that the HO-CO pathway is involved in ischemic vasodilation in the coronary microcirculation. Responses of epicardial coronary arterioles to ischemia (perfusion pressure approximately 40 mmHg; flow velocity decreased by approximately 50%; dL/dt reduced by approximately 60%) were measured using stroboscopic fluorescence microangiography in 34 open-chest anesthetized dogs. Ischemia caused vasodilation of coronary arterioles by 36 +/- 6%. Administration of N(G)-monomethyl-L-arginine (L-NMMA, 3 micromol.kg(-1).min(-1) intracoronary), indomethacin (10 mg/kg iv), and K(+) (60 mM, epicardial suffusion) to prevent the actions of nitric oxide, prostaglandins, and hyperpolarizing factors, respectively, partially inhibited dilation during ischemia (36 +/- 6 vs. 15 +/- 4%; P < 0.05). The residual vasodilation during ischemia after antagonist administration was inhibited by tin mesoporphyrin IX (SnMP, 10 mg/kg iv), which is an inhibitor of HO (15 +/- 4 vs. 7 +/- 2%; P < 0.05 vs. before SnMP). The guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (10(-5) M, epicardial suffusion) also inhibited vasodilation during ischemia in the presence of L-NMMA with indomethacin and KCl. Moreover, administration of heme-L-arginate, which is a substrate for HO, produced dilation after ischemia but not after control conditions. We conclude that during myocardial ischemia, HO-2 activation can produce cGMP-mediated vasodilation presumably via the production of CO. This vasodilatory pathway appears to play a backup role and is activated only when other mechanisms of vasodilation during ischemia are exhausted.     

Mechanism of thrombin-induced vasodilation in human coronary arterioles

Thrombin (Thromb), activated as part of the clotting cascade, dilates conduit arteries through an endothelial pertussis toxin (PTX)-sensitive G-protein receptor and releases nitric oxide (NO). Thromb also acts on downstream microvessels. Therefore, we examined whether Thromb dilates human coronary arterioles (HCA). HCA from right atrial appendages were constricted by 30-50% with endothelin-1. Dilation to Thromb (10(-4)-1 U/ml) was assessed before and after inhibitors with videomicroscopy. There was no tachyphylaxis to Thromb dilation (maximum dilation = 87.0%, ED(50) = 1.49 x 10(-2)). Dilation to Thromb was abolished with either hirudin or denudation but was not affected by PTX. Neither N(omega)-nitro-l-arginine methyl ester (n = 7), indomethacin (n = 9), (1)H-[1,2,4] oxadiazolo-[4,3-a]quinoxalin-1-one (n = 6), tetraethylammonium chloride (n = 5), nor iberiotoxin (n = 4) reduced dilation to Thromb. However, KCl (maximum dilation = 89 +/- 5 vs. 20 +/- 10%; P < 0.05; n = 7), tetrabutylammonium chloride (maximum dilation = 79 +/- 7 vs. 21 +/- 4%; P < 0.05; n = 5), and charybdotoxin (maximum dilation = 89 +/- 4 vs. 10 +/- 2%; P < 0.05; n = 4) attenuated dilation to Thromb. In contrast to animal models, Thromb-induced dilation in human arterioles is independent of G(i)-protein activation and NO release. However, Thromb dilation is endothelium dependent, is maintained on consecutive applications, and involves activation of K(+) channels. We speculate that an endothelium-derived hyperpolarizing factor contributes to Thromb-induced dilation in HCA.     

Nitric oxide-epoxygenase interactions and arachidonate-induced dilation of rat renal microvessels

Nitric oxide (NO) is an inhibitor of hemoproteins including cytochrome P-450 enzymes. This study tested the hypothesis that NO inhibits cytochrome P-450 epoxygenase-dependent vascular responses in kidneys. In rat renal pressurized microvessels, arachidonic acid (AA, 0.03-1 microM) or bradykinin (BK, 0.1-3 microM) elicited NO- and prostanoid-independent vasodilation. Miconazole (1.5 microM) or 6-(2-propargyloxyphenyl)hexanoic acid (30 microM), both of which are inhibitors of epoxygenase enzymes, or the fixing of epoxide levels with 11,12-epoxyeicosatrienoic acid (11,12-EET; 1 and 3 microM) inhibited these responses. Apamin (1 microM), which is a large-conductance Ca2+-activated K+ (BKCa) channel inhibitor, or 18alpha-glycyrrhetinic acid (30 microM), which is an inhibitor of myoendothelial gap junctional electromechanical coupling, also inhibited these responses. NO donors spermine NONOate (1 and 3 microM) or sodium nitroprusside (0.3 and 3 microM) but not 8-bromo-cGMP (100 microM), which is an analog of cGMP (the second messenger of NO), blunted the dilation produced by AA or BK in a reversible manner without affecting that produced by hydralazine. However, the non-NO donor hydralazine did not affect the dilatory effect of AA or BK. Spermine NONOate did not affect the dilation produced by 11,12-EET, NS-1619 (a BKCa channel opener), or cromakalim (an ATP-sensitive K+ channel opener). AA and BK stimulated EET production, whereas hydralazine had no effect. On the other hand, spermine NONOate (3 microM) attenuated basal (19 +/- 7%; P < 0.05) and AA stimulation (1 microM, 29 +/- 9%; P < 0.05) of renal preglomerular vascular production of all regioisomeric EETs: 5,6-; 8,9-; 11,12-; and 14,15-EET. These results suggest that NO directly and reversibly inhibits epoxygenase-dependent dilation of rat renal microvessels without affecting the actions of epoxides on K+ channels.     

Mechanism of coronary vasodilation to insulin and insulin-like growth factor I is dependent on vessel size

Insulin and insulin-like growth factor I (IGF-I) influence numerous metabolic and mitogenic processes; these hormones also have vasoactive properties. This study examined mechanisms involved in insulin- and IGF-I-induced dilation in canine conduit and microvascular coronary segments. Tension of coronary artery segments was measured after constriction with PGF(2alpha). Internal diameter of coronary microvessels (resting diameter = 112.6+/-10.1 microm) was measured after endothelin constriction. Vessels were incubated in control (Krebs) solution and were treated with N(omega)-nitro-L-arginine (L-NA), indomethacin, or K(+) channel inhibitors. After constriction, cumulative doses of insulin or IGF-I (0.1-100 ng/ml) were administered. In conduit arteries, insulin produced modest maximal relaxation (32 +/- 5%) compared with IGF-I (66+/-12%). Vasodilation was attenuated by nitric oxide synthase (NOS) and cyclooxygenase inhibition and was blocked with KCl constriction. Coronary microvascular relaxation to insulin and IGF-I was not altered by L-NA, indomethacin, tetraethylammonium chloride, glibenclamide, charybdotoxin, and apamin; however, tetrabutylammonium chloride attenuated the response. In conclusion, insulin and IGF-I cause vasodilation in canine coronary conduit arteries and microvessels. In conduit vessels, NOS/cyclooxygenase pathways are involved in the vasodilation. In microvessels, relaxation to insulin and IGF-I is not mediated by NOS/cyclooxygenase pathways but rather through K(+)-dependent mechanisms.     

Increased inactivation of nitric oxide is involved in coronary endothelial dysfunction in heart failure

Recent evidence suggests the possibility that enhanced inactivation of endothelium-derived nitric oxide (NO) by oxygen free radical (OFR) may cause endothelial dysfunction in heart failure (HF). To test this hypothesis, we examined the effect of antioxidant therapy on endothelium-dependent vasodilation of the coronary circulation in a canine model of tachycardia-induced HF. Endothelium-dependent vasodilation was less than that in controls, and OFR formation in coronary arterial and myocardial tissues was greater in HF dogs than those in controls. The immunohistochemical staining of 4-hydroxy-2-nonenal, OFR-induced lipid peroxides was detected in coronary microvessels of HF dogs. Intracoronary infusion of the cell-permeable OFR scavenger Tiron inhibited OFR formation and improved endothelium-dependent vasodilation in HF dogs but not in controls. The NO synthesis inhibitor N(G)-monomethyl-L-arginine (L-NMMA) diminished the beneficial effect of Tiron in HF dogs. Endothelium-independent vasodilation was similar between control and HF dogs, and no change in its response was noted by Tiron or Tiron plus L-NMMA in either group. In summary, antioxidant treatment with Tiron improved coronary vascular endothelium-dependent vasodilation by increasing NO activity in tachycardia-induced HF. Thus coronary endothelial dysfunction in HF may be, at least in part, due to increased inactivation of NO by OFR.     

Human coronary arteriolar dilation to adrenomedullin: role of nitric oxide and K(+) channels

Adrenomedullin (ADM) is a vasodilator produced by vascular endothelium and smooth muscle cells. Although plasma ADM levels are increased in patients with hypertension, heart failure, and myocardial infarction, little information exists regarding the microvascular response to ADM in the human heart. In the present study we tested the hypothesis that ADM produces coronary arteriolar dilation in humans and examined the mechanism of this dilation. Human coronary arterioles were dissected and cannulated with micropipettes. Internal diameter was measured by video microscopy. In vessels constricted with ACh, the diameter response to cumulative doses of ADM (10(-12)-10(-7) M) was measured in the presence and absence of human ADM-(22-52), calcitonin gene-related peptide-(8-37), N(omega)-nitro-L-arginine methyl ester (L-NAME), indomethacin (Indo), (1)H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, SQ-22536, or KCl (60 mM). ADM dilated human coronary arterioles through specific ADM receptors (maximum dilation = 69 +/- 11%). L-NAME or N-monomethyl-L-arginine attenuated dilation to ADM (for L-NAME, maximum dilation = 66 +/- 7 vs. 41 +/- 13%, P < 0.05). Thus the mechanism of ADM-induced dilation involves generation of nitric oxide. However, neither (1)H-[1,2,4]oxadiazolo-[4, 3-a]quinoxalin-1-one, SQ-22536, nor Indo alone altered dilation to ADM. High concentrations of KCl blocked dilation to ADM. The magnitude of ADM dilation was reduced in subjects with hypertension. We propose that, in human coronary arterioles, ADM elicits vasodilation in part through production of nitric oxide and in part through activation of K(+) channels, with little contribution from adenylyl cyclase. The former dilator mechanism is independent of the more traditional pathway involving activation of soluble guanylate cyclase.     

Shear stress-induced vasodilation in porcine coronary conduit arteries is independent of nitric oxide release

The present study was performed to determine the importance of nitric oxide in eliciting epicardial coronary artery dilation during sustained increases in shear stress in the absence of pulsatile flow. Isolated first-order porcine epicardial coronary conduit arteries (approximately 500 microm) were preconstricted (U-46619) and subjected to steady-state changes in flow in vitro. Nonpulsatile flow (shear stress range from 0 to approximately 100 dyn/cm2) produced a graded dilation of epicardial arteries. Inhibiting nitric oxide synthase with 10(-5) M N(omega)-nitro-L-arginine methyl ester (L-NAME) blocked bradykinin-induced vasodilation but did not affect the flow-diameter relation or the maximum change in diameter from static conditions (67 +/- 10 microm in control vs. 71 +/- 8 microm after L-NAME, P = not significant). The addition of indomethacin (10(-5) M) had no effect on flow-mediated vasodilation. Depolarizing vascular smooth muscle with KCl (60 mM) or removing the endothelium blocked bradykinin vasodilation and completely abolished flow-mediated responses. The K+ channel blocker tetraethylammonium chloride (TEA; 10(-4)M) attenuated flow-mediated vasodilation (maximum diameter change was 110 +/- 18 microm under control conditions vs. 58 +/- 10 microm after TEA, P < 0.001). These data indicate that epicardial coronary arteries dilate to steady-state changes in nonpulsatile flow via a mechanism that is independent of nitric oxide production. The ability to completely block this with KCl and attenuate it with TEA supports the hypothesis that epicardial coronary arteries dilate to steady levels of shear stress through hyperpolarization of vascular smooth muscle. This may be secondary to the release of an endothelium-dependent hyperpolarizing factor.     

Endothelium-derived hyperpolarizing factor in coronary microcirculation: responses to arachidonic acid

In coronary resistance vessels, endothelium-derived hyperpolarizing factor (EDHF) plays an important role in endothelium-dependent vasodilation. EDHF has been proposed to be formed through cytochrome P-450 monooxygenase metabolism of arachidonic acid (AA). Our hypothesis was that AA-induced coronary microvascular dilation is mediated in part through a cytochrome P-450 pathway. The canine coronary microcirculation was studied in vivo (beating heart preparation) and in vitro (isolated microvessels). Nitric oxide synthase (NOS) (N(omega)-nitro-L-arginine, 100 microM) and cyclooxygenase (indomethacin, 10 microM) or cytochrome P-450 (clotrimazole, 2 microM) inhibition did not alter AA-induced dilation. However, when a Ca(2+)-activated K(+) channel channel or cytochrome P-450 antagonist was used in combination with NOS and cyclooxygenase inhibitors, AA-induced dilation was attenuated. We also show a negative feedback by NO on NOS-cyclooxygenase-resistant AA-induced dilation. We conclude that AA-induced dilation is attenuated by cytochrome P-450 inhibitors, but only when combined with inhibitors of cyclooxygenase and NOS. Therefore, redundant pathways appear to mediate the AA response in the canine coronary microcirculation.     

Arachidonic acid- and prostaglandin E2-induced cerebral vasodilation is mediated by carbon monoxide, independent of reactive oxygen species in piglets

Arachidonic acid (AA) and prostaglandin (PG) E(2) stimulate carbon monoxide (CO) production, and AA metabolism is known to be associated with the generation of reactive oxygen species (ROS). This study was conducted to address the hypothesis that CO and/or ROS mediate cerebrovascular dilation in newborn pigs. Experiments were performed on anesthetized newborn pigs with closed cranial windows. Different concentrations of AA (10(-8)-10(-6) M), PGE(2) (10(-8)-10(-6) M), iloprost (10(-8)-10(-6) M), and their vehicle (artificial cerebrospinal fluid) were given. Piglets with PGE(2) and iloprost received indomethacin (5 mg/kg iv) to inhibit cyclooxygenase. AA, PGE(2), and iloprost caused concentration-dependent increases in pial arteriolar diameter. The effects of both AA and PGE(2) in producing cerebral vascular dilation and associated CO production were blocked by the heme oxygenase inhibitor chromium mesoporphyrin (2 × 10(-5) M), but not by the prostacyclin analog, iloprost. ROS inhibitor tempol (SOD mimetic) (1 × 10(-5) M) and the H(2)O(2) scavenger catalase (1,000 U/ml) also do not block these vasodilator effects of AA and PGE(2). Heme-L-lysinate-induced cerebrovascular dilation and CO production was blocked by chromium mesoporphyrin. Hypoxanthine plus xanthine oxidase, a combination that is known to generate ROS, caused pial arteriolar dilation and CO production that was inhibited by tempol and catalase. These data suggest that AA- and PGE(2)-induced cerebral vascular dilation is mediated by CO, independent of ROS.     

Chronic exercise training preserves prostaglandin-induced dilation of epicardial coronary artery during development of heart failure in awake dogs

Although it has been shown that long-term exercise training preserves endothelium-mediated nitric oxide vasodilator function in chronic heart failure (CHF), whether exercise training exerts similar beneficial effects on endothelial/prostaglandin-mediated vasodilator capacity in coronary circulation during the development of CHF has not been determined. Fifteen mongrel dogs were surgically instrumented for measurement of left ventricular pressure, aortic pressure, coronary blood flow and left circumflex coronary artery diameter. Dogs (n = 5) who underwent 4 weeks of cardiac pacing (210 b/min for 3 weeks and 240 b/min for the 4th week) developed CHF as characterized by significant reduction in left ventricular systolic pressure, mean arterial pressure and left ventricular dP/dt, increases in left ventricular end-diastolic pressure and heart rate, as well as clinical signs of CHF. Endothelial prostaglandin-mediated vasodilation of the epicardial coronary artery was impaired, as manifested by an attenuated arachidonic acid (AA)-induced dilation of the artery (epicardial artery diameter increased by: 0.78 +/- 0. 84% in CHF versus 4.6 +/- 0.89% in normal, P < 0.05); however, prostacyclin (PGI(2))-induced and nitroglycerin-induced vasodilation of the coronary circulation were not altered. In contrast, dogs (n = 6) with cardiac pacing plus daily exercise training (4.4 +/- 0.3 km/h, 2 h/day) only developed mild cardiac dysfunction, and the response of the epicardial coronary artery diameter to AA was preserved (epicardial artery diameter increased by 4.2 +/- 0.98% from baseline, P 0.05 compared to its respective control). Thus, long-term exercise training preserves endothelial/prostaglandin-mediated dilation of epicardial coronary artery during development of CHF.     

Simvastatin upregulates coronary vascular endothelial nitric oxide production in conscious dogs

Statin drugs can upregulate endothelial nitric oxide (NO) synthase (eNOS) in isolated endothelial cells independent of lipid-lowering effects. We investigated the effect of short-term simvastatin administration on coronary vascular eNOS and NO production in conscious dogs and canine tissues. Mongrel dogs were instrumented under general anesthesia to measure coronary blood flow (CBF). Simvastatin (20 mg. kg(-1). day(-1)) was administered orally for 2 wk; afterward, resting CBF was found to be higher compared with control (P < 0.05) and veratrine- (activator of reflex cholinergic NO-dependent coronary vasodilation) and ACh-mediated coronary vasodilation were enhanced (P < 0.05). Response to endothelium-independent vasodilators, adenosine and nitroglycerin, was not potentiated. After simvastatin administration, plasma nitrate and nitrite (NO(x)) levels increased from 5.22 +/- 1.2 to 7. 79 +/- 1.3 microM (P < 0.05); baseline and agonist-stimulated NO production in isolated coronary microvessels were augmented (P < 0.05); resting in vivo myocardial oxygen consumption (MVO(2)) decreased from 6.8 +/- 0.6 to 5.9 +/- 0.4 ml/min (P < 0.05); NO-dependent regulation of MVO(2) in response to NO agonists was augmented in isolated myocardial segments (P < 0.05); and eNOS protein increased 29% and eNOS mRNA decreased 50% in aortas and coronary vascular endothelium. Short-term administration of simvastatin in dogs increases coronary endothelial NO production to enhance NO-dependent coronary vasodilation and NO-mediated regulation of MVO(2).     

Cardioprotection initiated by reactive oxygen species is dependent on activation of PKCepsilon

To examine whether cardioprotection initiated by reactive oxygen species (ROS) is dependent on protein kinase Cepsilon (PKCepsilon), isolated buffer-perfused mouse hearts were randomized to four groups: 1) antimycin A (AA) (0.1 microg/ml) for 3 min followed by 10 min washout and then 30 min global ischemia (I) and 2 h reperfusion (R); 2) controls of I/R alone; 3) AA bracketed with 13 min of N-2-mercaptopropionyl- glycine (MPG) followed by I/R; and 4) MPG (200 microM) alone, followed by I/R. Isolated adult rat ventricular myocytes (ARVM) were exposed to AA (0.1 microg/ml), and lucigenin was used to measure ROS production. Murine hearts and ARVM were exposed to AA (0.1 microg/ml) with or without MPG, and PKCepsilon translocation was measured by cell fractionation and subsequent Western blot analysis. Finally, the dependence of AA protection on PKCepsilon was determined by the use of knockout mice (-/-) lacking PKCepsilon. AA exposure caused ROS production, which was abolished by the mitochondrial uncoupler mesoxalonitrile 4-trifluoromethoxyphenylhydrazone. In addition, AA significantly reduced the percent infarction-left ventricular volume compared with control I/R (26 +/- 4 vs. 43 +/- 2%; P < 0.05). Bracketing AA with MPG caused a loss of protection (52 +/- 7 vs. 26 +/- 4%; P < 0.05). AA caused PKCepsilon translocation only in the absence of MPG, and protection was lost on the pkcepsilon(-/-) background (38 +/- 3 vs. 15 +/- 4%; P < 0.001). AA causes ROS production, on which protection and PKCepsilon translocation depend. In addition, protection is absent in PKCepsilon null hearts. Our results imply that, in common with ischemic preconditioning, PKCepsilon is crucial to ROS-mediated protection.     

Hydrogen peroxide acts as an EDHF in the piglet pial vasculature in response to bradykinin

We investigated the mechanism of EDHF-mediated dilation to bradykinin (BK) in piglet pial arteries. Topically applied BK (3 micromol/l) induced vasodilation (62 +/- 12%) after the administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) and indomethacin, which was inhibited by endothelial impairment or by the BK(2) receptor antagonist HOE-140 (0.3 micromol/l). Western blotting showed the presence of BK(2) receptors in brain cortex and pial vascular tissue samples. The cytochrome P-450 antagonist miconazole (20 micromol/l) and the lipoxygenase inhibitors baicalein (10 micromol/l) and cinnamyl-3,4-dyhydroxy-alpha-cyanocinnamate (1 micromol/l) failed to reduce the BK-induced dilation. However, the H(2)O(2) scavenger catalase (400 U/ml) abolished the response (from 54 +/- 11 to 0 +/- 2 microm; P < 0.01). The ATP-dependent K(+) (K(ATP)) channel inhibitor glibenclamide (10 micromol/l) had a similar effect as well (from 54 +/- 11 to 16 +/- 5 microm; P < 0.05). Coapplication of the Ca(2+)-dependent K(+) channel inhibitors charybdotoxin (0.1 micromol/l) and apamin (0.5 micromol/l) failed to reduce the response. We conclude that H(2)O(2) mediates the non-nitric oxide-, non-prostanoid-dependent vasorelaxation to BK in the piglet pial vasculature. The response is mediated via BK(2) receptors and the opening of K(ATP) channels.     

Depressed modulation of oxygen consumption by endogenous nitric oxide in cardiac muscle from diabetic dogs

Our previous study indicated that nitric oxide (NO)-dependent coronary vasodilation was impaired in conscious dogs with diabetes. Our goal was to determine whether modulation of O(2) consumption by NO is depressed in canine cardiac muscle after diabetes. Diabetes was induced by injection of alloxan (40-60 mg/kg iv), dogs were killed after diabetes was induced (4-5 wk), and the cardiac muscle from the left ventricle was cut into 15- to 30-mg slices. O(2) uptake by the muscle slices was measured polarographically with a Clark-type O(2) electrode. S-nitroso-N-acetylpenicillamine decreased O(2) consumption in normal and diabetic tissues (10(-4) M, 61 +/- 7 vs. 61 +/- 8%, P > 0.05). Bradykinin (10(-4) M)- or carbachol (CCh, 10(-4) M)-induced inhibition of O(2) consumption was impaired in diabetic tissues (51 +/- 6 vs. 17 +/- 4% or 48 +/- 4 vs. 19 +/- 3%, respectively, both P < 0.05 compared with normal). The inhibition of O(2) consumption by kininogen or kallikrein was depressed in diabetic tissues as well. In coronary microvessels from diabetic dogs, bradykinin or ACh (10(-5) M) caused smaller increases in NO production than those from normal dogs. Our results indicate that the modulation of O(2) consumption by endogenous, but not exogenous, NO is depressed in cardiac muscle from diabetic dogs, most likely because of decreased release of NO from the vascular endothelium.     

Chronic administration of indomethacin increases role of nitric oxide in hypercapnic cerebrovasodilation in piglets.

Hypercapnia-induced cerebral vasodilation is associated with prostanoids in the piglet, but is a primarily nitric oxide (NO) associated response in many adult models. Hypercapnia-induced cerebral vasodilation is both NO and prostanoid associated in the juvenile pig. We hypothesized that with chronic administration of indomethacin the piglet would advance the role of the NO system in cerebrovascular responses. The closed cranial window technique was used in piglets to determine pial arteriolar response. Chronically indomethacin treated newborn animals dilated in response to CO2 similarly to control newborns (40.9+/-4.4% vs 48.4+/-4.1%). Topical n-nitro L-arginine (L-NA, 10(-3) M), attenuated CO2 induced dilation in the chronically indomethacin treated animals (11.7+/-3.3% vs 40.9+/-4.4%; p < 0.001), but had no effect on the response to hypercapnia of piglets not treated with indomethacin. Neither indomethacin nor L-NA altered response to topical isoproterenol (10(-6) M). We conclude that with chronic indomethacin administration there develops a significant hypercapnia-induced cerebral vasodilation in which NO has an important role. The chronic inhibition of the newborn's principal dilator system appears to increase the role of NO in newborn cerebral hemodynamics.     

Exercise training improves conduit vessel function in patients with coronary artery disease.

It is well established that endothelial dysfunction is present in coronary artery disease (CAD), although few studies have determined the effect of training on peripheral conduit vessel function in patients with CAD. A randomized, crossover design determined the effect of 8 wk of predominantly lower limb, combined aerobic and resistance training, in 10 patients with treated CAD. Endothelium-dependent dilation of the brachial artery was determined, by using high-resolution vascular ultrasonography, from flow-mediated vasodilation (FMD) after ischemia. Endothelium-independent vasodilation was measured after administration of glyceryl trinitrate (GTN). Baseline function was compared with that of 10 control subjects. Compared with matched healthy control subjects, FMD and GTN responses were significantly impaired in the untrained CAD patients [3.0 +/- 0.8 (SE) vs. 5.8 +/- 0.8% and 14.5 +/- 1.9 vs. 20.4 +/- 1.5%, respectively; both P < 0.05]. Training significantly improved FMD in the CAD patients (from 3.0 +/- 0.8 to 5.7 +/- 1.1%; P < 0.05) but not responsiveness to GTN (14.5 +/- 1.9 vs. 12.1 +/- 1.4%; P = not significant). Exercise training improves endothelium-dependent conduit vessel dilation in subjects with CAD, and the effect, evident in the brachial artery, appears to be generalized rather than limited to vessels of exercising muscle beds. These results provide evidence for the benefit of exercise training, as an adjunct to routine therapy, in patients with a history of CAD.     

Mechanism of dilation to reactive oxygen species in human coronary arterioles

We tested whether reactive oxygen species (ROS) generated from treatment with xanthine (XA) and xanthine oxidase (XO) alter vascular tone of human coronary arterioles (HCA). Fresh human coronary arterioles (HCA) from right atrial appendages were cannulated for video microscopy. ROS generated by XA (10(-4) M) + XO (10 mU/ml) dilated HCA (99 +/- 1%, 20 min after application of XA/XO). This dilation was not affected by denudation or superoxide dismutase (150 U/ml). Catalase (500 U/ml or 5,000 U/ml) attenuated the dilation early on, but a significant latent vasodilation appeared after 5 min peaking at 20 min (51 +/- 1%, 20 min after application of XA/XO + 500 U/ml catalase, P < 0.01 vs. control). KCl (40 mM) reduced the early and sustained vasodilation to XA/XO in the absence of catalase but 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 5 x 10(-5) M), diethyldithiocarbamate trihydrate (DDC, 10(-2) M), and deferoxamine (DFX, 10(-3) M) had no effect. In contrast, the catalase-resistant vasodilation was significantly attenuated by DDC, ODQ, and DFX as well as polyethylene-glycolated catalase (5,000 U/ml), but KCl had no effect. Confocal microscopy revealed that even in the presence of catalase, 2',7'-dichlorodihydrofluoresein diacetate fluorescence was observed in the vascular smooth muscle, but this was abolished by DDC. These data indicate that the exogenously generated superoxide anion (O2-*) by XA/XO is spontaneously converted to H2O2, which dilates HCA through vascular smooth muscle hyperpolarization. O2-* is also converted to H2O2 likely by superoxide dismustase within vascular cells and dilates HCA through a different pathway involving the activation of guanylate cyclase. These findings suggest that exogenously and endogenously produced H2O2 may elicit vasodilation by different mechanisms.     

NAD(P)H oxidase-derived reactive oxygen species contribute to age-related impairments of endothelium-dependent dilation in rat soleus feed arteries

We tested the hypothesis that age-related endothelial dysfunction in rat soleus muscle feed arteries (SFA) is mediated in part by NAD(P)H oxidase-derived reactive oxygen species (ROS). SFA from young (4 mo) and old (24 mo) Fischer 344 rats were isolated and cannulated for examination of vasodilator responses to flow and acetylcholine (ACh) in the absence or presence of a superoxide anion (O(2)(-)) scavenger (Tempol; 100 μM) or an NAD(P)H oxidase inhibitor (apocynin; 100 μM). In the absence of inhibitors, flow- and ACh-induced dilations were attenuated in SFA from old rats compared with young rats. Tempol and apocynin improved flow- and ACh-induced dilation in SFA from old rats. In SFA from young rats, Tempol and apocynin had no effect on flow-induced dilation, and apocynin attenuated ACh-induced dilation. To determine the role of hydrogen peroxide (H(2)O(2)), dilator responses were assessed in the absence and presence of catalase (100 U/ml) or PEG-catalase (200 U/ml). Neither H(2)O(2) scavenger altered flow-induced dilation, whereas both H(2)O(2) scavengers blunted ACh-induced dilation in SFA from young rats. In old SFA, catalase improved flow-induced dilation whereas PEG-catalase improved ACh-induced dilation. Compared with young SFA, in response to exogenous H(2)O(2) and NADPH, old rats exhibited blunted dilation and constriction, respectively. Immunoblot analysis revealed that the NAD(P)H oxidase subunit gp91phox protein content was greater in old SFA compared with young. These results suggest that NAD(P)H oxidase-derived reactive oxygen species contribute to impaired endothelium-dependent dilation in old SFA.     

Adenosine receptors mediate glutamate-evoked arteriolar dilation in the rat cerebral cortex

We tested the hypothesis that adenosine (Ado) mediates glutamate-induced vasodilation in the cerebral cortex by monitoring pial arteriole diameter in chloralose-anesthetized rats equipped with closed cranial windows. Topical application of 100 microM glutamate and 100 microM N-methyl-d-aspartate (NMDA) dilated pial arterioles (baseline diameter 25 +/- 2 microm) by 17 +/- 1% and 18 +/- 4%, respectively. Coapplication of the nonselective Ado receptor antagonist theophylline (Theo; 10 microM) significantly reduced glutamate- and NMDA-induced vasodilation to 4 +/- 2% (P < 0.01) and 6 +/- 2% (P < 0.05), whereas the Ado A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (0.1 microM) had no effect. Moreover, application of the Ado A(2A) receptor-selective antagonist 4-(2-[7-amino-2-(2-furyl)(1,2,4)triazolo(2,3-a)(1,3,5)triazin-5-ylamino]ethyl)phenol (ZM-241385), either by superfusion (0.1 microM, 1 microM) or intravenously (1 mg/kg), significantly inhibited the pial arteriole dilation response to glutamate. Neither Theo nor ZM-241385 affected vascular reactivity to mild hypercapnia induced by 5% CO(2) inhalation. These results suggest that Ado contributes to the dilation of rat cerebral arterioles induced by exogenous glutamate, and that the Ado A(2A) receptor subtype may be involved in this dilation response.     

Elevated glucose impairs cAMP-mediated dilation by reducing Kv channel activity in rat small coronary smooth muscle cells

Hyperglycemia impairs endothelium-dependent vasodilation. In this study, we examined the effect of high glucose (HG) on vascular smooth muscle function. Rat small coronary arteries were freshly isolated or incubated for 24 h with normal glucose (NG; 5.5 mmol/l) or HG (23 mmol/l). In freshly isolated arteries, dilation to isoproterenol (Iso) was reduced by 3 mmol/l 4-aminopyridine (4-AP; 44 +/- 10% vs. 77 +/- 4%; P < 0.05) and further reduced by 4-AP + iberiotoxin (IbTX; 100 nmol/l; 17 +/- 2%). Dilation to forskolin was abolished by 4-AP (-3 +/- 17 vs. 73 +/- 9%). cAMP production was similar in NG and HG vessels. Dilations to Iso and forskolin were significantly reduced in HG arteries (Iso, 41 +/- 5% vs. 70 +/- 6%; forskolin, 40 +/- 4% vs. 75 +/- 4%) compared with NG arteries. A similar reduction was also observed to the dilation to papaverine. Endothelial denudation had no effect on Iso-induced dilation. In HG vessels, the reduced 4-AP-sensitive component of Iso-induced dilation was greater compared with the IbTX-sensitive component. Iso increased whole cell K+ current in NG cells but had little effect in HG cells. Similarly, 4-AP-, but not IbTX-sensitive, K+ currents were reduced in HG cells. These results suggest that HG impairs cAMP-mediated dilation primarily by reducing Kv channel function. We speculate that in addition to the endothelial dysfunction, altered smooth muscle function may also contribute to the reduced coronary vasodilation in diabetes.