Tissue cGMP Research Articles

Local Action of Neprilysin Exacerbates Pressure Overload Induced Cardiac Remodeling.

[Figure: see text].

Antihypertensive Effect of a Novel Angiotensin II Receptor Blocker Fluorophenyl Benzimidazole: Contribution of cGMP, Voltage-dependent Calcium Channels, and BKCa Channels to Vasorelaxant Mechanisms.

Background: The current study presents the novel angiotensin II receptor blocker fluorophenyl benzimidazole (FPD) as an antihypertensive agent in the SHR model of hypertension. We investigated the role of cGMP, voltage-dependent L-type calcium channels, and BKCa channels in the vasorelaxant mechanisms of FPD in the rat superior mesenteric artery. Methods: The antihypertensive effect of FPD was examined using an invasive technique measuring blood pressure in SHR animals. Using a myograph, tension measurement was completed in the superior mesenteric artery to elucidate the mechanisms of vasorelaxation involving AT1 receptors, the NO/cGMP pathway, L-type calcium channels, and BKCa channels. Ion flux (Ca2+, K+) studies were conducted in aortic smooth muscle cells. Putative targets proteins were determined by in silico docking studies. A safety evaluation of FPD was carried out using Swiss albino mice. Results: FPD significantly decreased blood pressure in SHR. It relaxed superior mesenteric arteries in a concentration-dependent manner and significantly inhibited angiotensin II-induced contraction. The relaxation response was also mediated by an increase in tissue cGMP levels, inhibition of L-type calcium channels, and the opening of BKCa channels. FPD further enhanced efflux of K+ and inhibited Bay K8644-stimulated Ca2+ influx in aortic smooth muscle cells and docked well in an in silico study with the targets. It was well tolerated in the toxicity study. Conclusion: The present study reports the antihypertensive activity of novel AT-1 receptor blocker FPD at 50 and 100 mg kg−1 with cGMP, L-type calcium channels, and BKCa channels as putative targets of vasorelaxation, and was found safe in oral toxicity.

Effect of leech-centipede medicine on improving erectile function in diabetes-induced erectile dysfunction rats via PDE5 signalling pathway-related molecules

Context The leech and centipede granules have good curative effects on many diabetic vascular diseases, including diabetes-induced erectile dysfunction (DIED). Objective To explore the effect of leech and centipede on erectile function in rats with diabetes-induced erectile dysfunction and its possible mechanism. Materials and methods Thirty male Sprague–Dawley DIED rats were randomly divided into the model group (Group M), low-dose group (Group DD), high-dose group (Group DG) and tadalafil group (Group T) (n = 6); diabetic rats were induced by streptozotocin. Apomorphine was used to induce diabetic erectile dysfunction. The ‘leech-centipede’ granules (0.15 and 0.6 g/kg) were intragastrically administered in the DD and DG groups for 8 weeks. Blood glucose, serum insulin, testosterone, cGMP levels and protein expression changes were measured in each group. Results After 8 weeks, the erectile function of rats in the DG group significantly improved (1.26 ± 0.73). Penis tissue cGMP levels were higher in the DG group (1.48 ± 0.11) than in the M group (0.58 ± 0.15). Protein and mRNA expression levels of NOS were significantly higher (0.77 ± 0.05; 0.61 ± 0.02) but those of PDE5 (0.43 ± 0.05; 0.61 ± 0.03) were lower in the DG group than in the M group (0.37 ± 0.06; 0.51 ± 0.01; 0.78 ± 0.06; 0.81 ± 0.04). Conclusion The leech-centipede can improve erectile dysfunction in DIED rats by regulating the expression of cGMP, NOS, and PDE5-related molecules in the PDE5 pathway. This study provides a potential mechanism for the treatment of DIED with leech-centipede.

The NO-donor MPC-1011 stimulates angiogenesis and arteriogenesis and improves hindlimb ischemia via a cGMP-dependent pathway involving VEGF and SDF-1α

Background and aimsPeripheral arterial disease (PAD) is an important cause of morbidity and mortality with little effective medical treatment currently available. Nitric oxide (NO) is crucially involved in organ perfusion, tissue protection and angiogenesis. MethodsWe hypothesized that a novel NO-donor, MPC-1011, might elicit vasodilation, angiogenesis and arteriogenesis and in turn improve limb perfusion, in a hindlimb ischemia model. Hindlimb ischemia was induced by femoral artery ligation in Sprague-Dawley rats, which were randomized to receive either placebo, MPC-1011, cilostazol or both, up to 28 days. Limb blood flow was assessed by laser Doppler imaging. ResultsAfter femoral artery occlusion, limb perfusion in rats receiving MPC-1011 alone or in combination with cilostazol was increased throughout the treatment regimen. Capillary density and the number of arterioles was increased only with MPC-1011. MPC-1011 improved vascular remodeling by increasing luminal diameter in the ischemic limb. Moreover, MPC-1011 stimulated the release of proangiogenic cytokines, including VEGF, SDF1α and increased tissue cGMP levels, reduced platelet activation and aggregation, potentiated proliferation and migration of endothelial cells which was blunted in the presence of soluble guanylyl cyclase inhibitor LY83583. In MPC-1011-treated rats, Lin−/CD31+/CXCR4+ cells were increased by 92.0% and Lin−/VEGFR2+/CXCR4+ cells by 76.8% as compared to placebo. ConclusionsHere we show that the NO donor, MPC-1011, is a specific promoter of angiogenesis and arteriogenesis in a hindlimb ischemia model in an NO-cGMP-VEGF- dependent manner. This sets the basis to evaluate and confirm the efficacy of such therapy in a clinical setting in patients with PAD and impaired limb perfusion.

Skeletal muscle alterations in tachycardia-induced heart failure are linked to deficient natriuretic peptide signalling and are attenuated by RAS-/NEP-inhibition.

BackgroundHeart failure induced cachexia is highly prevalent. Insights into disease progression are lacking.MethodsEarly state of left ventricular dysfunction (ELVD) and symptomatic systolic heart failure (HF) were both induced in rabbits by tachypacing. Tissue of limb muscle (LM) was subjected to histologic assessment. For unbiased characterisation of early and late myopathy, a proteomic approach followed by computational pathway-analyses was performed and combined with pathway-focused gene expression analyses. Specimen of thoracic diaphragm (TD) served as control for inactivity-induced skeletal muscle alterations. In a subsequent study, inhibition of the renin-angiotensin-system and neprilysin (RAS-/NEP) was compared to placebo.ResultsHF was accompanied by loss of protein content (8.7±0.4% vs. 7.0±0.5%, mean±SEM, control vs. HF, p<0.01) and a slow-to-fast fibre type switch, establishing hallmarks of cachexia. In ELVD, the enzymatic set-up of LM and TD shifted to a catabolic state. A disturbed malate-aspartate shuttle went well with increased enzymes of glycolysis, forming the enzymatic basis for enforced anoxic energy regeneration. The histological findings and the pathway analysis of metabolic results drew the picture of suppressed PGC-1α signalling, linked to the natriuretic peptide system. In HF, natriuretic peptide signalling was desensitised, as confirmed by an increase in the ratio of serum BNP to tissue cGMP (57.0±18.6pg/ml/nM/ml vs. 165.8±16.76pg/ml/nM/ml, p<0.05) and a reduced expression of natriuretic peptide receptor-A. In HF, combined RAS-/NEP-inhibition prevented from loss in protein content (8.7±0.3% vs. 6.0±0.6% vs. 8.3±0.9%, Baseline vs. HF-Placebo vs. HF-RAS/NEP, p<0.05 Baseline vs. HF-Placebo, p = 0.7 Baseline vs. HF-RAS/NEP).ConclusionsTachypacing-induced heart failure entails a generalised myopathy, preceding systolic dysfunction. The characterisation of “pre-cachectic” state and its progression is feasible. Early enzymatic alterations of LM depict a catabolic state, rendering LM prone to futile substrate metabolism. A combined RAS-/NEP-inhibition ameliorates cardiac-induced myopathy independent of systolic function, which could be linked to stabilised natriuretic peptide/cGMP/PGC-1α signalling.

Cavernosal hydrogen sulfide levels are associated with nitric oxide and hemeoxygenase levels in diabetic rats.

Penile erection is a neuromuscular event modulated by psyche, hormones as well as neurotransmitters. This pre-clinical study aimed to assess hydrogen sulfide (H2S) relationship with nitric oxide (NO) and hemeoxygenase (HO) in the cavernous tissues of diabetic rats. Overall, 90 adult male rats were investigated (6 groups, n = 15 each). They were subdivided into the following groups; untreated rats, rats treated with H2S donor/inhibitor, induced diabetic rats, diabetic rats treated with H2S donor/inhibitor. At the 6th week, the rats were killed to assess cavernous tissue cGMP, NO, H2S, HO enzyme activity levels. The rats treated with H2S donor showed increased mean cavernous tissue cGMP, NO, H2S, and HO enzyme activity levels whereas induced diabetic rats and rats treated with H2S inhibitor showed significant decreases in these parameters compared with the untreated rats. On the other hands, diabetic rats treated with H2S donor showed elevated mean cavernous tissue cGMP, NO, H2S, and HO enzyme activity levels whereas diabetic rats treated with H2S inhibitor showed significant decreases in these parameters compared with diabetic rats. Cavernous tissue H2S levels exhibited significant positive correlations with the cavernous tissue levels cGMP, NO, and HO enzyme activity levels. From these results, it could be concluded that cavernous tissues H2S plays a role of male sexual health by affecting cavernous tissues NO and HO enzyme activity in general and in diabetics in particular.

Modulation of BAY 41-2272-induced-relaxation in normotensive and hypertensive rat aorta by perivascular adipose tissue

In spontaneously hypertensive rat (SHR), perivascular adipose tissue (PVAT) has been recently identified as the effector of vascular dysfunction. In order to restore this alteration, therapeutic strategies target the cGMP/PKG pathway which is involved in both vascular and adipose tissue functions. However, direct activation of soluble guanylate cyclase, a key enzyme of this signalling pathway has not been studied yet in arterial hypertension. This study was designed to determine whether relaxation induced by BAY 41-2272, a soluble guanylate cyclase stimulator agent, was modified in SHR aorta and whether PVAT modulates this effect. Aortic rings isolated from 12-week-old Wistar Kyoto (WKY) rats and SHR were mounted in organ baths and pre-constricted with phenylephrine. Cumulative concentration-response curves to BAY 41-2272 (0.1 nM to 30 μM) were constructed in different experimental conditions in the absence or presence of endothelium and PVAT. In the absence of PVAT, BAY 41-2272 produced concentration-dependent relaxation, which was inhibited by L-NAME (100 μM), a nitric oxide (NO) synthase inhibitor only in WKY rat aorta. Endothelium denudation enhanced the BAY 41-2272-induced-relaxation only in SHR aorta. In both rat strains, relaxant effect to BAY 41-2272 was attenuated by PVAT and this was associated with a decrease in tissue cGMP content. NO and cyclo-oxygenases (COX)-derived products do not appear to participate to this impairment since 100 μM L-NAME and 10 μM indomethacin, a non-specific COX inhibitor, do not modify the BAY 41-2272-induced-relaxation. We showed for the first time that BAY 41-2272 partially relaxes WKY rat aorta by NO-dependent-mechanism and that the endothelium negatively modulates the BAY 41-2272-induced-relaxation only in hypertensive rats. The decrease of BAY 41-2272-induced-relaxation in SHR aorta by PVAT suggests the release of adipose contracting factors that need further elucidation.

Enhancement of Nitric Oxide Production Is Responsible for Minimal Intimal Hyperplasia of Autogenous Rabbit Arterial Grafts.

Vascular endothelium induces smooth muscle cell (SMC) relaxation mainly mediated by endothelium-derived nitric oxide (EDNO) and endothelium-derived hyperpolarizing factor (EDHF). It has previously been reported that functions of these endothelium factors have been greatly impaired in vein grafts. The present study was undertaken to determine whether the functions of EDNO and EDHF might be altered in artery graft.Methods and Results:In rabbits, the right carotid artery was excised and implanted in its original position as an autogenous graft ("artery graft") and the non-operated left carotid artery served as the "control artery". Histochemical changes, acetylcholine (ACh)-induced effects on the intracellular concentration of Ca2+([Ca2+]i) in endothelial cells, endothelium-dependent SMC hyperpolarization and relaxation, and tissue cGMP content were examined on post-operative day 28. "Artery graft" displayed a minimal amount of intimal hyperplasia. When compared with the "control artery", it exhibited greater ACh-induced, endothelium-dependent relaxation, but the reverse was true when EDNO production was blocked. In the "artery graft" (vs. the "control artery"), basal cGMP content was greater, whereas the [Ca2+]iincrease in endothelial cells and the endothelium-dependent SMC-hyperpolarization induced by ACh were less. It is suggested that the [Ca2+]i-independent EDNO production covers the loss of function of endothelium-dependent SMC hyperpolarization and minimizes intimal hyperplasia caused by surgical operation in autogenous carotid artery graft.

Effects of Biotin Supplementation in the Diet on Adipose Tissue cGMP Concentrations, AMPK Activation, Lipolysis, and Serum-Free Fatty Acid Levels.

Several studies have shown that pharmacological concentrations of biotin decrease hyperlipidemia. The molecular mechanisms by which pharmacological concentrations of biotin modify lipid metabolism are largely unknown. Adipose tissue plays a central role in lipid homeostasis. In the present study, we analyzed the effects of biotin supplementation in adipose tissue on signaling pathways and critical proteins that regulate lipid metabolism, as well as on lipolysis. In addition, we assessed serum fatty acid concentrations. Male BALB/cAnN Hsd mice were fed a control or a biotin-supplemented diet (control: 1.76 mg biotin/kg; supplemented: 97.7 mg biotin/kg diet) over 8 weeks postweaning. Compared with the control group, biotin-supplemented mice showed an increase in the levels of adipose guanosine 3',5'-cyclic monophosphate (cGMP) (control: 30.3±3.27 pmol/g wet tissue; supplemented: 49.5±3.44 pmol/g wet tissue) and of phosphorylated forms of adenosine 5'-monophosphate-activated protein kinase (AMPK; 65.2%±1.06%), acetyl-coenzyme A (CoA), carboxylase-1 (196%±68%), and acetyl-CoA carboxylase-2 (78.1%±18%). Serum fatty acid concentrations were decreased (control: 1.12±0.04 mM; supplemented: 0.91±0.03 mM), and no change in lipolysis was found (control: 0.29±0.05 μmol/mL; supplemented: 0.33±0.08 μmol/mL). In conclusion, 8 weeks of dietary biotin supplementation increased adipose tissue cGMP content and protein expression of the active form of AMPK and of the inactive forms of acetyl-CoA carboxylase-1 and acetyl-CoA carboxylase-2. Serum fatty acid levels fell, and no change in lipolysis was observed. These findings provide insight into the effects of biotin supplementation on adipose tissue and support its use in the treatment of dyslipidemia.

Vasorelaxant effect of propentofylline in isolated equine digital veins

We evaluated the vasorelaxant effect of propentofylline (PPF), a methylxanthine derivative, and its mechanism of action in equine digital veins (EDVs). Cumulative concentration-response curves to PPF (1nM–300µM) were recorded in phenylephrine-precontracted EDV rings under different experimental conditions. PPF-induced relaxation was partially inhibited by endothelium removal, but was unaltered by CGS-15943 (an adenosine receptor antagonist; 3µM). PPF-induced relaxation was partially inhibited in the presence of L-NAME (a nitric oxide (NO) synthase inhibitor; 100µM), ODQ (an inhibitor of soluble guanylyl cyclase; 30µM) or Rp-8-Br-PET-cGMP-S (a protein kinase G inhibitor; 3µM). It was not modified by indomethacin (a non-selective cyclooxygenase (COX) inhibitor; 10µM), and was slightly potentiated by H-89 (a protein kinase A inhibitor; 2µM). In endothelium-intact EDVs, PPF-induced relaxation was associated with a 2.4- and 24.1-fold increase in the tissue cGMP and cAMP content respectively. PPF (100μM) did not shift the concentration–response curve to phenylephrine (1nM–300µM) but reduced the maximal effect. To investigate whether PPF can affect cAMP- and cGMP-induced relaxations, relaxation curves to forskolin (an activator of adenylate cyclase) and to sodium nitroprusside (SNP, a NO donor) were recorded in EDV rings pretreated with PPF (100µM). PPF only slightly potentiated the forskolin-induced relaxation without affecting the SNP-induced relaxation. We demonstrated that PPF-induced relaxation in EDVs is partially endothelium-dependent. The PPF-induced relaxation partially occurred via NO release and both cAMP and cGMP generation, through COX-independent mechanisms but could also result from the inhibition of cAMP-phosphodiesterase activity for the highest concentrations.

P13: Revascularization in chronically ischemic tissue is improved by dietary nitrate supplementation

Purpose Revascularization is an adaptive repair mechanism that restores blood flow to undersupplied ischemic tissue. Nitric oxide (NO ) plays an important role in this process. Whether dietary nitrate, serially reduced to nitrite by commensal bacteria in the oral cavity and subsequently to NO , enhances ischemia-induced remodeling of the vascular network is not known. The present study was to assess the effects of dietary nitrate supplementation on ischemia-induced revascularization. Methods Mice were treated with either nitrate (1 g/L sodium nitrate in drinking water) or sodium chloride (control) for 14 days. At day 7, unilateral hindlimb surgery with excision of the left femoral artery was conducted. Blood flow was determined by laser doppler. Capillary density, myoblast apoptosis, mobilization of CD34+/Flk-1+, migration of bone-marrow derived CD31+/CD45−, plasma nitrite, nitrate and nitrosothiols as well as skeletal tissue cGMP levels were assessed. EGFP (enhanced green fluorescence protein) transgenic mice were used for bone marrow transplantation. Results Dietary nitrate supplementation leads to increased circulating nitrosothiol levels. Moreover nitrate supplementation enhances revascularization, increases mobilization of CD34+/Flk-1+ and migration of bone-marrow derived CD31+/CD45− cells to the site of ischemia, and attenuates apoptosis of potentially regenerative myoblasts in chronically ischemic tissue. The regenerative effects of nitrate treatment were abolished by eradicating nitrate-reducing bacteria in the oral cavity through an antiseptic mouthwash. Conclusions Chronic dietary nitrate supplementation may represent a novel nutrition-based strategy to enhance ischemia-induced revascularization. Disclosure Nothing to disclose.

Contribution of Estrogen to Sex Dimorphic Expression of Cardiac Natriuretic Peptide and Nitric Oxide Synthase Systems in ANP Gene-Disrupted Mice

Background: Sex dimorphism in the prevalence, onset, development and progression of cardiovascular disease (CVD) is well recognized, but the mechanisms whereby sex hormones are believed to confer cardioprotection are still not fully understood. Objective: This study more closely delineates the effect of 17β-Estradiol (E2) on the expression and signaling of the cardiac NP and NOS systems, well-known cardioprotective modulators of the cardiac hypertrophy (CH) response, that both contribute to downstream production of cyclic guanosine 3’,5’-monophosphate (cGMP). Materials and Methods: Ovariectomized (OVX) female ANP+/+ and ANP-/- mice, 6 - 7 weeks old, were subjected to a five-week treatment with E2 (100 μg/100 μL/day) or vehicle (VEH). Left ventricle from these treatment groups, along with that from age-matched male ANP+/+ and ANP-/- mice was used to assess expression of these systems by real-time quantitative PCR (qPCR). Left ventricle tissue and plasma cGMP were measured by enzyme immunoassay to assess alterations in resultant downstream signaling. Results: NP system expression was unchanged across genotype, sex and E2 treatment. Sex-specific differences in NOS system expression were observed; female mice showed an increased expression of NOS system genes that were significantly elevated in all but one of the E2 treatment groups. Left ventricle tissue cGMP remained unchanged across genotype, sex and E2 treatment. Plasma cGMP levels were unchanged in ANP+/+ treatment groups. In ANP-/- treatment groups, plasma cGMP in the female OVX-E2 mice was significantly higher compared to male and female OVX-VEH mice. Conclusion: These findings demonstrate that in the absence of ANP, E2 upregulates cardiac NOS system expression to produce cGMP. This study confirms the importance of the cardiac NOS system in females; this particular system may be a promising future target for sex-specific treatments and therapies for CVD in women.

PDE5 inhibition against acute renal ischemia reperfusion injury in rats: does vardenafil offer protection?

To evaluate the effect of vardenafil on renal function after renal ischemia-reperfusion (IR) injury (IRI) in a rat model. Seventy-one Wistar rats were divided into 7 groups including (1) a vehicle-treated group, (2) a vehicle pretreated-IR group, (3-6) vardenafil pretreated-IR groups in doses of 0.02, 0.2, 2 and 20 μg/kg, respectively, (7) a group of IR followed by treatment with 2 μg/kg of vardenafil. Vardenafil or vehicle solution was administered one hour before unilateral nephrectomy and the induction of 45 min of ischemia on the contralateral kidney by clamping of renal pedicle. Four hours of reperfusion were allowed after renal ischemia. Studied parameters were serum creatinine, fractional excretion of sodium (FENa), and histological evaluation of renal specimens. In addition, renal tissue cGMP levels, ERK1/2 phosphorylation as well as renal function by renal scintigraphy were also evaluated. Administration of vardenafil before the induction of ischemia resulted in a significant reduction in creatinine and FENa levels as well as in less histological lesions observed in treated kidneys in comparison with the vehicle-treated group. The underlying mechanism of cytoprotection was cGMP depended and involved the phosphorylation of ERK proteins. Renal scintigraphy confirmed that PDE5 inhibition attenuates renal IRI. Vardenafil attenuates renal IRI. Based on similar results from relevant studies on other PDE-5 inhibitors in renal and cardiac IRI, it can be assumed that all PDE-5 inhibitors share a common mechanism of cytoprotection.

Dietary Nitrate Supplementation Improves Revascularization in Chronic Ischemia

Revascularization is an adaptive repair mechanism that restores blood flow to undersupplied ischemic tissue. Nitric oxide plays an important role in this process. Whether dietary nitrate, serially reduced to nitrite by commensal bacteria in the oral cavity and subsequently to nitric oxide and other nitrogen oxides, enhances ischemia-induced remodeling of the vascular network is not known. Mice were treated with either nitrate (1 g/L sodium nitrate in drinking water) or sodium chloride (control) for 14 days. At day 7, unilateral hind-limb surgery with excision of the left femoral artery was conducted. Blood flow was determined by laser Doppler. Capillary density, myoblast apoptosis, mobilization of CD34(+)/Flk-1(+), migration of bone marrow-derived CD31(+)/CD45(-), plasma S-nitrosothiols, nitrite, and skeletal tissue cGMP levels were assessed. Enhanced green fluorescence protein transgenic mice were used for bone marrow transplantation. Dietary nitrate increased plasma S-nitrosothiols and nitrite, enhanced revascularization, increased mobilization of CD34(+)/Flk-1(+) and migration of bone marrow-derived CD31(+)/CD45(-) cells to the site of ischemia, and attenuated apoptosis of potentially regenerative myoblasts in chronically ischemic tissue. The regenerative effects of nitrate treatment were abolished by eradication of the nitrate-reducing bacteria in the oral cavity through the use of an antiseptic mouthwash. Long-term dietary nitrate supplementation may represent a novel nutrition-based strategy to enhance ischemia-induced revascularization.

Chronic inhibition of nitric oxide synthase activity by NG-nitro-l-arginine induces nitric oxide synthase expression in the developing rat cerebellum

Studies on chronic inhibition of NO synthase (NOS) in the CNS suggest a plastic change in NO synthesis in areas related to motor control, which might protect the animal from the functional and behavioral consequences of NO deficiency. In the present study, the acute and chronic effect of the substrate analogue inhibitor N G -nitro- l -arginine (L-NNA) was examined on NO production, NO-sensitive cGMP levels and the expression of NOS isoforms in the developing rat cerebellum. Acute intraperitoneal administration of the inhibitor (5–200 mg/kg) to 21-day old rats reduced NOS activity and NO concentration dose dependently by 70–90% and the tissue cGMP level by 60–80%. By contrast, chronic application of L-NNA between postnatal days 4–21 diminished the total NOS activity and NO concentration only by 30%, and the tissue cGMP level by 10–50%. Chronic treatment of 10 mg/kg L-NNA induced nNOS expression in granule cells, as revealed by in situ hybridization, NADPH-diaphorase histochemistry and Western-blot, but it had no significant influence on tissue cGMP level or on layer formation of the cerebellum. However, a higher concentration (50 mg/kg) of L-NNA decreased the intensity of the NADPH-diaphorase reaction in granule cells, significantly reduced cGMP production, and retarded layer formation and induced iNOS expression and activity in glial cells. Treatments did not affect eNOS expression. The present findings suggest the existence of a concentration-dependent compensatory mechanism against experimentally-induced chronic inhibition of NOS, including nNOS or iNOS up-regulation, which might maintain a steady-state NO level in the developing cerebellum.

Chronic inhibition of nitric oxide synthase activity by NG-nitro-l-arginine induces nitric oxide synthase expression in the developing rat cerebellum

Studies on chronic inhibition of nitric oxide synthase (NOS) in the CNS suggest a plastic change in nitric oxide (NO) synthesis in areas related to motor control, which might protect the animal from the functional and behavioral consequences of NO deficiency. In the present study, the acute and chronic effect of the substrate analogue inhibitor NG-nitro-l-arginine (l-NNA) was examined on NO production, NO-sensitive cyclic guanosine monophosphate (cGMP) levels and the expression of NOS isoforms in the developing rat cerebellum. Acute intraperitoneal administration of the inhibitor (5–200mg/kg) to 21-day-old rats reduced NOS activity and NO concentration dose dependently by 70–90% and the tissue cGMP level by 60–80%. By contrast, chronic application of l-NNA between postnatal days 4–21 diminished the total NOS activity and NO concentration only by 30%, and the tissue cGMP level by 10–50%. Chronic treatment of 10mg/kg l-NNA induced neuronal (n)NOS expression in granule cells, as revealed by in situ hybridization, NADPH-diaphorase histochemistry and Western-blot, but it had no significant influence on tissue cGMP level or on layer formation of the cerebellum. However, a higher concentration (50mg/kg) of l-NNA decreased the intensity of the NADPH-diaphorase reaction in granule cells, significantly reduced cGMP production, and retarded layer formation and induced inducible (i)NOS expression & activity in glial cells. Treatments did not affect endothelial (e)NOS expression. The administration of the biologically inactive isomer D-NNA (50mg/kg) or saline was ineffective. The present findings suggest the existence of a concentration-dependent compensatory mechanism against experimentally-induced cronich inhibition of NOS, including nNOS or iNOS up-regulation, which might maintain a steady-state NO level in the developing cerebellum.

Towards a new treatment for equine acute laminitis: The importance of signalling pathways

We evaluated the vasorelaxant effect of propentofylline (PPF), a methylxanthine derivative, and its mechanism of action in equine digital veins (EDVs). Cumulative concentration-response curves to PPF (1 nM–300 µM) were recorded in phenylephrine-precontracted EDV rings under different experimental conditions. PPF-induced relaxation was partially inhibited by endothelium removal, but was unaltered by CGS-15943 (an adenosine receptor antagonist; 3 µM). PPF-induced relaxation was partially inhibited in the presence of L-NAME (a nitric oxide (NO) synthase inhibitor; 100 µM), ODQ (an inhibitor of soluble guanylyl cyclase; 30 µM) or Rp-8-Br-PET-cGMP-S (a protein kinase G inhibitor; 3 µM). It was not modified by indomethacin (a non-selective cyclooxygenase (COX) inhibitor; 10 µM), and was slightly potentiated by H-89 (a protein kinase A inhibitor; 2 µM). In endothelium-intact EDVs, PPF-induced relaxation was associated with a 2.4- and 24.1-fold increase in the tissue cGMP and cAMP content respectively. PPF (100 μM) did not shift the concentration–response curve to phenylephrine (1 nM–300 µM) but reduced the maximal effect. To investigate whether PPF can affect cAMP- and cGMP-induced relaxations, relaxation curves to forskolin (an activator of adenylate cyclase) and to sodium nitroprusside (SNP, a NO donor) were recorded in EDV rings pretreated with PPF (100 µM). PPF only slightly potentiated the forskolin-induced relaxation without affecting the SNP-induced relaxation. We demonstrated that PPF-induced relaxation in EDVs is partially endothelium-dependent. The PPF-induced relaxation partially occurred via NO release and both cAMP and cGMP generation, through COX-independent mechanisms but could also result from the inhibition of cAMP-phosphodiesterase activity for the highest concentrations.

Vasodilatory effect of pentoxifylline in isolated equine digital veins

The direct vasodilatory action of pentoxifylline (1-(5-oxohexyl)-3,7-dimethylxanthine) and its signalling pathway was evaluated in equine digital veins. Cumulative concentration-response curves to pentoxifylline (1 nM to 300 μM) were recorded in phenylephrine-precontracted equine digital vein rings under different experimental conditions. Relaxation to pentoxifylline was partially inhibited by endothelium removal, but was unaltered by CGS-15943 (a non-xanthine adenosine receptor antagonist; 3 μM). Nitric oxide synthase (NOS), soluble guanylate cyclase and cyclooxygenase (COX) inhibitors (Nω-nitro-L-arginine methyl ester (100 μM), ODQ (30 μM) and indomethacin (10 μM), respectively) significantly reduced the maximum relaxation induced by pentoxifylline. Moreover, pentoxifylline-induced relaxation was strongly reduced by Rp-8-Br-PET-cyclic guanosine monophosphate-S (a protein kinase G inhibitor; 3 μM), but remained unaffected by H-89 (a protein kinase A inhibitor; 2 μM). Pentoxifylline-induced relaxation was associated with a 3.4-fold increase in tissue cGMP content. To investigate whether pentoxifylline can affect cAMP- and cGMP-mediated relaxations, curves to forskolin, to sodium nitroprusside (SNP) and 8-bromo-cGMP were also recorded in endothelium-denuded equine digital vein rings pretreated with pentoxifylline (10 and 100 μM). Pentoxifylline only potentiated the SNP-mediated relaxation at the highest concentration (100 μM). Thus, pentoxifylline relaxed equine digital veins via endothelium-dependent and endothelium-independent components. The effect was mediated through both the NOS and COX pathways and could also result from inhibition of cGMP specific-phosphodiesterase activity at the highest concentrations used.

Increased cavernosal relaxation by Phoneutria nigriventer toxin, PnTx2-6, via activation at NO/cGMP signaling

Erectile dysfunction mechanisms in diabetic patients are multifactorial and often lead to resistance to current therapy. Animal toxins have been used as pharmacological tools to study penile erection. Human accidents involving the venom of Phoneutria nigriventer spider are characterized by priapism. We hypothesize that PnTx2-6 potentiates cavernosal relaxation in diabetic mice by increasing cGMP. This effect is nNOS dependent. Cavernosal strips were contracted with phenylephrine (10−5 M) and relaxed by electrical field stimulation (EFS, 20V, 1–32 Hz) in the presence or absence of PnTx2-6 (10−8 M).Cavernosal strips from nNOS and eNOS knocaut (KO) mice, besides nNOS inhibitor (10−5M), were used to evaluate the role of this enzyme in the potentiation effect evoked by PnTx2-6. Tissue cGMP levels were determined after stimulation with PnTx2-6 in presence or absence of L-NAME (10−4M) and ω-conotoxin GVIA (10−6M), an N-type calcium channel inhibitor. Results showed PnTx2-6 enhanced cavernosal relaxation in diabetic mice (65%) and eNOS KO mice, but not in nNOS KO mice. The toxin effect in the cavernosal relaxation was abolished by nNOS inhibitor. cGMP levels are increased by PnTx2-6, however L-NAME abolished this enhancement as well as ω-conotoxin GVIA. We conclude PnTx2-6 facilitates penile relaxation in diabetic mice through a mechanism dependent on nNOS, probably via increasing NO/cGMP production.

Differential relaxant responses of guinea-pig lung strips and bronchial rings to sodium nitroprusside: a mechanism independent of cGMP formation.

The biochemical mechanism subserving smooth muscle relaxant effects of sodium nitroprusside was examined on U46619, 9,11-dideoxy-9 alpha,11 alpha-methanoepoxy PGF2 alpha, precontracted guinea-pig lung strips and hilar bronchial rings. Lung strips were resistant to the relaxant action of sodium nitroprusside or sodium nitrite (NaNO2), whereas they markedly relaxed to 8-bromo-cyclic GMP (8-Br-cGMP), a membrane permeable analogue of cGMP. Precontracted bronchial rings completely relaxed to sodium nitroprusside, NaNO2, or 8-Br-cGMP in a concentration-dependent manner. Sodium nitroprusside (10 microM) substantially raised tissue cGMP level in lung strips. Conversely, sodium nitroprusside had no detectable effect on cGMP levels in bronchial rings. In the presence of 10 microM dipyridamole, an agent which preferentially inhibits cGMP-specific phosphodiesterase, cGMP levels in lung strips treated with sodium nitroprusside was significantly enhanced, but sodium nitroprusside demonstrated no relaxant effect on the preparations. However, dipyridamole potentiated sodium nitroprusside-induced precontracted bronchial ring relaxation without affecting the bronchial tissue cGMP level. In the presence of 10 microM LY83583 (6-anilino-5,8-quinoline-dione), a specific cGMP concentration-lowering agent, sodium nitroprusside-mediated elevation of cGMP level in lung strips was significantly reduced with no effect on the functional response. LY83583 demonstrated no inhibitory effect on either relaxation or cGMP level in bronchial rings treated with sodium nitroprusside. Our results suggest that precontracted smooth muscle in lung strips and in hilar bronchi respond distinctly to sodium nitroprusside. Furthermore, sodium nitroprusside mediates bronchial smooth muscle relaxation by mechanisms unrelated to cGMP.