Enhanced nitric oxide and cyclic GMP formation plays a role in the anti-platelet activity of simvastatin

BACKGROUND AND PURPOSE: It has been found that 3-hydroxy-3-methyl-glutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) exert various vascular protective effects, beyond their cholesterol-lowering property, including inhibition of platelet-dependent thrombus formation. The objective of the present study was to determine whether the nitric oxide (NO)/cyclic GMP-mediated processes in platelets contribute to the anti-aggregatory activity of simvastatin. EXPERIMENTAL APPROACH: After rabbit platelets were incubated with simvastatin for 5 min, aggregation was induced and the platelet aggregation, nitric oxide synthase activity, guanylyl cyclase activity, NO and cyclic GMP formation were measured appropriately. KEY RESULTS: Treatment with simvastatin concentration-dependently inhibited platelet aggregation induced by collagen or arachidonic acid with an IC(50) range of 52-158 microM. We also demonstrated that simvastatin (20-80 microM) concentration-dependently further enhanced collagen-induced NO and cyclic GMP formation through increasing NOS activity (from 2.64+/-0.12 to 3.52+/-0.21-5.10+/-0.14 micromol min(-1) mg protein(-1)) and guanylyl cyclase activity (from 142.9+/-7.2 to 163.5+/-17.5-283.8+/-19.5 pmol min(-1) mg protein(-1)) in the platelets. On the contrary, inhibition of platelet aggregation by simvastatin was markedly attenuated (by about 50%) by addition of a nitric oxide synthase inhibitor, a NO scavenger or a NO-sensitive guanylyl cyclase inhibitor. The anti-aggregatory effects of simvastatin were significantly increased by addition of a selective inhibitor of cyclic GMP phosphodiesterase. CONCLUSIONS AND IMPLICATIONS: Our findings indicate that enhancement of a NO/cyclic GMP-mediated process plays an important role in the anti-aggregatory activity of simvastatin.     

The Nitric Oxide Donor SIN-1 Is Free of Tolerance and Maintains Its Cyclic GMP Stimulatory Potency in Nitrate-Tolerant LLC-PK1 Cells

Purpose. Using an established cell culture model, the present study investigates whether linsidomine (SIN-1), a spontaneous donor of nitric oxide and active metabolite of the antianginal drug molsidomine, induces tolerance to its own cyclic GMP stimulatory action or shows a diminished response after tolerance induction with glyceryl trinitrate. Methods. Incubations with nitric oxide donors were carried out in LLC-PK₁, kidney epithelial cells. Intracellular levels of cyclic GMP, the vasodilatory second messenger of nitric oxide, were determined by radioimmunoassay. Results. A 5-h preincubation with glyceryl trinitrate (0.01–100 M) led to complete inhibition of a subsequent cyclic GMP stimulation by glyceryl trinitrate but left the cyclic GMP response to SIN-1 unaltered. Similarly, cyclic GMP elevations by the spontaneous nitric oxide donors sodium nitroprusside and spermine NONOate were not affected after pretreatment with glyceryl trinitrate. Moreover, pretreatment with SIN-1 (1–1000 M) had no significant effect on SIN-1-dependent cyclic GMP stimulation. Conclusions. Our results show that in LLC-PK₁, cells, SIN-1 is free of tolerance induction and not cross-tolerant to glyceryl trinitrate. This may be due to the spontaneous nitric oxide release from SIN-1, which in contrast to nitric acid esters does not require enzymatic bioactivation and may therefore be unaffected by nitrate tolerance.     

Flow-induced enhancement of vasoconstriction and blockade of endothelium-derived hyperpolarizing factor (EDHF) by ascorbate in the rat mesentery

BACKGROUND AND PURPOSE: We previously reported that ascorbate inhibits flow- and agonist-induced, EDHF-mediated vasodilatation in the bovine ciliary circulation. This study examined whether ascorbate had similar actions in the rat mesenteric vasculature. EXPERIMENTAL APPROACH: The effects of ascorbate were examined both in rat second order mesenteric arterial rings suspended in a static wire myograph and the rat mesentery perfused at different rates of flow. KEY RESULTS: Ascorbate (50 microM) had no effect on U46619-induced tone or acetylcholine-induced, EDHF-mediated vasodilatation in either rings of mesenteric artery or the perfused mesentery at rates of flow below 10 ml min(-1). At higher rates of flow, ascorbate produced two distinct effects in the rat mesentery: a rapid and maintained enhancement of vasoconstrictor tone and a slow (max at 3 h) inhibition of acetylcholine-induced, EDHF-mediated vasodilatation. The enhancement of vasoconstrictor tone appeared to be due to inhibition of flow-induced EDHF-like activity, since it was endothelium-dependent, but could be elicited during blockade of nitric oxide synthase and cyclooxygenase. Despite this, the classical inhibitors of EDHF, apamin and charybdotoxin, failed to affect the ascorbate-induced enhancement of tone, although they inhibited acetylcholine-induced vasodilatation. CONCLUSIONS AND IMPLICATIONS: Ascorbate inhibits both flow- and agonist-induced EDHF in the rat mesentery. The strikingly different timecourses of these two effects, together with their differential sensitivity to apamin and charybdotoxin, suggest that the flow- and agonist-induced EDHFs in the rat mesenteric vasculature may either be different entities or operate by different mechanisms.     

Characteristic changes in coronary artery at the early hyperglycaemic stage in a rat type 2 diabetes model and the effects of pravastatin

Background and purpose:

Diabetes is a risk factor for the development of coronary artery disease but it is not known whether the functions of endothelium-derived nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) in coronary arteries are altered in the early stage of diabetes. Such alterations and the effects of pravastatin were examined in left anterior descending coronary arteries (LAD) from Otsuka Long-Evans Tokushima Fatty (OLETF) rats (type 2 diabetes model) at the early hyperglycaemic stage [vs. non-diabetic Long-Evans Tokushima Otsuka (LETO) rats].

Experimental approach:

Isometric tension, membrane potential and superoxide production were measured, as were protein expression of NAD(P)H oxidase components and endothelial NO synthase (eNOS).

Key results:

Superoxide production and the protein expressions of both the nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] oxidase components and eNOS were increased in OLETF rats. These changes were normalized by pravastatin administration. Not only acetylcholine (ACh)-induced endothelial NO production but also functions of endothelium-derived NO [from (i) the absolute tension induced by epithio-thromboxane A₂ (STA₂) or high K⁺; (ii) enhancement of the STA₂-contraction by a nitric oxide synthase (NOS) inhibitor; and (iii) the ACh-induced endothelium-dependent relaxation of high K⁺-induced contraction] or EDHF [from (iv) ACh-induced endothelium-dependent smooth muscle cell hyperpolarization and relaxation in the presence of a NOS inhibitor] were similar between LETO and OLETF rats [whether or not the latter were pravastatin-treated or -untreated].

Conclusions and implications:

Under conditions of increased vascular superoxide production, endothelial function is retained in LAD in OLETF rats at the early hyperglycaemic stage, partly due to enhanced endothelial NOS protein expression. Inhibition of superoxide production may contribute to the beneficial vascular effects of pravastatin.     

Nitric Oxide and Carbon Monoxide Act as Inhibitory Neurotransmitters in the Longitudinal Muscle of C57BL/6J Mouse Distal Colon

The present study was designed to identify the inhibitory neurotransmitters mediating nonadrenergic noncholinergic relaxation in the longitudinal muscle of C57/BL mouse distal colon. Relaxation induced by electrical field stimulation (EFS) was recorded isotonically in the presence of atropine and guanethidine. Cyclic guanosine-3′,5′-monophosphate (cyclic GMP) content was measured by radioimmunoassay. EFS-induced relaxation was inhibited by nitro-l-arginine (l-NNA) and Sn (IV) protoporphyrin dichloride IX (SnPP-IX), a nitric oxide (NO) and carbon monoxide (CO) synthase inhibitor, respectively. A combination of both inhibitors produced an additive effect. ODQ, a soluble guanylate cyclase inhibitor, inhibited EFS-induced relaxation. NOR-1, a NO donor, and carbon monoxide-releasing molecule-2 (CORM-2), a CO donor, treatment relaxed the distal colon and increased cyclic GMP content. The effects of NOR-1 and CORM-2 were inhibited by ODQ. KT5823, a cyclic GMP–dependent protein kinase inhibitor, inhibited EFS-induced relaxation. EFS-induced relaxation in the presence of KT5823 was further inhibited byl-NNA, but not by SnPP-IX. In addition, KT5823 inhibited CORM-2–induced relaxation, but not NOR-1–induced relaxation. H89, a cyclic AMP–dependent protein kinase inhibitor, inhibited EFS-induced relaxation, and EFS-induced relaxation in the presence of H89 was further inhibited byl-NNA. These results suggested that NO and CO function as inhibitory neurotransmitters in the longitudinal muscle of C57BL mouse distal colon.     

The effects of perhexiline on the rat coronary vasculature

The predominant site and mechanism(s) of perhexiline-induced coronary vasodilatation were investigated in the rat heart. Perhexiline was more potent in the Langendorff perfused heart than in the left anterior descending coronary artery (EC₅₀; 0.27 μM, confidence limits 0.19–0.39: 2.7 μM, 2.0–3.4, respectively). Selective endothelial inactivation with Triton X-100 in the perfused heart, reduced the response to perhexiline 1 μM (76+8% to 30+3% of control). 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) 3 μM, N-nitro- -arginine 100 μM, or a combination of the latter with indomethacin 10 μM, had no significant effect on responses to perhexiline in the perfused heart. Unlike bradykinin-induced vasodilatation, responses to perhexiline were not inhibited by tetrabutylammonium 1 mM, or charybdotoxin 20 nM. SKF525A 5 μM inhibited both perhexiline and bradykinin responses, while apamin 1 μM and glibenclamide 3 μM inhibited neither. Perhexiline exerts partially endothelium-dependent coronary vasodilator effects in the rat, predominantly on small coronary arteries, which appear to be independent of nitric oxide (NO), prostacyclin and the endothelium-derived hyperpolarising factor (EDHF) released by bradykinin.     

Interactions between endothelium-derived relaxing factors in the rat hepatic artery: focus on regulation of EDHF

1. In rat isolated hepatic arteries contracted with phenylephrine, acetylcholine and the calcium ionophore A23187 each elicit endothelium-dependent relaxations, which involve both nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF). However, the contribution of prostanoids to these responses, and the potential interaction between EDHF and other endothelium-derived relaxing factors have not been examined.
2. In the presence of the NO synthase inhibitor N^G-nitro-L-arginine (L-NOARG, 0.3 mM) and a mixture of charybdotoxin (0.3 μM) and apamin (0.3 μM), inhibitors of the target potassium (K) channel(s) for EDHF, acetylcholine and {"type":"entrez-nucleotide","attrs":{"text":"A23187","term_id":"833253","term_text":"A23187"}}A23187 each induced a concentration-dependent and almost complete relaxation, which was abolished in the additional presence of indomethacin (10 μM). Thus, in addition to EDHF and NO, a relaxing factor(s) generated by cyclo-oxygenase (COX) contributes to endothelium-dependent relaxation in the rat hepatic artery.
3. The resting membrane potentials of endothelium-intact and endothelium-denuded vascular segments were −57 mV and −52 mV, respectively (P>0.05). In intact arteries, the resting membrane potential was not affected by L-NOARG plus indomethacin, but reduced to −47 mV in the presence of charybdotoxin plus apamin. Acetylcholine and {"type":"entrez-nucleotide","attrs":{"text":"A23187","term_id":"833253","term_text":"A23187"}}A23187 (10 μM each) elicited a hyperpolarization of 13 mV and 15 mV, respectively. The hyperpolarization induced by these agents was not affected by L-NOARG plus indomethacin (12 mV and 14 mV, respectively), but reduced in the presence of charybdotoxin plus apamin (7 mV and 10 mV, respectively), and abolished in the combined presence of charybdotoxin, apamin and indomethacin.
4. The NO donor 3-morpholino-sydnonimine (SIN-1) induced a concentration-dependent relaxation, which was unaffected by charybdotoxin plus apamin, but abolished by the selective soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ, 10 μM). SIN-1 (10 μM) did not alter the resting membrane potential in endothelium-denuded vascular segments.
5. The COX-dependent relaxation induced by acetylcholine was abolished following exposure to 30 mM KCl, but unaffected by glibenclamide (10 μM). The prostacyclin analogue iloprost induced a concentration-dependent relaxation, which was also abolished in 30 mM KCl and unaffected by the combined treatment with glibenclamide, charybdotoxin and apamin. Iloprost (10 μM) induced a glibenclamide-resistant hyperpolarization (8 mV with and 9 mV without glibenclamide) in endothelium-denuded vascular segments.
6. Exposure to SIN-1 or iloprost did not affect the EDHF-mediated relaxation induced by acetylcholine (i.e. in the presence of L-NOARG and indomethacin). Replacement of L-NOARG with the NO scavenger oxyhaemoglobin (10 μM) or the soluble guanylate cyclase inhibitor ODQ (10 μM) or methylene blue (10 μM), which all significantly inhibited responses to endothelium-derived NO, did not affect the acetylcholine-induced relaxation in the presence of indomethacin, indicating that endogenous NO also does not suppress EDHF-mediated responses.
7. These results show that, in addition to EDHF and NO, an endothelium-derived hyperpolarizing factor(s) generated by COX contributes significantly to endothelium-dependent relaxation in the rat heptic artery. Neither this factor nor NO seems to regulate EDHF-mediated responses. Thus, EDHF does not serve simply as a `back-up'' system for NO and prostacyclin in this artery. However, whether EDHF modulates the NO and COX pathways remains to be determined.

     

呼出气一氧化氮与慢性咳嗽吸入糖皮质激素治疗疗效的关系

【摘要】 目的：探讨呼出气一氧化氮在慢性咳嗽吸入糖皮质激素治疗疗效中的作用。方法：采用回顾性的方法观察2010年1月一2010年12月在我科就诊的慢性咳嗽患者,进行呼出气一氧化氮（FENO）检测以及沙丁胺醇舒张试验,收集相关临床资料,没有临床资料通过电话回访和问卷调查。结果：①共计62名慢性咳嗽患者进入研究,吸入糖皮质激素（ICS）治疗应答和无应答的患者在年龄、性别、体重指数、FEV1%预测值等方面差异无统计学意义;②ICS治疗应答组患者FENO的水平为48.13±15.66ppb,明显高于ICS治疗无应答组患者的24.90±9.26ppb,差异有统计学意义（P<0.05）;③22名呼出气NO正常慢性咳嗽患者,给予ICS治疗,仅有2名患者治疗有效;④判断ICS治疗有无应答的FENO的临界值为34ppb。结论：FENO水平对慢性咳嗽进行ICS治疗有预测作用,高的FENO水平提示慢性咳嗽对ICS治疗有应答,而低FENO提示ICS治疗效果差,这将有助于慢性咳嗽患者的评价和治疗。     

Effect of hydroxocobalamin on vasodilatations to nitrergic transmitter, nitric oxide and endothelium-derived relaxing factor in guinea-pig basilar artery

In endothelium-denuded guinea-pig isolated basilar artery preparations, hydroxocobalamin (30, 100 and 300 μM) concentration-dependently inhibited the vasodilator responses to exogenous nitric oxide (NO), whereas the vasodilator responses to nitrergic nerve stimulation were slightly reduced by high (100 and 300 μM) but not by the low (30 μM) concentration of hydroxocobalamin. Vasodilatation in response to sodium nitroprusside (10–100 nM) was totally abolished by 300 μM hydroxocobalamin. In endothelium-intact preparations, vasodilator responses to acetylcholine (0.3–3 μM) were significantly reduced or abolished by hydroxocobalamin (30–300 μM). The mean reduction by hydroxocobalamin of relaxations to acetylcholine was significantly greater than that of the equivalent response evoked by nitrergic nerve stimulation. The findings suggest that the nitrergic transmitter in the guinea-pig basilar artery may be quantitatively less susceptible than the endothelium-derived relaxing factor to the NO scavenger hydroxocobalamin.     

Involvement of protein kinase C in reduced relaxant responses to the NO/cyclic GMP pathway in piglet pulmonary arteries contracted by the thromboxane A2-mimetic U46619

1. Impairment of nitric oxide (NO)/cyclic GMP production and/or increased activities of thromboxane A₂ (TXA₂) and endothelin-1 (ET-1) have been associated with pulmonary hypertension. We have analysed the interactions of noradrenaline (NA), the TXA₂-mimetic U46619 and ET-1 with the relaxation induced via cyclic GMP in isolated piglet intrapulmonary arteries.
2. The contractions induced by NA were augmented by endothelium removal or by methylene blue and pre-contracted rings were fully relaxed by acetylcholine, sodium nitroprusside (SNP), atrial natriuretic peptide and 8-bromo-cyclic GMP. In contrast, U46619- and ET-1 induced contractions were endothelium-independent and only partially relaxed by the latter vasodilators. Whereas the reduced responses to SNP in arteries contracted by U46619 were independent of the U46619-induced tone, a higher concentration of ET-1 (tone higher than that induced by NA) was required to reduce the vasodilator responses to SNP. NA, U46619 and ET-1 had no effect on the SNP-induced increases in cyclic GMP.
3. The reduced relaxant responses to SNP in arteries pre-contracted by U46619 were specific for piglet pulmonary arteries since they were not observed in piglet mesenteric or coronary arteries or in rat pulmonary arteries. Furthermore, there were no differences in the relaxant response to the adenylate cyclase activator forskolin in piglet pulmonary arteries pre-contracted by either NA, U46619 or ET-1.
4. SNP-induced relaxation was inhibited by thapsigargin (but not by inhibition of the membrane Na⁺/K⁺ ATPase nor K⁺ channels) indicating a role for Ca²⁺ sequestration by the Ca²⁺ ATPase in the effects of SNP.
5. The phorbol ester 12-myristate, 13-acetate inhibited the relaxant response to SNP. The inhibitory effect of U46619 on SNP-induced relaxation was abolished by the protein kinase C inhibitor (PKC) staurosporine suggesting that PKC may be a part of the signal transduction mechanism.
6. In summary, piglet pulmonary arteries when activated by a TXA₂-mimetic show abnormally reduced relaxant responses to the NO/cyclicGMP pathway. This effect appears to be mediated by activation of PKC.

     

Re(I) and Tc(I) Complexes for Targeting Nitric Oxide Synthase: Influence of the Chelator in the Affinity for the Enzyme

Aiming to design ^99mTc complexes for probing nitric oxide synthase (NOS) by SPECT, we synthesized conjugates ( L4 – L6 ) comprising a NOS‐recognizing moiety connected to a diamino‐propionic acid (dap) chelating unit. The conjugates led to complexes of the type fac‐[M(CO)₃(?³‐L)] (M = Re/^99mTc; Re4 / Tc4 : L =  L4 ; Re5 / Tc5 : L =  L5 ; Re6 / Tc6 : L =  L6 ). Enzymatic studies showed that L4 and L5 , but not L6 , gave complexes ( Re4 and Re5 ) that are less potent than the conjugates. To rationalize these results, we performed docking and molecular dynamics simulations. The high affinity of L4 and L5 is due to the strong interactions between the dap chelator and polar residues of the binding cavity. These interactions are hampered by metallation resulting in complexes with lower affinity. The higher potency of Re5 compared to Re4 was assigned to the increased bulkiness of Re5 and the presence of additional anchoring groups that better fit the active site and provide more extensive contacts. In turn, Re6 is too bulky and its organometallic tail is oriented toward the peripheral pocket of iNOS, leading to loss of contacts and a lower affinity. These results were compared with our previous results obtained with analogue complexes stabilized by a pyrazolyl‐diamine chelating unit.     

Nitric oxide as a metabolic regulator during exercise: effects of training in health and disease

1. Accumulating animal and human data suggest that nitric oxide (NO) is important for both coronary and peripheral haemodynamic control and metabolic regulation during performance of exercise. 2. While still controversial, NO of endothelial origin is thought to potentiate exercise-induced hyperaemia, both in the peripheral and coronary circulations. The mechanism of release may include both acetylcholine derived from the neuromuscular junction and vascular shear stress. 3. A splice variant of neuronal nitric oxide synthase (NOS), nNOSmicro, incorporating an extra 34 amino acids, is expressed in human skeletal muscle. In addition to being a potential modulator of blood flow, skeletal muscle-derived NO is an important regulator of muscle contraction and metabolism. In particular, recent human data indicate that NO modulates muscle glucose uptake during exercise, independently of blood flow. 4. Exercise training in healthy individuals promotes adaptations in the various NO systems, which can increase NO bioavailability through a variety of mechanisms, including increased NOS enzyme expression and activity. Such adaptations likely contribute to increased exercise capacity and protection from cardiovascular events. 5. Cardiovascular risk factors, including hypercholesterolaemia, hypertension, diabetes and smoking, as well as established disease, are associated with impairment of the various NO systems. Given that NO is an important signalling mechanism during exercise, such impairment may contribute to limitations in exercise capacity through inadequate coronary or peripheral blood delivery and via metabolic effects. 6. Exercise training in individuals with elevated cardiovascular risk or established disease can increase NO bioavailability and may represent an important mechanism by which exercise training provides benefit in the setting of secondary prevention.     

Increased Contextual Fear Conditioning in iNOS Knockout Mice: Additional Evidence for the Involvement of Nitric Oxide in Stress-Related Disorders and Contribution of the Endocannabinoid System

Background:

Inducible or neuronal nitric oxide synthase gene deletion increases or decreases anxiety-like behavior in mice, respectively. Since nitric oxide and endocannabinoids interact to modulate defensive behavior, the former effect could involve a compensatory increase in basal brain nitric oxide synthase activity and/or changes in the endocannabinoid system. Thus, we investigated the expression and extinction of contextual fear conditioning of inducible nitric oxide knockout mice and possible involvement of endocannabinoids in these responses.

Methods:

We evaluated the effects of a preferential neuronal nitric oxide synthase inhibitor, 7-nitroindazol, nitric oxide synthase activity, and mRNA changes of nitrergic and endocannabinoid systems components in the medial prefrontal cortex and hippocampus of wild-type and knockout mice. The effects of URB597, an inhibitor of the fatty acid amide hydrolase enzyme, which metabolizes the endocannabinoid anandamide, WIN55,212-2, a nonselective cannabinoid agonist, and AM281, a selective CB1 antagonist, on contextual fear conditioning were also evaluated.

Results:

Contextual fear conditioning expression was similar in wild-type and knockout mice, but the latter presented extinction deficits and increased basal nitric oxide synthase activity in the medial prefrontal cortex. 7-Nitroindazol decreased fear expression and facilitated extinction in wild-type and knockout mice. URB597 decreased fear expression in wild-type and facilitated extinction in knockout mice, whereas WIN55,212-2 and AM281 increased it in wild-type mice. Nonconditioned knockout mice showed changes in the mRNA expression of nitrergic and endocannabinoid system components in the medial prefrontal cortex and hippocampus that were modified by fear conditioning.

Conclusion:

These data reinforce the involvement of the nitric oxide and endocannabinoids (anandamide) in stress-related disorders and point to a deregulation of the endocannabinoid system in situations where nitric oxide signaling is increased.     

Modulation of relaxation to levcromakalim by S-nitroso-N-acetylpenicillamine (SNAP) and 8-bromo cyclic GMP in the rat isolated mesenteric artery

1. Levcromakalim caused concentration-dependent relaxations of methoxamine-induced tone in both endothelium-denuded and intact vessels. Its potency was reduced by the nitric oxide donor, S-nitroso-N-acetylpenicillamine (SNAP; 0.1 μM or 1 μM) in both denuded and intact vessels. The maximal relaxation (R_max) was reduced only in denuded vessels.
2. SNAP was more potent in endothelium-denuded than intact vessels but there were no differences in R_max. Glibenclamide (10 μM) did not affect relaxation to SNAP in endothelium-denuded or intact vessels.
3. The soluble guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 μM) increased the potency and R_max of levcromakalim in endothelium-intact vessels. ODQ had no effect in denuded vessels.
4. ODQ (10 μM) reduced the vasorelaxant potency of SNAP in both intact and endothelium-denuded vessels by 190-fold and 620-fold, respectively.
5. 8-bromo cyclic GMP (10 or 30 μM) reduced both the potency and R_max of levcromakalim in de-endothelialized vessels, but had no effect in intact vessels although it reduced both the potency and R_max of levcromakalim in intact vessels incubated with ODQ (10 μM).
6. In the presence of ODQ (10 μM), SNAP (0.1 μM or 1 μM) reduced the potency of levcromakalim in intact vessels, without altering R_max, but had no effect in denuded vessels. SNAP (50 μM) reduced both the potency and R_max of levcromakalim in intact and endothelium-denuded vessels.
7. Therefore, although SNAP causes relaxation principally through generation of cyclic GMP, it can modulate the actions of levcromakalim through mechanisms both dependent on, and independent of, cyclic GMP; the former predominate in endothelium-denuded vessels and the latter in intact vessels.

     

Basilar artery remodelling in the genetically hypertensive rat: effects of nitric oxide synthase inhibition and treatment with valsartan and enalapril

1. The structure of the basilar artery and the relationship of structure to blood pressure and ventricular hypertrophy was examined in genetically hypertensive (GH) rats, their control normotensive (N) Wistar strain, GH given the nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) and GH given L-NAME and either valsartan or enalapril. 2. Systolic blood pressure (SBP; tail-cuff) was measured weekly from age 7-12 weeks. At the end of the experiment at 12 weeks, the basilar artery was fixed by perfusion and embedded in Technovit (Heraeus Kulzer GmbH, Werheim, Germany). Serial sections were cut and stained and stereological analysis applied to quantify the morphology of the vessels. Left ventricular (LV) mass was determined. 3. Both SBP and LV mass were significantly increased in GH compared with N (P < 0.001) and increased further in GH given L-NAME (P < 0.05). The GH L-NAME + valsartan and GH L-NAME + enalapril groups had significantly lower (P < 0.001) SBP and LV mass than the GH L-NAME group. 4. Basilar arteries in GH (which are frankly hypertensive, but have no apparent endothelial defect) showed hypotrophic inward remodelling compared with the N control group with no change in media to lumen ratio. 5. In the GH L-NAME group, further inward remodelling occurred and the media to lumen ratio was increased compared with N (P < 0.01) and GH (P < 0.05). Valsartan treatment in GH L-NAME rats caused eutrophic outward remodelling. Enalapril caused hypertrophic outward remodelling, suggesting that the angiotensin II-stimulated growth was not entirely suppressed with an angiotensin-converting enzyme inhibitor or that there was a bradykinin effect with enalapril. 6. In GH with an endothelial defect induced by treatment with L-NAME, the further remodelling, together with an increased media to lumen ratio and the development of a stroke-like syndrome, indicates the NOS-inhibited GH rat may be a useful model for essential hypertension (where it is known that endothelial abnormalities exist) and where stroke can develop as a consequence of the hypertension.     

Contribution of K+ channels and ouabain-sensitive mechanisms to the endothelium-dependent relaxations of horse penile small arteries

1. Penile small arteries (effective internal lumen diameter of 300–600 μm) were isolated from the horse corpus cavernosum and mounted in microvascular myographs in order to investigate the mechanisms underlying the endothelium-dependent relaxations to acetylcholine (ACh) and bradykinin (BK).
2. In arteries preconstricted with the thromboxane analogue U46619 (3–30 nM), ACh and BK elicited concentration-dependent relaxations, pD₂ and maximal responses being 7.71±0.09 and 91±1% (n=23), and 8.80±0.07 and 89±2% (n=24) for ACh and BK, respectively. These relaxations were abolished by mechanical endothelial cell removal, attenuated by the nitric oxide (NO) synthase (NOS) inhibitor, N^G-nitro-L-arginine (L-NOARG, 100 μM) and unchanged by indomethacin (3 μM). However, raising extracellular K⁺ to concentrations of 20–30 mM significantly inhibited the ACh and BK relaxant responses to 63±4% (P<0.01, n=7) and to 59±4% (P<0.01, n=6), respectively. ACh- and BK-elicited relaxations were abolished in arteries preconstricted with K⁺ in the presence of 100 μM L-NOARG.
3. In contrast to the inhibitor of ATP-sensitive K⁺ channels, the blockers of Ca²⁺-activated K⁺ (K_Ca) channels, charybdotoxin (30 nM) and apamin (0.3 μM), each induced slight but significant rightward shifts of the relaxations to ACh and BK without affecting the maximal responses. Combination of charybdotoxin and apamin did not cause further inhibition of the relaxations compared to either toxin alone. In the presence of L-NOARG (100 μM), combined application of the two toxins resulted in the most effective inhibition of the relaxations to both ACh and BK. Thus, pD₂ and maximal responses for ACh and BK were 7.65±0.08 and 98±1%, and 9.17±0.09 and 100±0%, respectively, in controls, and 5.87±0.09 (P<0.05, n=6) and 38±11% (P<0.05, n=6), and 8.09±0.14 (P<0.01, n=6) and 98±1% (n=6), respectively, after combined application of charybdotoxin plus apamin and L-NOARG.
4. The selective inhibitor of guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 5 μM) did not alter the maximal responses to either ACh or BK, but slightly decreased the sensitivity to both agonists, δpD₂ being 0.25±0.07 (P<0.05, n=6) and 0.62±0.12 (P<0.01, n=6) for ACh and BK, respectively. Combined application of ODQ and charybdotoxin plus apamin produced further inhibition of the sensitivity to both ACh (δpD₂=1.39±0.09, P<0.01, n=6) and BK (1.29±0.11, P<0.01, n=6), compared to either ODQ or charybdotoxin plus apamin alone.
5. Exogenous nitric oxide (NO) present in acidified solutions of sodium nitrite (NaNO₂) and S-nitroso-cysteine (SNC) both concentration-dependently relaxed penile resistance arteries, pD₂ and maximal responses being 4.84±0.06 and 82±3% (n=12), and 6.72±0.07 and 85±4% (n=19), respectively. Charybdotoxin displaced to the right the dose-relaxation curves for both NO (δpD₂ 0.38±0.06, P<0.01, n=6) and SNC (δpD₂ 0.50±0.10, P<0.01, n=5), whereas apamin only reduced sensitivity (δpD₂=0.35±0.12, P<0.05, n=5) and maximum response (65±9%, P<0.05, n=6) to SNC. ODQ shifted to the right the dose-relaxation curves to both NO and SNC. The relaxant responses to either NO or SNC were not further inhibited by a combination of ODQ and charybdotoxin or ODQ and charybdotoxin plus apamin, respectively, compared to either blocker alone.
6. In the presence of 3 μM phentolamine, 5 μM ouabain contracted penile resistance arteries by 50±6% (n=17) of K-PSS, but did not significantly change the relaxant responses to either ACh, BK or NO. However, in the presence of L-NOARG ouabain reduced the ACh- and BK-elicited relaxation from 94±3% to 16±5% (P<0.0001, n=6), and from 98±2% to 13±3% (P<0.0001, n=5), respectively. Combined application of ODQ and ouabain inhibited the relaxations to NO from 92±2% to 26±3% (P<0.0001, n=6).
7. The present results demonstrate that the endothelium-dependent relaxations of penile small arteries involve the release of NO and a non-NO non-prostanoid factor(s) which probably hyperpolarize(s) smooth muscle by two different mechanisms: an increased charybdotoxin and apamin-sensitive K⁺ conductance and an activation of the Na⁺-K⁺ATPase. These two mechanisms appear to be independent of guanylate cyclase stimulation, although NO itself can also activate charybdotoxin-sensitive K⁺ channels and the Na⁺-K⁺ pump through both cyclic GMP-dependent and independent mechanisms, respectively.

     

GTP-binding proteins in cell survival and demise: the emerging picture in the pancreatic beta-cell

It is widely believed that guanine nucleotide-binding regulatory proteins (G-proteins) play central roles as "molecular switches" in a variety of cellular processes ranging from signal transduction to protein and vesicle trafficking. To achieve these regulatory functions, G-proteins form complexes with a wide range of effector molecules whose activities are altered upon interaction with the G-protein. These effector molecules can be either soluble or membrane bound, and it is likely that some are localized to secretory granules where they direct the movement, docking, and fusion of granules during exocytosis. The effector molecules regulated by G-proteins are diverse and include phospholipases, protein kinases, protein phosphatases, ion channels, adenylate cyclases, cytoskeletal elements, as well as secretory vesicle and plasma membrane-associated fusion-proteins. The majority of studies performed in the pancreatic beta-cell have focused on the role of G-proteins in the regulation of insulin secretion, whereas very little attention has been focused on their potential involvement in other cellular processes. Such studies have identified and implicated both heterotrimeric (comprising alpha, beta, and gamma subunits) and monomeric (low molecular mass) G-proteins in the regulation of insulin secretion, but intriguing recent evidence has also begun to emerge which favors the view that they may be involved in the maintenance of beta-cell viability. In the present commentary, we will review this evidence and discuss the current understanding of the role of G-proteins in the life and death of the beta-cell.     

Recent developments in the inhibition of angiogenesis: examples from studies on platelet factor-4 and the VEGF/VEGFR system

Inhibition of angiogenesis is an important strategy to block tumor growth and invasion. We discuss herein results from our ongoing investigations on platelet factor-4 (PF-4) and the VEGF/VEGFR system. Platelet factor-4 (PF-4) is an anti-angiogenic ELR-negative chemokine. PF-4 inhibits endothelial cell proliferation and migration, and angiogenesis in vitro and in vivo. We have studied the structure and anti-angiogenic activities of a C-terminal fragment of PF-4 named PF-4 CTF. This molecule retains anti-angiogenic activity, blocks the interaction of angiogenesis factors with their receptors and may also be improved by mutation or domain-swapping. It seems, therefore, to be a good candidate for further development. Furthermore, we have developed a cyclic vascular endothelial growth inhibitor (Cyclo VEGI) from the structure of VEGF-A. In aqueous solution, cyclo-VEGI adopts an alpha helix conformation. Cyclo-VEGI inhibits binding of iodinated VEGF(165) to endothelial cells and angiogenesis. Furthermore, cyclo-VEGI significantly blocks the growth of established intracranial glioma in nude and syngeneic mice and improves survival.     

Nitric oxide has a role in regulating VLA-4-integrin expression on the human neutrophil cell surface

Recent research demonstrates that the beta1 integrins may be involved in neutrophil migration. Here, we investigate the role of nitric oxide in the expression and function of the very late antigen-4 (VLA-4) and Mac-1 integrins on human neutrophils. Human blood neutrophils were treated with N(omega)-nitro-L-arginine methyl ester (L-NAME) and their adhesion to fibronectin (FN) and serum observed. Adhesion of neutrophils to FN and serum increased significantly following incubation with 0.1mM L-NAME by 65.5 and 44.6%, respectively. Increased adhesions to FN and serum were abolished by a VLA-4-specific monoclonal antibody, HP2/1, and a Mac-1-specific monoclonal antibody, ICRF 44, respectively. The microfilament- and microtubule-depolymerizing agents, dihydrochalasin B and nocodazole, were also able to reverse L-NAME-induced adhesion to both FN and serum. L-NAME induced a discrete increase in the expression of CD49d (VLA-4, 25.3+/-4.8%), but not CD11b, on the neutrophil cell surface, as detected by flow cytometry. Results indicate that NO has a role in regulating VLA-4 and Mac-1 function on the human neutrophil cell surface and that this modulation in integrin function is accompanied by cytoskeletal rearrangements and changes in the ability of the neutrophil to adhere to the extracellular matrix.     

Notoginsenoside Ft1 activates both glucocorticoid and estrogen receptors to induce endothelium-dependent,nitric oxide-mediated relaxations in rat mesenteric arteries

Panax notoginseng (Burk.) F.H. Chen has been used traditionally for the treatment of cardiovascular diseases. Notoginsenoside Ft1 (Ft1) is a bioactive saponin from the leaves of P. notoginseng. Experiments were designed to determine whether or not Ft1 is an endothelium-dependent vasodilator. Rat mesenteric arteries were suspended in organ chambers for the measurement of isometric tension during phenylephrine-induced contractions. The cyclic guanosine monophosphate (cGMP) level was assessed using enzyme immunoassay. The phosphorylation and protein expressions of endothelial nitric oxide synthase (eNOS), glucocorticoid receptors (GR), estrogen receptors beta (ERß), protein kinase B (Akt) and extracellular signal-regulated kinase 1/2 (ERK1/2) were determined by Western blotting. The localization of GR and ERß were determined by immunofluorescence staining. Ft1 caused endothelium-dependent relaxations, which were abolished by l-NAME (inhibitor of nitric oxide synthases) and ODQ (inhibitor of soluble guanylyl cyclase). Ft1 increased the cGMP level in rat mesenteric arteries. GR and ERß were present in the endothelial layer and their antagonism by RU486 and PHTPP, respectively, inhibited Ft1-induced endothelium-dependent relaxations and phosphorylations of eNOS, Akt and ERK1/2. Inhibition of phosphoinositide-3-kinase (PI3K) by wortmannin and ERK1/2 by U0126 reduced Ft1-evoked relaxations and eNOS phosphorylation. Taken in conjunction, the present findings suggest that Ft1 stimulates endothelial GRs and ERßs with subsequent activation of the PI3K/Akt and ERK1/2 pathways in rat mesenteric arteries. This results in phosphorylation of eNOS and the release of NO, which activates soluble guanylyl cyclase in the vascular smooth muscle cells leading to relaxations.