Microvascular and myocardial contractile responses to ischemia: influence of exercise training

Late-in-life treadmill training rejuvenates autophagy, protein aggregate clearance, and function in mouse hearts

Protein quality control mechanisms decline during the process of cardiac aging. This enables the accumulation of protein aggregates and damaged organelles that contribute to age-associated cardiac dysfunction. Macroautophagy is the process by which post-mitotic cells such as cardiomyocytes clear defective proteins and organelles. We hypothesized that late-in-life exercise training improves autophagy, protein aggregate clearance, and function that is otherwise dysregulated in hearts from old vs. adult mice. As expected, 24-month-old male C57BL/6J mice (old) exhibited repressed autophagosome formation and protein aggregate accumulation in the heart, systolic and diastolic dysfunction, and reduced exercise capacity vs. 8-month-old (adult) mice (all p < 0.05). To investigate the influence of late-in-life exercise training, additional cohorts of 21-month-old mice did (old-ETR) or did not (old-SED) complete a 3-month progressive resistance treadmill running program. Body composition, exercise capacity, and soleus muscle citrate synthase activity improved in old-ETR vs. old-SED mice at 24 months (all p < 0.05). Importantly, protein expression of autophagy markers indicate trafficking of the autophagosome to the lysosome increased, protein aggregate clearance improved, and overall function was enhanced (all p < 0.05) in hearts from old-ETR vs. old-SED mice. These data provide the first evidence that a physiological intervention initiated late-in-life improves autophagic flux, protein aggregate clearance, and contractile performance in mouse hearts.

Vasoreactivity of the Murine External Jugular Vein and Carotid Artery

INTRODUCTION

Impaired venous reactivity has potential to contribute to clinically significant pathologies such as arteriovenous fistula (AVF) maturation failure. Vascular segments commonly used in murine preclinical models of AVF include the carotid artery and external jugular vein. Detailed descriptions of isometric procedures to evaluate function of murine external jugular vein ex vivo have not been previously published.

OBJECTIVE

To establish isometric procedures to measure naive murine external jugular vein reactivity ex vivo.

METHODS

Vasomotor responses of external jugular veins and ipsilateral common carotid arteries from C57BL/6 mice were evaluated using isometric tension procedures.

RESULTS

External jugular veins developed tension (p < 0.05) to potassium chloride and U-46619, but not to phenylephrine, whereas common carotid arteries responded to all 3 agents (p < 0.05). While maximal responses to acetylcholine (ACh) were similar between the venous and arterial segments, the dose required to achieve this value was lower (p < 0.05) in the artery versus vein. Nitric oxide synthase inhibition attenuated (p < 0.05) but did not abolish ACh-evoked vasorelaxation in both vascular segments, whereas cyclooxygenase blockade had no effect. Endothelium-independent vasorelaxation to sodium nitroprusside was similar in the artery and vein.

CONCLUSION

Vasorelaxation and vasocontraction can be reliably assessed in the external jugular vein in C57BL/6 mice using isometric procedures.

Therapeutic potential of quercetin as a cardiovascular agent

Flavonoids are integral components of various vegetation and in foods; consequently, they represent an inevitable part of the diet. Historical and epidemiological proof recommend that diet plans consisting of flavonoids such as quercetin have positive health benefits, especially on the heart. Flavonoids have been proven to be active against hypertension, inflammation, diabetes and vascular diseases. Quercetin exhibits significant heart related benefits as inhibition of LDL oxidation, endothelium-independent vasodilator effects, reduction of adhesion molecules and other inflammatory markers, the protective effect on nitric oxide and endothelial function under conditions of oxidative stress, prevention of neuronal oxidative and inflammatory damage and platelet antiaggregant effects. Searching for experimental evidence to validate the cardioprotective effects of quercetin, we review here the recent detailed in vivo studies. Quercetin and its derivatives lead to an enhancement in heart features, indicating the prospective for quercetin to be used therapeutically in the treatment of cardiac diseases. Several evidence-based studies suggest mechanisms to observe cardiovascular diseases such as aging effects, hypertension, angiotensin-converting enzyme activity and endothelial-dependent and independent functions. Different animal models including human are also used to elucidate the in vivo role of quercetin in cardiovascular diseases. The role of quercetin and its derivatives may go beyond their existence in food and has potential as a lead molecule in drug development programs.

Voluntary exercise training restores anticontractile effect of NO in coronary arteries of adult rats with antenatal/early postnatal hypothyroidism

INTRODUCTION

Our recent study showed that NO-mediated anticontractile effect of endothelium is absent in coronary arteries of adult rats, which suffered from antenatal/early postnatal hypothyroidism. This study tested the hypothesis that exercise training would improve such detrimental consequences of early thyroid deficiency.

DESIGN AND METHODS

Wistar dams received propylthiouracil (PTU, 7 ppm) in drinking water during gestation and two weeks postpartum; control dams received tap water. Six-week-old male offspring of control (CON) and PTU dams was divided into sedentary (CON-Sed, n = 12; PTU-Sed, n = 10) and trained (CON-Tr, n = 12; PTU-Tr, n = 10) groups; the latter had 24-h access to running wheels. Eight weeks later coronary arteries were studied by wire myography. Anticontractile effect of NO was assessed by the effects of NOS inhibitor L-NNA on the basal tone and contractile response to U46619. Oxidative phosphorylation complexes and eNOS were estimated by Western blotting.

RESULTS

T₃/T₄ and TSH levels (ELISA) were normalized in the progeny of PTU-treated dams at the age of 6 weeks and were not affected by training. Total running distance did not differ between CON-Tr and PTU-Tr. The contents of oxidative phosphorylation complexes were increased post-training in triceps brachii muscle from CON-Tr and PTU-Tr and in heart from PTU-Tr. Coronary arteries of PTU-Sed compared to CON-Sed demonstrated higher basal tone and contractile response to U46619, which were not further increased by L-NNA. The effects of L-NNA on the basal tone and contractile response to U46619 did not differ in CON-Tr and PTU-Tr groups, but were elevated in PTU-Tr compared to PTU-Sed group. PTU-Tr rats in comparison to PTU-Sed group had higher eNOS content in heart. Responses of coronary arteries to DEA/NO did not differ among all experimental groups.

CONCLUSIONS

Long-lasting coronary endothelial dysfunction resulted from transient thyroid deficiency during the antenatal/early postnatal period can be corrected by voluntary exercise training.

Heat and α1-adrenergic responsiveness in human skeletal muscle feed arteries: the role of nitric oxide

Increased local temperature exerts a sympatholytic effect on human skeletal muscle feed arteries. We hypothesized that this attenuated α(1)-adrenergic receptor responsiveness may be due to a temperature-induced increase in nitric oxide (NO) bioavailability, thereby reducing the impact of the α(1)-adrenergic receptor agonist phenylephrine (PE). Thirteen human skeletal muscle feed arteries were harvested, and wire myography was used to generate PE concentration-response curves at 37 °C and 39 °C, with and without the NO synthase (NOS) inhibitor N(G)-monomethyl-L-arginine (L-NMMA). A subset of arteries (n = 4) were exposed to 37 °C or 39 °C, and the protein content of endothelial NOS (eNOS) and α(1)-adrenergic receptors was determined by Western blot analysis. Additionally, cultured bovine endothelial cells were exposed to static or shear stress conditions at 37 °C and 39 °C and assayed for eNOS activation (phosphorylation at Ser(1177)), eNOS expression, and NO metabolites [nitrate + nitrite (NOx)]. Maximal PE-induced vasocontraction (PE(max)) was lower at 39 °C than at 37 °C [39 ± 10 vs. 84 ± 30% maximal response to 100 mM KCl (KCl(max))]. NO blockade restored vasocontraction at 39 °C to that achieved at 37 °C (80 ± 26% KCl(max)). Western blot analysis of the feed arteries revealed that heating increased eNOS protein, but not α(1)-adrenergic receptors. Heating of bovine endothelial cells resulted in greater shear stress-induced eNOS activation and NOx production. Together, these data reveal for the first time that, in human skeletal muscle feed arteries, NO blockade can restore the heat-attenuated α(1)-adrenergic receptor-mediated vasocontraction and implicate endothelium-derived NO bioavailability as a major contributor to heat-induced sympatholysis. Consequently, these findings highlight the important role of vasodilators in modulating the vascular response to vasoconstrictors.

Human skeletal muscle feed arteries studied in vitro: the effect of temperature on α(1)-adrenergic responsiveness

Heat and cold exposure can decrease and increase total peripheral resistance, respectively, in humans. With unique access to human skeletal muscle feed arteries, we sought both to characterize these vessels and to determine the interaction between temperature and α(1)-adrenergic receptor responsiveness. We hypothesized that α(1)-mediated vasocontraction of human feed arteries would be attenuated in response to 39 or 35°C. Skeletal muscle feed arteries were harvested from thirty-two human volunteers and studied using isometric techniques. Vessel function was assessed using KCl, sodium nitroprusside (SNP), phenylephrine (PE) and ACh dose-response curves to characterize non-receptor- and receptor-mediated vasocontraction and vasorelaxation. Single doses of PE (1 mm) and KCl (100 mm) were administered at 37°C and then, in a balanced design, repeated at both 35 and 39°C. The KCl and PE dose-response curves elicited significant vasocontraction (2009 ± 407 and 1974 ± 508 mg developed tension, respectively), whereas SNP and ACh induced the expected vasorelaxation (102 ± 6 and 73 ± 10% relaxation, respectively). Altering the temperature had no effect on inherent smooth muscle function (KCl response), but both a reduction (35°C) and an increase in temperature (39°C) decreased the vasocontractile response to 1 mm PE (37°C, 1478 ± 338 mg; 35°C, 546 ± 104 mg; and 39°C, 896 ± 202 mg; P < 0.05) or across PE dose (P < 0.05, 35 and 39 versus 37°C). Despite clear heterogeneity between both the human volunteers and the feed arteries themselves, this novel approach to the procurement of human vessels revealed a robust 'inverted U' response to altered temperature, such that α(1)-mediated vasocontraction was attenuated with either warming or cooling.

Influence of Vascular Oxidative Stress and Inflammation on the Development and Progression of Atherosclerosis

Cardiovascular disease (CVD) risk factors such as hypertension, diabetes, dyslipidemia, smoking, physical inactivity, and obesity increase production of vascular reactive oxygen species (ROS), which results in a reduction of bioavailable nitric oxide and ultimately endothelial dysfunction and endothelial cell activation. ROS appears to mediate the inflammatory pathways that participate in the development and progression of atherosclerosis. There are numerous markers of oxidative stress and inflammation available for assessing the therapeutic response to interventions, but few are currently recommended for clinical use. Exercise training improves endothelial function via several mechanisms, including increased endothelial nitric oxide synthase—nitric oxide (eNOS-NO)— mediated production, increased activity and amount of antioxidants, attenuated ROS production, and an apparent reduction in systemic inflammation, possibly related to an increase in myokines resulting from skeletal muscle activation. Dietary antioxidant supplementation may improve endothelial function, oxidative stress, and inflammation, but much controversy exists regarding the use of antioxidant supplementation in primary and secondary CVD prevention. The purpose of this article is to review the contribution of vascular oxidative stress and activation of the inflammatory pathways in the pathogenesis of CVD and to review common methods used in clinical research to assess vascular oxidative stress and inflammation in response to therapeutic lifestyle interventions.

Regulation of mitochondrial uncoupling respiration during exercise in rat heart: role of reactive oxygen species (ROS) and uncoupling protein 2

The physiological significance of cardiac mitochondrial uncoupling protein 2 (UCP2)-mediated uncoupling respiration in exercise is unknown. In the current study, mitochondrial respiratory function, UCP2 mRNA level, UCP2-mediated respiration (UCR), and reactive oxygen species (ROS) generation, as well as manganese superoxide dismutase (MnSOD) activity were determined in rat heart with or without endurance training after an acute bout of exercise of different duration. In the untrained rats, state 4 respiration and UCR-independent respiration rates were progressively increased with exercise time and were 64 and 70% higher, respectively, than resting rate at 150 min, whereas UCR was elevated by 86% with no significant change in state 3 respiration. UCP2 mRNA level showed a 5- and 4-fold increase, respectively, after 45 and 90 min of exercise, but returned to resting level at 120 and 150 min. Mitochondrial ROS production and membrane potential (Deltapsi) increased progressively until 120 min, followed by a decrease to the resting level at 150 min. MnSOD mRNA abundance showed a 2-fold increase at 120 min but MnSOD activity did not change with exercise. Training significantly increased mitochondrial ATP synthetase activity, ADP to oxygen consumption (P/O) ratio, respiratory control ratio, and MnSOD activity, whereas exercise-induced state 4 respiration, UCR, ROS production, and Deltapsi were attenuated in the trained rats. We conclude that (1) UCP2 mRNA expression and activity in rat heart can be upregulated during prolonged exercise, which may reduce cross-membrane Deltapsi and thus ROS production; and (2) endurance training can blunt exercise-induced UCP2 and UCR, and improve mitochondrial efficiency of oxidative phosphorylation due to increased removal of ROS.

Physical (in)activity and endothelium-derived constricting factors: overlooked adaptations

The inner surrounding of arterial vessels, the endothelium, is optimally located to detect changes in blood characteristics or blood flow that may result from changes in physical activity or from diseases. In response to physical stimuli, the endothelium varies its release of circulating vasoactive substances and serves as a source of local and systemic endothelium-derived dilator and vasoconstrictor factors. Endothelial dysfunction is one of the earliest markers of vascular abnormalities observed in cardiovascular disease and ageing. Exercise training is an efficient therapeutic strategy to improve endothelial function. Traditionally, studies on endothelial dysfunction and physical (in)activity-related effects on vascular adaptations are primarily focused on vasodilator substances (i.e. nitric oxide). One may suggest that augmentation of vasoconstrictor pathways (such as endothelin-1 and angiotensin II) contributes to the endothelial dysfunction observed after physical inactivity. Moreover, these pathways may also explain the exercise-induced beneficial cardiovascular adaptations. This review summarizes the current knowledge on the effects of physical (in)activity on several endothelium-derived vasoconstrictor substances.

Quercetin-supplemented diets lower blood pressure and attenuate cardiac hypertrophy in rats with aortic constriction

Quercetin (Q), a flavonoid found in berries and onions, can reduce blood pressure in hypertensive animals and inhibit signal transduction pathways in vitro that regulate cardiac hypertrophy. We hypothesized that quercetin could prevent cardiovascular complications in rats with abdominal aortic constriction (AAC). Rats consumed standard or Q-supplemented chow (1.5 g Q/kg chow) for 7 days before AAC or sham surgery (SHAM, n = 15; AAC, n = 15; SHAMQ, n = 15; AACQ, n = 14). Fourteen days after surgery, plasma and liver Q concentrations were elevated (P < 0.05) and hepatic lipid oxidation was reduced (P < 0.05) in Q-treated versus untreated rats. Carotid arterial blood pressure and cardiac hypertrophy were attenuated (P < 0.05), and cardiac protein kinase C betaII translocation was normalized (P < 0.05) in AACQ versus AAC. Expression of cardiac beta-myosin heavy-chain mRNA was also reduced in AACQ versus AAC (P < 0.05). However, extracellular regulated kinase 1/2 phosphorylation was similar in AAC versus AACQ. The level of aortic endothelial dysfunction (wire myography) was also similar between AAC and AACQ, in spite of reduced aortic thickening in AACQ. Importantly, Q-treated rats did not show any deleterious changes in myocardial function (echocardiography). Our data supports an antihypertensive and antihypertrophic effect of Q in vivo in the absence of changes concerning vascular and myocardial function.

Nandrolone decanoate impairs exercise-induced cardioprotection: role of antioxidant enzymes

The beneficial effects of exercise in reducing the incidence of cardiovascular diseases are well known and the abuse of anabolic androgenic steroids (AAS) has been associated to cardiovascular disorders. Previous studies showed that heart protection to ischemic events would be mediated by increasing the antioxidant enzyme activities. Here, we investigated the impact of exercise and high doses of the AAS nandrolone decanoate (DECA), 10 mgkg(-1) body weight during 8 weeks, in cardiac tolerance to ischemic events as well as on the activity of antioxidant enzymes in rats. After a global ischemic event, hearts of control trained (CT) group recovered about 70% of left ventricular developed pressure, whereas DECA trained (DT), control sedentary (CS) and DECA sedentary (DS) animals recovered only about 20%. Similarly, heart infarct size was significantly lower in the CT group compared to animals of the three other groups. The activities of the antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GR) were significantly higher in CT animals than in the other three groups, whereas catalase activity was not affected in any group. Together, these results indicate that chronic treatment with DECA cause an impairment of exercise induction of antioxidant enzyme activities, leading to a reduced cardioprotection upon ischemic events.

Vascular dysfunction produced by hyperhomocysteinemia is more severe in the presence of low folate

Earlier we reported that dietary folate depletion causes hyperhomocysteinemia (HHcy) and arterial dysfunction in rats (Symons JD, Mullick AE, Ensunsa JL, Ma AA, and Rutledge JC. Arterioscler Thromb Vasc Biol 22: 772-780, 2002). Both HHcy and low folate (LF) are risk factors for cardiovascular disease. Therefore, the dysfunction we observed could have resulted from HHcy, LF, and/or their combination (HHcy + LF). We tested the hypothesis that HHcy-induced vascular dysfunction is more severe in the presence of LF. Four groups of rats consumed diets for approximately 10 wk that produced plasma homocysteine (microM) and liver folate (microg folate/g liver) concentrations, respectively, of 7 +/- 1 and 15 +/- 1 (Control; Con; n = 16), 17 +/- 2 and 15 +/- 2 (HHcy; n = 17), 10 +/- 1 and 8 +/- 1 (LF; n = 14), and 21 +/- 2 and 8 +/- 1 (HHcy + LF; n = 18). We observed that maximal ACh-evoked vasorelaxation was greatest in aortas and mesenteric arteries from Con rats vs. all groups. While the extent of dysfunction was similar between LF and HHcy animals, it was less severe compared with arteries from HHcy + LF rats. Maximal ACh-evoked vasorelaxation in coronary arteries was not different between Con and LF rats, but both were greater than HHcy + LF animals. In segments of aortas, 1) ACh-evoked vasorelaxation was similar among groups after incubation with the nonenzymatic intracellular O2(-) scavenger Tiron, 2) vascular O2(-) estimated using dihydroethidium staining was greatest in HHcy + LF vs. all groups, and 3) tension development in response to nitric oxide (NO) synthase inhibition was greatest in Con vs. all other groups. We conclude that HHcy + LF evokes greater dysfunction than either HHcy alone (aortas, mesentery) or LF alone (aortas, mesentery, coronary), likely by producing more O2(-) within the vasculature and thereby reducing NO bioavailability.

Reducing arginase activity via dietary manganese deficiency enhances endothelium-dependent vasorelaxation of rat aorta

L-Arginine is a common substrate for the enzymes arginase and nitric oxide synthase (NOS). Acute inhibition of arginase enzyme activity improves endothelium-dependent vasorelaxation, presumably by increasing availability of substrate for NOS. Arginase is activated by manganese (Mn), and the consumption of a Mn-deficient (Mn-) diet can result in low arginase activity. We hypothesize that endothelium-dependent vasorelaxation is greater in rats fed Mn- versus Mn sufficient (Mn+) diets. Newly weaned rats fed Mn+ diets (0.5 microg Mn/g; n = 12) versus Mn+ diets (45 microg Mn/g; n = 12) for 44 +/- 3 days had (i) lower liver and kidney Mn and arginase activity (P < or = 0.05), (ii) higher plasma L-arginine (P < or = 0.05), (iii) similar plasma and urine nitrate + nitrite, and (iv) similar staining for endothelial nitric oxide synthase in thoracic aorta. Vascular reactivity of thoracic aorta (approximately 720 microm i.d.) and small coronary arteries (approximately 110 microm i.d.) was evaluated using wire myographs. Acetylcholine (ACh; 10(-8)-10(-4) M) produced greater (P < or = 0.05) vasorelaxation in thoracic aorta from Mn- rats (e.g., maximal percent relaxation, 79 +/- 7%) versus Mn + rats (e.g., maximal percent relaxation, 54 +/- 9%) at 5 of 7 evaluated doses. Tension produced by NOS inhibition using N(G) monomethyl-L-arginine (L-NMMA; 10(-3) M) and vasorelaxation evoked by (i) arginase inhibition using difluoromethylornithine (DFMO; 10(-7) M), (ii) ACh (10(-8)-10(-4) M) in the presence of DFMO, and (iii) sodium nitroprusside (10(-9)-10(-4) M) were unaffected by diet. No differences existed between groups concerning these responses in small coronary arteries. These findings support our hypothesis that endothelium-dependent vasorelaxation is greater in aortic segments from rats that consume Mn- versus Mn+ diets; however, responses from small coronary arteries were unaffected.

Exercise training preserves coronary flow and reduces infarct size after ischemia-reperfusion in rat heart

The effect of endurance training on the resistance of the heart to left ventricular (LV) functional deficit and infarction after a transient regional ischemia and subsequent reperfusion was examined. Female Sprague-Dawley rats were randomly assigned to an endurance exercise training (Tr) group or a sedentary (Sed) control group. After 20 wk of training, hearts were excised, perfused, and instrumented for assessment of LV mechanical function, and the left anterior descending coronary artery was occluded to induce a transient regional ischemia (1 h) that was followed by 2 h of reperfusion. Throughout much of the regional ischemia-reperfusion protocol, coronary flow rates, diastolic function, and LV developed pressure were better preserved in hearts from Tr animals. During the regional ischemia, coronary flow to myocardium outside the ischemic zone at risk (ZAR) was maintained in Tr hearts, whereas it progressively fell in Sed hearts. On release of the coronary artery ligature, flow to the ZAR was greater in Tr than in Sed hearts. Infarct size, expressed as a percentage of the ischemic ZAR, was significantly smaller in hearts from Tr rats (24 +/- 3 vs. 32 +/- 2% of ZAR, P < 0.05). Mn- and CuZn-SOD protein expression were higher in the LV myocardium of Tr animals (P < 0.05 for both isoforms). Our data indicate that long-term exercise training leads to infarct sparing and better maintenance of coronary flow and mechanical function after ischemia-reperfusion.

Effects of statins on myocardial and coronary artery response to ischemia-reperfusion

This study tested the hypotheses that (i) lipophilic statins (atorvastatin and simvastatin) impair ventricular recovery from myocardial ischemia–reperfusion, owing to their greater myocyte permeability, compared with a hydrophilic statin (pravastatin), and (ii) statins enhance endothelium-dependent vasodilation of isolated coronary arteries from the ischemic region. Farm pigs consumed chow supplemented with atorvastatin (2.5 mg·kg–1·d–1; n = 6), pravastatin (10 (n = 3) or 20 (n = 2) mg·kg–1·d–1), simvastatin (5 mg·kg–1·d–1; n = 6), or no statin (control; n = 6) for 3 weeks. Animals were anesthetized and instrumented to measure regional (% segment shortening) and global (dP/dt max) left ventricular (LV) function during coronary artery occlusion (10 min) and reperfusion (30 min). Coronary resistance (i.d. = 119 ± 3 µm) and conductance (i.d. = 487 ± 11 µm) arteries were isolated from the ischemic region to measure receptor-dependent (acetylcholine (ACh)) and -independent (KCl) vasoconstriction, and endothelium-dependent (bradykinin (BK)) and -independent (sodium nitroprusside (SNP)) vasodilation. At 30 min reperfusion, neither percent recovery of regional ventricular function (atorvastatin, 24% ± 15%; pravastatin, 36% ± 13%; simvastatin, 29% ± 13%; control, 36% ± 13%) nor percent recovery of global LV cardiac function differed among groups. However, BK-induced vasorelaxation of coronary conductance vessels was greater (P < 0.05) in statins versus controls, and ACh-induced vasoconstriction was less in simvastatin-treated animals, suggesting the potential for enhanced coronary arterial blood flow to the jeopardized region. In conclusion, our data suggest that ischemia-induced myocardial stunning is similar among pigs treated for 3 weeks with atorvastatin, pravastatin, or simvastatin, even though statin treatment appears to augment endothelium-dependent vasodilation of conductance, but not resistance, vessels subjected to ischemia–reperfusion.Key words: ischemia, reperfusion, statins, vascocontriction–dilation, ventricular function.

Improved coronary vascular function evoked by high-intensity treadmill training is maintained in arteries exposed to ischemia and reperfusion

We hypothesized that myocardial contractile function and coronary arterial function are greater after ischemia and reperfusion in high-intensity treadmill-trained vs. sedentary rats. Rats performed 10 x 4-min bouts of treadmill running consisting of 2 min at 13 m/min + 2 min at 45-60 m/min (Etr) or were sedentary (Sed) for 12 wk. Animals then were instrumented to measure left ventricular (LV) contractility in response to three 15-min coronary occlusion (O) and 5-min reperfusion (R) cycles (Isc) or a sham operation (Sham). After the Isc and Sham protocols, hearts were excised and coronary arterial ( approximately 105 microm ID) function was evaluated by using isometric techniques. LV developed pressure, the first derivative of LV pressure at a developed pressure of 40 mmHg, and systolic blood pressure were not different between Etr (n = 14) and Sed (n = 7) rats before or after the Sham protocol. Furthermore, hemodynamic variables were similar in Etr (n = 14) and Sed (n = 13) animals before the Isc protocol and were depressed to the same degree by the three O-R cycles. Therefore, Etr did not alter myocardial contractile function in rats that were (i.e., Isc) or were not (i.e., Sham) exposed to ischemia and reperfusion. Acetylcholine-evoked relaxation (10-8 to 3 x 10-5 M) was greater (P < 0.05) in coronary arteries from Sham-Etr vs. Sham-Sed animals (5 of 8 doses tested) and Isc-Etr vs. Isc-Sed rats (3 of 8 doses tested). Maximal relaxation produced by sodium nitroprusside (10-4 M) was similar among groups. Vasocontractile responses produced by KCl (10-100 mM) and endothelin-1 (10-11-10-4 M) were greater (P < 0.05) in the presence vs. the absence of nitric oxide synthase inhibition (10-6 M NG-monomethyl-l-arginine) in vessels from Sham-Etr but not Sham-Sed rats and from Isc-Etr but not Isc-Sed rats. These findings suggest that Etr-evoked improvements in coronary function are maintained in small arteries even when exposed to ischemia and reperfusion.

Coronary smooth muscle adaptation to exercise: does it play a role in cardioprotection?

Substantial evidence exists supporting the role of chronic exercise in reducing the incidence and severity of coronary vascular disease. Physical inactivity is an independent risk factor for coronary heart disease suggesting that the cardioprotective effect of exercise is due, in part, to an intrinsic adaptation within the coronary vasculature. Surprisingly, a paucity of information exists regarding the intrinsic cellular changes within the coronary vasculature associated with exercise training and even less is known regarding the effect of physical activity on long-term phenotypic modulation of coronary smooth muscle (CSM). The purpose of this symposium is to provide a concise update on the current knowledge regarding CSM adaptation to exercise training and the potential for these adaptations to contribute to exercise-induced cardioprotection. The potential role of CSM in exercise-induced cardioprotection will be approached from two perspectives. First, endurance exercise training effects on the regulation of coronary vasomotor tone via changes in CSM calcium regulation will be reviewed, i.e. short-term functional adaptation. Secondly, we will discuss potential long-term consequences of this altered calcium regulation, i.e. exercise-induced phenotypic modulation of CSM. We propose that exercise training alters CSM intracellular calcium regulation to reduce Ca2+-dependent activation of the contractile apparatus and Ca2+-dependent gene transcription and increase activation of sarcolemmal potassium channels. The overall effect is to increase the gain of the vasomotor system and maintain a stable, contractile CSM phenotype.

Hyperhomocysteinemia evoked by folate depletion: effects on coronary and carotid arterial function

High circulating concentrations of homocysteine (ie, hyperhomocysteinemia [Hhcy]) impair the vascular function of peripheral conduit arteries and arterioles perfusing splanchnic and skeletal muscle regions. The effects of HHcy on coronary resistance vessel function and other indexes of vascular function, ie, arterial permeability and stiffening, are unclear. We tested the hypotheses that HHcy impairs coronary resistance vessel reactivity; increases carotid arterial permeability; and initiates arterial stiffening. Male rats that consumed folate-replete (CON, n=44) or folate-deplete (HHcy, n=48) chow for 4 to 5 weeks had total plasma homocysteine concentrations of 7+/-2 or 58+/-4 micromol/L, respectively. Maximal acetylcholine-evoked relaxation (approximately 40% vs approximately 60%) and tension development from baseline in response to nitric oxide synthase inhibition (approximately 20% vs approximately 40%) were lower (both P<0.05) in coronary resistance vessels (approximately 120 microm, internal diameter) isolated from HHcy versus CON animals, respectively, whereas sodium nitroprusside-evoked relaxation and contractile responses to serotonin and potassium chloride were similar between groups. Permeability to 4400 MW and 65 000 MW fluorescently labeled (TRITC) dextran reference macromolecules (quantitative fluorescence microscopy) was approximately 44% and approximately 24% greater (P<0.05), respectively, in carotid arteries from HHcy versus CON rats. Maximal strain, evaluated by using a vessel elastigraph, was less ( approximately 32% vs 42%, P<0.05) in carotid arterial segments from HHcy versus CON animals, respectively. Finally, estimates of oxidative (copper-zinc+manganese superoxide dismutase activity) and glycoxidative (pentosidine) stress were elevated (P<0.05) in arterial tissue from HHcy versus CON rats. These findings suggest that moderately severe HHcy evoked by folate-depletion impairs endothelium-dependent relaxation of coronary resistance vessels, increases carotid arterial permeability, and initiates arterial stiffening. HHcy may produce these effects by a mechanism associated with increased oxidative and glycoxidative stress.

Volume overload left ventricular hypertrophy: effects on coronary microvascular reactivity in rabbits

The mechanisms controlling the coronary vascular responses of vessels perfusing the left ventricular (LV) myocardium that is hypertrophied from chronic volume overload are unclear. We hypothesised that endothelial function is compromised, and receptor-mediated contraction is exacerbated, in coronary resistance vessels from rabbits with LV hypertrophy compared to controls. The mitral valve of 10 rabbits was damaged surgically to cause mitral regurgitation and chronic volume overload, resulting in LV hypertrophy (LV hypertrophy rabbits). Echocardiographic assessment at 12 weeks verified that mitral regurgitation was present in LV hypertrophy but not sham-operated, weight- and age-matched animals (control rabbits; n = 17). Percentage increases from weeks 0 to 12 in LV cross-sectional area (47 +/- 7 % vs. 2 +/- 8 %), LV volume (47 +/- 14 % vs. 7 +/- 10 %) and LV mass (27 +/- 4 % vs. 3 +/- 6 %), were greater (all P < 0.05) in LV hypertrophy vs. control rabbits, respectively. At 12 weeks, coronary resistance vessel (approximately 130 microm, internal diameter) reactivity was evaluated using wire myography. Endothelium-dependent (i.e. acetylcholine, 10(-8)-10(-5) M) and -independent (i.e. sodium nitroprusside, 10(-9)-10(-4) M) relaxation, and receptor-mediated vasocontraction (i.e. endothelin-1, 10(-11)-10(-7) M) were similar between groups. However, tension development in response to nitric oxide synthase inhibition (10(-6) M N (G)-monomethyl-L-arginine) was greater (P < 0.05) in LV hypertrophy compared to control rabbits. These results indicate that while coronary resistance vessel function is similar between groups, our estimate of basal nitric oxide production is greater in vessels from LV hypertrophy than control rabbits.

Short-term exercise improves myocardial tolerance to in vivo ischemia-reperfusion in the rat

These experiments examined the independent effects of short-term exercise and heat stress on myocardial responses during in vivo ischemia-reperfusion (I/R). Female Sprague-Dawley rats (4 mo old) were randomly assigned to one of four experimental groups: 1) control, 2) 3 consecutive days of treadmill exercise [60 min/day at 60-70% maximal O2 uptake (VO2 max)], 3) 5 consecutive days of treadmill exercise (60 min/day at 60-70% VO2 max), and 4) whole body heat stress (15 min at 42 degrees C). Twenty-four hours after heat stress or exercise, animals were anesthetized and mechanically ventilated, and the chest was opened by thoracotomy. Coronary occlusion was maintained for 30-min followed by a 30-min period of reperfusion. Compared with control, both heat-stressed animals and exercised animals (3 and 5 days) maintained higher (P < 0.05) left ventricular developed pressure (LVDP), maximum rate of left ventricular pressure development (+dP/dt), and maximum rate of left ventricular pressure decline (-dP/dt) at all measurement periods during both ischemia and reperfusion. No differences existed between heat-stressed and exercise groups in LVDP, +dP/dt, and -dP/dt at any time during ischemia or reperfusion. Both heat stress and exercise resulted in an increase (P < 0.05) in the relative levels of left ventricular heat shock protein 72 (HSP72). Furthermore, exercise (3 and 5 days) increased (P < 0.05) myocardial glutathione levels and manganese superoxide dismutase activity. These data indicate that 3-5 consecutive days of exercise improves myocardial contractile performance during in vivo I/R and that this exercise-induced myocardial protection is associated with an increase in both myocardial HSP72 and cardiac antioxidant defenses.

Na(+)/H(+) exchange subtype 1 inhibition reduces endothelial dysfunction in vessels from stunned myocardium

Myocardial ischemia and reperfusion cause myocyte and vascular dysfunction, frequently termed "stunning." We hypothesized that inhibiting the Na(+)/H(+) exchanger subtype 1 isoform (NHE(1)) during ischemia and reperfusion limits myocardial and coronary microvascular stunning. Anesthetized rats completed 2 x 10-min coronary artery occlusions separated by 5-min of reperfusion, followed by 15 or 60 min of reperfusion. Vehicle (saline) or the NHE(1) inhibitor cariporide (HOE-642) was administered 15 min before ischemia and was continued throughout each protocol. After reperfusion, hearts were excised, and the reactivity of resistance arteries (internal diameter, approximately 120 microm) was assessed. The first derivative of left ventricular (LV) pressure, LV developed pressure, and LV systolic wall thickening were depressed (P < 0.05) similarly in vehicle- and cariporide-treated rats during ischemia and after 15 or 60 min of reperfusion compared with sham-operated animals that were not exposed to ischemia (i.e., controls). In vessels obtained after 15 min of reperfusion, the maximal response to acetylcholine-induced relaxation (10(-8)-10(-4) M) was blunted (P < 0.05) in vessels from vehicle- (approximately 35%) and cariporide-treated rats (approximately 55%) compared with controls (approximately 85%). However, the percent relaxation to acetylcholine was greater (P < 0.05) in cariporide-treated rats compared with vehicle-treated rats. Maximal contractile responses to endothelin-1 (10(-11)-10(-7) M) were increased (P < 0.05) similarly in vehicle- and cariporide-treated rats compared with controls. Relaxation to sodium nitroprusside (10(-4) M) was not different among groups. Results were similar in vessels obtained from animals after 60 min of reperfusion. These findings suggest that NHE(1) inhibition before coronary occlusion lessens ischemia-induced microvascular dysfunction for 15-60 min after reperfusion but does not alter myocardial contractile function in the area at risk.

Effects of red wine, alcohol, and quercetin on coronary resistance and conductance arteries

Moderate consumption of alcoholic beverages is associated with a reduced risk of coronary heart disease (CHD). Some evidence suggests that red wine is particularly beneficial in this regard and may account in part for the French paradox, although the mechanism of this effect is unknown. We assessed the effects of red wine, ethanol, and quercetin, a major flavonoid constituent of red wine, in coronary resistance vessels (80-150 microm, i.d.) and conductance vessels (300-525 microm, i.d.) of the rabbit. Vessel wall tension was measured in isolated segments maintained in a wire-type myograph (37 degrees C) and preconstricted with 30 mM K+. At an alcohol concentration (14 mM) equivalent to moderate consumption, red wine evoked a small, transient constrictor effect in resistance and conductance vessels (9+/-4%, n = 5; 8+/-1%, n = 7, respectively; p < 0.05). Ethanol alone at this concentration was without effect. Quercetin (5.6, 8, and 30 microM) significantly relaxed resistance (-32+/-4%, n = 10; -47+/-2%, n = 7; -82+/-6%, n = 8, respectively) and conductance (-20+/-3%, n = 8; -32+/-4%, n = 8; -72+/-7%, n = 8, respectively) coronary arteries. Vasorelaxation by quercetin was endothelium-independent and was significantly greater in resistance than in conductance vessels. These data suggest that red wine and ethanol do not evoke relaxation in small coronary arteries at concentrations associated with moderate consumption. Quercetin elicits marked coronary vasorelaxation that is endothelium-independent. However, the concentrations of quercetin necessary to achieve this action are not attained with moderate red wine consumption.

Glutathione supplementation and training increases myocardial resistance to ischemia-reperfusion in vivo

The present study examined the effects of oral reduced glutathione (GSH) supplementation in conjunction with endurance training on contractile function, antioxidant defense, and oxidative damage in response to ischemia-reperfusion (I/R) in rat hearts. Female Sprague-Dawley rats (age 4 mo, n = 72) were randomly assigned to a treadmill-trained (T; 25 m/min, 15% grade, for 75 min/day, 5 days/wk, for 10 wk) or untrained (U) group. Each group was further divided into rats receiving 5 g GSH/kg diet during the final 17 days of training (GSH-S) and control (C) groups. One-half of each group of rats was subjected to I/R by surgical occlusion of the main coronary artery for 45 min, followed by 30-min reperfusion or sham operation. Left ventriclar (LV) peak systolic pressure (LVSP) and contractility (+dP/dt), measured with a catheter inserted into the LV via the carotid artery, decreased with I/R in all groups (P < 0.05). However, LVSP with I/R in the T/GSH-S group was 9.5%, 17%, and 18% higher (P < 0.05) than that in the U/GSH-S, T/C, and U/C groups, respectively. +dP/dt with I/R was 19%, 27%, and 29% (P < 0.05) greater in the T/GSH-S group versus the T/C, U/GSH-S, and U/C groups, respectively. I/R decreased heart GSH content by 12-17% (P < 0.05) and increased oxidized glutathione (GSSG) by 20-27% (P < 0.05). T/GSH-S hearts showed 15% higher GSH (P < 0.05) and a 32% higher GSH-to-GSSG ratio (P < 0.05) than the U/C group at the end of I/R. Myocardial superoxide dismutase, GSH peroxidase, glutathione reductase, and gamma-glutamyl transpeptidase activities were increased with treadmill training in both GSH-S and C rats. I/R induced myocardial lipid peroxidation and lactate dehydrogenase release were attenuated with T/GSH-S treatment. The present data indicate that training in conjunction with dietary GSH supplementation can increase myocardial GSH content and antioxidant defense capacity, thereby protecting the intact heart against oxidative damage and functional retardation caused by I/R.