Vascular Hypercontractility Research Articles

Unraveling endothelin-1 induced hypercontractility of human pulmonary artery smooth muscle cells from patients with pulmonary arterial hypertension.

Contraction of human pulmonary artery smooth muscle cells (HPASMC) isolated from pulmonary arterial hypertensive (PAH) and normal (non-PAH) subject lungs was determined and measured with real-time electrical impedance. Treatment of HPASMC with vasoactive peptides, endothelin-1 (ET-1) and bradykinin (BK) but not angiotensin II, induced a temporal decrease in the electrical impedance profile mirroring constrictive morphological change of the cells which typically was more robust in PAH as opposed to non-PAH cells. Inhibition with LIMKi3 and a cofilin targeted motif mimicking cell permeable peptide (MMCPP) had no effect on ET-1 induced HPASMC contraction indicating a negligible role for these actin regulatory proteins. On the other hand, a MMCPP blocking the activity of caldesmon reduced ET-1 promoted contraction pointing to a regulatory role of this protein and its activation pathway in HPASMC contraction. Inhibition of this MEK/ERK/p90RSK pathway, which is an upstream regulator of caldesmon phosphorylation, reduced ET-1 induced cell contraction. While the regulation of ET-1 induced cell contraction was found to be similar in PAH and non-PAH cells, a key difference was the response to pharmacological inhibitors and to siRNA knockdown of Rho kinases (ROCK1/ROCK2). The PAH cells required much higher concentrations of inhibitors to abrogate ET-1 induced contractions and their contraction was not affected by siRNA against either ROCK1 or ROCK2. Lastly, blocking of L-type and T-type Ca2+ channels had no effect on ET-1 or BK induced contraction. However, inhibiting the activity of the sarcoplasmic reticulum Ca2+ ATPase blunted ET-1 and BK induced HPASMC contraction in both PAH and non-PAH derived HPASMC. In summary, our findings here together with previous communications illustrate similarities and differences in the regulation PAH and non-PAH smooth muscle cell contraction relating to calcium translocation, RhoA/ROCK signaling and the activity of caldesmon. These findings may provide useful tools in achieving the regulation of the vascular hypercontractility taking place in PAH.

Vascular dysfunction in obese diabetic db/db mice involves the interplay between aldosterone/mineralocorticoid receptor and Rho kinase signaling

Activation of aldosterone/mineralocorticoid receptors (MR) has been implicated in vascular dysfunction of diabetes. Underlying mechanisms are elusive. Therefore, we investigated the role of Rho kinase (ROCK) in aldosterone/MR signaling and vascular dysfunction in a model of diabetes. Diabetic obese mice (db/db) and control counterparts (db/+) were treated with MR antagonist (MRA, potassium canrenoate, 30 mg/kg/day, 4 weeks) or ROCK inhibitor, fasudil (30 mg/kg/day, 3 weeks). Plasma aldosterone was increased in db/db versus db/+. This was associated with enhanced vascular MR signaling. Norepinephrine (NE)-induced contraction was increased in arteries from db/db mice. These responses were attenuated in mice treated with canrenoate or fasudil. Db/db mice displayed hypertrophic remodeling and increased arterial stiffness, improved by MR blockade. Vascular calcium sensitivity was similar between depolarized arteries from db/+ and db/db. Vascular hypercontractility in db/db mice was associated with increased myosin light chain phosphorylation and reduced expression of PKG-1α. Vascular RhoA/ROCK signaling and expression of pro-inflammatory and pro-fibrotic markers were exaggerated in db/db mice, effects that were attenuated by MRA. Fasudil, but not MRA, improved vascular insulin sensitivity in db/db mice, evidenced by normalization of Irs1 phosphorylation. Our data identify novel pathways involving MR-RhoA/ROCK-PKG-1 that underlie vascular dysfunction and injury in diabetic mice.

Endothelial Nitric Oxide Synthase-Induced Hypertrophy and Vascular Dysfunction Contribute to the Left Ventricular Dysfunction in Caveolin-1−/− Mice

BackgroundCaveolin-1 (Cav1)−/− mice display impaired development of left ventricular pressure and increased left ventricular wall thickness but no dilated ventricle; these are typical findings in patients with heart failure with preserved ejection fraction (HfpEF). Aiming to clarify if dysfunctional endothelial nitric oxide synthase (eNOS) influences cardiomyocyte contractility, cardiac conduction system, or afterload/vascular resistance, we studied Cav1−/−/eNOS−/− mice. MethodsCardiac function was assessed in vivo by pressure-volume-catheterization of the left ventricle, echocardiography and electrocardiography. In addition, isolated tissue experiments were performed to evaluate cardiomyocyte contractility (atria) and vessel morphology and function (aorta). Histology, immunoblotting and quantitative polymerase chain reaction were applied to characterise radical formation and oxidative stress in the heart. ResultsCardiac hypertrophy was completely reversed in Cav1−/−/eNOS−/− mice. The impaired pump function in Cav1−/− mice was significantly improved in Cav1−/−/eNOS−/− mice, but no complete alignment with eNOS−/− controls was achieved, indicating an additional eNOS-independent mechanism contributing to HFpEF in Cav1−/− mice. It is unlikely that frequently occurring arrhythmias contributed to HFpEF in Cav1−/− mice. In contrast, numerous eNOS-dependent and eNOS-independent vascular abnomalities could explain the cardiac phenotypes of Cav1−/− mice. ConclusionsSynergistic effects between eNOS-related cardiac hypertrophy and vascular hypercontractility appear to underlie the left ventricular dysfunction in Cav1−/−mice. These findings provide insights relevant to the poorly understood pathophysiology of HFpEF.

Abstract 029: Nox5 is a Pro-contractile Nox Isoform - Implications in Vascular Contraction and Cardiac Fibrosis

The functional significance of Nox5 is unknown. Considering the fact that Nox5 is closely associated with changes in [Ca 2+ ] and that it generates ROS, both of which are important in contraction, we questioned whether Nox5 plays a role in pro-contractile signaling and whether it influences vascular function. We generated humanised Nox5 mice with Nox5 expressed in a VSMC-specific manner (Nox5+SM22+). Vascular contraction was measured by myography. ROS production was assessed by HPLC, amplex red and ELISA. Protein levels were evaluated by immunoblotting. Fibrosis was assessed by Picro Sirius red staining and polarized microscopy. Contraction to U46619 was increased in Nox5+/SM22+ mice (5.8±0.3 mN vs WT: 4.2±0.2 mN, p<0.05), an effect blocked by a NAC (ROS scavenger), calmidazolium (calmodulin inhibitor), dantrolene (ryanodine receptor Ca 2+ channel inhibitors) and CDN1163 (SERCA channel activator). ONOO - levels were increased in vessels from Nox5+/SM22+ (5.8±0.9 vs WT 3.4±0.1 AU/mg, p<0.05). ZIPK is an important regulator of MYPT1 inactivation. In vessels from Nox5+/SM22+ mice, ZIPK activation was increased (58.6±3.64 vs 27.73±7.64 AU, p<0.05). VSMC-Nox5 exhibited increased cardiac levels of superoxide (WT: 606.3±78.5 vs 1456.0±184.8 nmol/mg of protein), H2O2 (WT: 11.1±1.3 vs 23.88±5.1 μM/μg of protein) lipid peroxidation (WT: 0.70±0.09 vs 1.18±0.18 nmol/ μg of protein), cardiac fibrosis (WT: 3.46±1.71 vs 4.39±0.04 AU), p38 MAPK activation (WT:0.98±0.04 vs 1.61±0.12 AU) and fibronectin expression (WT:1.23±0.07 vs 2.31±0.29 AU) (p<0.05). Moreover, peroxiredoxin oxidation was increased (WT: 1.43±0.4 vs 6.28±2.0 AU, p<0.05). In VSMCs, downregulation of Nox5, but not Nox1,2,4, by siRNA was associated with reduced phosphorylation of MLC20 and MYPT1. In conclusion, our results demonstrate that Nox5 regulates vascular contraction through processes that involve , ROS, calmodulin, ryanodine and ER-Ca 2+ channels. Nox5 may be an important regulator of the contractile machinery in VSMCs. In addition, VSMC-Nox5 induces oxidative stress in the heart, leading to fibrosis. Our study defines a novel role for Nox5 as a pro-contractile Nox isoform that may have important implications in conditions associated with vascular hypercontractility.

Matrix Metalloproteinase-2 Activity is Associated with Divergent Regulation of Calponin-1 in Conductance and Resistance Arteries in Hypertension-induced Early Vascular Dysfunction and Remodelling.

Matrix metalloproteinase (MMP)-2 participates in hypertension-induced maladaptive vascular remodelling by degrading extra- and intracellular proteins. The consequent extracellular matrix rearrangement and phenotype switch of vascular smooth muscle cells (VSMCs) lead to increased cellular migration and proliferation. As calponin-1 degradation by MMP-2 may lead to VSMC proliferation during hypertension, the hypothesis of this study is that increased MMP-2 activity contributes to early hypertension-induced maladaptive remodelling in conductance and resistance arteries via regulation of calponin-1. The main objective was to analyse whether MMP-2 exerts similar effects on the structure and function of the resistance and conductance arteries during early hypertension. Two-kidney, one-clip (2K-1C) hypertensive male rats and corresponding controls were treated with doxycycline (30 mg/kg/day) or water until reaching one week of hypertension. Systolic blood pressure was increased in 2K-1C rats, and doxycycline did not reduce it. Aortas and mesenteric arteries were analysed. MMP-2 activity and expression were increased in both arteries, and doxycycline reduced it. Significant hypertrophic remodelling and VSMC proliferation were observed in aortas but not in mesenteric arteries of 2K-1C rats. The contractility of mesenteric arteries to phenylephrine was increased in 2K-1C rats, and doxycycline prevented this alteration. The potency of phenylephrine to contract aortas of 2K-1C rats was increased, and doxycycline decreased it. Whereas calponin-1 expression was increased in 2K-1C mesenteric arteries, calponin-1 was reduced in aortas. Doxycycline treatment reverted changes in calponin-1 expression. MMP-2 contributes to hypertrophic remodelling in aortas by decreasing calponin-1 levels, which may result in VSMC proliferation. On the other hand, MMP-2-dependent increased calponin-1 in mesenteric arteries may contribute to vascular hypercontractility in 2K-1C rats. Divergent regulation of calponin-1 by MMP-2 may be an important mechanism that leads to maladaptive vascular effects in hypertension.

Sildenafil (Viagra®) Prevents Cox-1/ TXA2 Pathway-Mediated Vascular Hypercontractility in ApoE-/- Mice

Background/Aims: The atherosclerotic apolipoprotein E-deficient (apoE^-/-) mouse exhibits impaired vasodilation and enhanced vasoconstriction responsiveness. The objectives of this study were: a) to determine the relative contribution of cyclooxygenases (Cox-1 and Cox-2), thromboxane A2 (TXA2) and endothelin-1 (ET-1) to enhancing vascular hyperresponsiveness in this model of atherosclerosis and b) to investigate the beneficial effects of the phosphodiesterase 5 inhibitor sildenafil on this endothelial dysfunction. Methods: Adult male apoE^-/- mice were treated with sildenafil (40 mg/kg/day, for 3 weeks) and compared with non-treated ApoE^-/- and wild-type mice. The beneficial effects of sildenafil on vascular contractile response to phenylephrine (PE) in aortic rings were evaluated before and after incubation with Cox-1 (SC-560) or Cox-2 (NS-398) inhibitors or the TP antagonist SQ-29548, and on contractile responsiveness to ET-1. Results: ApoE^-/- mice exhibited enhanced vasoconstriction to PE (R_max ∼35%, p<0.01), which was prevented by treatment with sildenafil. The enhanced PE-induced contractions were abolished by both Cox-1 inhibition and TP antagonist, but were not modified by Cox-2 inhibition. Aortic rings from ApoE^-/- mice also exhibited enhanced contractions to ET-1 (R_max ∼30%, p<0.01), which were attenuated in sildenafil-treated ApoE^-/- mice. In addition, we observed augmented levels of vascular proinflammatory cytokines in ApoE^-/- mice, which were partially corrected by treatment with sildenafil (IL-6, IL-10/IL-6 ratio and MCP-1). Conclusion: The present data show that the Cox-1/TXA2 pathway prevails over the Cox-2 isoform in the mediation of vascular hypercontractility observed in apoE^-/-mice. The results also show a beneficial effect of sildenafil on this endothelial dysfunction and on the proinflammatory cytokines in atherosclerotic animals, opening new perspectives for the treatment of other endothelium-related cardiovascular abnormalities.

High fat diet confers vascular hyper-contractility against angiotensin II through upregulation of MLCK and CPI-17.

Obesity is a critical risk factor for the hypertension. Although angiotensin II (Ang II) in obese individuals is known to be upregulated in obesity-induced hypertension, direct evidence that explains the underlying mechanism for increased vascular tone and consequent increase in blood pressure (BP) is largely unknown. The purpose of this study is to investigate the novel mechanism underlying Ang II-induced hyper-contractility and hypertension in obese rats. Eight-week old male Sprague-Dawley rats were fed with 60% fat diet or normal diet for 4 months. Body weight, plasma lipid profile, plasma Ang II level, BP, Ang II-induced vascular contraction, and expression of regulatory proteins modulating vascular contraction with/without Ang II stimulation were measured. As a result, high fat diet (HFD) accelerated age-dependent body weight gaining along with increased plasma Ang II concentration. It also increased BP and Ang II-induced aortic contraction. Basal expression of p-CPI-17 and myosin light chain (MLC) kinase was increased by HFD along with increased phosphorylation of MLC. Ang II-induced phosphorylation of CPI-17 and MLC were also higher in HFD group than control group. In conclusion HFD-induced hypertension is through at least in part by increased vascular contractility via increased expression and activation of contractile proteins and subsequent MLC phosphorylation induced by increased Ang II.

Aging-related alterations in eNOS and nNOS responsiveness and smooth muscle reactivity of murine basilar arteries are modulated by apocynin and phosphorylation of myosin phosphatase targeting subunit-1

Aging causes major alterations of all components of the neurovascular unit and compromises brain blood supply. Here, we tested how aging affects vascular reactivity in basilar arteries from young (<10 weeks; y-BA), old (>22 months; o-BA) and old (>22 months) heterozygous MYPT1-T-696A/+ knock-in mice. In isometrically mounted o-BA, media thickness was increased by ∼10% while the passive length tension relations were not altered. Endothelial denudation or pan-NOS inhibition (100 µmol/L L-NAME) increased the basal tone by 11% in y-BA and 23% in o-BA, while inhibition of nNOS (1 µmol/L L-NPA) induced ∼10% increase in both ages. eNOS expression was ∼2-fold higher in o-BA. In o-BA, U46619-induced force was augmented (pEC50 ∼6.9 vs. pEC50 ∼6.5) while responsiveness to DEA-NONOate, electrical field stimulation or nicotine was decreased. Basal phosphorylation of MLC20-S19 and MYPT1-T-853 was higher in o-BA and was reversed by apocynin. Furthermore, permeabilized o-BA showed enhanced Ca2+-sensitivity. Old T-696A/+ BA displayed a reduced phosphorylation of MYPT1-T696 and MLC20, a lower basal tone in response to L-NAME and a reduced eNOS expression. The results indicate that the vascular hypercontractility found in o-BA is mediated by inhibition of MLCP and is partially compensated by an upregulation of endothelial NO release.

Correction of vascular hypercontractility in spontaneously hypertensive rats using shRNAs-induced delta protein kinase C gene silencing

Potassium conductance in vascular smooth muscle (VSM) is known to be altered in arterial hypertension. High level of protein kinase C (PKC) activity is a common feature for hypertension of different genesis. The main goal of this study was to investigate the efficacy of the RNA interference (RNAi) technique targeting PKC delta-isoform gene as a possible pharmacological tool to restore vasodilator potential in spontaneously hypertensive rats (SHR). Experimental design of the study comprised RNAi and patch-clamp techniques, RT-PCR analysis and standard acetylcholine test. Total outward currents and acetylcholine-induced endothelium-dependent relaxant responses were blunted in SHR. BKCa alpha subunit mRNA expression in SHR was unchanged whereas KV and KATP mRNA expression appeared significantly increased. PKC inhibitor, chelerythrine (100nM), restored potassium channels activity in SHR. PKC-delta-isoform protein expression and PKC-delta-isoform mRNA expression are 2.5–4 fold increased in VSM from SHR. PKC gene silencing with the short hairpin RNAs (shRNAs)-plasmid delivery system administered intravenously led to an increment in maximal amplitude of acetylcholine-relaxation, restored outward K+ currents and PKC-delta-isoform mRNA and protein expression. Arterial blood pressure in SHR was normalized following shRNAs administration. We conclude that BKCa channels are likely to be the most PKC-dependent member of K+ channels family responsible for vascular hypercontractility in SHR while Kv and KATP channels may constitute a reserve mechanism for the maintenance of vasodilator potential under BKCa channelopathy. It is likely that RNAi technique is a good therapeutic approach to inactivate PKC gene and to normalize vascular functions and high arterial blood pressure in SHR.

Diabetes mellitus modifies endothelial SERCA activity producing a prostaglandin dependent vascular hypercontractility

To assess the underlying mechanism of diabetes mellitus (DM)‐induced vascular hypercontractility, we evaluated the participation of the sarcoendoplasmic reticulum calcium ATPase (SERCA), the protein kinase C (PKC) and prostaglandins during the contraction induced by phenylephrine (PE) of aorta rings from a 10 weeks streptozotocin (STZ)‐induced DM rat model.PE produced a stronger contraction of DM aorta rings with endothelium vs control (CTRL), (Emax: DM .69 ± .06 vs CTRL .38 ± .07 g. p&lt;0.02). This vascular hypercontractility was eliminated by: a) indomethacin (10μM) pretreatment (Emax: DM .64 ± .07 vs CTRL .55 ± .11 g. ns), and b) endothelium removal (Emax: DM 1 ± .07 vs CTRL .93 ± .04 g., ns). On the other hand, Gö6976 (1μM), a PKC inhibitor, decreased the contractile response in CTRL more than in DM (Emax: DM .55 ± .06 vs CTRL .28 ± .04 g., p&lt;0.01). Also, 1μM thapsigargin (T), a SERCA blocker, increased the CTRL concentration dependent contraction (Emax: CTRL .40 ± .08 vs CTRL+T .76 ± .09, p&lt;0.001), but was not different in DM rings (Emax: DM .66 ± .10 vs DM+T .69 ± .06 g., ns), nor between groups (Emax DM+T .69 ± .07 vs CTRL+T .76 ± .08 g., ns).ConclusionsDuring STZ‐induced DM, endothelial cells release a contractile prostaglandin, perhaps TXA2, that induces vascular hypercontractility.Supported by: P/PIFI‐2010‐24MSU0011E‐13.

The BKCa channels deficiency as a possible reason for radiation-induced vascular hypercontractility

It is likely that large-conductance Ca2+-activated K+ (BKCa) channels channelopathy tightly involved in vascular malfunctions and arterial hypertension development. In the present study, we compared the results of siRNAs-induced α-BKCa gene silencing and vascular abnormalities produced by whole-body ionized irradiation in rats. The experimental design comprised RT-PCR and patch clamp technique, thoracic aorta smooth muscle (SM) contractile recordings and arterial blood pressure (BP) measurements on the 30th day after whole body irradiation (6Gy) and following siRNAs KCNMA1 gene silencing in vivo. The expression profile of BKCa mRNA transcripts in SM was significantly decreased in siRNAs-treated rats in a manner similar to irradiated SM. In contrast, the mRNA levels of Kv and KATP were significantly increased while L-type calcium channels mRNA transcripts demonstrated tendency to increment. The SMCs obtained from irradiated animals and after KCNMA1 gene silencing showed a significant decrease in total K+ current density amplitude. Paxilline (500 nM)-sensitive components of outward current were significantly decreased in both irradiated and gene silencing SMCs. KCNMA1 gene silencing increased SM sensitivity to norepinephrine while Ach-induced relaxation had decreased. The silencing of KCNMA1 had no significant effect on BP while radiation produced sustained arterial hypertension. Therefore, radiation alters the form and function of the BKCa channel and this type of channelopathy may contribute to related vascular abnormalities. Nevertheless, it is unlikely that BKCa can operate as a crucial factor for radiation-induced arterial hypertension.

Blast-induced phenotypic switching in cerebral vasospasm

Vasospasm of the cerebrovasculature is a common manifestation of blast-induced traumatic brain injury (bTBI) reported among combat casualties in the conflicts in Afghanistan and Iraq. Cerebral vasospasm occurs more frequently, and with earlier onset, in bTBI patients than in patients with other TBI injury modes, such as blunt force trauma. Though vasospasm is usually associated with the presence of subarachnoid hemorrhage (SAH), SAH is not required for vasospasm in bTBI, which suggests that the unique mechanics of blast injury could potentiate vasospasm onset, accounting for the increased incidence. Here, using theoretical and in vitro models, we show that a single rapid mechanical insult can induce vascular hypercontractility and remodeling, indicative of vasospasm initiation. We employed high-velocity stretching of engineered arterial lamellae to simulate the mechanical forces of a blast pulse on the vasculature. An hour after a simulated blast, injured tissues displayed altered intracellular calcium dynamics leading to hypersensitivity to contractile stimulus with endothelin-1. One day after simulated blast, tissues exhibited blast force dependent prolonged hypercontraction and vascular smooth muscle phenotype switching, indicative of remodeling. These results suggest that an acute, blast-like injury is sufficient to induce a hypercontraction-induced genetic switch that potentiates vascular remodeling, and cerebral vasospasm, in bTBI patients.

Vascular hypercontractility to endothelin 1 in mice lacking endothelial PPARG

Peroxisome proliferator‐activated receptor gamma (PPARG), a ligand‐activated nuclear hormone receptor, plays an important role in modulating blood pressure. This is evidenced by observations that thiazolidinediones, synthetic PPARG ligands used as antidiabetic drugs, lower blood pressure, while certain PPARG dominant negative (DN) mutations cause diabetes and early onset severe hypertension in humans. As PPARG is expressed in the vasculature, we postulated that it may exert its effect on blood pressure by modulating vascular function and reactivity. In order to test this hypothesis, we generated mice in which PPARG is knocked out in the endothelium (PPARG−/−), using the Cre‐LoxP system. Vascular function was assessed by studying the response of aortas from ePPARG−/− mice to an array of vasodilators and constrictors under baseline conditions. Vasorelaxation in response to acetylcholine and sodium nitroprusside, as well as vasoconstriction to serotonin and protaglandin F2a were normal. Endothelin 1 (ET‐1) mediated vasoconstriction was, however, significantly enhanced in ePPARG−/− mice. This finding is in step with high fat diet‐induced hypertension in ePPARG−/− mice reported previously, as well as findings that DN PPARG mutations cause ET‐1 mediated hypercontractility. Together these findings indicate that endothelial PPARG may play an essential role in modulating vascular reactivity to ET‐1.

A New Insight Into the Pathogenesis of Coronary Vasospasm

See related article, pages 682–689 To elucidate the control mechanisms of coronary vascular tone is one of the central interests in cardiac pathophysiology, because ischemic heart disease is one of the major causes of death in many countries. Although the coronary vascular tone is finally determined by the contractile state of smooth muscle, exo-smooth muscle mechanisms including autonomic nerves, endothelial cells, and blood cells have been shown indispensable for the control. Particular types of receptors, ion channels, and intracellular signal-cascades exist in coronary smooth muscle cells and mediate the controls by exo-smooth muscle elements (Figure). For example, stimulation of α1-adrenergic receptor, which is physiologically achieved by noradrenaline (NA) released from sympathetic presynapses, increases the intracellular Ca2+ (Ca2+i) via phosphatidylinositol (PI)-turnover and also probably via opening of receptor-activated Ca2+-permeable TRP channel. Membrane depolarization does so via opening voltage-dependent Ca2+ channels. The augmentation of Ca2+i results in contraction of the smooth muscle cells and thus constriction of the coronary artery.1 Activation of β2-adrenergic receptor, in turn, inhibits the coronary smooth muscle contraction through protein-kinase A pathway.2 The contraction is also suppressed by protein-kinase G activated by a dilating factor, nitric oxide (NO), which is produced in the endothelial cells. The mechanism for control of vascular tone . Activation of voltage-gated Ca2+ channel at the presynapse of sympathetic nerve increases intracellular Ca2+, which triggers a release of norepinephrine (NE). NE stimulates adrenergic α1 receptor (α1R) in the smooth muscle cells and drives PI-turnover as described in this scheme. The intracellular Ca2+, which flows into the cells via smooth-muscle’s Ca2+ channel or moves from endoplasmic reticulum (ER), contracts the cells. The constriction of smooth muscle cells is prevented by activation …

Insulin-Sensitizing and Cardiovascular Effects of the Sodium-Hydrogen Exchange Inhibitor, Cariporide, in the JCR

The effects of the sodium-hydrogen (Na/H) exchange inhibitor cariporide (HOE642), on insulin sensitivity and vascular function were studied in the JCR:LA-cp rat and the db/db mouse. In the insulin-resistant rat, cariporide reduced fasting insulin levels (42%, P < 0.02) and insulin response in a meal tolerance test (50%, P < 0.01), indicating increased insulin sensitivity. The ACE inhibitor, ramipril, used as a reference agent, reduced the insulin response to the meal, but not fasting levels. The EC50 for acetylcholine-mediated relaxation of phenylephrine-precontracted aortic rings was significantly lower in cariporide-treated rats (P < 0.002), but not in ramipril-treated rats. Flow response of the coronary circulation to bradykinin was significantly greater in both cariporide- and ramipril-treated rats, (3-fold decrease in the EC50, P < 0.05). Cariporide-treated hearts were smaller, slower beating, with greater developed LVP. In the obese db/db mouse, chronic treatment with cariporide obviated vascular hypercontractility and improved endothelial function. Thus, cariporide had beneficial effects on the abnormal insulin metabolism and associated vascular dysfunction in the JCR:LA-cp insulin-resistant rat, which develops advanced cardiovascular disease and ischemic myocardial lesions. It also improved vascular function in a similar mouse model of insulin resistance. These effects were markedly greater than those of ramipril.

Ischemia-reperfusion increases gastric motility and endothelin-1-induced vasoconstriction.

The purpose of our study was to 1) examine the effect of ischemia-reperfusion on gastric vascular resistance and motility, 2) determine whether endothelin-1 (ET-1)-induced vasoconstriction is enhanced after ischemia-reperfusion, and 3) assess the effect of superoxide dismutase (SOD) on these ischemia-reperfusion-induced alterations. These experiments used a mechanically perfused ex vivo gastric segment of chloralose-anesthetized dogs. We first evaluated the effect of varying the duration of total ischemia on reperfusion-induced changes in gastric vascular resistance and motility. In other experiments, responses to ET-1 (10(-10) M) were compared before and after 30-min ischemia and 30-min reperfusion, with saline or SOD (10 U/ml) infused intra-arterially to the stomach during reperfusion. Our results show that 1) after ischemia, vasodilation is seen initially on reperfusion followed by a slowly developing, progressive increase in vascular resistance, 2) the force of gastric contractions was reduced during ischemia but elevated immediately on reperfusion, 3) vasoconstrictor responses to ET-1 are enhanced after ischemia-reperfusion, and 4) SOD reduced the enhanced response to ET-1 and force of contractions. Our findings support the hypothesis that reactive oxygen metabolites contribute to augmented vascular reactivity and hypercontractility after ischemia-reperfusion.