Relative Contribution Of Nitric Oxide Research Articles

Cutaneous Microvascular Responses to Local Heating on Ventral and Dorsal Aspects of the Forearm

The cutaneous microvasculature is considered a representative vascular bed and is regularly used to interrogate the mechanisms of microvascular function in healthy and diseased humans. For instance, cutaneous dilation in response to local heating can provide an index of nitric oxide (NO) bioavailability. While the skin of the forearm is typically used for local heating studies, some studies have used the ventral forearm while others have used the dorsal forearm skin for this assessment. Since the dorsal aspect of the forearm typically has more hair and receives greater sun exposure than the ventral side, there is speculation that cutaneous dilation may differ from one side of the forearm to the other, in magnitude and/or mechanism. As such, studies utilizing different sides of the forearm may not be comparable. Therefore, we aimed to test the hypothesis that cutaneous local heating responses differ between the ventral and dorsal aspects of the forearm in response to the two most common temperature stimuli, 39°C and 42°C.MethodsTen young, normotensive individuals (6 men/4 women, age: 26 ± 2 years) were studied on two separate occasions separated by 2‐7 days. At each visit, 4 intradermal microdialysis fibers were placed in either the ventral or dorsal forearm, in a random order. Two fibers were perfused with Ringer’s solution to serve as control sites and the other 2 fibers were perfused with 10 mM N(G)‐Nitro‐L‐arginine methyl ester (L‐NAME) to inhibit NO synthase. Red blood cell flux (RBCF) was assessed at all sites via laser Doppler flowmetry. Each pair of sites (control and L‐NAME) was heated to either 39°C or 42°C for ~40‐45 min until RBCF plateaued. All sites were then infused with 28 mM sodium nitroprusside and heated to 43°C to establish maximal RBCF. Cutaneous vascular conductance (CVC) was calculated as RBCF / mean arterial pressure measured during the plateau and maximal phases. Plateau results are reported as a percentage of maximal CVC at each respective site. The relative NO contribution is reported as: [(control plateau – L‐NAME plateau)/control plateau] x 100.ResultsNo differences were observed at the control site between ventral and dorsal aspects of the forearm when heated to 39°C (62 ± 13 vs. 62 ± 16 % CVCmax, P=0.99). Likewise, the heating response to 42°C was similar across the forearm (ventral: 90 ± 9 vs. dorsal: 86 ± 12% CVCmax, P=0.21). The relative contribution of NO to the plateau was comparable across the forearm at 39°C (ventral: 70 ± 20 vs. dorsal: 66 ± 21%, P=0.71) and 42°C (ventral: 63 ± 16 vs. dorsal: 69 ± 11%, P=0.11).DiscussionThese preliminary findings suggest that cutaneous vasodilation elicited by local heating is similar on both sides of the forearm at both 39°C and 42 °C. Additionally, it appears that the relative contribution of NO to local heating‐induced microvascular vasodilation is not different across the forearm.

Aortic Relaxation in Castrated Male Rats and Responses to Estrogen Treatment

Previous studies suggest that risk factors for cardiovascular diseases (CVD) have increased in the transgender population after they undergo cross‐sex hormone therapy (CSHT). Several studies, including ours in animal models as well as in humans, have shown that estrogen exerts direct beneficial effects on the vessel wall in healthy females. A growing body of evidence also suggests that androgen exhibits protective actions on the cardiovascular system. However, the effects of CSHT in cardiovascular physiology in males or females are less understood.The current study was, therefore, undertaken to evaluate the effects of estrogen treatment on aortic reactivity in castrated (CAS) male rats. Specifically, we investigated the effects of in vivo treatment with 17β‐estradiol (E2) on the aortic responses of CAS male as well as ovariectomized (OVX) female rats.Age‐matched CAS male and OVX female rats were implanted subcutaneously with either 17β‐estradiol (E2,1.5 mg) or a placebo‐containing pellet for 30 days. Endothelium‐dependent vasorelaxation (EDV) in response to acetylcholine (ACh, 10‐8 to 10‐5 M) in aorta precontracted with phenylephrine (PE, 2 µM) was measured before and after pretreatment with indomethacin (10 µM, cyclooxygenase inhibitor), followed by N‐nitro‐ L‐arginine methyl ester [L‐NAME, 200 µM, a nonselective nitric oxide synthase (NOS) inhibitor]. Endothelium‐independent vasorelaxation was assessed by measuring sodium nitroprusside (SNP)‐induced relaxation response in endothelium‐denuded rings in addition to the contractile response curves to PE before and after pretreatment with L‐NAME in aortic rings.EDV to ACh was significantly impaired in aortic rings from E2‐treated CAS rats compared to their placebo‐treated counterparts and E2‐treated OVX rats. The impairment of EDV to ACh in E2‐treated CAS rats was accompanied by a significant decrease in nitric oxide (NO) contribution to ACh‐induced relaxation in this group. The smooth muscle sensitivity to NO as measured by SNP relaxation response curve was not altered, whereas the responsiveness to PE was slightly enhanced in the aortas of E2‐treated CAS group compared to those in other experimental groups. Endothelium‐derived NO release during smooth muscle contraction, as assessed by the potentiation of the response to PE after NOS inhibition, was not different in the aortas of experimental groups.Overall, our data demonstrate that aortic function was altered in E2‐treated CAS male rats. Here, we provide the first evidence of impairment in aortic relaxation in E2‐treated CAS male rats, possibly via a significant decrease in the relative contribution of NO to the regulation of vascular relaxation response. Furthermore, the comparison of current data in the CAS male rats with our recently published data on the aortic reactivity in the intact males appears to rule out any effect of testosterone deprivation on the stimulated release of NO in male rat aortas. Additional studies will be needed to document the direction and magnitude of CSHT interaction with vasculatures.

AT1 Receptor Antagonism Improves Structural, Functional, and Biomechanical Properties in Resistance Arteries in a Rodent Chronic Kidney Disease Model.

The renin-angiotensin system, in particular Angiotensin II (AngII), plays a significant role in the pathogenesis of hypertension in chronic kidney disease (CKD). Effects of chronic AT1 receptor antagonism were investigated in a genetic hypertensive rat model of CKD, the Lewis polycystic kidney (LPK) rat. Mixed-sex LPK and Lewis control rats (total n = 31) were split between treated (valsartan 60 mg/kg/day p.o. from 4 to 18 weeks) and vehicle groups. Animals were assessed for systolic blood pressure and urine biochemistry, and after euthanasia, blood collected for urea and creatinine analysis, confirming the hypertensive and renal phenotype. Mesenteric resistance vasculature was assessed using pressure myography and histology. Valsartan treatment improved vascular structure in LPK rats, increasing internal and external diameter values and reducing wall thickness (untreated vs. treated LPK: 53.19 ± 3.29 vs. 33.93 ± 2.17 μm) and wall-lumen ratios (untreated vs. treated LPK: 0.52 ± 0.09 vs. 0.16 ± 0.01, all P < 0.0001). Endothelium dysfunction, as measured by maximal response to acetylcholine (Rmax), was normalized with treatment (untreated vs. treated LPK: 69.56 ± 4.34 vs. 103.05 ± 4.13, P < 0.05), increasing the relative contributions of nitric oxide and endothelium-derived hyperpolarization to vasorelaxation while downregulating the prostanoid contribution. Biomechanical properties also improved with treatment, as indicated by an increase in compliance, decrease in intrinsic stiffness and alterations in the artery wall composition, which included decreases in collagen density and collagen/elastin ratio. Our results highlight the importance of AngII as a driver of resistance vessel structural, functional, and biomechanical dysfunction and provide insight as to how AT1 receptor blockade exerts therapeutic efficacy in CKD.

Endothelial dysfunction in renal arcuate arteries of obese Zucker rats: The roles of nitric oxide, endothelium-derived hyperpolarizing factors, and calcium-activated K+ channels.

The roles of nitric oxide (NO), endothelium-derived hyperpolarizing factors (EDHF), and calcium-activated K+ (KCa) channels in diabetes-associated endothelial dysfunction of small renal arteries are not clear. The present study investigated acetylcholine (ACh)-induced vasorelaxation of renal arcuate arteries from obese Zucker (OZ) rats at different diabetes durations, and the relative contribution of NO, EDHF, and KCa channels to the endothelial dysfunction. OZ rats of 7 weeks (prediabetic stage), 12 weeks (early diabetic stage), and 20 weeks (late diabetic stage), and time-matched lean control rats, were studied. Segments of arcuate arteries (130 to 180 μm) were isolated, cannulated and pressurized. Vascular endothelial functions were tested using ACh-induced vasodilation. Our experiments demonstrated: (1) ACh-elicited vasodilation was impaired in OZ rats of 20 weeks, but not in rats of 7 and 12 weeks; (2) inhibition of NO or EDHF (contributed by epoxyeicosatrienoic acids [EETs]) production significantly decreased ACh-induced vasodilation in both lean and OZ rats of 20 weeks. The reduction of ACh-induced vasodilation by inhibition of NO or EDHF formation was less in OZ rats, as compared to lean rats; and (3) inhibition of KCa channels markedly reduced ACh-induced vasodilation in lean control rats, but not in OZ rats of 20 weeks. Our observations indicated that endothelium-dependent vasodilation in renal arcuate arteries is impaired in diabetes mellitus; NO and EDHF, mainly EETs, dominate the ACh-induced vasodilation in renal arcuate arteries; the contribution of NO and EETs is impaired in diabetic rats; KCa channels are involved in ACh-induced vasodilation; and the activity of KCa channels is downregulated in diabetes mellitus.

Coronary microvascular dysfunction after long-term diabetes and hypercholesterolemia.

Coronary microvascular dysfunction (CMD) has been proposed as an important component of diabetes mellitus (DM)- and hypercholesterolemia-associated coronary artery disease (CAD). Previously we observed that 2.5 mo of DM and high-fat diet (HFD) in swine blunted bradykinin (BK)-induced vasodilation and attenuated endothelin (ET)-1-mediated vasoconstriction. Here we studied the progression of CMD after 15 mo in the same animal model of CAD. Ten male swine were fed a HFD in the absence (HFD, n = 5) or presence of streptozotocin-induced DM (DM + HFD, n = 5). Responses of small (∼300-μm-diameter) coronary arteries to BK, ET-1, and the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine were examined in vitro and compared with those of healthy (Normal) swine (n = 12). Blood glucose was elevated in DM + HFD (17.6 ± 4.5 mmol/l) compared with HFD (5.1 ± 0.4 mmol/l) and Normal (5.8 ± 0.6 mmol/l) swine, while cholesterol was markedly elevated in DM + HFD (16.8 ± 1.7 mmol/l) and HFD (18.1 ± 2.6 mmol/l) compared with Normal (2.1 ± 0.2 mmol/l) swine (all P < 0.05). Small coronary arteries showed early atherosclerotic plaques in HFD and DM + HFD swine. Surprisingly, DM + HFD and HFD swine maintained BK responsiveness compared with Normal swine due to an increase in NO availability relative to endothelium-derived hyperpolarizing factors. However, ET-1 responsiveness was greater in HFD and DM + HFD than Normal swine (both P < 0.05), resulting mainly from ETB receptor-mediated vasoconstriction. Moreover, the calculated vascular stiffness coefficient was higher in DM + HFD and HFD than Normal swine (both P < 0.05). In conclusion, 15 mo of DM + HFD, as well as HFD alone, resulted in CMD. Although the overall vasodilation to BK was unperturbed, the relative contributions of NO and endothelium-derived hyperpolarizing factor pathways were altered. Moreover, the vasoconstrictor response to ET-1 was enhanced, involving the ETB receptors. In conjunction with our previous study, these findings highlight the time dependence of the phenotype of CMD.

Prenatal Testosterone Induces Sex-Specific Dysfunction in Endothelium-Dependent Relaxation Pathways in Adult Male and Female Rats1

Prenatal testosterone (T) exposure impacts postnatal cardiovascular function, leading to increases in blood pressure with associated decreased endothelium-dependent vascular relaxation in adult females. Endothelial function in males is not known. Furthermore, which of the endothelial pathways contributes to endothelial dysfunction and if there exists sex differences are not known. The objective of this study was to characterize the relative contribution of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) to the impaired endothelium-dependent vasodilation in prenatal T-exposed adult males and females. Offspring of pregnant rats treated with T propionate or its vehicle were examined. Telemetric blood pressure levels and endothelium-dependent vascular reactivity were assessed with wire myography. Levels of nitric oxide synthase (NOS3) and Kcnn3 and Kcnn4 channel expression were examined in mesenteric arteries. Mean arterial pressure was significantly higher in T males and females than in controls. Endothelium-dependent acetylcholine relaxation was significantly lower in both T males and females. EDHF-mediated relaxation was specifically blunted in T males (Emax = 48.64% ± 3.73%) compared to that in control males (Emax = 81.71% ± 3.18%); however, NO-mediated relaxation was specifically impaired in T females (Emax = 36.01% ± 4.29%) compared with that in control females (Emax = 54.56% ± 6.37%). Relaxation to sodium nitroprusside and levcromakalim were unaffected with T-treatment. NOS3 protein was decreased in T females but not in T males. Kcnn3 expression was decreased in both T males and females compared to controls. These findings suggest that prenatal T leads to an increase in blood pressure in the adult offspring, associated with blunting of endothelial cell-associated relaxation and that the effects are sex-specific: EDHF-related in males and NO-related in females.

L-NAME Iontophoresis

Decreased endothelial Nitric oxide (NO) bioavailability is one of the earliest events of endothelial dysfunction. Assessment of microvascular blood flow using a Laser Doppler Imager during local noninvasive administration of L-N-Arginine-Methyl-Ester (L-NAME) by skin iontophoresis may help discriminate the relative contributions of NO and non-NO pathways during a skin thermal hyperemic test. In healthy nonsmokers, the effects of thermal vasodilation and sodium nitroprusside-mediated vasodilation were tested on skin pretreated with 0.9% saline solution, 2% L-NAME iontophoresis (n = 12), or intradermal injection of 25 nmol L-NAME (n = 10). The effects of L-NAME iontophoresis were also measured in a group of smokers (n = 10). L-NAME iontophoresis and intradermal injection of L-NAME decreased the skin response to local heating to a similar degree (-41% ± 4% vs. -44% ± 6%). L-NAME iontophoresis site-to-site and day-to-day coefficients of correlation were 0.83 and 0.76, respectively (P < 0.01). The site-to-site and day-to-day coefficients of correlation of L-NAME injection were lower than those of iontophoresis at 0.66 (P < 0.05) and 0.12, respectively (P = not significant). Sodium nitroprusside-induced skin hyperemia was not affected by L-NAME administration. L-NAME iontophoresis-mediated inhibition of skin thermal hyperemia was greater in smokers than in nonsmokers (P < 0.05). Laser Doppler Imager assessment of skin thermal hyperemia after L-NAME iontophoresis provides a reproducible and selective bedside method of qualitatively analyzing the contribution of the NO pathway to microvascular vasomotor function.

Role of nitric oxide synthase on local sweat rate in older adults during intermittent exercise in the heat

Studies suggest that nitric oxide (NO) has a role in sweating. Older adults have a lower production of and sensitivity to NO which may explain why older adults have lower local sweat rates (LSR) compared with their younger counterparts during exercise. We examined the role of NO synthase (NOS) on LSR during intermittent exercise in the heat. Ten young (Y) and ten older (O) participants completed 3 × 15 min of cycling (rate of metabolic heat production of 600 W) separated by 15 min recovery in the heat (35ºC, 30% RH). Intradermal microdialysis probes were inserted in the forearm and perfused with either 0.9% saline (CON) or 10 mM L‐NAME (a NOS inhibitor). LSR was measured directly over each membrane. LSR was similar between Y and O during the exercise bouts at the CON (average of the 3 exercise bouts: Y; 0.96 ± 0.20 vs. O; 0.87 ± 0.25 mg·min−1·cm−2 p=0.327) and the LNAME (Y: 0.74 ± 0.18 vs. O: 0.83 ± 0.27 mg·min−1·cm−2 p=0.327) sites. However, the relative contribution of NO to the sweating response was reduced in Y (CON: 0.96 ± 0.20 vs. L‐NAME: 0.74 ± 0.18 mg·min−1·cm−2, p=0.017), but not O (CON: 0.87 ± 0.25 vs. L‐NAME: 0.83 ± 0.27 mg·min−1·cm−2, p=0.965). We conclude that the exercise‐induced increase in sweating is influenced by NO in younger adults. However, it appears that the level of influence is blunted in older individuals during high intensity exercise in the heat.This research was funded by Natural Sciences and Engineering Research Council (RGPIN‐298159–2009, held by Dr. Kenny).

Contributions of nitric oxide and prostaglandins to exercise hyperemia in young obese adults

Nitric oxide (NO) and prostaglandins (PGs) play important roles in exercise hyperemia in healthy humans, but the role of NO &amp; PGs in young obese (OB) adults is currently unknown. We hypothesized the relative contribution of NO and PGs to exercise hyperemia would be lower in young OB adults when compared to lean adults. 11 healthy lean (27±2yrs, BMI=23±1) and 7 OB adults (23±2yrs, BMI=38±4) performed two 10‐minute trials of dynamic forearm exercise (20 contractions/minute) at 15% of maximal voluntary contraction. A brachial artery catheter was used for local infusion of the NO synthase inhibitor, L‐NMMA, alone or in combination with the cycloxygenase inhibitor, ketorolac. L‐NMMA or ketoroloac was infused during the last 5 minutes of each exercise trial to achieve single and double blockade respectively. Forearm blood flow (FBF) was measured using Doppler ultrasound, and forearm vascular conductance (FVC) was calculated (FBF÷BP=FVC). From steady state exercise, the relative change in FVC with L‐NMMA was similar between groups (Lean−34±10 vs. OB−35±15%). With the addition of ketorolac, the relative change in FVC was opposite between groups (Lean−7±8 vs. OB+30±17%, p=0.02). We conclude the contribution of NO to exercise hyperemia appears intact in young OB adults, although they may produce more vasoconstrictor PGs that alter blood flow regulation. Support: NIH R01 HL105820.

Lisinopril augments the combined effect of nitric oxide and potassium channels on endothelium‐dependent relaxation in spontaneously hypertensive rats

Endothelium‐dependent relaxation is reported to be impaired in hypertension. However, there is equivocal evidence on the exact nature of the underlying dysfunction and whether it could be affected by antihypertensive drugs specifically angiotensin‐converting enzyme inhibitors. This study was conducted to evaluate the contribution of NO and potassium channels to endothelial function after lisinopril treatment in spontaneously hypertensive rats. Male animals (10–12 weeks old) were treated with lisinopril (20mg/Kg/day) for 10 weeks. ACh (0.1 nM–10μM)‐induced relaxation of third order mesenteric arteries was measured on a wire myograph with isometric recording in the presence and absence of different blockers. In the presence of inhibitor of nitric oxide synthase (LNMMA 100uM), the maximum relaxation of arteries from untreated (UT) and treated (T) rats to ACh was reduced by 19±3.5% and 5.0±01.6% respectively, while in the presence of SK and IK channel blockers (apamin 100nM and TRAM‐34 10μM) it was reduced by 35±3.5% and 34%±6.25%; respectively (n=10–22). With combined blockade, ACh‐induced relaxation was inhibited by 29±6.2% UT and 65±3.2 % T. Our results suggest that chronic treatment with lisinopril, although it reduced the relative contribution of nitric oxide alone it enhanced the combined effect of nitric oxide and potassium channels towards more endothelium‐dependent relaxation.

Resistance to First-Line Anti-TB Drugs Is Associated with Reduced Nitric Oxide Susceptibility in Mycobacterium tuberculosis

Background and ObjectiveThe relative contribution of nitric oxide (NO) to the killing of Mycobacterium tuberculosis in human tuberculosis (TB) is controversial, although this has been firmly established in rodents. Studies have demonstrated that clinical strains of M. tuberculosis differ in susceptibility to NO, but how this correlates to drug susceptibility and clinical outcome is not known.MethodsIn this study, 50 sputum smear- and culture-positive patients with pulmonary TB in Gondar, Ethiopia were included. Clinical parameters were recorded and drug susceptibility profile and spoligotyping patterns were investigated. NO susceptibility was studied by exposing the strains to the NO donor DETA/NO.ResultsClinical isolates of M. tuberculosis showed a dose- and time-dependent response when exposed to NO. The most frequent spoligotypes found were CAS1-Delhi and T3_ETH in a total of nine known spoligotypes and four orphan patterns. There was a significant association between reduced susceptibility to NO (>10% survival after exposure to 1 mM DETA/NO) and resistance against first-line anti-TB drugs, in particular isoniazid (INH). Patients infected with strains of M. tuberculosis with reduced susceptibility to NO showed no difference in cure rate or other clinical parameters but a tendency towards lower rate of weight gain after two months of treatment, independent of antibiotic resistance.Conclusion:There is a correlation between resistance to first-line anti-TB drugs and reduced NO susceptibility in clinical strains of M. tuberculosis. Further studies including the mechanisms of reduced NO susceptibility are warranted and could identify targets for new therapeutic interventions.

Mechanisms of aggregation inhibition by aspirin and nitrate-aspirin prodrugs in human platelets

Aspirin is the mainstay of anti-platelet therapy in the secondary prevention of cardiovascular disease. However, problems with aspirin safety and resistance demand clinical strategies based on multiple pharmacological approaches. Prodrugs of aspirin may offer beneficial effects in terms of gastro-intestinal safety and multiple pharmacological approaches. However, the pharmacological profile of aspirin prodrugs in human platelets has not been completed yet. We aimed to compare the effects of aspirin and prodrugs of aspirin (1-5) on human platelet aggregation stimulated by ADP and collagen and associated receptor expression (GPIIb/IIIa and P-selectin) in platelet-rich plasma (PRP) and washed platelets (WP). As aspirin is released from prodrugs following esterase hydrolysis we studied the expression and activity of butyrylcholineterase (BuChE) and carboxyesterase (CE) in plasma and platelets. The mechanism of prodrug-induced platelet aggregation inhibition was explored by studying the effects of plasma and purified human BuChE on aggregation. Finally, the relative contribution of nitric oxide (NO) bioactivity to nitrate-containing prodrugs of aspirin-induced inhibition of aggregation was determined using 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ,) a selective inhibitor of the soluble guanylyl cyclase. ST0702, 2, a nicotinic acid-aspirin codrug was equipotent with aspirin with respect to inhibition of collagen-induced platelet aggregation. Compound 4, a NO releasing aspirin was the most potent inhibitor of ADP-induced platelet aggregation, an effect partially reversed by ODQ. The platelet inhibitory effects of aspirin prodrugs were time-dependent as the maximal inhibitory effects against collagen-induced aggregation were achieved by aspirin at 2 min, 1 at 5 min and ST0702 at 15 min. The aspirin prodrugs were significantly less potent in WP than in PRP and the reverse was true of aspirin. In the presence of complete BuChE inhibition in PRP, there was almost complete loss of aspirin prodrug, but not aspirin anti-aggregatory activity. Interestingly, CE activity was observed in WP and platelet lysate with pNPA substrate. Accordingly, 1 and ST0702 retained 50% and 100% anti-aggregatory activity at maximal concentrations in WP, which was attenuated in the presence of esterase inhibitor phenylmethylsulphonyl fluoride. The inhibitory effect of aspirin prodrugs in PRP is due to prodrug activation by BuChE. In contrast, the platelet-inhibitory effects of aspirin prodrugs in WP may be mediated through the activity of platelet CE. Compound 4, a NO-containing aspirin prodrug, may exert dual inhibitory effects in platelets. Thus, aspirin prodrugs effectively inhibit human platelet aggregation and as such may be an alternative to conventional aspirin.

The relative efficacy of aminoguanidine and pentoxifylline in modulating endotoxin-induced cardiac stress

This study investigates the effect of aminoguanidine (AG), a selective inducible nitric oxide synthase (iNOS) inhibitor, and pentoxifylline (PTX), a tumour necrosis factor-alpha (TNF-α) inhibitor, on lipopolysaccharide (LPS)-induced cardiac stress. Rats were divided into four groups: group I served as a control, group II (LPS) received a single intraperitoneal injection of LPS (10 mg·kg(-1) ), group III (LPS+AG) and group IV (LPS+PTX) were injected with either AG (100 mg·kg(-1) ) or PTX (150 mg·kg(-1) ) intraperitoneally 10 days prior to LPS administration. Normalization of cardiac levels of nitrite/nitrate (NO(X) ), malondialdehyde (MDA), glutathione (GSH), heme oxygenase-1 (HO-1), glutathione peroxidase (GPx) and Na(+) , K(+) -ATPase activities was evident in the AG group. Both AG and PTX decreased the elevated serum TNF-α levels, the activities of lactate dehydrogenase (LDH), creatine kinase (CK) and cardiac myeloperoxidase (MPO). The levels of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and phosphocreatine (PCr) were enhanced following AG and PTX pretreatments. Calcium (Ca(2+) ) levels were altered, and the histopathological observations supported the described results. Conclusively, the study highlights the cardioprotective potential of AG and PTX with superior results from AG. These findings reveal the relative contribution of nitric oxide and TNF-α to oxidative stress and energy failure during endotoxemia.

Obesity Up-Regulates Intermediate Conductance Calcium-Activated Potassium Channels and Myoendothelial Gap Junctions to Maintain Endothelial Vasodilator Function

The mechanisms involved in altered endothelial function in obesity-related cardiovascular disease are poorly understood. This study investigates the effect of chronic obesity on endothelium-dependent vasodilation and the relative contribution of nitric oxide (NO), calcium-activated potassium channels (K(Ca)), and myoendothelial gap junctions (MEGJs) in the rat saphenous artery. Obesity was induced by feeding rats a cafeteria-style diet (∼30 kJ as fat) for 16 to 20 weeks, with this model reflecting human dietary obesity etiology. Age- and sex-matched controls received standard chow (∼12 kJ as fat). Endothelium-dependent vasodilation was characterized in saphenous arteries by using pressure myography with pharmacological intervention, Western blotting, immunohistochemistry, and ultrastructural techniques. In saphenous artery from control, acetylcholine (ACh)-mediated endothelium-dependent vasodilation was blocked by NO synthase and soluble guanylate cyclase inhibition, whereas in obese rats, the ACh response was less sensitive to such inhibition. Conversely, the intermediate conductance K(Ca) (IK(Ca)) blocker 1-[(2-chlorophenyl)diphenyl-methyl]-1H pyrazole attenuates ACh-mediated dilation in obese, but not control, vessels. In a similar manner, putative gap junction block with carbenoxolone increased the pEC(50) for ACh in arteries from obese, but not control, rats. IK1 protein and MEGJ expression was up-regulated in the arteries of obese rats, an observation absent in control. Addition of the small conductance K(Ca) blocker apamin had no effect on ACh-mediated dilation in either control or obese rat vessels, consistent with unaltered SK3 expression. Up-regulation of distinct IK(Ca)- and gap junction-mediated pathways at myoendothelial microdomain sites, key mechanisms for endothelial-derived hyperpolarization-type activity, maintains endothelium-dependent vasodilation in diet-induced obese rat saphenous artery. Plasticity of myoendothelial coupling mechanisms represents a significant potential target for therapeutic intervention.

Gender differences in the effects of streptozotocin-induced diabetes on parasympathetic vasodilatation in the rat submandibular gland

Objectives Submandibular vasodilatory responses are impaired in male streptozotocin-diabetic rats. However, the effects of diabetes on submandibular vascular reactivity in female rats have not been examined. The purpose of this study was to determine whether there are gender differences in the effects of diabetes on parasympathetic vasodilatation in the rat submandibular gland. Methods Diabetes was induced using streptozotocin, and vascular responses (calculated as the % increase in submandibular vascular conductance) to parasympathetic stimulation (1–10 Hz) were measured using laser-Doppler flowmetry. To estimate the relative contributions of nitric oxide (NO), prostacyclin (PGI 2) and endothelium-derived hyperpolarizing factor (EDHF), vascular conductance was measured before and after inhibition of cyclooxygenase (COX) and NO synthase (NOS). Results Frequency-dependent increases in blood flow were observed in both male and female rats, but the contribution of EDHF was greater in females than in males. Further, PGI 2 appeared to play a role only in males. Vasodilatory responses were diminished in all diabetic animals, and when compared with their respective controls the degree of impairment was similar in males and females. However, in diabetic males inhibition of COX and NOS had little or no effect, whereas inhibition of NO, but not COX, resulted in a further significant decrease in vascular responses in diabetic females. Conclusions Parasympathetic vasodilatation in the rat submandibular gland is diminished equally in diabetic males and females. However, in males diabetes predominantly impairs PGI 2- and NO-dependent vasodilatation, whereas in females the contribution of EDHF-mediated pathways are affected and NO-dependent vasodilatation is preferentially maintained.

Nitrite directly vasodilates hypoxic vasculature via nitric oxide‐dependent and ‐independent pathways

It is postulated that nitrite requires reduction to nitric oxide in order to exert its relaxant effect upon isolated hypoxic vessels. Herein, we evaluate the relative contribution of nitric oxide and characterize the downstream mechanisms of nitrite-induced vasorelaxation. Aortic rings were treated with pharmacological agents and exposed to hypoxia (<1% O(2)). Following pre-constriction, nitrite (10 microM final) was added to appropriate baths; isometric tension was recorded throughout. Nitrite (under hypoxic conditions at physiological pH) is capable of exerting physiological effects that cannot be completely inhibited by the inhibitor of soluble guanylate cyclase (sGC), 1H [1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one or a nitric oxide scavenger (carboxy-2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide). Simultaneous blockade of both sGC and cyclooxygenase (COX) completely inhibited the response to nitrite. With regard to the nitric oxide-dependent component, we confirm that aldehyde oxidase, but not xanthine oxidase or endothelial nitric oxide synthase, was important for the actions of nitrite in our model. Nitric oxide generated from nitrite is not exclusively responsible for the physiological actions observed in isolated hypoxic vessels. Nitrite operates via different pathways dependent on the presence or absence of endothelium to produce vasorelaxation. In intact vessels, both sGC and COX enzymes appear to be important. Irrespective of this difference in relaxation mechanism, nitrite is capable of producing the same maximum relaxation, regardless of the presence of endothelium. Having investigated possible nitrite reduction sites, we confirm that aldehyde oxidase is important for the actions of nitrite.

Skin blood flow and nitric oxide during body heating in type 2 diabetes mellitus

Individuals with type 2 diabetes mellitus (T2DM) often exhibit microvascular dysfunction that may contribute to impaired thermoregulation, but potential mechanisms remain unclear. Our goals were to quantify skin blood flow responses and nitric oxide-mediated vasodilation during body heating in individuals with T2DM compared with nondiabetic control subjects of similar age. We measured skin blood flow (laser-Doppler flowmetry) in conjunction with intradermal microdialysis of N(G)-nitro-l-arginine methyl ester (l-NAME; nitric oxide synthase inhibitor) or vehicle during 45-60 min of whole body heating (WBH) in 10 individuals with T2DM and 14 control subjects. In six individuals from each group, we also measured forearm blood flow (FBF) by venous occlusion plethysmography on the contralateral forearm. FBF responses showed diminished absolute cutaneous vasodilation during WBH in the T2DM group (P(ANOVA) < 0.01; peak FBF in control 13.1 +/- 1.7 vs. T2DM 9.0 +/- 1.6 ml.100 ml(-1).min(-1)). However, the relative contribution of nitric oxide to the cutaneous vasodilator response (expressed as % of maximal cutaneous vascular conductance) was not different between groups (P > 0.05). We conclude that cutaneous vasodilator responses to WBH are decreased in individuals with T2DM, but the contribution of nitric oxide to this smaller vasodilation is similar between T2DM and control individuals. This decrease in cutaneous vasodilation is likely an important contributor to impaired thermoregulation in T2DM.

Rebuttal from Drs. Thijssen and Hopman

POINT-COUNTERPOINTRebuttal from Drs. Thijssen and HopmanPublished Online:01 Sep 2008https://doi.org/10.1152/japplphysiol.90570.2008cMoreSectionsPDF (33 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Reading through Drs. Green, Maiorana, and Cable's argument, we hit on another of Oscar Wilde's wisdoms: “The truth is rarely pure and never simple.”In a series of experiments, Dr. Green and colleagues demonstrated that typical changes in shear pattern, characterized by an increase in retrograde flow, are linked with endothelial NO release in the nonactive regions (4). Although it might be tempting to relate vascular adaptation in inactive regions to alterations in shear pattern, we believe that the truth is not that simple. In nonactive vascular beds during exercise, an enhanced release of vasoconstrictors is present, such as endothelin-1 (5), angiotensin II (7), and vasopressin (8). The actions of these local vasoconstrictors, combined with enhanced activity of the sympathetic nervous system (2), likely outweigh the beneficial effects of NO.The role for shear rate in exercise-induced vascular adaptations is well recognized, but shear rate is not the only factor involved; unfortunately the truth is never simple. Hypoxia, through release of growth factors such as VEGF, importantly contributes to exercise-induced vascular adaptations (6). Notably, hypoxia and VEGF also contribute to the release and homing of circulating bone marrow-derived endothelial progenitor cells (1). These progenitor cells predict the occurrence of cardiovascular events and death (9), possibly through their capability for endothelial repair, arteriogenesis, and angiogenesis. Appreciating a key role for hypoxia in exercise-induced vascular adaptations casts doubt on vascular adaptations in nonactive muscles during exercise where this essential physiological stimulus is absent (3).Interestingly, blood flow and related shear patterns vary markedly among different locations and sizes of arteries at rest and during exercise. The prominent retrograde component in the nonactive brachial artery blood flow pattern is hypothesized to result from an increased downstream vasoconstriction (4). In contrast, arteries supplying highly metabolic tissues (i.e., heart and legs) have marked vasodilation and will therefore not demonstrate this blood flow pattern. Therefore, one may question whether findings in the brachial artery during leg exercise can be extrapolated to the coronary vascular bed, since shear rate as well as other physiological stimuli will be markedly different.Taken together, the central question in this discussion is which stimuli are obligatory, either alone or in combination with others, to result in exercise-induced vascular adaptations in the active and nonactive regions. We enjoyed discussing this topic and hope we presented our arguments in line with Oscar Wilde's “One should always play fairly when one has the winning cards.”REFERENCES1 Asahara T, Murohara T, Sullivan A, Silver M, van der Zee R, Li T, Witzenbichler B, Schatteman G, Isner JM. Isolation of putative progenitor endothelial cells for angiogenesis. Science 275: 964–967, 1997.Crossref | PubMed | ISI | Google Scholar2 Buckwalter JB, Clifford PS. The paradox of sympathetic vasoconstriction in exercising skeletal muscle. Exerc Sport Sci Rev 29: 159–163, 2001.Crossref | PubMed | Google Scholar3 Calbet JA, Gonzalez-Alonso J, Helge JW, Sondergaard H, Munch-Andersen T, Boushel R, Saltin B. Cardiac output and leg and arm blood flow during incremental exercise to exhaustion on the cycle ergometer. J Appl Physiol 103: 969–978, 2007.Link | ISI | Google Scholar4 Green DJ, Bilsborough W, Naylor LH, Reed C, Wright J, O'Driscoll G, Walsh JH. Comparison of forearm blood flow responses to incremental handgrip and cycle ergometer exercise: relative contribution of nitric oxide. J Physiol 562: 617–628, 2005.Crossref | PubMed | ISI | Google Scholar5 Maeda S, Miyauchi T, Sakane M, Saito M, Maki S, Goto K, Matsuda M. Does endothelin-1 participate in the exercise-induced changes of blood flow distribution of muscles in humans? J Appl Physiol 82: 1107–1111, 1997.Link | ISI | Google Scholar6 Prior BM, Yang HT, Terjung RL. What makes vessels grow with exercise training? J Appl Physiol 97: 1119–1128, 2004.Link | ISI | Google Scholar7 Stebbins CL, Symons JD. Role of angiotensin II in hemodynamic responses to dynamic exercise in miniswine. J Appl Physiol 78: 185–190, 1995.Link | ISI | Google Scholar8 Stebbins CL, Symons JD. Vasopressin contributes to the cardiovascular response to dynamic exercise. Am J Physiol Heart Circ Physiol 264: H1701–H1707, 1993.Link | ISI | Google Scholar9 Werner N, Kosiol S, Schiegl T, Ahlers P, Walenta K, Link A, Bohm M, Nickenig G. Circulating endothelial progenitor cells and cardiovascular outcomes. New Engl J Med 353: 999–1007, 2005.Crossref | PubMed | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 105Issue 3September 2008Pages 1007-1007 Copyright & PermissionsCopyright © 2008 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.90570.2008cHistory Published online 1 September 2008 Published in print 1 September 2008 Metrics

Exercise and cardiovascular risk reduction: time to update the rationale for exercise?

although it is generally accepted that the promotion of exercise accords with clinical best practice, the anecdotal experience of many primary care physicians, cardiologists, and exercise physiologists is that, even when exercise prescriptions are adhered to, risk factors often fail to demonstrate

Vasodilator prostanoids compensate for attenuated nitric oxide mediated vasodilation in type 1 diabetes

Background Previous research examining endothelial function and the biochemical pathways mediating vasodilation in type 1 diabetes has been conflicting. Both impaired and preserved nitric oxide (NO) mediated vasodilation have been reported whilst some authors have suggested enhanced vasodilator prostanoid (P) activity. The aim of this study was to determine the relative contributions of NO and P to endothelial function in a homogenous group of type 1 diabetic patients free of other confounding factors that may influence vascular behaviour.^f ^Methods and results Endothelial function was assessed using forearm venous plethysmography in 16 patients with uncomplicated type 1 (duration of diabetes 16.8±2.5 years (mean±SEM), HbA1C7.53±0.21% ) and 15 non-diabetic age and sex matched healthy control subjects. Forearm responses to the endothelium-dependent vasodilator, acetylcholine (ACh) (7.5, 15 and 30 µg/min), were recorded at baseline and after intra-arterial infusion of L-NMMA (a NO synthase inhibitor). Responses to ACh were re-examined following co-infusion of L-NMMA and indomethacin (a cyclo-oxygenase inhibitor). Responses to ACh were calculated as areas under the curve (AUC). At baseline vasodilator responses to ACh were similar (p=0.3) in diabetic and non-diabetic subjects. However, L-NMMA reduced ACh mediated responses to a lesser extent in diabetic subjects than control subjects (3±6% versus 18±3%; p&lt;0.03 respectively). Co-infusion with indomethacin further reduced blood flow, but the relative decrease in AUC was greater in the diabetic group (28±3% vs. 14±3%; p&lt;0.001). The contribution of biochemical pathways other than NO and P were similar in both diabetic and control groups (69±7% vs. 68±4%; p=0.45).Conclusions Vasodilator responses to ACh were unchanged in type 1 diabetes but this was reliant up on enhanced P mediated activity compensating for attenuated NO activity. Furthermore, vasoactive substances in addition to NO and P contribute significantly to vascular tone in both diabetic and non-diabetic subjects.