AJP - Heart Information on EB 2010
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Heart Circ Physiol 295: H1470-H1480, 2008. First published July 18, 2008; doi:10.1152/ajpheart.00016.2008
0363-6135/08 $8.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
295/4/H1470    most recent
00016.2008v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Moien-Afshari, F.
Right arrow Articles by Laher, I.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Moien-Afshari, F.
Right arrow Articles by Laher, I.

Exercise restores coronary vascular function independent of myogenic tone or hyperglycemic status in db/db mice

Farzad Moien-Afshari,1 Sanjoy Ghosh,3 Shahrzad Elmi,1 Majid Khazaei,2 Mohammad M. Rahman,1 Nada Sallam,1 and Ismail Laher1

1Department of Pharmacology and Therapeutics, Faculty of Medicine, and 3Department of Pediatrics, Child and Family Research Institute, University of British Columbia, Vancouver, British Columbia, Canada; and 2Department of Physiology, Isfahan University of Medical Sciences, Isfahan, Iran

Submitted 7 January 2008 ; accepted in final form 2 July 2008


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Regulation of coronary function in diabetic hearts is an important component in preventing ischemic cardiac events but remains poorly studied. Exercise is recommended in the management of diabetes, but its effects on diabetic coronary function are relatively unknown. We investigated coronary artery myogenic tone and endothelial function, essential elements in maintaining vascular fluid dynamics in the myocardium. We hypothesized that exercise reduces pressure-induced myogenic constriction of coronary arteries while improving endothelial function in db/db mice, a model of type 2 diabetes. We used pressurized mouse coronary arteries isolated from hearts of control and db/db mice that were sedentary or exercised for 1 h/day on a motorized exercise-wheel system (set at 5.2 m/day, 5 days/wk). Exercise caused a ~10% weight loss in db/db mice and decreased whole body oxidative stress, as measured by plasma 8-isoprostane levels, but failed to improve hyperglycemia or plasma insulin levels. Exercise did not alter myogenic regulation of arterial diameter stimulated by increased transmural pressure, nor did it alter smooth muscle responses to U-46619 (a thromboxane agonist) or sodium nitroprusside (an endothelium-independent dilator). Moderate levels of exercise restored ACh-simulated, endothelium-dependent coronary artery vasodilation in db/db mice and increased expression of Mn SOD and decreased nitrotyrosine levels in hearts of db/db mice. We conclude that the vascular benefits of moderate levels of exercise were independent of changes in myogenic tone or hyperglycemic status and primarily involved increased nitric oxide bioavailability in the coronary microcirculation.

coronary artery; manganese superoxide dismutase; diabetes; endothelium; oxidative stress

CARDIOVASCULAR DISEASE is the leading cause of mortality in patients with diabetes (29). Endothelium-dependent vasodilation is markedly reduced and myogenic tone of resistance arteries is increased in animal models of type 2 diabetes mellitus (DM) (3, 25, 53). These changes are likely to reduce tissue blood perfusion. Blood flow is regulated by the influence of several constrictors (e.g., increased intravascular pressure, endothelial constrictors) and dilators (e.g., reduced intravascular pressure, endothelial dilators) (35). In many cases, endothelial dysfunction precedes the onset of cardiovascular disease in type 2 DM. It is likely that loss of endothelial regulation results in a mismatch of myocardial supply and demand, thus provoking cardiac ischemia and myocardial infarction (32, 39).

The cardiovascular benefits of regular exercise in patients with type 2 DM are well accepted. Exercise alters myocardial redox status and calcium handling, improves energy metabolism, and induces the formation of heat shock proteins and other cardioprotective molecules (2, 26). Exercise also reduces insulin resistance, an important cause for the elevated plasma glucose and insulin levels in humans and animals with diabetes (37). However, the mechanisms by which exercise promotes improved coronary microcirculatory function in type 2 DM hearts are incompletely understood, especially in relation to altered myogenic tone and endothelial function in coronary resistance arteries. We hypothesized that exercise reduces pressure-induced myogenic constriction of coronary arteries while simultaneously improving endothelial function in db/db mice, a frequently used animal model of type 2 DM. We found that the vascular benefits of moderate levels of exercise in our study were independent of changes in myogenic tone or hyperglycemic status and primarily involved increased nitric oxide (NO) bioavailability in the coronary microcirculation.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Animals. All experimental procedures were approved by the Animal Care Committee of the University of British Columbia. Five-week-old male db/db (BKS.Cg-m+/+ Leprdb/J) and age-matched control (BKS.cg-m+/+ Leprdb/+/J) mice, simply referred to as wild-type (WT) in the present study, were purchased from Jackson Laboratory. Mice were housed in standard animal facility conditions with 12:12-h light-dark cycles at 26°C and allowed free access to standard chow and water. WT and db/db mice were divided into exercised and sedentary subgroups (8–10 in each group).

Exercise protocol. Mice (5 wk old) assigned to the exercise group were trained to run on a motorized exercise-wheel system (Lafayette Instrument) for 8 wk. Exercise intensity was incrementally increased to allow for animal acclimatization during the first 2 wk of training. The initial exercise speed of 2.5 m/min for 1 h (150 m) per day was gradually increased to a target of 1 h of exercise at 5.2 m/min, which represents a daily forced exercise of 312 m. Mice were exercised daily, 5 days/wk for 8 wk, at a set time each day. Mice were housed in the animal facility between exercise sessions. Sedentary animals were placed in the nonrotating wheels for the same duration as the exercised group.

Blood and tissue samples. At 13 wk of age, mice were anesthetized by intraperitoneal injection of pentobarbital sodium (Somnotol; 30 mg/kg) and heparin sodium (50 U/kg). Blood samples were collected from the inferior vena cava via a 5-ml syringe and a 21-gauge needle. Plasma was generated by centrifugation at 14,000 rpm for 10 min and stored in separate Eppendorff tubes at –76°C for later biochemical assay. After blood collection, animals were killed. Hearts were excised and placed in ice-cold physiological salt solution (PSS; see Chemicals and solutions). After the hearts were weighed, coronary septal arteries were dissected for pressure myograph studies; the remaining heart tissue was stored at –76°C for SOD protein, catalase, nitrotyrosine, and endothelial NO synthase (eNOS) quantification. A piece of thigh adductor muscle was flash frozen using liquid nitrogen and kept at –76°C for citrate synthase (CS) assay.

Oral glucose tolerance test. Mice underwent an oral glucose tolerance test (OGTT) at 10 wk of age (i.e., after 5 wk of exercise). After 6 h of fasting, mice were loaded with glucose (1.5 g/kg) by oral gavage of a 40% glucose solution, and blood samples were taken at 0, 10, 20, 60, and 120 min. Plasma was separated by centrifugation and stored at –76°C for later analysis of glucose. For reduction of short-term treatment effects, animals were not exercised for 24 h before the OGTT.

CS enzyme assay. Frozen thigh adductor muscles were homogenized on ice in 100 mM Tris buffer (pH 8) containing 0.1% Triton X-100 and 0.5 mM EDTA (pH 8) using a glass homogenizer (14). Tissue debris was removed by centrifugation of the homogenates at 4°C for 5 min at 13,200 rpm. The supernatant was assayed for CS activity at 30°C at the linear portion of the activity curve (1–2 min). Reaction mixtures consisted of 50 mM Tris (pH 8), 0.1 mM oxaloacetate, 0.1 mM acetyl-CoA, and 0.1 mM 5,5-dithiobis(2-nitrobenzoic acid). Briefly, the reaction was initiated by addition of 25 µl of muscle extract and linking of the release of free CoA to 5,5-dithiobis(2-nitrobenzoic acid), a colorimetric agent. The CS activity was monitored at 412 nm using a spectrophotometer (Lambda 35 UV/VIS, Perkin Elmer). Calculations of activity used a millimolar extinction coefficient of 13.6 and were corrected for background acetyl-CoA deacylase activity by determination of the rate of change in absorbance at 412 nm in the absence of oxaloacetate. CS activity was expressed as micromoles per minute per milligram protein of the extract (measured by Bradford assay).

Western blot analysis. Pieces of whole hearts were ground in liquid nitrogen and homogenized in a Polytron homogenizer three times for 30 s each in ice-cold homogenization buffer (20 mM Tris·HCl, 250 mM EGTA, 200 mM EDTA, 100 mM PMSF, 100 mM NaF, 2-mercaptoethanol, leupeptin, aprotinin, NP-40, 10% SDS, and 5% DCA). The protein contents of the homogenates were quantified using a Bradford protein assay. The homogenates were diluted and boiled with sample loading dye, and samples corresponding to 50 µg of protein were used in SDS-PAGE. After transfer, nitrocellulose membranes were blocked in 5% skim milk overnight in Tris-buffered saline containing 0.1% Tween 20. Membranes were incubated with antibodies raised in rabbit [endothelial NO synthase (eNOS, or NOS3), catalase, and extracellular SOD (SOD3)], sheep [Cu,Zn SOD (or SOD1), Mn SOD (or SOD2)], and mouse (nitrotyrosine) for 2 h at room temperature. The membranes were washed three times in Tris-buffered saline containing 0.1% Tween 20 and then incubated for 2 h at room temperature with secondary goat anti-rabbit, goat anti-mouse, donkey anti-sheep, or donkey anti-goat horseradish peroxidase-conjugated antibodies and visualized using an enhanced chemiluminescence detection kit (18). Controls for equal protein loading were performed using an anti-goat polyclonal antibody raised against GAPDH (Genscript, Piscataway, NJ).

Immunofluorescence. Part of the left ventricle was fixed in 10% neutral buffered formalin and embedded in paraffin, and 5-µm sections were prepared. Double immunostaining was performed for von Willebrand factor (vWF) and Mn SOD. For the first vWF labeling, sections were deparaffinized in xylene and rehydrated using various grades of ethanol. Nonspecific binding of IgGs was blocked by incubation of the sections in 10% BSA for 20 min. vWF immunolabeling was accomplished by exposure to a mouse monoclonal anti-vWF antibody (1:50 dilution; Novocastra Labs) for 2 h at 37°C and Alexa Fluor 594-conjugated goat anti-mouse IgG (Molecular Probes) for 90 min at 37°C. For the second labeling, the same sections were incubated with primary sheep anti-Mn SOD antibody (1:200 dilution; Calbiochem) overnight at room temperature and secondary donkey anti-sheep antibody conjugated with FITC (Sigma). Sections were finally counterstained with 4',6-diamidino-2-phenylindole (DAPI) for visualization of nuclei and examined using confocal microscopy. Slides were visualized using FITC, DAPI, and Texas Red filters under a confocal microscope.

Resistance artery preparation. Mouse coronary septal arteries were located through a right ventricular wall opening, dissected, and cleaned of adherent cardiac muscle tissue (31). For all functional studies, a 0.8- to 1.2-mm segment of the artery (60–150 µm ID) at the level of the superior papillary muscle was excised and mounted at both ends onto glass cannulas in a pressure myograph chamber (Living Systems Instrumentation, Burlington, VT). Both ends of the artery were tied using single strands teased from a 4-0 surgical silk thread, and the chamber was placed on an inverted microscope stage for measurement of arterial diameter. One cannula was occluded to prevent flow through the vessel, and the other was connected through a pressure transducer to a peristaltic feedback pump to maintain constant pressure (20 mmHg) and also to monitor transmural diameter. The vessels were continuously superfused with bubbled (95% O2-5% CO2) PSS (pH 7.35–7.4) at 37°C. Pressure-constriction curves were determined in all artery segments. Intravascular pressure was incrementally increased to 80 mmHg. Vessels that did not develop a leak were equilibrated for 1 h at this pressure for development of myogenic tone (vessels that did not develop spontaneous constriction were excluded). After development of pressure-induced constriction, transmural pressure was reduced to 10 mmHg and then increased in a stepwise manner at 5-min intervals to 120 mmHg. The internal diameter was recorded at each step and then compared with diameters in a calcium-free PSS at the end of the experiment for determination of the degree of myogenic tone at each pressure. The artery was incubated for 0.5 h with bosentan (10 µM), and the protocol was repeated to determine the effect of endogenous endothelin on the myogenic response (48). Then, at 20 mmHg pressure, arteries were preconstricted up to 50% of their initial diameter using a thromboxane agonist (U-46619, 10–7 M) (31). Cumulative concentrations (1 nM–10 µM) of ACh and sodium nitroprusside (SNP) were added to the bath separately. The ACh concentration-response curve was repeated in arteries incubated for 45 min with SOD (120 U/ml) or L-arginine (L-Arg, 10–3 M) + tetrahydrobiopterin (BH4, 10 µM). After washout, U-46610 concentration-response curves were generated by addition of cumulative concentrations (5 nM–5 µM). Finally, arterial diameter was measured in response to a stepwise increase in intraluminal pressure in calcium-free PSS containing EGTA for calculation of arterial distensibility (see below).

Glucose and insulin. Plasma glucose levels were measured by Trinder assay using a commercially available kit (Diagnostic Chemicals, Oxford, CT). Insulin levels were determined in plasma using the Mercodia Ultrasensitive Mouse Insulin Assay Kit (Alpco, Salem, NH). Photometric measurements were performed by the Dimension Clinical Chemistry System (GMI, Ramsey, MN).

Chemicals and solutions. All buffer reagents were purchased from BDH; U-46619 from Cayman Chemicals (Ann Arbor, MI); and ACh, SNP, Cu,Zn SOD, L-Arg, and BH4 from Sigma (St. Louis, MO). Bosentan was a generous gift from Actelion Phamaceuticals. The composition of the PSS (mM) was as follows: 119 NaCl, 4.7 KCl, 1.18 KH2PO4, 1.17 MgSO4, 24.9 NaHCO3, 0.023 EDTA, 1.6 CaCl2, and 11.1 dextrose. The composition of calcium-free solution was similar to that of PSS but did not include calcium and contained 10–3 M EGTA.

Statistical analysis and calculations. Values are means ± SE. Data were analyzed using NCSS-2000 computer software. Repeated-measures or one-way ANOVA with multiple comparisons using Bonferroni's test was performed where appropriate. GraphPad Prism (version 3.02-2000) was used for curve fit and dose-response analysis. The results of statistical tests were considered significant at P < 0.05. Myogenic tone was calculated as percentage of arterial constriction at each pressure step as follows: %constriction = 100 x (DCa free,P – DP)/DCa free,P, where DCa free,P is arterial diameter at pressure P in calcium-free PSS and DP is diameter in PSS at pressure P. Percentage of relaxation/dilation of the arteries in response to ACh and SNP was calculated as follows: 100 x (D20U[drug] – D20U)/(D20Ca free – D20U), where D20U[drug] is diameter of a U-46619-preconstricted vessel at 20 mmHg pressure in PSS in the presence of a particular concentration of drug (ACh or SNP), D20U is diameter in PSS at 20 mmHg pressure in the presence of U-46619, and D20Ca free is passive diameter in calcium-free PSS at 20 mmHg pressure. Passive vascular distensibility was calculated as 100 x passive DP/DCa free,10, where passive DP is vascular diameter in Ca-free PSS at pressure P.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Exercise, body weight, heart weight, and plasma parameters. Moderate-intensity exercise decreased body weight of db/db mice (~10%) compared with their sedentary littermates, whereas exercise did not alter body weight of WT mice. Heart weight appeared lower in db/db than in WT mice; however, the difference was not significant (158 ± 6 vs. 177 ± 6 mg). Exercise did not increase heart weight significantly in either group (170 ± 7 and 184 ± 6 mg, respectively; Table 1). Plasma glucose and plasma insulin levels were significantly higher in db/db than in age-matched lean WT mice. Eight weeks of moderate-intensity exercise did not significantly alter plasma glucose and insulin levels in db/db mice (Table 1). As an indicator of the physiological effectiveness of our exercise protocol, CS activity was significantly increased in exercised WT and db/db mice (Table 1). An OGTT was performed after 5 wk of exercise in db/db and WT mice (Table 2). Exercise did not alter plasma glucose levels in db/db or WT mice within 120 min after an oral glucose load (Table 2). There was a significant difference between db/db and WT groups at all time points.


View this table:
[in this window]
[in a new window]

  		Table 1. General characteristics of the animals

 

View this table:
[in this window]
[in a new window]

  		Table 2. Summary of OGTT results from mice that were exercised for 5 wk

 
Exercise decreases whole body and tissue oxidative stress. Whole body oxidative stress was estimated by measurement of plasma 8-isoprostane, a lipid peroxidation by-product (36). Plasma levels of 8-isoprostane were elevated in db/db mice and were significantly reduced by exercise (Table 1). Estimation of antioxidant protein expression in the whole heart by Western blotting revealed that Mn SOD was significantly decreased and nitrotyrosine was significantly increased in db/db mice compared with their age-matched lean WT mice. Exercise significantly increased Mn SOD (Fig. 1A) and extracellular SOD (Fig. 1F) and lowered nitrotyrosine levels in db/db hearts (Fig. 1D). However, exercise did not alter the protein expression levels of Cu,Zn SOD and catalase in db/db or WT mouse hearts (Fig. 1, B and C). Nitrotyrosine levels increased in the absence of changes in cardiac eNOS levels, which were unaffected by diabetes or exercise (Fig. 1E). To ensure that the increases in SOD were localized to the coronary arteries, we utilized an immunofluorescence approach (Fig. 2).


Figure 1
View larger version (40K):
[in this window]
[in a new window]

  		Fig. 1. Protein expression of antioxidants and endothelial nitric oxide synthase (eNOS) in whole heart. A: Mn SOD was significantly decreased in whole heart extract of db/db mice compared with lean wild-type (WT) mice. Exercise significantly increased Mn SOD in db/db mice hearts. B: Cu,Zn SOD (SOD1) expression was not different in hearts from exercise and sedentary groups. C: catalase expression was not significantly different among the groups. D: nitrotyrosine levels were significantly higher in db/db hearts; exercise decreased levels significantly in db/db hearts. E: eNOS expression was not significantly different among the groups. F: extracellular SOD (SOD3) expression increased with exercise in db/db hearts compared with nonexercised littermates and lean WT mice. Exe, exercise; OD, optical density. Values are means ± SE (n = 6 in all groups). *P < 0.05 (1-way ANOVA).

 

Figure 2
View larger version (124K):
[in this window]
[in a new window]

  		Fig. 2. Intracardiac localization of Mn SOD by immunofluorescence. Formalin-fixed heart sections were analyzed by double immunostaining for von Willebrand factor (red, vWF) to label endothelial cells and Mn SOD (green, SOD2). A–C: lean WT control hearts. D–F: exercised WT hearts. G–I: db/db hearts. J–L: exercised db/db hearts. A, D, G, and J represent sections of hearts and coronary arteries stained for vWF (white arrow in A). B, E, H, and K represent sections stained with Mn SOD (white arrows). Mn SOD staining was increased in myocardium and endothelial cells (block arrows in K and L). C, F, I, and L represent composite images counterstained with 4',6-diamidino-2-phenylindole (blue), representing the nucleus. Magnification x630.

 
Exercise and coronary arteriolar tone. Pressure-constriction curves (10–120 mmHg transmural pressure) were not statistically different in sedentary and exercised db/db and WT mice (Fig. 3, Table 3). Bosentan did not have a significant effect on myogenic tone in coronary arteries of sedentary and exercised WT or db/db mice (Fig. 3, C–F). We found no significant difference in arterial distensibility or passive diameter at 80 mmHg between db/db and WT mice (Fig. 3B, Table 3). Agonist-induced constriction by U-46619 (10–6 M) was also the same in WT and db/db coronary arteries, and exercise did not cause a significant change in this response (Table 3).


Figure 3
View larger version (17K):
[in this window]
[in a new window]

  		Fig. 3. Myogenic tone and passive distensibility in coronary septal arteries. A: myogenic tone was not significantly different in coronary arteries of db/db and WT mice. B: passive distensibility of coronary arteries was not statistically different in sedentary and exercised db/db and WT mice. C and E: myogenic tone with or without bosentan in coronary arteries of sedentary and exercised WT mice. D and F: myogenic tone with or without bosentan in coronary arteries of sedentary and exercised db/db mice. Incubation with bosentan indicated that endogenous endothelin-1 does not have a significant effect on vascular myogenic tone. Values are means ± SE (n = 8–10 in each group).

 

View this table:
[in this window]
[in a new window]

  		Table 3. Vasomotor responses of isolated coronary arteries

 
Exercise and endothelium-dependent arteriolar relaxation. Endothelium-dependent coronary vasodilation induced by cumulative concentrations of ACh was significantly attenuated in coronary arteries of db/db compared with WT mice (Figs. 4 and 5). EC50 values for the ACh response were similar in coronary arteries of db/db and WT mice in sedentary (–log EC50 = 7.12 ± 0.08 and 7.26 ± 0.08, respectively) and exercised (–log EC50 = 7.18 ± 0.11 and 7.28 ± 0.09, respectively) groups. The maximal relaxation in response to ACh (Emax) was significantly lower in db/db than in lean WT mice (51.3 ± 1.7 vs. 91.3 ± 2.7%). Exercise significantly improved Emax of the ACh response in db/db mice (85.3 ± 3.5%; Figs. 4 and 5). The endothelium-independent coronary vasodilatory response to an exogenous NO donor (SNP) was not different in WT and db/db mice (Figs. 4 and 5). There were no statistical differences in Emax and EC50 of the responses to SNP within the sedentary (Emax = 86.9 ± 3.4 and 82.7 ± 4.9% for WT and db/db, respectively; –log EC50 = 7.2 ± 0.1 and 7.0 ± 0.2 for WT and db/db, respectively) and exercised (Emax = 85.8 ± 2.9 and 85.1 ± 3.6% for WT and db/db, respectively; –log EC50 = 7.0 ± 0.1 and 6.9 ± 0.1 for WT and db/db, respectively) groups.


Figure 4
View larger version (18K):
[in this window]
[in a new window]

  		Fig. 4. Endothelium-dependent responses in coronary septal arteries. Traces illustrate diameter of septal coronary arteries from WT (A), db/db (B), and exercised db/db (C) mice that were preconstricted with U-46619 (10–7 M) and challenged with cumulative concentrations of ACh (an endothelium-dependent vasodilator) and sodium nitroprusside (SNP, an endothelium-independent vasodilator). In WT mice (A), ACh and SNP caused ~80–90% relaxation (increase in diameter) of coronary arteries. ACh-induced relaxation was markedly attenuated (~50% relaxation) in db/db mice (B), while SNP-mediated relaxation was unchanged. Exercise improved ACh-induced aortic relaxation to 80% in db/db mice (C).

 

Figure 5
View larger version (26K):
[in this window]
[in a new window]

  		Fig. 5. Concentration-response curves for endothelium-dependent (ACh-mediated, A) and endothelium-independent (SNP-mediated, B) vasorelaxation in coronary arteries. ACh-induced vasodilation declined markedly in db/db mice compared with WT mice. Values are means ± SE (n = 8–10 in each group). *P < 0.05 (repeated-measures ANOVA). Exercise preserved endothelium-dependent ACh-mediated vasodilation in db/db mice. C and D: EC50 and Emax of ACh and SNP response in coronary arteries. EC50 was not statistically different among groups for ACh and SNP response. Emax was significantly decreased in db/db compared with WT mice. Values are means ± SE (n = 8–10 in each group). *P < 0.05 (repeated-measures ANOVA). Exercise significantly increased Emax in db/db mice. For SNP response there was no significant difference in Emax among groups.

 
Exercise and endothelial NO bioavailability. We repeated ACh concentration-response curves in the presence of L-Arg (an eNOS substrate, 10–3 M) + BH4 (an eNOS cofactor, 10 µM) and Cu,Zn SOD (120 U/ml). Incubation of db/db coronary septal arteries with L-Arg + BH4 or SOD significantly improved endothelium-dependent relaxation (Fig. 6A) without affecting ACh-induced vasodilation in arteries from exercised db/db mice (Fig. 6B) or sedentary and exercised WT mice (data not shown). Incubation with L-Arg + BH4 or SOD did not change EC50 of ACh in db/db arteries (–log EC50 = 7.12 ± 0.08, 6.93 ± 0.08, and 7.09 ± 0.11 for untreated db/db arteries, db/db arteries treated with L-Arg + BH4, and SOD-treated db/db arteries, respectively; Fig. 6C) but significantly improved Emax of the ACh response (51.3 ± 1.7, 96.1 ± 3.2, and 91.3 ± 3.9% for untreated db/db arteries, db/db arteries treated with L-Arg + BH4, and SOD-treated db/db arteries, respectively; Fig. 6D).


Figure 6
View larger version (30K):
[in this window]
[in a new window]

  		Fig. 6. Effect of L-Arg + tetrahydrobiopterin (BH4) and SOD incubation on ACh-mediated vasorelaxation in coronary septal arteries of sedentary and exercised db/db mice. Decreased ACh-induced vasodilation was significantly improved after incubation with L-Arg + BH4 or SOD in db/db (A and B), but not exercised db/db, mice. C and D: Emax and EC50 values for ACh concentration-response curves before and after L-Arg + BH4 and SOD incubation. Values are means ± SE (n = 8–10 in each group). *P < 0.01 (repeated-measures ANOVA).

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
Although the cardiac benefits of lifestyle improvements such as exercise are well known in the management of diabetes, the majority of studies focused on cardiac muscle alterations via improvements in metabolic and mitochondrial activity or upregulation of genes and proteins that lead to cardioprotection (2, 9, 24, 56). The role of improved coronary artery microcirculatory function in exercise-induced cardiac health benefits in mouse models of diabetes is relatively unexplored, largely because of the technical difficulties in studying the coronary resistance arteries from animals such as the db/db mice. Our results indicate a marked endothelial dysfunction in coronary septal arteries of db/db mice, a model of type 2 DM, that can be reversed by exercise. At the time of death (13 wk of age), plasma glucose and insulin were significantly higher in db/db than in WT mice, probably as a result of increased insulin resistance. Endothelial dysfunction is a hallmark of diabetes (10, 21, 46). Reductions in hyperglycemia and insulin resistance improve endothelial function and vasodilation (37). In our study, despite a significant decrease in body weight, 8 wk of chronic moderate-intensity exercise did not decrease plasma insulin or glucose levels in db/db mice, demonstrating that moderate levels of exercise did not change hyperglycemic status. We assessed the effect of exercise on blood sugar by two methods at two different time points, OGTT at 10 wk of age and glucose levels at the time of death; these methods showed that exercise did not have a significant effect on hyperglycemia in db/db mice. The lack of change in OGTT could be related to the exercise protocol, since repeated short periods of daily exercise are more effective in reducing OGTT than a longer period of exercise of the same duration everyday (15). Regarding other metabolic effects of exercise in the mice, we reported previously that the exercise intensity used in the present study lowers triglycerides and LDL cholesterol without changing HDL (34). This effect may be related to improved vascular endothelial function in exercised mice.

Hyperglycemia in diabetes results in increased production of reactive oxygen and nitrogen species in the cell, leading to oxidative stress (38, 41). Free radicals play a major role in endothelial dysfunction during hyperglycemia (10, 21, 47). Oxidative stress arises from an imbalance between the production of free radicals and their neutralization by endogenous antioxidants. Because our exercise regimen did not lead to a reduction in high plasma glucose levels in db/db mice, we reasoned that the stimulus for production of free oxygen radicals was not likely to have been diminished by exercise. Therefore, we anticipated an increase in antioxidant defenses with exercise. Free radicals such as superoxide quench NO and decrease the bioavailability of this endothelial vasodilator (28). Additionally, superoxides also lead to the formation of peroxynitrite, a potent inducer of irreversible oxidative damage (41). SODs are endogenous antioxidants: they compete with NO for reaction with superoxides and, thus, are able to neutralize them. Exercise decreases whole body oxidative stress, as indicated by lowered plasma 8-isoprostane levels in exercised db/db mice. Inasmuch as the total protein levels in coronary arteries were too low for direct immunoblotting experiments, we used whole hearts from db/db mice to demonstrate that exercise increased Mn SOD expression and decreased nitrotyrosine levels (used as a biomarker for increased peroxynitrite activity) in the heart (41). Using immunofluorescence techniques, we further confirmed our finding of increased Mn SOD in coronary arteries after exercise in WT and db/db hearts. Our finding of potentiation of Mn SOD expression by exercise in diabetes is important, since increased mitochondrial SOD eliminates oxygen free radicals generated by mitochondria, which is the primary source of these compounds in diabetes (5). This will reduce the extent of free radical-induced cellular damage by mitigating the four major sources of vascular/endothelial dysfunction in diabetes, including the polyol pathway, advanced glycation end products, protein kinase C, and activated hexosamine pathway (5). The mechanisms whereby exercise induces Mn SOD expression are unknown; however, there are some probable explanations. For example, bouts of exercise-induced oxidative stress increase Mn SOD levels (57). Mn SOD can also be induced by cytokines such as TNF{alpha} and IL-1β (57), which are increased secondary to elevation of NF-{kappa}B (54) in altered redox states (22), such as exercise. It appears that only moderate-intensity (and not low-intensity) exercise increases Mn SOD (34). This could be related to the higher oxidative stress threshold required for induction of Mn SOD (57). Other than the heart muscle, it is likely that oxidative stress in coronary arteries from db/db mice is also related to reduced SOD expression/activity, since addition of exogenous SOD completely restored ACh-induced vasodilation in arteries from sedentary db/db mice; this finding is consistent with previous reports of reversal of endothelial dysfunction in diabetic vessels by exogenous SOD (4, 43, 47). Exercise probably increases SOD expression/activity in diabetic coronary arterioles (49), which is evident from reduced effectiveness of exogenous SOD on endothelium-dependent vasodilation in coronary arteries from exercised db/db mice.

Although unlikely in the light of unchanged catalase levels, it is also possible that accumulation of H2O2, formed from the increased dismutation of superoxides by various SODs after exercise, may also be partly responsible for vasorelaxation in the study groups. H2O2, a product of O2– dismutation generated from uncoupled eNOS, plays an important role in endothelium-dependent relaxation under conditions of BH4 deficiency (11). Therefore, conversion of H2O2 to H2O and O2 by catalase significantly decreases endothelium-dependent relaxation in BH4-deficient states (11). Under such conditions, SOD can improve endothelium-dependent relaxation by converting eNOS-generated O2– to H2O2. Because db/db mice are BH4 deficient, it is likely that catalase levels would decrease and addition of SOD would increase endothelium-dependent relaxation in response to ACh. However, it has been reported that catalase and SOD failed to improve ACh-induced vasodilation in mesenteric arteries from db/db mice (43), whereas findings in coronary arteries and aorta (4, 34) suggest regional variations.

Exaggerated coronary myogenic tone or increased arterial stiffness in coronary arteries from diabetic hearts may lead to increased cardiac ischemia. (50). Lagaud et al. (30) and Frisbee et al. (17), in separate studies on db/db mouse and Zucker rat models of type 2 DM, reported that myogenic tone is increased in mesenteric and skeletal muscle arterioles, respectively. Crijns et al. (13) demonstrated increased arterial stiffness in streptozocin-induced type 1 diabetic rats. Our results suggest that, in the coronary vascular bed, the myogenic response and passive distensibility are the same in db/db and WT mice. Exercise did not have a significant effect on myogenic tone or arterial passive distensibility in WT or db/db mice. Moreover, our study shows that the constrictor responses of smooth muscle cells to pressure and a thromboxane agonist were similar in diabetic and WT mice. Therefore, an increased myogenic response or decreased vascular compliance cannot completely account for reduced cardiac function in db/db mice (23).

We observed a marked reduction in ACh-induced, endothelium-dependent NO-mediated vasodilation in coronary septal arteries isolated from db/db mice. It is possible that since the arterioles were preconstricted with U-46619, the lower dilator response to ACh was related to a greater preconstriction by U-46619, as reported in some arteries from db/db mice (27, 55). However, the concentration-response curves to U-46619 were similar in sedentary and exercised db/db and WT mice in our study. Alterations in ACh receptor activity in DM may also lead to decreases in ACh-mediated relaxation in db/db mice (7, 8). However, our finding of a decline in ACh Emax in the absence of a change in EC50 indicates that ACh receptor function remained relatively unaltered in diabetic arteries.

The reduced NO-mediated relaxation in arteries of db/db mice was not due to decreased expression of NO-generating enzyme protein (eNOS), in agreement with other studies showing an unaltered or even upregulated eNOS protein expression in DM (12, 40). Although eNOS is present, it is possible that the activity and/or regulation of this enzyme may be negatively altered in DM (16). Moreover, it is unlikely that smooth muscle cell sensitivity to NO or activation of vascular smooth muscle cell guanylate cyclase is altered in diabetic mice, since the SNP-mediated vasodilation was unaltered by exercise.

Alterations in the cofactor and substrate regulation in eNOS activity have been reported in diabetes (6, 20). Moderate levels of exercise in db/db mice corrected the relative deficiency of L-Arg and BH4 in db/db coronary arteries. In sedentary db/db mice, incubation of coronary arteries with L-Arg + BH4 reversed the impaired ACh response. Such a deficiency of cofactors (6, 42, 43) and substrates (44, 45) of NOS was reported previously and considered to be due to enhanced consumption of the substrate (20) or direct degradation of BH4 by excessive free radicals such as peroxynitrite (33), a common feature of DM (41). It is likely that exercise ameliorates oxidative stress in the whole body and the heart (e.g., reduction in nitrotyrosine, a biomarker for peroxynitrite activity) and coronary arteries (e.g., endothelium-dependent relaxation was not further improved by incubation with L-Arg + BH4 or SOD) in exercised db/db mice.

The incidence of ischemic heart disease is greater in diabetic patients (50, 52). Alterations in myogenic regulation of arteriolar diameter are likely to detrimentally affect regional myocardial blood flow. Since the pressure-constriction curves were similar in coronary arteries from control and diabetic mice, we speculate that a greater myogenic tone in coronary arteries of diabetic mice is unlikely to be the primary cause of cardiac ischemia in this model of type 2 DM (1). The markedly reduced ACh-induced, NO-mediated coronary vasodilation in db/db mice was related to a greater oxidative stress and reduced NO bioavailability in diabetes, likely leading to an imbalance between cardiac oxygen supply and demand during activity. Moreover, during ischemia-reperfusion during myocardial infarction in diabetes, poorer outcome is often predicted because of more extensive myocardial damage as a consequence of low antioxidant levels (19, 51). According to our study, a moderate level of exercise not only increases myocardial antioxidant levels but also increases NO bioavailability, thus leading to improved endothelium-dependent vasodilation and better perfusion of the diabetic heart.


   GRANTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This work was supported by grants from the Canadian Heart and Stroke Foundation of British Columbia and Yukon (I. Laher), the Li Tze Fong Memorial Fellowship (F. Moien-Afshari), the Michael Smith Foundation for Health Research (S. Ghosh), and the Canadian Diabetes Association (S. Ghosh).


   FOOTNOTES
 

Address for reprint requests and other correspondence: I. Laher, Dept. of Pharmacology and Therapeutics, Faculty of Medicine, Univ. of British Columbia, 2176 Health Sciences Mall, Vancouver, BC, Canada V6T 1Z3 (e-mail: ilaher{at}interchange.ubc.ca)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. Anzawa R, Bernard M, Tamareille S, Baetz D, Confort-Gouny S, Gascard JP, Cozzone P, Feuvray D. Intracellular sodium increase and susceptibility to ischaemia in hearts from type 2 diabetic db/db mice. Diabetologia 49: 598–606, 2006.[CrossRef][Web of Science][Medline]
  2. Ascensao A, Ferreira R, Magalhaes J. Exercise-induced cardioprotection—biochemical, morphological and functional evidence in whole tissue and isolated mitochondria. Int J Cardiol 117: 16–30, 2007.[CrossRef][Web of Science][Medline]
  3. Bagi Z, Erdei N, Toth A, Li W, Hintze TH, Koller A, Kaley G. Type 2 diabetic mice have increased arteriolar tone and blood pressure: enhanced release of COX-2-derived constrictor prostaglandins. Arterioscler Thromb Vasc Biol 25: 1610–1616, 2005.[Abstract/Free Full Text]
  4. Bagi Z, Koller A, Kaley G. Superoxide-NO interaction decreases flow- and agonist-induced dilations of coronary arterioles in type 2 diabetes mellitus. Am J Physiol Heart Circ Physiol 285: H1404–H1410, 2003.[Abstract/Free Full Text]
  5. Brownlee M. Biochemistry and molecular cell biology of diabetic complications. Nature 414: 813–820, 2001.[CrossRef][Web of Science][Medline]
  6. Cai S, Khoo J, Mussa S, Alp NJ, Channon KM. Endothelial nitric oxide synthase dysfunction in diabetic mice: importance of tetrahydrobiopterin in eNOS dimerisation. Diabetologia 48: 1933–1940, 2005.[CrossRef][Web of Science][Medline]
  7. Carrier GO, Aronstam RS. Altered muscarinic receptor properties and function in the heart in diabetes. J Pharmacol Exp Ther 242: 531–535, 1987.[Abstract/Free Full Text]
  8. Carrier GO, Aronstam RS. Increased muscarinic responsiveness and decreased muscarinic receptor content in ileal smooth muscle in diabetes. J Pharmacol Exp Ther 254: 445–449, 1990.[Abstract/Free Full Text]
  9. Church TS, Cheng YJ, Earnest CP, Barlow CE, Gibbons LW, Priest EL, Blair SN. Exercise capacity and body composition as predictors of mortality among men with diabetes. Diabetes Care 27: 83–88, 2004.[Abstract/Free Full Text]
  10. Cohen G, Riahi Y, Alpert E, Gruzman A, Sasson S. The roles of hyperglycaemia and oxidative stress in the rise and collapse of the natural protective mechanism against vascular endothelial cell dysfunction in diabetes. Arch Physiol Biochem 113: 259–267, 2007.[CrossRef][Medline]
  11. Cosentino F, Barker JE, Brand MP, Heales SJ, Werner ER, Tippins JR, West N, Channon KM, Volpe M, Luscher TF. Reactive oxygen species mediate endothelium-dependent relaxations in tetrahydrobiopterin- deficient mice. Arterioscler Thromb Vasc Biol 21: 496–502, 2001.[Abstract/Free Full Text]
  12. Cosentino F, Hishikawa K, Katusic ZS, Luscher TF. High glucose increases nitric oxide synthase expression and superoxide anion generation in human aortic endothelial cells. Circulation 96: 25–28, 1997.[Abstract/Free Full Text]
  13. Crijns FR, Wolffenbuttel BH, De Mey JG, Struijker Boudier HA. Mechanical properties of mesenteric arteries in diabetic rats: consequences of outward remodeling. Am J Physiol Heart Circ Physiol 276: H1672–H1677, 1999.[Abstract/Free Full Text]
  14. Da Silva PA, Lambertucci RH, Gorjao R, Dos Reis SL, Curi R. Effect of a single session of electrical stimulation on activity and expression of citrate synthase and antioxidant enzymes in rat soleus muscle. Eur J Appl Physiol 102: 119–126, 2007.[CrossRef][Web of Science][Medline]
  15. Eriksen L, Dahl-Petersen I, Haugaard SB, Dela F. Comparison of the effect of multiple short-duration with single long-duration exercise sessions on glucose homeostasis in type 2 diabetes mellitus. Diabetologia 50: 2245–2253, 2007.[CrossRef][Web of Science][Medline]
  16. Forstermann U, Munzel T. Endothelial nitric oxide synthase in vascular disease: from marvel to menace. Circulation 113: 1708–1714, 2006.[Abstract/Free Full Text]
  17. Frisbee JC, Maier KG, Stepp DW. Oxidant stress-induced increase in myogenic activation of skeletal muscle resistance arteries in obese Zucker rats. Am J Physiol Heart Circ Physiol 283: H2160–H2168, 2002.[Abstract/Free Full Text]
  18. Ghosh S, Novak EM, Innis SM. Cardiac proinflammatory pathways are altered with different dietary n-6 linoleic to n-3 {alpha}-linolenic acid ratios in normal, fat-fed pigs. Am J Physiol Heart Circ Physiol 293: H2919–H2927, 2007.[Abstract/Free Full Text]
  19. Ghosh S, Pulinilkunnil T, Yuen G, Kewalramani G, An D, Qi D, Abrahani A, Rodrigues B. Cardiomyocyte apoptosis induced by short-term diabetes requires mitochondrial GSH depletion. Am J Physiol Heart Circ Physiol 289: H768–H776, 2005.[Abstract/Free Full Text]
  20. Giugliano D, Ceriello A, Paolisso G. Oxidative stress and diabetic vascular complications. Diabetes Care 19: 257–267, 1996.[Abstract]
  21. Graier WF, Posch K, Fleischhacker E, Wascher TC, Kostner GM. Increased superoxide anion formation in endothelial cells during hyperglycemia: an adaptive response or initial step of vascular dysfunction? Diabetes Res Clin Pract 45: 153–160, 1999.[CrossRef][Web of Science][Medline]
  22. Hayashi T, Ueno Y, Okamoto T. Oxidoreductive regulation of nuclear factor-{kappa}B. Involvement of a cellular reducing catalyst thioredoxin. J Biol Chem 268: 11380–11388, 1993.[Abstract/Free Full Text]
  23. How OJ, Aasum E, Severson DL, Chan WY, Essop MF, Larsen TS. Increased myocardial oxygen consumption reduces cardiac efficiency in diabetic mice. Diabetes 55: 466–473, 2006.[Abstract/Free Full Text]
  24. Hu FB, Stampfer MJ, Solomon C, Liu S, Colditz GA, Speizer FE, Willett WC, Manson JE. Physical activity and risk for cardiovascular events in diabetic women. Ann Intern Med 134: 96–105, 2001.[Abstract/Free Full Text]
  25. Ito I, Jarajapu YP, Guberski DL, Grant MB, Knot HJ. Myogenic tone and reactivity of rat ophthalmic artery in acute exposure to high glucose and in a type II diabetic model. Invest Ophthalmol Vis Sci 47: 683–692, 2006.[Abstract/Free Full Text]
  26. Kemi OJ, Ellingsen O, Smith GL, Wisloff U. Exercise-induced changes in calcium handling in left ventricular cardiomyocytes. Front Biosci 13: 356–368, 2008.[CrossRef][Web of Science][Medline]
  27. Khazaei M, Moien-Afshari F, Kieffer TJ, Laher I. Effect of exercise on augmented aortic vasoconstriction in the db/db mouse model of type-II diabetes. Physiol Res. In press.
  28. Kojda G, Hambrecht R. Molecular mechanisms of vascular adaptations to exercise. Physical activity as an effective antioxidant therapy? Cardiovasc Res 67: 187–197, 2005.[Abstract/Free Full Text]
  29. Laakso M. Hyperglycemia and cardiovascular disease in type 2 diabetes. Diabetes 48: 937–942, 1999.[Abstract]
  30. Lagaud GJ, Masih-Khan E, Kai S, van Breemen C, Dube GP. Influence of type II diabetes on arterial tone and endothelial function in murine mesenteric resistance arteries. J Vasc Res 38: 578–589, 2001.[CrossRef][Web of Science][Medline]
  31. Leung FP, Yung LM, Leung HS, Au CL, Yao X, Vanhoutte PM, Laher I, Huang Y. Therapeutic concentrations of raloxifene augment nitric oxide-dependent coronary artery dilatation in vitro. Br J Pharmacol 152: 223–229, 2007.[CrossRef][Web of Science][Medline]
  32. Mahgoub MA, Abd-Elfattah AS. Diabetes mellitus and cardiac function. Mol Cell Biochem 180: 59–64, 1998.[CrossRef][Web of Science][Medline]
  33. Milstien S, Katusic Z. Oxidation of tetrahydrobiopterin by peroxynitrite: implications for vascular endothelial function. Biochem Biophys Res Commun 263: 681–684, 1999.[CrossRef][Web of Science][Medline]
  34. Moien-Afshari F, Ghosh S, Khazaei M, Kieffer TJ, Brownsey RW, Laher I. Exercise restores endothelial function independently of weight loss or hyperglycaemic status in db/db mice. Diabetologia 51: 1327–1337, 2008.[CrossRef][Web of Science][Medline]
  35. Moien-Afshari F, Skarsgard PL, McManus BM, Laher I. Cardiac transplantation and resistance artery myogenic tone. Can J Physiol Pharmacol 82: 840–848, 2004.[CrossRef][Web of Science][Medline]
  36. Montuschi P, Barnes P, Roberts LJ. Insights into oxidative stress: the isoprostanes. Curr Med Chem 14: 703–717, 2007.[CrossRef][Web of Science][Medline]
  37. Nassis GP, Papantakou K, Skenderi K, Triandafillopoulou M, Kavouras SA, Yannakoulia M, Chrousos GP, Sidossis LS. Aerobic exercise training improves insulin sensitivity without changes in body weight, body fat, adiponectin, and inflammatory markers in overweight and obese girls. Metabolism 54: 1472–1479, 2005.[CrossRef][Web of Science][Medline]
  38. Nishikawa T, Edelstein D, Du XL, Yamagishi S, Matsumura T, Kaneda Y, Yorek MA, Beebe D, Oates PJ, Hammes HP, Giardino I, Brownlee M. Normalizing mitochondrial superoxide production blocks three pathways of hyperglycaemic damage. Nature 404: 787–790, 2000.[CrossRef][Web of Science][Medline]
  39. Nitenberg A, Paycha F, Ledoux S, Sachs R, Attali JR, Valensi P. Coronary artery responses to physiological stimuli are improved by deferoxamine but not by L-arginine in non-insulin-dependent diabetic patients with angiographically normal coronary arteries and no other risk factors. Circulation 97: 736–743, 1998.[Abstract/Free Full Text]
  40. Okon EB, Szado T, Laher I, McManus B, van Breemen C. Augmented contractile response of vascular smooth muscle in a diabetic mouse model. J Vasc Res 40: 520–530, 2003.[CrossRef][Web of Science][Medline]
  41. Pacher P, Szabo C. Role of peroxynitrite in the pathogenesis of cardiovascular complications of diabetes. Curr Opin Pharmacol 6: 136–141, 2006.[CrossRef][Web of Science][Medline]
  42. Pannirselvam M, Simon V, Verma S, Anderson T, Triggle CR. Chronic oral supplementation with sepiapterin prevents endothelial dysfunction and oxidative stress in small mesenteric arteries from diabetic (db/db) mice. Br J Pharmacol 140: 701–706, 2003.[CrossRef][Web of Science][Medline]
  43. Pannirselvam M, Verma S, Anderson TJ, Triggle CR. Cellular basis of endothelial dysfunction in small mesenteric arteries from spontaneously diabetic (db/db–/–) mice: role of decreased tetrahydrobiopterin bioavailability. Br J Pharmacol 136: 255–263, 2002.[CrossRef][Web of Science][Medline]
  44. Pieper GM, Dondlinger LA. Plasma and vascular tissue arginine are decreased in diabetes: acute arginine supplementation restores endothelium- dependent relaxation by augmenting cGMP production. J Pharmacol Exp Ther 283: 684–691, 1997.[Abstract/Free Full Text]
  45. Pieper GM, Jordan M, Adams MB, Roza AM. Restoration of vascular endothelial function in diabetes. Diabetes Res Clin Pract 31 Suppl: S157–S162, 1996.[CrossRef][Medline]
  46. Pieper GM, Meier DA, Hager SR. Endothelial dysfunction in a model of hyperglycemia and hyperinsulinemia. Am J Physiol Heart Circ Physiol 269: H845–H850, 1995.[Abstract/Free Full Text]
  47. Pieper GM, Siebeneich W. Oral administration of the antioxidant, N-acetylcysteine, abrogates diabetes-induced endothelial dysfunction. J Cardiovasc Pharmacol 32: 101–105, 1998.[CrossRef][Web of Science][Medline]
  48. Rahman MM, Elmi S, Chang TK, Bai N, Sallam NA, Lemos VS, Moien-Afshari F, Laher I. Increased vascular contractility in isolated vessels from cigarette smoking rats is mediated by basal endothelin release. Vasc Pharmacol 46: 35–42, 2007.[CrossRef]
  49. Rush JW, Laughlin MH, Woodman CR, Price EM. SOD-1 expression in pig coronary arterioles is increased by exercise training. Am J Physiol Heart Circ Physiol 279: H2068–H2076, 2000.[Abstract/Free Full Text]
  50. Shehadeh A, Regan TJ. Cardiac consequences of diabetes mellitus. Clin Cardiol 18: 301–305, 1995.[Web of Science][Medline]
  51. Tao L, Gao E, Jiao X, Yuan Y, Li S, Christopher TA, Lopez BL, Koch W, Chan L, Goldstein BJ, Ma XL. Adiponectin cardioprotection after myocardial ischemia/reperfusion involves the reduction of oxidative/nitrative stress. Circulation 115: 1408–1416, 2007.[Abstract/Free Full Text]
  52. Turner RC, Millns H, Neil HA, Stratton IM, Manley SE, Matthews DR, Holman RR. Risk factors for coronary artery disease in non-insulin-dependent diabetes mellitus: United Kingdom Prospective Diabetes Study (UKPDS: 23). Br Med J 316: 823–828, 1998.[Abstract/Free Full Text]
  53. Ungvari Z, Pacher P, Kecskemeti V, Papp G, Szollar L, Koller A. Increased myogenic tone in skeletal muscle arterioles of diabetic rats. Possible role of increased activity of smooth muscle Ca2+ channels and protein kinase C. Cardiovasc Res 43: 1018–1028, 1999.[Abstract/Free Full Text]
  54. Verma IM, Stevenson JK, Schwarz EM, Van Antwerp D, Miyamoto S. Rel/NF-{kappa}B/I{kappa}B family: intimate tales of association and dissociation. Genes Dev 9: 2723–2735, 1995.[Free Full Text]
  55. Verma S, Arikawa E, Lee S, Dumont AS, Yao L, McNeill JH. Exaggerated coronary reactivity to endothelin-1 in diabetes: reversal with bosentan. Can J Physiol Pharmacol 80: 980–986, 2002.[CrossRef][Web of Science][Medline]
  56. Wing RR, Goldstein MG, Acton KJ, Birch LL, Jakicic JM, Sallis JF Jr, Smith-West D, Jeffery RW, Surwit RS. Behavioral science research in diabetes: lifestyle changes related to obesity, eating behavior, and physical activity. Diabetes Care 24: 117–123, 2001.[Abstract/Free Full Text]
  57. Yamashita N, Hoshida S, Otsu K, Asahi M, Kuzuya T, Hori M. Exercise provides direct biphasic cardioprotection via manganese superoxide dismutase activation. J Exp Med 189: 1699–1706, 1999.[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 Am. J. Physiol. Heart Circ. Physiol.Home page
N. Villalba, P. Martinez, A. M. Briones, A. Sanchez, M. Salaices, A. Garcia-Sacristan, M. Hernandez, S. Benedito, and D. Prieto
Differential structural and functional changes in penile and coronary arteries from obese Zucker rats
Am J Physiol Heart Circ Physiol, August 1, 2009; 297(2): H696 - H707.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Renal Physiol.Home page
S. Ghosh, M. Khazaei, F. Moien-Afshari, L. S. Ang, D. J. Granville, C. B. Verchere, S. R. Dunn, P. McCue, A. Mizisin, K. Sharma, et al.
Moderate exercise attenuates caspase-3 activity, oxidative stress, and inhibits progression of diabetic renal disease in db/db mice
Am J Physiol Renal Physiol, April 1, 2009; 296(4): F700 - F708.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
295/4/H1470    most recent
00016.2008v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Moien-Afshari, F.
Right arrow Articles by Laher, I.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Moien-Afshari, F.
Right arrow Articles by Laher, I.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online
Copyright © 2008 by the American Physiological Society.