Exercise training enhances flow-induced vasodilation in skeletal muscle resistance arteries of aged rats: role of PGI2 and nitric oxide

Flow-induced vasodilation is attenuated with old age in rat skeletal muscle arterioles. The purpose of this study was to determine whether diminished cyclooxygenase (COX) signaling contributes to the age-induced attenuation of flow-induced vasodilation in gastrocnemius muscle arterioles and to determine whether, and through which mechanism(s), exercise training restores this deficit in old rats. Fischer 344 rats (3 and 22 mo old) were assigned to a sedentary or exercise-trained group. First-order arterioles were isolated from the gastrocnemius muscles, cannulated, and pressurized to 70 cm H(2)O. Diameter changes were determined in response to graded increases in intraluminal flow in the presence and absence of nitric oxide synthase (NOS) inhibition [10(-5) M N(G)-nitro-L-arginine methyl ester (L-NAME)], COX inhibition (10(-5) M indomethacin), or combination NOS (10(-5) M L-NAME) plus COX (10(-5) M indomethacin) inhibition. Aging reduced flow-induced vasodilation in gastrocnemius muscle arterioles. Exercise training restored responsiveness to flow in arterioles of aged rats and enhanced flow-induced vasodilation in arterioles from young rats. L-NAME inhibition of flow-induced vasodilation was greater in arterioles from old rats compared with those from young rats and was increased after exercise training in arterioles from both young and old rats. Although the indomethacin-sensitive portion of flow-induced dilation was not altered by age or training, both COX-1 mRNA expression and PGI(2) production increased with training in arterioles from old rats. These data demonstrate that exercise training restores flow-induced vasodilation in gastrocnemius muscle arterioles from old rats and enhances flow-induced vasodilation in gastrocnemius muscle arterioles from young rats. In arterioles from both old and young rats, the exercise training-induced enhancement of flow-induced dilation occurs primarily through a NOS mechanism.     

Hypercholesterolemia promotes inflammation and microvascular dysfunction: role of nitric oxide and superoxide

Relatively brief periods (days) of hypercholesterolemia can exert profound effects on endothelium-dependent functions of the microcirculation, including dilation of arterioles, fluid filtration across capillaries, and regulation of leukocyte recruitment in postcapillary venules. Hypercholesterolemia appears to convert the normal anti-inflammatory phenotype of the microcirculation to a proinflammatory phenotype. This phenotypic change appears to result from a decline in nitric oxide (NO) bioavailability that results from a reduction in NO biosynthesis, inactivation of NO by superoxide (O(2)(*)(-)), or both. A consequence of the hypercholesterolemia-induced microvascular responses is an enhanced vulnerability of the microcirculation to the deleterious effects of ischemia and other inflammatory conditions. Hence, therapeutic strategies that are directed towards preventing the early microcirculatory dysfunction and inflammation caused by hypercholesterolemia may prove effective in reducing the high mortality associated with ischemic tissue diseases. Agents that act to maintain the normal balance between NO and reactive oxygen species (ROS) in vascular endothelial cells may prove particularly useful in this regard.     

A role for nitric oxide in muscle repair: nitric oxide-mediated activation of muscle satellite cells

Muscle satellite cells are quiescent precursors interposed between myofibers and a sheath of external lamina. Although their activation and recruitment to cycle enable muscle repair and adaptation, the activation signal is not known. Evidence is presented that nitric oxide (NO) mediates satellite cell activation, including morphological hypertrophy and decreased adhesion in the fiber-lamina complex. Activation in vivo occurred within 1 min after injury. Cell isolation and histology showed that pharmacological inhibition of nitric oxide synthase (NOS) activity prevented the immediate injury-induced myogenic cell release and delayed the hypertrophy of satellite cells in that muscle. Transient activation of satellite cells in contralateral muscles 10 min later suggested that a circulating factor may interact with NO-mediated signaling. Interestingly, satellite cell activation in muscles of mdx dystrophic mice and NOS-I knockout mice quantitatively resembled NOS-inhibited release of normal cells, in agreement with reports of displaced and reduced NOS expression in dystrophin-deficient mdx muscle and the complete loss of NOS-I expression in knockout mice. Brief NOS inhibition in normal and mdx mice during injury produced subtle alterations in subsequent repair, including apoptosis in myotube nuclei and myotube formation inside laminar sheaths. Longer NOS inhibition delayed and restricted the extent of repair and resulted in fiber branching. A model proposes the hypothesis that NO release mediates satellite cell activation, possibly via shear-induced rapid increases in NOS activity that produce "NO transients."     

Exercise training increases acetylcholine-stimulated endothelium-derived nitric oxide release in spontaneously hypertensive rats

This study investigated the effects of exercise training on the regional release of endothelium-derived nitric oxide (EDNO) in spontaneously hypertensive rats (SHR). Male SHR and Wistar-Kyoto rats were divided into control and training groups, respectively. The training groups received moderate exercise by running on a drum exerciser for 60 min/day, 5 days/week for 10 weeks. At the end of experiments, thoracic aortae and common carotid arteries were excised. Acetylcholine (ACh)-induced relaxing responses due to EDNO release were evaluated in the presence of indomethacin. Vascular relaxing responses to A23187 or to sodium nitroprusside (SNP) were also studied. Our results indicated that after training, (1) the vascular sensitivity of thoracic aortae to ACh-induced relaxation was elevated when indomethacin was present; this effect was absent in the common carotid artery and it was abolished by adding N-nitro-L-arginine, and (2) no significant changes in SNP- or A23187-induced vascular relaxing responses, both being nonreceptor-mediated processes, were observed. We can conclude that for both hypertensive and normotensive rats, exercise training may increase receptor-mediated agonist-stimulated EDNO release in the thoracic aorta, but not in the common carotid artery.     

Upregulation of neuronal nitric oxide synthase in skeletal muscle by swim training

Exercise enhances cardiac output and blood flow to working skeletal muscles but decreases visceral perfusion. The alterations in nitric oxide synthase (NOS) activity and/or expression of the cardiopulmonary, skeletal muscle, and visceral organs induced by swim training are unknown. In sedentary and swim-trained rats (60 min twice/day for 3-4 wk), we studied the alterations in NOS in different tissues along with hindquarter vasoreactivity in vivo during rest and mesenteric vascular bed reactivity in vitro. Hindquarter blood flow and conductance were reduced by norepinephrine in both groups to a similar degree, whereas N(G)-nitro-L-arginine methyl ester reduced both indexes to a greater extent in swim-trained rats. Vasodilator responses to ACh, but not bradykinin or S-nitroso-N-acetyl-penicillamine, were increased in swim-trained rats. Ca(2+)-dependent NOS activity was enhanced in the hindquarter skeletal muscle, lung, aorta, and atria of swim-trained rats together with increased expression of neuronal NOS in the hindquarter skeletal muscle and endothelial NOS in the cardiopulmonary organs. Mesenteric arterial bed vasoreactivity was unaltered by swim training. Physiological adaptations to swim training are characterized by enhanced hindquarter ACh-induced vasodilation with upregulation of neuronal NOS in skeletal muscle and endothelial NOS in the lung, atria, and aorta.     

Critical role of endothelial cell-derived nitric oxide synthase in sickle cell disease-induced microvascular dysfunction

Superoxide, which can limit nitric oxide bioavailability, has been implicated in blood cell-vessel wall interactions observed in sickle cell transgenic (beta(S)) mice. Here we report that nonselective chemical inhibition of nitric oxide synthase isoforms dramatically reduces the enhanced leukocyte and platelet adhesion normally observed in cerebral venules of beta(S) mice. Although genetic deficiency of vascular wall inducible nitric oxide synthase does not alter adhesion responses in beta(S) mice, a significant attenuation is noted in beta(S) mice with vascular wall endothelial nitric oxide synthase (eNOS) deficiency, while the adhesion responses are exacerbated when eNOS is overexpressed in microvessels. The eNOS-mediated enhancement of blood cell adhesion is reversible by pretreatment with sepiapterin (which generates the eNOS cofactor tetrahydrobiopterin) or polyethyleneglycol-superoxide dismutase, implicating a role for eNOS-dependent superoxide production. These findings suggest that an imbalance between eNOS-derived nitric oxide and superoxide, both generated by the vessel wall, is critical to the proinflammatory and prothrombogenic phenotype that is assumed by the microvasculature in sickle cell disease.     

The role of nitric oxide in muscle fibers with oxidative phosphorylation defects

NO has been pointed as an important player in the control of mitochondrial respiration, especially because of its inhibitory effect on cytochrome c oxidase (COX). However, all the events involved in this control are still not completely elucidated. We demonstrate compartmentalized abnormalities on nitric oxide synthase (NOS) activity on muscle biopsies of patients with mitochondrial diseases. NOS activity was reduced in the sarcoplasmic compartment in COX deficient fibers, whereas increased activity was found in the sarcolemma of fibers with mitochondrial proliferation. We observed increased expression of neuronal NOS (nNOS) in patients and a correlation between nNOS expression and mitochondrial content. Treatment of skeletal muscle culture with an NO donor induced an increase in mitochondrial content. Our results indicate specific roles of NO in compensatory mechanisms of muscle fibers with mitochondrial deficiency and suggest the participation of nNOS in the signaling process of mitochondrial proliferation in human skeletal muscle.     

Endogenous vascular remodeling in ischemic skeletal muscle: a role for nitric oxide.

To test the hypothesis that nitric oxide (NO) production is essential for endogenous vascular remodeling in ischemic skeletal muscle, 22 New Zealand White rabbits were chronically instrumented with transit-time flow probes on the common iliac arteries and underwent femoral ligation to produce unilateral hindlimb ischemia. Iliac blood flow and arterial pressure were recorded at rest and during a graded exercise test. An osmotic pump connected to a femoral arterial catheter continuously delivered N-nitro-l-arginine methyl ester (a NO synthase inhibitor) or a control solution (N-nitro-d-arginine methyl ester or phenylephrine) to the ischemic limb over a 2-wk period. At 1, 3, and 6 wk after femoral ligation, maximal treadmill exercise blood flow in the ischemic limb was reduced compared with baseline in each group. However, maximal exercise blood flow was significantly (P < 0.05) lower in the l-NAME-treated group than in controls for the duration of the study: 48 +/- 4 vs. 60 +/- 5 ml/min at 6 wk. Consistent with the reduction in maximal blood flow response, the duration of voluntary exercise was also substantially (P < 0.05) shorter in the l-NAME-treated group: 539 +/- 67 vs. 889 +/- 87 s. Resting blood flow was unaffected by femoral ligation in either group. The results of this study show that endogenous vascular remodeling, which partially alleviated the initial deficit in blood flow, was interrupted by NO synthase inhibition. Therefore, we conclude that NO is essential for endogenous collateral development and angiogenesis in ischemic skeletal muscle in the rabbit.     

Exercise training blunts microvascular rarefaction in the metabolic syndrome

Reduced skeletal muscle microvessel density (MVD) in the obese Zucker rat (OZR) model of the metabolic syndrome is a function of a chronic reduction in vascular nitric oxide (NO) bioavailability. Previous studies suggest that exercise can improve NO bioavailability and reduce chronic inflammation and that low vascular NO bioavailability may be associated with impaired angiogenic responses via increased matrix metalloproteinase (MMP)-2 and MMP-9 activity. As such, we hypothesized that chronic exercise (EX) would increase NO bioavailability in OZR and blunt microvascular rarefaction through reduced MMP activity, and potentially via altered plasma cytokine levels. Ten weeks of treadmill exercise (1 h/day, 5 days/wk, 22 m/min) reduced body mass and fasting insulin and triglyceride levels in EX-OZR vs. sedentary (SED) OZR. In EX-OZR, gastrocnemius muscle MVD was improved by 19 +/- 4%, whereas skeletal muscle arteriolar dilation and conduit arterial methacholine-induced NO release were increased. In EX-OZR, functional hyperemia was improved vs. SED-OZR, and minimum vascular resistance within perfused gastrocnemius muscle was reduced, although no change in arteriolar stiffness was identified. Western blotting and gelatin zymography demonstrated that neither expression nor activity of MMP-2 or MMP-9 was altered in skeletal muscle of EX vs. SED animals. Plasma markers of inflammation associated with angiogenesis, monocyte chemoattractant protein-1 and IL-1beta, were increased in SED-OZR and were reduced with training, whereas IL-13 was reduced in SED-OZR and increased with exercise. These data suggest that exercise-induced improvements in skeletal muscle MVD in OZR are associated with increased NO bioavailability and may stem from altered inflammatory profiles rather than MMP function.     

Exercise training improves aortic endothelium-dependent vasorelaxation and determinants of nitric oxide bioavailability in spontaneously hypertensive rats.

The present study examined in vitro vasomotor function and expression of enzymes controlling nitric oxide (NO) bioavailability in thoracic aorta of adult male normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) that either remained sedentary (Sed) or performed 6 wk of moderate aerobic exercise training (Ex). Training efficacy was confirmed by elevated maximal activities of both citrate synthase (P = 0.0024) and beta-hydroxyacyl-CoA dehydrogenase (P = 0.0073) in the white gastrocnemius skeletal muscle of Ex vs. Sed rats. Systolic blood pressure was elevated in SHR vs. WKY (P < 0.0001) but was not affected by Ex. Despite enhanced endothelium-dependent relaxation to 10(-8) M ACh in SHR vs. WKY (P = 0.0061), maximal endothelium-dependent relaxation to 10(-4) M ACh was blunted in Sed SHR (48 +/- 12%) vs. Sed WKY (84 +/- 6%, P = 0.0067). Maximal endothelium-dependent relaxation to 10(-4) M ACh was completely restored in Ex SHR (93 +/- 9%) vs. Sed SHR (P = 0.0011). N(omega)-nitro-l-arginine abolished endothelium-dependent relaxation in all groups (P 相似文献   

Role of endothelial nitric oxide in microvascular oxygen delivery and consumption

Nitric oxide (NO) is an important signaling molecule modulating diverse processes such as vasodilation, neurotransmission, long-term potentiation, and immune responses. The endothelium contributes a significant fraction of NO from endothelial NO synthase (eNOS). The objective of this work was to analyze the role of eNOS in the modulation of oxygen supply to the tissues and in adaptation to maintain oxygenation uncompromised. Oxygen delivery and consumption were measured in the microcirculation of homozygous mutant endothelial nitric oxide synthase-deficient (eNOS(-/-)) and wild-type mice. Animals were implanted with a dorsal window chamber, allowing us to assess the intact microvascular system. Hemodynamics and oxygen tension were assessed in the microcirculation of conscious animals. The eNOS(-/-) mice had significantly higher blood pressure and lower heart rate (146 +/- 8 mm Hg, 401 +/- 17 bpm) than wild type (127 +/- 6 mm Hg, 428 +/- 20 bpm). Microvascular hemodynamic parameters were not significantly different between groups. The eNOS(-/-) animals delivered less oxygen to the microcirculation and released more oxygen to the tissue; both differences were statistically significant compared to wild type. The arteriolar vessel wall oxygen gradient, a measure of vascular smooth muscle cells and endothelial cell wall oxygen consumption, was significantly lower for eNOS(-/-) than for wild type, suggesting that the inhibition of eNOS is an antianoxia (oxygen sparing) mechanism. Finally, the findings of the study support the argument that NO availability limits oxygen consumption by the tissue.     

Exercise training improves endogenous nitric oxide mechanisms within the paraventricular nucleus in rats with heart failure

Previously, we have demonstrated that an altered endogenous nitric oxide (NO) mechanism within the paraventricular nucleus (PVN) contributes to increased renal sympathetic nerve activity (RSNA) in heart failure (HF) rats. The goal of this study was to examine the effect of exercise training (ExT) in improving the endogenous NO mechanism within the PVN involved in the regulation of RSNA in rats with HF. ExT significantly restored the decreased number of neuronal NO synthase (nNOS)-positive neurons in the PVN (129 +/- 17 vs. 99 +/- 6). nNOS mRNA expression and protein levels in the PVN were also significantly increased in HF-ExT rats compared with HF-sedentary rats. To examine the functional role of NO within the PVN, an inhibitor of NOS, N(G)-monomethyl-L-arginine, was microinjected into the PVN. Dose-dependent increases in RSNA, arterial blood pressure (BP), and heart rate (HR) were produced in all rats. There was a blunted increase in these parameters in HF rats compared with the sham-operated rats. ExT significantly augmented RSNA responses in rats with HF (33% vs. 20% at the highest dose), thus normalizing the responses. The NO donor sodium nitroprusside, microinjected into the PVN, produced dose-dependent decreases in RSNA, BP, and HR in both sham and HF rats. ExT significantly improved the blunted decrease in RSNA in HF rats (36% vs. 17% at the highest dose). In conclusion, our data indicate that ExT improves the altered NO mechanism within the PVN and restores NO-mediated changes in RSNA in rats with HF.     

一氧化氮在17-β雌二醇抑制血管平滑肌细胞增殖和原癌基因c -fos表达中的作用

实验利用大鼠血管平滑肌细胞（vascular smooth muscle cells,VSMC)作为模型,观察17-β雌二醇（E2）对VSMC增殖和原癌基因c-fos表达的影响,并探讨VSMC源性一氧化氮（NO）在基中的作用,检测指标包括NO释放的测定,细胞计数、^3H-Tdr掺入,噻唑蓝（MTT）测定和c-fosmRNA表达,结果显示,E2（10^-12-10^-8mol/L)呈浓度依赖性地促进VSMC中NO的释放;10^-8mol/LE2能明显抑制10%小牛血清（FCS）和10^-7mol/L内皮素-1（ET-1）诱导的细胞增殖和DNA合成,E2的抑制作用均可被雌激素受体（ER）拮抗剂tamoxifen(10^-7mol/L)和一氧化氮合酶抑制剂L-NAME（10^-6mol/L)明显减轻;E2（10^-8mol/L)可明显抑制10^-7mol/LET-1诱导的VSMCc-fos表达,这种抑制作用可被L-NAME（10^-6mol/L)明显减轻,这些结果提示E2能抑制VSMC增殖和原癌基因c-fos表达,这种促进VSMC的NO释放密切相关,而且该作用至少部分通过ER介导。     

Exercise training restores oxidative stress and nitric oxide synthases in the rostral ventrolateral medulla of renovascular hypertensive rats

Abstract

We hypothesize that exercise training (EX) reverses the level of nitric oxide (NO) and oxidative stress into rostral ventrolateral medulla (RVLM) of renovascular hypertensive rats (two kidneys, one clip - 2K1C). Microinjections of L-arginine (5 nmol), L-NAME (10 nmol), or saline (100 nl) were made into RVLM of 2K1C and normotensive (SHAM) rats sedentary (SED) or subjected to swimming for 4 weeks. mRNA expression (by qRT-PCR) of nitric oxide synthases isoforms (nNOS, eNOS, and iNOS), manganese superoxide dismutase (MnSOD), copper and zinc superoxide (Cu/ZnSOD), catalase (CAT), NADPH oxidase subunit p22^phox, concentration of thiobarbituric acid-reactive substances (TBARS), and CAT activity into RVLM were evaluated. The mean arterial pressure was reduced in 2K1C EX compared with that in 2K1C SED rats. L-arginine into RVLM induced hypertensive effect in 2K1C and SHAM SED rats, while L-NAME prevented hypertensive effect only in SHAM-SED. EX reduced hypertensive effect of L-arginine in SHAM and 2K1C rats. mRNA expression of NOS isoforms, p22^phox, and concentration of TBARS were increased while CAT and Cu/ZnSOD expression and CAT activity decreased into RVLM of 2K1C-SED compared with SHAM-SED rats. Additionally, EX reversed mRNA expression of CAT and NOS isoforms, concentration of TBARS, and CAT activity into RVLM of 2K1C-EX rats. These data suggest that the levels of NOS and oxidative stress into RVLM are important to determine the level of hypertension. Furthermore, EX can restore the blood pressure by reversing the levels of NOS and CAT expression, and reducing TBARS concentration into RVLM for the physiological state.     

The physiological role of nitric oxide

The review is devoted to exposition of a physiological role of a nitric oxide (NO), free radical gas, in various physiological functions. The number of those NO involvements is extremely high: bacteriocidal, cytotoxic and antitumor leukocyte effects, a relaxation of smooth-muscle cells of both vessels and gastrointestinal tract, the name just a few. The scheme of NO formation in various biological systems and its targets were shown and neuromodulator functions of NO in a brain were analyzed by the review presented. The findings of own researches on a role of NO in function of neuro-muscular synapse were included by the authors.     

Comparative haemodynamic studies of resting and active skeletal muscle in anaesthetised rats: role of nitric oxide.

Our previous studies have indicated that nitric oxide takes part in the basal regulation of vascular tone in skeletal muscle. The purpose of this study was to investigate whether nitric oxide has a role in the active hyperaemic response of a working muscle in a resting subject. Haemodynamic effects of nitric oxide synthase (NOS) inhibition (L-NAME, 10 mg/kg/30 min i.v. infusion) were determined simultaneously in the resting m. quadriceps femoris and in the working (breathing) m. rectus abdominis in anaesthetised rats (86Rb accumulation technique). L-NAME increased blood pressure and total peripheral resistance (TPR) while it decreased cardiac output. Blood flow (BF) decreased and vascular resistance (VR) increased both in resting (BF: 8.91+/-1.97-->5.92+/-2.59 ml/min/100 g, p<0.05: VR: 106+/-29.9-->212+/-113 R, p<0.01) and working (BF: 17.0+/-4.78-->6.93+/-2.15 ml/min/100 g, p<0.001; VR: 57.0+/-18.5-->160+/-56.7 R, p<0.01) muscle following NOS inhibition, but the percentile change of BF was higher in the working muscle (59%) than in the resting one (34%, p<0.001). There was a positive correlation between the cardiac output and the blood flow of the resting muscle with or without L-NAME administration, but blood flow of the working muscle failed to have any correlation with the cardiac output in control animals. However, L-NAME administration decreased both the cardiac output and the blood flow and similarly to the resting muscle a positive correlation was found. In conclusion, the haemodynamic effects of NOS inhibition are higher in working muscle than in the resting one: the nitric oxide may have important role in vasodilatation during muscle activity.     

Pharmacological preconditioning with resveratrol: role of nitric oxide

Resveratrol (trans-3,4',5-trihydroxystilbene), a recently described grape-derived polyphenolic antioxidant, has been found to protect the heart from ischemic-reperfusion injury. The present study sought to determine the mechanism of cardioprotection by investigating the ability of resveratrol to precondition the heart. Isolated perfused rat hearts were randomly divided into six groups: group I was perfused for 15 min with Kreb-Henseleit buffer (KHB) only; group II was perfused with 10 microM resveratrol; group III was perfused with 10 microM resveratrol plus 100 microM N(G)-nitro-L-arginine methyl ester (L-NAME), a nonselective nitric oxide (NO) synthase (NOS) inhibitor; group IV was perfused with 10 microM resveratrol plus 100 microM aminoguanidine (AG), an inducible NOS (iNOS) blocker; and groups V and VI consisted of hearts perfused with L-NAME and AG, respectively. The perfusion was then switched to working mode, and all hearts were made globally ischemic for 30 min followed by 2 h of reperfusion. Preconditioning of the hearts with resveratrol provided cardioprotection as evidenced by improved postischemic ventricular functional recovery (developed pressure and aortic flow) and reduced myocardial infarct size and cardiomyocyte apoptosis. Resveratrol-mediated cardioprotection was completely abolished by both L-NAME and AG. In a separate study, hearts were examined for iNOS mRNA induction. Resveratrol caused an induction of the expression of iNOS mRNA beginning at 30 min after reperfusion, increasing steadily up to 60 min of reperfusion, and then decreasing progressively up to 2 h after reperfusion. Preperfusion of the hearts with AG almost completely blocked the induction of iNOS. The results of our study demonstrate that resveratrol can pharmacologically precondition the heart in a NO-dependent manner.     

Possible role of nitric oxide in transmitting information from vasodilator nerve to cerebroarterial muscle

Treatment with L-NG-monomethyl arginine (L-NMMA), an inhibitor of nitric oxide (NO) synthesis from L-arginine, suppressed the relaxant response of dog cerebral artery strips to transmural electrical stimulation and nicotine, as did oxyhemoglobin. The inhibition by L-NMMA was reversed or prevented by L-, but not D-, arginine. It is concluded that NO or an NO-related compound may play a crucial role in transmitting information from excited vasodilator nerves to cerebroarterial smooth muscle.     

The role of nitric oxide in the spatial heterogeneity of basal microvascular blood flow in the rat diaphragm

The effects of N-nitro-L-arginine (L-NOARG) and N^G-monomethyl-L-arginine (L-NMMA) on the spatialdistribution of diaphragmatic microvascular blood flow were assessed in anesthetized, mechanically ventilated rats. Microvascular blood flow was measured after different periods at either a fixed site (Q_stat) or 25 different sites (Q_scan) using computer-aided laser-Doppler flowmetry (LDF) scanning. The value of Q_stat was unaffected after 15–20 min superfusion with any one of the following agents: L-NOARG (0.1 mM), L-NMMA (0.1 mM), L-arg (10 mM). The cumulative frequency histogram of the Q_scan value in the control group displayed a non-Gaussian distribution that was not significantly affected after 15 min superfusion with the vehicle of L-NOARG. Superfusion with either L-NMMA or L-NOARG at 0.1 mM for 15 min displaced the histogram of cumulative frequency to the left, with the median value of blood flow decreasing by 10 to 20%. However, skewness and kurtosis of the distribution of basal Q_scan were unaffected after superfusion of either of the L-arg analogues. Pretreatment with L-arg (10 mM), followed by co-administration of L-arg (10 mM) with L-NOARG (0.1 mM) only partially prevented L-NOARG from exerting this inhibitory effect on the distribution of basal Q_scan, while pretreatment with L-arg in the same manner could prevent L-NMMA from exerting its inhibitory effect. There was a weak but significant linear relationship between the magnitude of basal Q_scan and normalized changes in basal Q_scan after superfusion of either of the L-arg analogues. In conclusion, a basal NO activity is present in the diaphragmatic microvascular bed of rats. LDF scanning rather may yield more vivid information about the extent of overall tissue perfusion than conventional LDF whenever basal NO activity is involved. Moreover, the parallel flow profiles after NO synthase blockade suggest that the spatial inhomogeneity of basal diaphragmatic microvascular blood flow is not dependent on basal NO formation.     

Role of nitric oxide in human pulmonary microvascular endothelial cell adhesion

Cyclopentenylcytosine (CPEC) is cytotoxic to HT-29 cells in vitro and in vivo. Treatment with CPEC resulted in sensitizing HT-29 cells to cisplatin (CDDP), as evidenced by synergistic cytotoxicity. CPEC exhibits potent cytotoxicity to HT-29 cells in vitro, 2 and 24 h exposure providing an LC50 of 2.4 and 0.46 microM, respectively. Exposure of HT-29 cells to CDDP for 2 h resulted in an LC50 of 26 microM. Treatment of HT-29 cells with 1.0 or 1.25 microM CPEC and then incubating with CDDP showed synergistic cytotoxicity. Lesser synergy at very high concentrations of CPEC was demonstrated when HT-29 cells were first exposed to CDDP and then incubated with CPEC. Combination index calculations showed synergistic cytotoxicity in HT-29 cells when CPEC was combined with CDDP. Synergistic antitumor activity was demonstrable in vivo in mice transplanted with HT-29 tumor when treated with a combination of CPEC and CDDP without undue toxicity, since no excessive loss in mouse body weight or overt pathology was observed. CPEC had no influence on the total DNA adduct formation and CDDP did not affect the intracellular levels of CPEC or its metabolites, suggesting that enhanced CDDP cytotoxicity resulted from a step subsequent to excision of platinum-cross-linked DNA. These studies support a new approach for augmenting cytotoxic effect of CPEC with CDDP in treating human colon carcinoma.