Vasorelaxation In Resistance Arteries Research Articles

L-Citrulline ameliorates pathophysiology in a rat model of superimposed preeclampsia.

Preeclampsia, characterized by hypertension, proteinuria and restriction of fetal growth, is one of the leading causes of maternal and perinatal mortality. So far, there is no effective pharmacological therapy for preeclampsia. The present study was conducted to investigate the effects of supplementation with l-citrulline in Dahl salt-sensitive rats, a model of superimposed preeclampsia. Parental Dahl salt-sensitive rats were treated with l-citrulline (2.5g·L-1 in drinking water) from the day of mating to the end of lactation period. Blood pressure was monitored throughout pregnancy and markers of preeclampsia were assessed. Endothelial function of the pregnant Dahl salt-sensitive rats was assessed by wire myograph. In Dahl salt-sensitive rats, l-citrulline supplementation significantly reduced maternal blood pressure, proteinuria and levels of circulating soluble fms-like tyrosine kinase 1. l-Citrulline improved maternal endothelial function by augmenting the production of nitric oxide in the aorta and improving endothelium-derived hyperpolarizing factor-mediated vasorelaxation in resistance arteries. l-Citrulline supplementation improved placental insufficiency and fetal growth, which were associated with an enhancement of angiogenesis and reduction of fibrosis and senescence in the placentas. In addition, l-citrulline down-regulated genes involved in the TLR4 and NF-κB signalling pathways. This study shows that l-citrulline supplementation reduced gestational hypertension and improved placentation and fetal growth in a rat model of superimposed preeclampsia. l-Citrulline supplementation may provide an effective and safe therapeutic strategy for preeclampsia that benefits both the mother and the fetus.

Enhanced Mobilization of Endothelial Ca2+ by SKA‐31 Contributes to the Restoration of Agonist‐mediated Vasorelaxation in Resistance Arteries from Type 2 Diabetic Rats

Endothelial dysfunction is a common early pathogenic event in patients with type 2 diabetes (T2D). In isolated hearts from T2D Goto‐Kakizaki (GK) rats, we have observed that SKA‐31, a positive modulator of the endothelial Ca2+‐activated K+ (KCa) channels KCa2.3 and KCa3.1, increases total coronary flow and restores agonist‐evoked elevations in flow to the levels observed in Wistar control hearts. The goal of the current study was to investigate the cellular mechanisms by which SKA‐31 restores vascular responsiveness in T2D vessels. In cannulated, myogenically active cremaster and cerebral resistance arteries from 24 week old, male T2D GK rats, and small intra‐thoracic arteries from T2D patients, a threshold concentration of SKA‐31 (0.3 μM) enhanced the ability of 0.3 μM acetylcholine and 0.1 μM bradykinin to inhibit developed tone at 70 mmHg. This effect of SKA‐31 was not disrupted by treatment with L‐NAME (0.1 mM) and indomethacin (10 μM), demonstrating that endothelial nitric oxide synthase and cyclooxygenase activities do not contribute to SKA‐31 mediated enhancement of agonist‐evoked vasorelaxation in T2D arteries. Using single cell Fura‐2 fluorescence imaging, we observed that Ca2+ mobilization evoked by the muscarinic agonist carbachol (1 μM) was significantly impaired in acutely isolated endothelial cells from GK arteries compared with Wistar controls and that treatment with 0.3 μM SKA‐31 was able to reverse this defect in response. Ca2+ mobilization evoked by the SERCA inhibitor cyclopiazonic acid (20 μM) was not different in endothelial cells from Wistar and T2D GK arteries, suggesting that the internal Ca2+ store, per se, is not dysfunctional in GK endothelial cells. In summary, we have identified a novel cellular mechanism to restore agonist‐mediated inhibition of myogenic tone in T2D resistance arteries that involves “priming” of endothelial KCa channels by a small molecule activator (e.g. SKA‐31). Our data further reveal that SKA‐31 is able to augment agonist‐evoked Ca2+ mobilization in T2D endothelial cells, which likely contributes to the functional restoration of agonist‐evoked vasorelaxation in T2D arteries.Support or Funding InformationThis study was supported by research funding to APB from the CIHR.

PP42 - Endogenous hydrogen sulfide production and vasorelaxation in resistance arteries of the rat

PP42 - Endogenous hydrogen sulfide production and vasorelaxation in resistance arteries of the rat

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Objectives While obesity is a major risk factor for preeclampsia, which is new-onset hypertension in pregnancy, the mechanisms linking obesity and hypertension during preeclampsia are not understood. Hypertension in preeclampsia is associated with placental ischemia-induced release of factors such as anti-angiogenic sFlt-1 into the maternal circulation which antagonizes vascular endothelial growth factor (VEGF) and promotes endothelial dysfunction. The purpose of this study was to determine the effect of obesity on angiogenic factors and endothelial function in obese melanocortin 4 receptor (MC4R) knockout rats (MC4R+/−, n = 4–9) and lean control MC4R+/+ rats ( n = 4–8). Methods EchoMRI for measuring total body fat mass; carotid arterial catheters for measuring mean arterial blood pressure; ELISAs; wire myography. Results At gestational day (GD) 18, body weight (362 ± 6 vs. 336 ± 5 g) and total body fat mass (62 ± 6 vs. 45 ± 5 g) were greater ( P P P P Conclusions These data indicate that during normal pregnancy, obesity is associated with greater circulating VEGF levels and nitric oxide-dependent vasorelaxation in resistance arteries. Because soluble factors from the ischemic placental target reduce nitric oxide bioavailability, we propose that the hypertensive and endothelial dysfunction responses to reductions in uterine perfusion may be exaggerated in obese pregnant animals. Funding: HL105324, HL51971. Disclosures F.T. Spradley: None. A.C. Palei: None. J.P. Granger: None.

GW25-e4145 Anti-peroxynitrite Treatment Ameliorated Vasorelaxation of Resistance Arteries in Aging Rats: Involvement with NO-sGC-cGKs Pathway

Declined vasorelaxation function in aging resistance arteries is responsible for aging related multiple organ dysfunctions. The aim of the present study is to explore the role of peroxynitrite (ONOO-) in aging resistance arterial vasorelaxation dysfunction and the possible mechanism. In the present

Abstract 278: Enhanced Vasorelaxation Response of Resistance Arteries From Obese Mc4r Deficient Pregnant Rats

While obesity is a major risk factor for preeclampsia, the mechanisms linking obesity and hypertension during preeclampsia are unclear. Hypertension in preeclampsia is associated with placental ischemia-induced release of factors such as anti-angiogenic sFlt-1 into the maternal circulation, which antagonizes vascular endothelial growth factor (VEGF) and endothelial function. The purpose of this study was to determine the effect of obesity on angiogenic factors and endothelial function in obese melanocortin 4 receptor (MC4R) knockout rats (MC4R+/-, n=4-9) and lean control MC4R+/+ rats (n=4-8). Pre-pregnancy body weight (298±6 vs. 266±3g) and total body fat mass (EchoMRI: 56±3 vs. 44±1g) was greater (P<0.05) in MC4R+/- vs. MC4R+/+ at 15 weeks old when timed-pregnant rats were generated. At gestational day (GD) 18, body weight (362±6 vs. 336±5g) and total body fat mass (62±6 vs. 45±5g) were greater (P<0.05) in MC4R+/- and MC4R+/+ pregnant rats, respectively. Mean arterial blood pressure (indwelling carotid catheter) was similar in MC4R+/- (113±4mmHg) and MC4R+/+ (109±4mmHg) rats. Plasma sFlt-1 was not significantly elevated in MC4R+/- vs. MC4R+/+ (228±86 vs. 141±53 pg/mL). Interestingly, VEGF was greater in the obese pregnant rats (4091±336 vs. 2854±475pg/mL, P<0.05). Wire myography demonstrated in third-order mesenteric arteries that sensitivity (logEC50) to acetylcholine (endothelial dependent)-induced vasorelaxation (-11.4±0.7 vs. -6.9±0.7M, P<0.05) and sodium nitroprusside (exogenous nitric oxide donor) (-8.3±0.1 vs. -7.5±0.2M, P<0.05) was greater in obese MC4R+/- vs. lean MC4R+/+ pregnant rats. These data indicate that during normal pregnancy, obesity is associated with greater circulating VEGF levels and nitric oxide-dependent vasorelaxation in resistance arteries. Because soluble factors from the ischemic placenta target and reduce nitric oxide bioavailability, we propose that the hypertensive and endothelial dysfunction responses to reductions in uterine perfusion may be exaggerated in obese pregnant animals.

Impaired endothelium‐dependent vasorelaxation contributes to hypertension in leukocyte‐specific protein 1 (LSP1)‐deficient mice

LSP1 is an intracellular, Ca2+‐and F‐actin‐binding protein expressed in leukocytes and endothelial cells. Adult male LSP1‐deficient (Lsp1−/−) mice had higher blood pressure than their WT counterparts. By Western blot, LSP1 was found present in aorta and mesenteric artery tissues in WT mice but not in Lsp1−/− mice. The role of LSP1 in regulating arterial vascular tone was studied. The contraction of aorta and mesenteric arteries in response to phenylephrine and angiotensin II was similar in WT and Lsp1−/− mice. The relaxation of aorta artery was more sensitive to sodium nitroprusside and methacholine in Lsp1−/− mice than in WT mice. The phenylephrine‐constricted mesenteric arteries showed identical relaxation curve to sodium nitroprusside in these two strains of mice, but had no relaxation to methacholine in Lsp1−/− mice or in denuded WT mesenteric arteries. Methacholine‐induced mesenteric arterial relaxation in WT mice was suppressed partially by the pretreatment of L‐NAME or the combination of apamin + TRAM‐34, abolished completely by the combination of L‐NAME + apamin + TRAM‐34, but not changed by indomethacin. Our results demonstrate the defects in endothelium‐dependent vasorelaxation in resistance arteries in mice deficient in LSP1 revealing an important role for LSP1 in endothelium‐dependent vasodilation in small resistance arteries and blood pressure regulation.

Endothelial alkalinisation inhibits gap junction communication and endothelium‐derived hyperpolarisations in mouse mesenteric arteries

Abstract Gap junctions mediate intercellular signalling in arteries and contribute to endothelium-dependent vasorelaxation, conducted vascular responses and vasomotion. Considering its putative role in vascular dysfunction, mechanistic insights regarding the control of gap junction conductivity are required. Here, we investigated the consequences of endothelial alkalinisation for gap junction communication and endothelium-dependent vasorelaxation in resistance arteries. We studied mesenteric arteries from NMRI mice by myography, confocal fluorescence microscopy and electrophysiological techniques. Removing CO2/HCO3(-), reducing extracellular [Cl(-)] or adding 4,4-diisothiocyanatostilbene-2,2-disulphonic acid inhibited or reversed Cl(-)/HCO3(-) exchange, alkalinised the endothelium by 0.2-0.3 pH units and inhibited acetylcholine-induced vasorelaxation. NO-synthase-dependent vasorelaxation was unaffected by endothelial alkalinisation whereas vasorelaxation dependent on small- and intermediate-conductance Ca(2+)-activated K(+) channels was attenuated by ∼75%. The difference in vasorelaxation between arteries with normal and elevated endothelial intracellular pH (pHi) was abolished by the gap junction inhibitors 18β-glycyrrhetinic acid and carbenoxolone while other putative modulators of endothelium-derived hyperpolarisations - Ba(2+), ouabain, iberiotoxin, 8Br-cAMP and polyethylene glycol catalase - had no effect. In the absence of CO2/HCO3(-), addition of the Na(+)/H(+)-exchange inhibitor cariporide normalised endothelial pHi and restored vasorelaxation to acetylcholine. Endothelial hyperpolarisations and Ca(2+) responses to acetylcholine were unaffected by omission of CO2/HCO3(-). By contrast, dye transfer between endothelial cells and endothelium-derived hyperpolarisations of vascular smooth muscle cells stimulated by acetylcholine or the proteinase-activated receptor 2 agonist SLIGRL-amide were inhibited in the absence of CO2/HCO3(-). We conclude that intracellular alkalinisation of endothelial cells attenuates endothelium-derived hyperpolarisations in resistance arteries due to inhibition of gap junction communication. These findings highlight the role of pHi in modulating vascular function.

Relaxation evoked by extracellular Ca 2+ in rat aorta is nerve-independent and involves sarcoplasmic reticulum and L-type Ca 2+ channel

The perivascular nerve network expresses a Ca 2+ receptor that is activated by high extracellular Ca 2+ concentrations and causes vasorelaxation in resistance arteries. We have verified the influence of perivascular nerve fibers on the Ca 2+-induced relaxation in aortic rings. To test our hypothesis, either pre-contracted aortas isolated from rats after sensory denervation with capsaicin or aortic rings acutely denervated with phenol were stimulated to relax with increasing extracellular Ca 2+ concentration. We also studied the role of the endothelium on the Ca 2+-induced relaxation, and we verified the participation of endothelial/nonendothelial nitric oxide and cyclooxygenase–arachidonic acid metabolites. Additionally, the role of the sarcoplasmic reticulum, K + channels and L-type Ca 2+ channels on the Ca 2+-induced relaxation were evaluated. We have observed that the Ca 2+-induced relaxation is completely nerve independent, and it is potentiated by endothelial nitric oxide (NO). In endothelium-denuded aortic rings, indomethacin and AH6809 (PGF 2α receptor antagonist) enhance the relaxing response to Ca 2+. This relaxation is inhibited by thapsigargin and verapamil, while was not altered by tetraethylammonium. In conclusion, we have shown that perivascular nervous fibers do not participate in the Ca 2+-induced relaxation, which is potentiated by endothelial NO. In endothelium-denuded preparations, indomethacin and AH6809 enhance the relaxation induced by Ca 2+. The relaxing response to Ca 2+ was impaired by verapamil and thapsigargin, revealing the importance of L-type Ca 2+ channels and sarcoplasmic reticulum in this response.