Endothelium-dependent blunting of myogenic responsiveness after chronic hypoxia

Blunted agonist-induced vasoconstriction after chronic hypoxia is associated with endothelium-dependent vascular smooth muscle (VSM) cell hyperpolarization and decreased vessel-wall Ca(2+) concentration ([Ca(2+)]). We hypothesized that myogenic vasoconstriction and pressure-induced Ca(2+) influx would also be attenuated in vessels from chronically hypoxic (CH) rats. Mesenteric resistance arteries isolated from CH [barometric pressure (BP), 380 Torr for 48 h] or normoxic control (BP, 630 Torr) rats were cannulated and pressurized. VSM cell resting membrane potential was recorded at intraluminal pressures of 40-120 Torr under normoxic conditions. VSM cells in vessels from CH rats were hyperpolarized compared with control rats at all pressures. Inner diameter was maintained for vessels from control rats, whereas vessels from CH rats developed less tone as pressure was increased. Pressure-induced increases in vessel-wall [Ca(2+)] were also attenuated for arteries from CH rats. Endothelium removal restored myogenic constriction to vessels from CH rats and normalized VSM cell resting membrane potential and pressure-induced Ca(2+) responses to control levels. Myogenic constriction and pressure-induced vessel-wall [Ca(2+)] increases remained blunted in the presence of nitric oxide (NO) synthase inhibition for arteries from CH rats. We conclude that blunted myogenic reactivity after chronic hypoxia results from a non-NO, endothelium-dependent VSM cell hyperpolarizing influence.     

慢性缺氧对大鼠肺动胍内皮依赖性舒张反应及CGMP含量的影响

This experiment was designed to investigate whether chronic hypoxia affect rat pulmonary artery (PA) endothelium-dependent relaxation and the content of cGMP in PA. Both ACh and ATP could induce endothelium-dependent relaxation of PA, not prevented by indomethacin, but completely abolished by methylene blue. These results indicated that vasodilatation of PA induced by both ACh and ATP is mediated by EDRF (endothelium-derived relaxing factor). Chronic hypoxia significantly depressed PA endothelium-dependent relaxation. The percent relaxation of IPPA and EPPA by 10(-6) mol/L ACh was 61.3% and 59.2% of those in control, and the percent relaxation of IPPA and EPPA by 1.8 x 10(-5) mol/L ATP was 64.9% and 55.3% respectively of the control. Chronic hypoxia also depressed SNP-induced endothelium-independent relaxation. Chronic hypoxia significantly decreased the content of cGMP in PA. The basic level of cGMP was 51.9 +/- 5.7 (n = 14) in hypoxia group and 84.9 +/- 9.7 (n = 14) pmol/g wet wt. in control group (P less than 0.01). After treatment of PA with ACh (10(-7) mol/L), the content of cGMP was 91.4 +/- 7.3 (n = 5) pmol/g wet wt. in hypoxic group and 240.8 +/- 30.6 (n = 5) pmol/g wet wt. in control group (P less than 0.01). Our data suggest that chronic hypoxia might depress rat pulmonary artery endothelium-dependent relaxation through the inhibition of soluble guanylate cyclase in vascular smooth muscle cells.     

Correction of NO-dependent cardiovascular disorders by adaptation to hypoxia

Spontaneously hypertensive rats (SHR-SP) were adapted to intermittent hypobaric hypoxia in an altitude chamber for 40 days. The adaptation to hypoxia prevented an excessive endothelium-dependent relaxation and hypotension characteristic of myocardial infarction. The adaptation also attenuated the increase in blood pressure and prevented impairment of the endothelium-dependent relaxation in SHR-SP. The universal nature of the adaptation allows to use it for correcting many cardiovascular disorders related to diverse alterations of NO metabolism.     

Upregulation of eNOS in pregnant ovine uterine arteries by chronic hypoxia

We tested the hypothesis that chronic high-altitude (3,820 m) hypoxia during pregnancy was associated with the upregulation of endothelial nitric oxide (NO) synthase (eNOS) protein and mRNA in ovine uterine artery endothelium and enhanced endothelium-dependent relaxation. In pregnant sheep, norepinephrine-induced dose-dependent contractions were increased by removal of the endothelium in both control and hypoxic uterine arteries. The increment was significantly higher in hypoxic tissues. The calcium ionophore A23187-induced relaxation of the uterine artery was significantly enhanced in hypoxic compared with control tissues. However, sodium nitroprusside- and 8-bromoguanosine 3',5'-cyclic monophosphate-induced relaxations were not changed. Accordingly, chronic hypoxia significantly increased basal and A23187-induced NO release. Chronic hypoxia increased eNOS protein and mRNA levels in the endothelium from uterine but not femoral or renal arteries. In nonpregnant animals, chronic hypoxia increased eNOS mRNA in uterine artery endothelium but had no effects on eNOS protein, NO release, or endothelium-dependent relaxation. Chronic hypoxia selectively augments pregnancy-associated upregulation of eNOS gene expression and endothelium-dependent relaxation of the uterine artery.     

Cellular mechanisms of transitory smooth muscle contraction of the coronary arteries during hypoxia: role of intracellular Ca2+

In experiments on isolated porcine and canine coronary artery rings it was shown that vascular smooth muscle (VSM) during hypoxia (decreasing bath PO2 with 147 to 20-15 mm Hg) response to biphasic constriction-dilation reaction. Transient hypoxic contractions (THC) of VSM preserved completely in Ca2+-free solution and partially (up 50-60%) in the presence of Ca2+-channel blockers, but abolished by procaine. THC of VSM skinned by saponin significantly depressed at depletion of Ca2+-store sarcoplasmic reticulum (SR) by caffeine nd abolished after SR destruction. THC is not linked with Na+-K+-ATPase inhibition because it preserved (or increased) at ouabain treatment. THC significantly depressed under selective glycolysis blockade by monoiodoacetic acid and pyruvate and also after inositol-1 monophosphatase inhibition by lithium (the phase of hypoxic relaxation of VSM was augmented in this condition). Our results indicate that transient contraction of coronary arteries under hypoxia may be mediated mainly by release of Ca2+ from SR and linked obviously with production of inositol-1,4,5-trisphosphate. The participation of glycolysis in this process is unknown.     

Role of nitric oxide in adaptation to hypoxia and adaptive defense

Adaptation to hypoxia is beneficial in cardiovascular pathology related to NO shortage or overproduction. However, the question about the influence of adaptation to hypoxia on NO metabolism has remained open. The present work was aimed at the relationship between processes of NO production and storage during adaptation to hypoxia and the possible protective significance of these processes. Rats were adapted to intermittent hypobaric hypoxia in an altitude chamber. NO production was determined by plasma nitrite/nitrate level. Vascular NO stores were evaluated by relaxation of the isolated aorta to diethyldithiocarbamate. Experimental myocardial infarction was used as a model of NO overproduction; stroke-prone spontaneously hypertensive rats (SHR-SP) were used as a model of NO shortage. During adaptation to hypoxia, the plasma nitrite/nitrate level progressively increased and was correlated with the increase in NO stores. Adaptation to hypoxia prevented the excessive endothelium-dependent relaxation and hypotension characteristic for myocardial infarction. At the same time, the adaptation attenuated the increase in blood pressure and prevented the impairment of endothelium-dependent relaxation in SHR-SP. The data suggest that NO stores induced by adaptation to hypoxia can either bind excessive NO to protect the organism against NO overproduction or provide a NO reserve to be used in NO deficiency.     

Muscarinic receptor M1 and phosphodiesterase 1 are key determinants in pulmonary vascular dysfunction following perinatal hypoxia in mice

Perinatal adverse events such as limitation of nutrients or oxygen supply are associated with the occurrence of diseases in adulthood, like cardiovascular diseases and diabetes. We investigated the long-term effects of perinatal hypoxia on the lung circulation, with particular attention to the nitric oxide (NO)/cGMP pathway. Mice were placed under hypoxia in utero 5 days before delivery and for 5 days after birth. Pups were then bred in normoxia until adulthood. Adults born in hypoxia displayed an altered regulation of pulmonary vascular tone with higher right ventricular pressure in normoxia and increased sensitivity to acute hypoxia compared with controls. Perinatal hypoxia dramatically decreased endothelium-dependent relaxation induced by ACh in adult pulmonary arteries (PAs) but did not influence NO-mediated endothelium-independent relaxation. The M(3) muscarinic receptor was implicated in the relaxing action of ACh and M(1) muscarinic receptor (M(1)AChR) in its vasoconstrictive effects. Pirenzepine or telenzepine, two preferential inhibitors of M(1)AChR, abolished the adverse effects of perinatal hypoxia on ACh-induced relaxation. M(1)AChR mRNA expression was increased in lungs and PAs of mice born in hypoxia. The phosphodiesterase 1 (PDE1) inhibitor vinpocetine also reversed the decrease in ACh-induced relaxation following perinatal hypoxia, suggesting that M(1)AChR-mediated alteration of ACh-induced relaxation is due to the activation of calcium-dependent PDE1. Therefore, perinatal hypoxia leads to an altered pulmonary circulation in adulthood with vascular dysfunction characterized by impaired endothelium-dependent relaxation and M(1)AChR plays a predominant role. This raises the possibility that muscarinic receptors could be key determinants in pulmonary vascular diseases in relation to "perinatal imprinting."     

Interaction of myogenic mechanisms and hypoxic dilation in rat middle cerebral arteries

The goal of this study was to determine how myogenic responses and vascular responses to reduced Po(2) interact to determine vascular smooth muscle (VSM) transmembrane potential and active tone in isolated middle cerebral arteries from Sprague-Dawley rats. Stepwise elevation of transmural pressure led to depolarization of the VSM cells and myogenic constriction, and reduction of the O(2) concentration of the perfusion and superfusion reservoirs from 21% O(2) to 0% O(2) caused vasodilation and VSM hyperpolarization. Myogenic constriction and VSM depolarization in response to transmural pressure elevation still occurred at reduced Po(2). Arterial dilation in response to reduced Po(2) was not impaired by pressure elevation but was significantly reduced at the lowest transmural pressure (60 mmHg). However, the magnitude of VSM hyperpolarization was unaffected by transmural pressure elevation. This study demonstrates that myogenic activation in response to transmural pressure elevation does not override hypoxic relaxation of middle cerebral arteries and that myogenic responses and hypoxic relaxation can independently regulate vessel diameter despite substantial changes in the other variable.     

High-salt diet impairs vascular relaxation mechanisms in rat middle cerebral arteries

Male Sprague-Dawley rats were maintained on a low-salt (LS) diet (0.4% NaCl) or a high-salt (HS) diet (4% NaCl) for 3 days or 4 wk. PO(2) reduction to 40-45 mmHg, the stable prostacyclin analog iloprost (10 pg/ml), and stimulatory G protein activation with cholera toxin (1 ng/ml) caused vascular smooth muscle (VSM) hyperpolarization, increased cAMP production, and dilation in cerebral arteries from rats on a LS diet. Arteries from rats on a HS diet exhibited VSM depolarization and constriction in response to hypoxia and iloprost, failed to dilate or hyperpolarize in response to cholera toxin, and cAMP production did not increase in response to hypoxia, iloprost, or cholera toxin. Low-dose angiotensin II infusion (5 ng x kg(-1) x min(-1) i.v.) restored normal responses to reduced PO(2) and iloprost in arteries from animals on a HS diet. These observations suggest that angiotensin II suppression with a HS diet leads to impaired relaxation of cerebral arteries in response to vasodilator stimuli acting at the cell membrane.     

Exercise attenuates the effects of hypercholesterolemia on endothelium-dependent relaxation in coronary arteries from adult female pigs.

We tested the hypothesis that exercise training (Ex) attenuates the effects of hypercholesterolemia on endothelium-dependent relaxation in left anterior descending coronary arteries. Adult female pigs were fed a normal-fat (NF) or high-fat (HF) diet for 20 wk. Four weeks after the diet was initiated, pigs were trained or remained sedentary (Sed) for 16 wk, yielding four groups of pigs: 1) NF-Sed, 2) NF-Ex, 3) HF-Sed, and 4) HF-Ex. Sensitivity (EC(50)) to bradykinin (BK) was impaired in HF-Sed arteries. Ex improved BK-induced relaxation such that the EC(50) and maximal response to BK in HF-Ex arteries was not different from that in NF-Sed and NF-Ex. ACh-induced constriction was less in HF-Ex arteries than in HF-Sed, NF-Sed, and NF-Ex. To determine the mechanism(s) by which HF and Ex affected responses to BK and ACh, vasoactive responses were assessed in the presence of N(G)-nitro-L-arginine methyl ester [L-NAME; to inhibit nitric oxide (NO) synthase], indomethacin (Indo; to inhibit cyclooxygenase), and L-NAME + Indo. L-NAME inhibited BK-induced relaxation in NF (not HF) arteries. Indo did not significantly alter relaxation to BK in NF arteries; however, relaxation was enhanced in HF-Sed arteries. Double blockade with L-NAME + Indo attenuated BK-induced relaxation in NF arteries and eliminated relaxation in HF arteries. Neither L-NAME nor Indo altered constrictor responses to ACh in NF or HF arteries; however, double blockade with L-NAME + Indo attenuated constriction to ACh in NF-Ex arteries. Endothelium-independent relaxation to sodium nitroprusside was enhanced in HF-Sed and HF-Ex arteries. Collectively, these results indicate that HF impaired endothelial function in coronary arteries by impairing production of NO and by enhancing production of a constrictor that was inhibited by Indo. Ex attenuated the effects of hypercholesterolemia by improving NO-mediated, endothelium-dependent relaxation and by reducing the influence of the Indo-sensitive constrictor.     

Estrogen replacement reduces PGHS-2-dependent vasoconstriction in the aged rat

The reduction in estrogen in postmenopausal women contributes to an increase in vascular dysfunction. Models of aging have shown that this is due, in part, to increased prostaglandin H synthase (PGHS)-dependent vasoconstriction. We showed previously that inducible PGHS-2-dependent vasoconstriction is increased with aging. In the present study, we hypothesized that estrogen suppresses PGHS-2-dependent constriction in the aged rat. Isolated mesenteric arteries from placebo- or estrogen-treated, ovariectomized aged (24 mo) Fisher rats were assessed for endothelium-dependent relaxation in the absence or presence of PGHS inhibitors. PGHS inhibition (meclofenamate, 1 micromol/l) enhanced methacholine-induced relaxation only in the placebo group. Specific PGHS-2 inhibition (NS-398, 10 micromol/l) increased arterial relaxation to a greater extent than PGHS-1 inhibition (valeryl salicylate, 3 mmol/l). Estrogen prevented the PGHS-dependent constrictor effect but did not enhance nitric oxide-dependent relaxation in this model. PGHS-1 and endothelial nitric oxide synthase were not altered by estrogen, whereas PGHS-2 expression was decreased in the estrogen-replaced rats (P < 0.05). In summary, estrogen replacement improved vasodilation in aged rats by decreasing PGHS-dependent constriction.     

Effect of adaptation to periodic hypoxia on post-infarction fall of blood pressure and hyperactivation of the endothelium

Acute stress concomitant to the experimental myocardial infarction has induced endothelial hyperactivation of the rat aorta exhibited in an increase of inhibition of norepinephrine-induced contractions of vascular smooth muscle, enhanced endothelium-dependent relaxation correlating with a fall of systemic blood pressure. Preliminary adaptation of rats to intermittent hypobaric hypoxia greatly prevented the stress-induced endothelial hyperactivation and beneficially affected the postinfarction time course of blood pressure.     

Acetylcholine causes endothelium-dependent contraction of mouse arteries

The goal of this study was to determine whether acetylcholine evokes endothelium-dependent contraction in mouse arteries and to define the mechanisms involved in regulating this response. Arterial rings isolated from wild-type (WT) and endothelial nitric oxide (NO) synthase knockout (eNOS(-/-)) mice were suspended for isometric tension recording. In abdominal aorta from WT mice contracted with phenylephrine, acetylcholine caused a relaxation that reversed at the concentration of 0.3-3 microM. After inhibition of NO synthase [with N(omega)-nitro-l-arginine methyl ester (l-NAME), 1 mM], acetylcholine (0.1-10 microM) caused contraction under basal conditions or during constriction to phenylephrine, which was abolished by endothelial denudation. This contraction was inhibited by the cyclooxygenase inhibitor indomethacin (1 muM) or by a thromboxane A(2) (TxA(2)) and/or prostaglandin H(2) receptor antagonist SQ-29548 (1 microM) and was associated with endothelium-dependent generation of the TxA(2) metabolite TxB(2.) Also, SQ-29548 (1 microM) abolished the reversal in relaxation evoked by 0.3-3 microM acetylcholine and subsequently enhanced the relaxation to the agonist. The magnitude of the endothelium-dependent contraction to acetylcholine (0.1-10 microM) was similar in aortas from WT mice treated in vitro with l-NAME and from eNOS(-/-) mice. In addition, we found that acetylcholine (10 microM) also caused endothelium-dependent contraction in carotid and femoral arteries of eNOS(-/-) mice. These results suggest that acetylcholine initiates two competing responses in mouse arteries: endothelium-dependent relaxation mediated predominantly by NO and endothelium-dependent contraction mediated most likely by TxA(2).     

Age-dependent modulation of endothelium-dependent vasodilatation by chronic hypoxia in ovine cranial arteries.

Although abundant evidence indicates that chronic hypoxia can induce pulmonary vascular remodeling, very little is known of the effects of chronic hypoxia on cerebrovascular structure and function, particularly in the fetus. Thus the present study explored the hypothesis that chronic hypoxemia also influences the size and shape of cerebrovascular smooth muscle and endothelial cells, with parallel changes in the reactivity of these cells to endothelium-dependent vasodilator stimuli. To test this hypothesis, measurements of endothelial and vascular smooth muscle cell size and density were made in silver-stained common carotid and middle cerebral arteries from term fetal and nonpregnant adult sheep maintained at an altitude of 3,820 m for 110 days. Chronic hypoxia induced an age-dependent remodeling that led to smooth muscle cells that were larger in fetal arteries but smaller in adult arteries. Chronic hypoxia also increased endothelial cell density in fetal arteries but reduced it in adult arteries. These combined effects resulted in an increased (adult carotid), decreased (adult middle cerebral), or unchanged (fetal arteries) per cell serosal volume of distribution for endothelial factors. Despite this heterogeneity, the magnitude of endothelium-dependent vasodilatation to A23187, measured in vitro, was largely preserved, although sensitivity to this relaxant was uniformly depressed. N(G)-nitro-L-arginine methyl ester, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, and endothelium denudation each independently blocked A23187-induced vasodilation without unmasking any residual vasoconstrictor effect. Indomethacin did not significantly attenuate A23187-induced relaxation except in the hypoxic adult middle cerebral, where a small contribution of prostanoids was evident. Vascular sensitivity to exogenous nitric oxide (NO) was uniformly increased by chronic hypoxia. From these results, we conclude that chronic hypoxia reduced endothelial NO release while also upregulating some component of the NO-cGMP-PKG vasodilator pathway. These offsetting effects appear to preserve endothelium-dependent vasodilation after adaptation to chronic hypoxia.     

48-h Hypoxic exposure results in endothelium-dependent systemic vascular smooth muscle cell hyperpolarization

Chronic hypoxia (CH) results in reduced sensitivity to vasoconstrictors in conscious rats that persists upon restoration of normoxia. We hypothesized that this effect is due to endothelium-dependent hyperpolarization of vascular smooth muscle (VSM) cells after CH. VSM cell resting membrane potential was determined for superior mesenteric artery strips isolated from CH rats (PB = 380 Torr for 48 h) and normoxic controls. VSM cells from CH rats studied under normoxia were hyperpolarized compared with controls. Resting vessel wall intracellular Ca(2+) concentration ([Ca(2+)](i)) and pressure-induced vasoconstriction were reduced in vessels isolated from CH rats compared with controls. Vasoconstriction and increases in vessel wall [Ca(2+)](i) in response to the alpha(1)-adrenergic agonist phenylephrine (PE) were also blunted in resistance arteries from CH rats. Removal of the endothelium normalized resting membrane potential, resting vessel wall [Ca(2+)](i), pressure-induced vasoconstrictor responses, and PE-induced constrictor and Ca(2+) responses between groups. Whereas VSM cell hyperpolarization persisted in the presence of nitric oxide synthase inhibition, heme oxygenase inhibition restored VSM cell resting membrane potential in vessels from CH rats to control levels. We conclude that endothelial derived CO accounts for persistent VSM cell hyperpolarization and vasoconstrictor hyporeactivity after CH.     

Cytochrome p-450 epoxygenase products contribute to attenuated vasoconstriction after chronic hypoxia

The systemic vasculature exhibits attenuated vasoconstriction following chronic hypoxia (CH) that is associated with endothelium-dependent vascular smooth muscle (VSM) cell hyperpolarization. We hypothesized that increased production of arachidonic acid metabolites such as the cyclooxygenase product prostacyclin or cytochrome p-450 (CYP) epoxygenase-derived epoxyeicosatrienoic acids (EETs) contributes to VSM cell hyperpolarization following CH. VSM cell resting membrane potential (Em) was measured in superior mesenteric artery strips isolated from rats with control barometric pressure (Pb, congruent with 630 Torr) and CH (Pb, 380 Torr for 48 h). VSM cell Em was normalized between groups following administration of the CYP inhibitors 17-octadecynoic acid and SKF-525A. VSM cell hyperpolarization after CH was not altered by cyclooxygenase inhibition, whereas the selective CYP2C9 inhibitor sulfaphenazole normalized VSM cell Em between groups. Iberiotoxin also normalized VSM cell Em, which suggests that large-conductance, Ca2+-activated K+ (BKCa) channel activity is increased after CH. Sulfaphenazole administration restored phenylephrine-induced and myogenic vasoconstriction and Ca2+ responses of mesenteric resistance arteries isolated from CH rats to control levels. Western blot experiments demonstrated that CYP2C9 protein levels were greater in mesenteric arteries from CH rats. In addition, 11,12-EET levels were elevated in endothelial cells from CH rats compared with controls. We conclude that enhanced CYP2C9 expression and 11,12-EET production following CH contributes to BKCa channel-dependent VSM cell hyperpolarization and attenuated vasoreactivity.     

Influence of constriction, wall tension, smooth muscle activation and cellular deformation on rat resistance artery vasodilator reactivity

This study investigated how vasoconstriction (tone), wall tension, smooth muscle activation, and vascular wall deformation influence resistance artery vasodilator reactivity. Resistance arteries, from two different regional circulations (splanchnic, uterine) and from pregnant and non-pregnant rats, were cannulated and pressurized, or mounted on a wire myograph under isometric conditions prior to being exposed to both endothelium-dependent (acetylcholine, ACh) and -independent (sodium nitroprusside, SNP) vasodilator agonists. A consistent pattern of reduced vasodilator sensitivity was noted as a function of extent of preconstriction for both agonists noted in pressurized arteries. A similar pattern regarding activation was noted in wire-mounted arteries in response to SNP but not ACh. Wall tension proved to be a major determinant of vascular smooth muscle vasodilator reactivity and its normalization reversed this pattern, as more constricted vessels were more sensitive to ACh relaxation without any change in SNP sensitivity, suggesting that endothelial deformation secondary to vasoconstriction augments its vasodilator output. To our knowledge, this is the first study to dissect out the complex interplay between biophysical forces impinging on VSM (pressure, wall tension), the ambient level of tone (vasoconstriction, smooth muscle cell activation), and consequences of cellular (particularly endothelial) deformation secondary to constriction in determining resistance artery vasodilatory reactivity.     

Hyperpolarization of murine small caliber mesenteric arteries by activation of endothelial proteinase-activated receptor 2

Activation of endothelial proteinase-activated receptor 2 (PAR-2) relaxes vascular smooth muscle (VSM) and causes hypotension by nitric oxide (NO)-prostanoid-dependent and -independent mechanisms. We investigated whether endothelium-dependent hyperpolarization of VSM was the mechanism whereby resistance caliber arteries vasodilated independently of NO. VSM membrane potentials and isometric tension were measured concurrently to correlate the electrophysiological and mechanical changes in murine small caliber mesenteric arteries. In uncontracted arteries, the PAR-2 agonist, SLIGRL-NH2 (0.1 to 10 micromol/L), hyperpolarized the VSM membrane potential only in endothelium-intact arterial preparations. This response was unaltered by treatment of arteries with inhibitors of NO synthases (L-NAME), soluble guanylyl cyclase (ODQ), and cyclooxygenases (indomethacin). L-NAME, ODQ, and indomethacin also failed to inhibit SLIGRL-NH2-induced hyperpolarization and of cirazoline-contracted mesenteric arteries. However, in blood vessels that were depolarized and contracted with 30 mmol/L KCl, the effects of the SLIGRL-NH2 on membrane potential and tension were not observed. SLIGRL-NH2-induced hyperpolarization and relaxation was inhibited completely by the combination of apamin plus charybdotoxin, but only partially inhibited after treatment with the combination of barium plus ouabain, suggesting an important role for SKCa and IKCa channels and a lesser role for Kir channels and Na+/K+ ATPases in the hyperpolarization response. We concluded that activation of endothelial PAR-2 hyperpolarized the vascular smooth muscle (VSM) cells of small caliber arteries, without requiring the activation of NO synthases, cyclooxygenases, or soluble guanylyl cyclase. Indeed, this hyperpolarization may be a primary mechanism for PAR-2-induced hypotension in vivo.     

冷暴露小鼠尾动脉舒缩功能变化以及血管活性药物的作用特征

目的：研究不同温度条件下血管舒缩功能变化及哌唑嗪、山莨菪碱扩张血管作用变化特征,评价VitE在低温条件下的内皮保护作用,探讨上述药物在冻伤预防过程中的应用前景。方法：利用血管条技术,观察小鼠尾动脉血管在8℃、16℃、25℃、37℃四个温度条件下的收缩及舒张反应特点,比较哌唑嗪、山莨菪碱在不同温度条件下扩血管作用差异。在冷暴露处理的同时预敷Vit E,观察其对低温条件下血管内皮依赖性舒张功能的改善作用。结果：①不同温度条件下苯肾上腺素诱发的血管收缩反应存在明显差异,温度越低,收缩幅度越小;②硝普钠浓度依赖的扩血管作用随着温度的降低明显增强;③与硝普钠作用特点类似,哌唑嗪、山莨菪碱在低温条件下的扩血管作用强于37℃组;④低温能够降低乙酰胆碱内皮依赖的扩血管作用,Vit E能够剂量依赖地对抗低温的影响。结论：随着温度的降低,苯肾上腺素作用下的血管收缩明显减弱,平滑肌靶点扩血管药物的作用显著增强。乙酰胆碱内皮依赖的扩血管作用随温度的下降有所降低,Vit E能够在一定程度上减小低温对乙酰胆碱扩血管作用的影响。