Contraction Of Rat Aorta Research Articles

NS-398, a Cyclooxygenase-2-Specific Inhibitor, Delays Skeletal Muscle Healing by Decreasing Regeneration and Promoting Fibrosis

Nonsteroidal anti-inflammatory drugs are often prescribed after muscle injury. However, the effect of nonsteroidal anti-inflammatory drugs on muscle healing remains primarily controversial. To further examine the validity of using these drugs after muscle injury, we investigated the working mechanism of NS-398, a cyclooxygenase-2-specific inhibitor. In vitro experiments showed that NS-398 inhibited the proliferation and maturation of differentiated myogenic precursor cells, suggesting a detrimental effect on skeletal muscle healing. Using a mouse laceration model, we analyzed the in vivo effect of NS-398 on skeletal muscle healing at time points up to 4 weeks after injury. The in vivo results revealed delayed muscle regeneration at early time points after injury in the NS-398-treated mice. Compared to controls, lacerated muscles treated with NS-398 expressed higher levels of transforming growth factor-beta1, which corresponded with increased fibrosis. In addition, transforming growth factor-beta1 co-localized with myostatin, a negative regulator of skeletal muscle growth. We also found reduced neutrophil and macrophage infiltration in treated muscles, indicating that the delayed skeletal muscle healing observed after NS-398 treatment could be influenced by the anti-inflammatory effect of NS-398. Our findings suggest that the use of cyclooxygenase-2-specific inhibitors to treat skeletal muscle injuries warrants caution because they may interfere with muscle healing.

Chronic Ethanol Consumption Enhances Phenylephrine-Induced Contraction in the Isolated Rat Aorta

Changes in reactivity to phenylephrine in aortas isolated from 2-, 6-, and 10-week ethanol-treated rats and their age-matched control and isocaloric rats were investigated. Chronic ethanol consumption enhances the contractile response of endothelium-intact and -denuded rat aortic rings to phenylephrine, a response that is time-independent. Pretreatment with indomethacin reduced E(max) for phenylephrine in denuded aortas from ethanol-treated rats but not control or isocaloric rats. After indomethacin treatment, no differences in E(max) from phenylephrine were observed among the groups. SQ29548 ([1S-[1alpha-2alpha(Z)3alpha,4alpha]]-7-[3-[[(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid), an antagonist of prostaglandin H(2)/thromboxane A(2) (TXA(2)) receptors, did not alter phenylephrine-induced contraction in control or isocaloric aortas. However, in ethanol-treated aortas, E(max) was reduced to control level. Moreover, phenylephrine-stimulated release of thromboxane B(2), a stable metabolite of TXA(2), was higher in tissues from ethanol-treated rats. Simultaneous measurement of the changes in [Ca(2+)](i) and contraction induced by phenylephrine showed that both parameters are higher in the rat aorta from ethanol-treated rats. CaCl(2)-induced contraction in free Ca(2+) solution containing phenylephrine was increased in ethanol-treated aortas. Additionally, the enhancement in CaCl(2)-induced contraction was prevented by SQ29548. The major contribution of the present study is that it demonstrates a detailed description of the mechanisms involved in the enhancement of phenylephrine-induced contraction in rat aorta from ethanol-treated rats. We provided evidence that this response was not different among the three periods of treatment employed in this study and that it is maintained by two mechanisms: an increased release of vascular smooth muscle-derived vasoconstrictor prostanoids (probably TXA(2)) and an enhanced extracellular Ca(2+) influx.

Vascular contractile effect of urotensin II in young and aged rats: Influence of aging and contribution of endothelial nitric oxide

To elucidate whether aging influences the vascular contractile effect of urotensin II in rat thoracic aorta, and to evaluate the contribution of endothelial vasodilating substances in mediating the effect of urotensin II, the effect of urotensin II was examined in the vessels of young (2–3-month-old) and aged rat. Isolated rat aortic rings incubated in Krebs–Henseleit solution gassed with 95% O 2/5% CO 2 were stimulated with urotensin II, and the developed tension was measured. Urotensin II increased the developed tension, which was decreased by aging. In 2–3-months-old young aorta without endothelium, urotensin II (10 −10 to 10 −7) elicited a concentration-dependent aortic contraction to the maximal response almost equivalent to high KCl-induced contraction (79.4 ± 11.3% of KCl max). In the presence of endothelium, the urotensin II-induced vasoconstriction in young aorta was significantly attenuated to 33.3 ± 4.6% of KCl max. However, the contractile response was greater in the pretreatment with N G-nitro- l-arginine ( l-NNA) (100 μM) (50.3 ± 8.4% of KCl max in endothelial denuded aorta), suggesting the vasorelaxing role of endothelial nitric oxide. In 25–27-months-old aged rat aorta, the urotensin II-mediated contraction was remarkably decreased, both in the presence (6.3 ± 2.0% of KCl max) and absence (11.7 ± 3.0% of KCl max) of endothelium. A cyclooxygenase inhibitor, diclofenac (10 μM), did not have any effect on the urotensin II-induced contraction. These results suggest that urotensin II can induce vascular smooth muscle contraction in rat aorta, and there was an aging-related decline in the urotensin II-induced contraction. Endothelial production of nitric oxide in response to urotensin II but not cyclooxygenase metabolites such as prostacyclin may play a role in reducing the vascular constriction especially in young aorta.

8-NH2-Boldine, an Antagonist of α1Aand α1BAdrenoceptors without Affinity for the α1DSubtype: Structural Requirements for Aporphines at α1-Adrenoceptor Subtypes

Structure-activity analysis of 21 aporphine derivatives was performed by examining their affinities for cloned human alpha (1A), alpha (1B) and alpha (1D) adrenoceptors (AR) using membranes prepared from rat-1 fibroblasts stably expressing each alpha (1)-AR subtype. All the compounds tested competed for [ (125)I]-HEAT binding with steep and monophasic curves. The most interesting compound was 8-NH (2)-boldine, which retains the selective affinity for alpha(1A)-AR (pKi = 6.37 +/- 0.21) vs. alpha(1B)-AR (pKi = 5.53 +/- 0.11) exhibited by 1,2,9,10-tetraoxygenated aporphines, but shows low affinity for alpha(1D)-AR (pKi < 2.5). Binding studies on native adrenoceptors present in rat cerebral cortex confirms the results obtained for human cloned alpha (1)-AR subtypes. The compounds selective for the alpha (1A) subtype discriminate two binding sites in rat cerebral cortex confirming a mixed population of alpha (1A)- and alpha (1B)-AR in this tissue. All compounds are more selective as inhibitors of [ (3)H]-prazosin binding than of [ (3)H]-diltiazem binding to rat cerebral cortical membranes. A close relationship was found between affinities obtained for cloned alpha (1A)-AR and inhibitory potencies on noradrenaline-induced contraction or inositol phosphate accumulation in tail artery, confirming that there is a homogeneous functional population of alpha(1A)-AR in this vessel. On the contrary, a poor correlation seems to exist between the affinity of 8-NH (2)-boldine for cloned alpha (1D)-AR and its potency as an inhibitor of noradrenaline-induced contraction or inositol phosphate accumulation in rat aorta, which confirms that a heterogeneous population of alpha (1)-AR mediates the adrenergic response in this vessel.

Estrogen potentiates vasopressin-induced contraction of female rat aorta by enhancing cyclooxygenase-2 and thromboxane function

To determine the roles of estrogen and constrictor prostanoids in vasopressin (VP)-induced contraction of female rat aorta, vascular reactivity to VP was determined in thoracic aortas of intact, ovariectomized, and ovariectomized + estrogen-replaced female rats in the presence of indomethacin (Indo), NS-398, SQ-29,548, or vehicle control. The effects of estrogen on vascular reactivity to the thromboxane A(2) analog U-46619 were also examined. Maximal contractile response to VP in intact female rats (5,567 +/- 276 mg/mg of aortic ring wt) was markedly attenuated by ovariectomy (2,485 +/- 394 mg; P < 0.001) and restored by estrogen replacement with 17beta-estradiol (5,059 +/- 194 mg; P > 0.1). Indo and NS-398 significantly attenuated maximal responses to VP in intact female rats to a similar extent [3,176 +/- 179 (P < 0.0001) and 3,258 +/- 152 mg (P < 0.0001), respectively]. Ovariectomy abolished and estrogen replacement restored the inhibitory effects of Indo, NS-398, and SQ-29,548. Contractile responses of rat aorta to U-46619 were significantly greater (P < 0.0001) in females (5,040 +/- 238 mg) than in males (3,679 +/- 96 mg). Ovariectomy markedly attenuated (3,923 +/- 84 mg; P < 0.01) and estrogen replacement restored (5,024 +/- 155 mg; P > 0.1) responses to U-46619 in female aortas. These data reveal that estrogen is an important regulator of the contractile responses of female rat aorta to VP, which appears to potentiate both cyclooxygenase-2 and constrictor prostanoid function in the vascular wall.

Dihydropyridines, Nitric Oxide and Vascular Protection

For more than decades calcium antagonists (CEBs) have been widely used for the treatment of myocardial ischaemia (angina pectoris). Among the classes of CEBs, the 1,4-dihidropyridine (DHPs) have been used for this indication because of their haemodynamic and electrophysiological properties. In particular, DHPs are compounds capable of vascular protection on both smooth muscle and endothelium. The main protective activity is related to their calcium antagonist activity. In addition, they present vascular dilatation function, which has been related to an anti-endothelin efficacy. The newer DHPs are endowed with slow onset and long duration of vasodilator activity and reduce coronary resistance with little or no effect on heart rate. The more lipophilic DHP, lacidipine, is also able to reduce the formation of atheroma plaque in animal models at therapeutic doses. It has potent and long-lasting antihypertensive properties and appears to protect the arterial wall against the development of atherosclerotic lesions in animal models or human subjects with severe and multiple risk factors. Additionally, it has been observed that: i) NO/cyclic GMP pathway facilitates the inhibitory effect of Ca(++) antagonists on KCl-evoked contraction in rat aorta; ii) Vasodilator effect of lacidipine was significantly attenuated in the presence of NO-synthase inhibitors; iii) DHPs stimulate an electrochemical activity related to the nitric oxide (NO) system within the aortic vessel tissue, in rats and mice. In particular, they implement endothelial NO at "useful" and not toxic nanomolar levels. These activities join the already described positive effects of these compounds upon vascular functions.

A Phenoxazine Compound, 2-Amino-4,4.ALPHA.-dihydro-4.ALPHA.-7-dimethyl-3H-phenoxazine-3-one Reverses the Phenylephrine or High-K+ Induced Contraction of Smooth Muscles in Rat Aorta and Guinea Pig Tenia Cecum

2-Amino-4,4alpha-dihydro-4alpha-7-dimethyl-3H-phenoxazine-3-one (Phx-1) reversed concentration dependently the contraction of both rat aorta and guinea pig tenia cecum induced by phenylephrine or high-K(+). Since Phx-1 suppresses the responses of human mononuclear cells to phytohemagglutinin, (Akazawa et al. Tohoku J. Exp. Med., 196, 185-192, 2002), Phx-1 may be useful for developing new vasorelaxing agents with immunosuppressive action.

Antihypertensive and Neuroprotective Effects of Astaxanthin in Experimental Animals

Astaxanthin is a natural antioxidant carotenoid that occurs in a wide variety of living organisms. We investigated, for the first time, antihypertensive effects of astaxanthin (ASX-O) in spontaneously hypertensive rats (SHR). Oral administration of ASX-O for 14 d induced a significant reduction in the arterial blood pressure (BP) in SHR but not in normotensive Wistar Kyoto (WKY) strain. The long-term administration of ASX-O (50 mg/kg) for 5 weeks in stroke prone SHR (SHR-SP) induced a significant reduction in the BP. It also delayed the incidence of stroke in the SHR-SP. To investigate the action mechanism of ASX-O, the effects on PGF(2alpha)-induced contractions of rat aorta treated with NG-nitro-L-arginine methyl ester (L-NAME) were studied in vitro. ASX-O (1 to 10 microM) induced vasorelaxation mediated by nitric oxide (NO). The results suggest that the antihypertensive effect of ASX-O may be due to a NO-related mechanism. ASX-O also showed significant neuroprotective effects in ischemic mice, presumably due to its antioxidant potential. Pretreatment of the mice with ASX-O significantly shortened the latency of escaping onto the platform in the Morris water maze learning performance test. In conclusion, these results indicate that astaxanthin can exert beneficial effects in protection against hypertension and stroke and in improving memory in vascular dementia.

Vasorelaxant Effects of Forsythiaside from the Fruits of Forsythia suspensa

The vasorelaxant effects of forsythiaside (compound 1) from the fruits of Forsythia suspensa on isolated rat aortic rings were studied. Compound 1 showed a slow relaxation activity against norepinephrine (NE)-induced contractions of rat aorta with/without endothelium. This compound did not affect contractions induced by a high concentration of potassium (K(+) 60 mM), while it inhibited NE-induced vasocontraction in the presence of nicardipine. These results show that the inhibition by compound 1 of NE-induced vasocontraction is due to a decrease in calcium influx from the extracellular space caused by NE.

Pharmacological evaluation of both enantiomers of (R,S)-BM-591 as thromboxane A2 receptor antagonists and thromboxane synthase inhibitors

The aim of this work is to evaluate the anti-thromboxane activity of two pure enantiomers of (R,S)-BM-591, a nitrobenzene sulfonylurea chemically related to torasemide, a loop diuretic. The drug affinity for thromboxane A2 receptor (TP) of human washed platelets has been determined. In these experiments, (R)-BM-591 (IC50 = 2.4 ± 0.1 nM) exhibited a significant higher affinity than (S)-BM-591 (IC50 = 4.2 ± 0.15 nM) for human washed platelets TP receptors. Both enantiomers were stronger ligands than SQ-29548 (IC50 = 21.0 ± 1.0 nM) and sulotroban (IC50 = 930 ± 42 nM), two reference TXA2 receptor antagonists. Pharmacological characterisations of (S)-BM-591 and (R)-BM-591 were compared in several models. Thus, (R)-BM-591 strongly prevented platelet aggregation induced by arachidonic acid (AA) (600 μM) and U-46619 (1 μM) while (S)-BM-591 showed a lower activity. On isolated tissues pre-contracted by U-46619, a stable TXA2 agonist, (S)-BM-591 was more potent in relaxing guinea-pig trachea (EC50 = 0.272 ± 0.054 μM) and rat aorta (EC50 = 0.190 ± 0.002 μM) than (R)-BM-591 (EC50 of 9.60 ± 0.63 μM and 0.390 ± 0.052 μM, respectively). Moreover, at 1 μM, (R)-BM-591 totally inhibited TXA2 synthase activity, expressed as TXB2 production from human platelets, while at the same concentration, (S)-BM-591 poorly reduced the TXB2 synthesis (22%). Finally, in rats, both enantiomers lost the diuretic activity of torasemide. In conclusion, (R)-BM-591 exhibits a higher affinity and antagonism on human platelet TP receptors than (S)-BM-591 as well as a better thromboxane synthase inhibitory potency. In contrast, (S)-BM-591 is more active than the (R)-enantiomer in relaxing smooth muscle contraction of rat aorta and trachea guinea pig. Consequently, (R)-BM-591 represents the best candidate for further development in the field of thrombosis disorders.

Mechanisms of hydroxyl radical-induced contraction of rat aorta

The present study was designed to investigate the effects of hydroxyl radicals ( OH), generated via the Fe 2+-mediated Fenton reaction, on isolated rat aortic rings with and without endothelium. In the absence of any vasoactive agent, generation of OH alone elicited an endothelium-independent contraction in rat aortic rings in a concentration-dependent manner. Hydroxyl radical-induced contractions of denuded rat aortic rings appeared, however, to be slightly stronger than those on intact rat aortic rings. The contractile responses to OH were neither reversible nor reproducible in the same ring; even small concentrations of OH radicals resulted in tachyphylaxis. Removal of extracellular calcium ions (Ca 2+) or buffering intracellular Ca 2+ with 10 μM acetyl methyl ester of bis( o-aminophenoxy) ethane- N, N, N′, N′,-tetraacetic acid (BAPTA-AM) significantly attenuated the contractile actions of OH radicals. The presence of 1 μM staurosporine, 1 μM bisindolylmaleimide I, 1 μM Gö6976 [inhibitor of protein kinase C (PKC)], 2 μM PD-980592 (inhibitor of ERK), 10 μM genistein, and 1 μM wortmannin significantly inhibited the contractions induced by OH. Proadifen (10 μM), on the other hand, significantly potentiated the hydroxyl radical-induced contractions. Exposure of primary cultured aortic smooth muscle cells to OH produced significant, rapid rises of intracellular free Ca 2+ ([Ca 2+] i). Several, specific antagonists of possible endogenously formed vasoconstrictors did not inhibit or attenuate either hydroxyl radical-induced contractions or the elevation of [Ca 2+] i. Our new results suggest that hydroxyl radical-triggered contractions on rat aortic rings are Ca 2+-dependent. Several intracellular signal transduction systems seem to play some role in hydroxyl radical-induced vasoconstriction of rat aortic rings.

Clonidine induces rat aorta relaxation by nitric oxide-dependent and -independent mechanisms

The α 1- and α 2-adrenoceptors coexist in vascular smooth muscle cells producing vascular contraction and relaxation. This study was designed to investigate which is the mechanism activated by clonidine in the rat aorta, and the endothelial factors possibly involved in the relaxation induced by clonidine. The α 2-adrenoceptors agonist clonidine relaxed rat aortas pre-contracted with phenylephrine, with or without endothelium. In non-contracted denuded arteries, clonidine produced contractions instead of relaxation. In intact endothelium aortic rings, clonidine induced greater relaxation than in denuded aortic rings. In aortas with intact endothelium, the NO-synthase inhibitor l-NAME (10 μmol/L) and the NO-scavenger hemoglobin (10 μmol/L) reduced the relaxation to clonidine. On the other hand, indomethacin (10 μmol/L) failed to alter the relaxation induced by clonidine. These results suggest the participation of NO, but not prostacyclin in clonidine-induced relaxation. In aortic rings pre-contracted with KCl (60 mmol/L) the relaxation induced by clonidine was abolished; however, the K + channel blockers glibenclamide (K ATP), tetraethylamonium (K Ca), and the combination of apamin and charybdotoxin (K Ca) did not change the relaxation induced by clonidine. The relaxation induced by clonidine on PGF2α-contracted arteries was not affected by prazosin. However, in the absence of prazosin, clonidine had an additional contractile effect in PGF2α-contracted arteries. In conclusion, our results show that in rat aorta clonidine can activate α 2-adrenoceptors in the smooth muscle cells and α 2-adrenoceptors in the endothelial cells that activates NO production, but not prostacyclin and/or EDHF. In the absence of phenylephrine and prazosin, clonidine can also activate α 1-adrenoceptors and rat aorta contraction.

Mechanism of Human Urotensin II-Induced Contraction in Rat Aorta

Urotensin II induced sustained contraction with an EC50 value of 2.29 ± 0.12 nM in rat aorta. Urotensin II (100 nM) transiently increased cytosolic Ca2+ level ([Ca2+]i), followed by a small sustained phase superimposed with rhythmic oscillatory change. In the presence of verapamil and La3+, the [Ca2+]i oscillation was completely inhibited, although a small transient increase in [Ca2+]i remained. The urotensin II-induced contraction was also partially inhibited by verapamil and La3+. Combined application of verapamil, La3+, and thapsigargin completely inhibited the increase in [Ca2+]i with only partial inhibition of the contraction elicited by urotensin II. Urotensin II increased myosin light chain (MLC) phosphorylation to a level greater than that induced by 72.7 mM KCl (high K+). Pretreatment with Go6983 (PKC inhibitor), U0126 (MEK inhibitor), or SB203580 (p38MARK inhibitor) partially inhibited the urotensin II-induced contraction with no effects on the high K+-induced contractions. Wortmannin (MLC kinase inhibitor) only partially inhibited urotensin II-induced contraction, although it completely inhibited the high K+-induced contraction. These results suggest that urotensin II-induced contraction is mediated by the Ca2+/calmodulin/MLC kinase system and modulated by the Ca2+ sensitization mechanisms to increase MLC phosphorylation. In addition, activations of PKC, p38MAPK, and ERK1/2 modulate the contractility mediated by urotensin II in rat aorta.

SR 33557, a novel calcium-antagonist: interaction with [3H]-(�)-nitrendipine and [3H]-(?)-desmethoxy-verapamil binding sites in cerebral membranes

We investigated the pharmacological properties of SR 33557, a novel compound with calcium-antagonist properties, in both functional tests in vitro and radioligand binding studies. SR 33557 potently antagonized calcium-induced contraction of potassium-depolarized rat aorta in vitro with an IC50 value of 5.6 +/- 0.9 nM, but was a much weaker inhibitor of noradrenaline-induced contraction of the same tissue (IC50 = 96 +/- 22 nM). SR 33557 totally inhibited [3H]-(+/-)-nitrendipine binding to rat brain membranes with a Ki value of 0.19 +/- 0.03 nM. Diltiazem, which used alone increases [3H]-(+/-)-nitrendipine binding, reversed this inhibition indicating that SR 33557 allosterically regulates [3H]-(+/-)-nitrendipine binding. SR 33557 also fully inhibited [3H]-(-)-desmethoxyverapamil binding to cerebral membranes, but inhibition curves were biphasic. IC50 value calculated for that part of the curve which reflects the high affinity binding site of SR 33557 (IC50 = 0.20 +/- 0.02 nM) was very similar to the Ki value determined for inhibition of [3H]-(+/-)-nitrendipine binding. Kinetic evidences indicate that SR 33557 binds to a site which is distinct from the 1,4-dihydropyridine or the phenylalkylamine binding sites associated with the calcium channel. To test the pharmacological specificity of these interactions, the ability of SR 33557 to interact with eight other receptors in cerebral or heart membranes was assessed by binding assays. No high-affinity interaction was observed between SR 33557 and any of the receptors investigated. We conclude that SR 33557 binds specifically and with a high affinity to a site closely associated with the voltage-operated calcium channel in cerebral membranes.

Mechanisms of ADRF release from rat aortic adventitial adipose tissue.

Blood vessels are surrounded by variable amounts of adipose tissue. We showed earlier that adventitial adipose tissue inhibits rat aortic contraction by release of a transferable factor, adventitium-derived relaxing factor (ADRF), which activates smooth muscle K(+) channels. However, little is known about the mechanisms of ADRF release. Using isolated rat aortic rings and isometric contraction measurements, we show that ADRF release depends on extracellular [Ca(2+)] (EC(50) approximately 4.7 mM). ADRF effects do not involve neuronal presynaptic N-type Ca(2+) and Na(+) channels or vanilloid, cannabinoid, and CGRP receptors. ADRF release is strongly inhibited by the protein tyrosine kinase inhibitors genistein and tyrphostin A25. In contrast, daidzein, an inactive genistein analog, and the protein tyrosine kinase inhibitor ST638 had no effect. Protein kinase A inhibition by H89 also inhibited ADRF release, whereas the protein kinase G inhibitor KT-5823 had no effect. We propose that ADRF release is Ca(2+) dependent and is regulated by intracellular signaling pathways involving tyrosine kinase and protein kinase A. Furthermore, ADRF release does not depend on perivascular nerve endings.

Vasorelaxant activity of N-caffeoylamino acids

Twelve N-caffeoylamino acids and N-cinnamoylamino acids were synthesized and their vasorelaxation activity against norepinephrine (NE)-induced contraction of rat aorta was examined. The following structure-activity relationships were found. 1) On the benzene ring, the caffeoyl structure is effective for vasorelaxation, while the cinnamoyl structure reduced vasorelaxation activity. 2) Four to six carbons are more effective as the carbon chain connecting the acylamino and carboxyl terminal groups. N-Caffeoyl-beta-alanine and N-caffeoyltranexamic acid were used to investigate the action mechanism of vasorelaxing activities. It is believed that these compounds antagonize NE-induced vasocontraction by inhibiting receptor-operated calcium channels.

Salt 스트레스에 의한 흰쥐 적출대동맥의 수축력 변화양상

To examine whether salt stress would alter or not contractility of isolated rat aorta, under anesthesia with sodium pentobarbital(50 mg kg-1 i.p.), male Sprague Dawley rats(300-330 g) were subjected to 0, 50, and 150 mM of sodium chloride at 37<TEX>$^{\circ}C$</TEX> for 60 min. where as the sham group was left at modified Krebs-bicarbonate solution. To measure contractile response of vascular ring preparation isolated from rat was determined in organ bath and was recorded on physiograph connected to isometric transducer. And the strip was checked for expression of heat shock protein(Hsp) by Western blotting. One, three and eight hours later, we measured vascular contractility of isolated rat aorta treated with KCI, phenylephrine from organ bath study. The dose-vascular responses of potassium chloride and phenylephrine showed a little augmentation by NaCl concentration in the strips exposed to NaCl for 8 hours. And the response of relaxation induced by nitroprusside and acetylcholine was not influenced by NaCl stress in isolated aorta ring for 8 hours, respectively. Expression pattern of Hsp 70 of vascular muscle in isolated rat aorta showed a little increase in 150 mM NaCl group at 8 hours after NaCl treatment but not at 3 hours, and Hsp 60 expression of rat aorta was markedly increased in 50 mM NaCl group at 8 hours after NaCl treatment. Taken together, NaCl induced dose-and time dependent accumulation of the Hsp but not affected contraction of rat aorta. These data suggest that short term high salt stress was not sufficient to induce hypertension of rat aorta.

Strain-specific effects of acidic pH on contractile state of aortas from Wistar and Wistar Kyoto rats

The effects of acidosis were investigated on the resting and precontracted aortas from Wistar and Wistar Kyoto (WKY) rats. Decrease in pH from 7.4 to 6.5, having no effect on the resting tension of Wistar aorta, induced a marked contraction of WKY aorta. Acidic pH markedly relaxed the contraction to 300 nM phenylephrine in Wistar aorta, whereas in WKY aorta, it produced a biphasic response, an initial relaxation followed by potentiation of the contraction. In aortas loaded with fura 2-AM, phenylephrine caused an increase in intracellular Ca 2+ ([Ca 2+] i) and a contraction in both Wistar and WKY rats. pH 6.5 produced a decrease in [Ca 2+] i to a near-basal level and almost abolished the phenylephrine-induced contraction in Wistar rat aorta. However, in WKY aorta, a biphasic response, an initial decline and later a recovery of [Ca 2+] i level, was observed. Interestingly, at similar sustained [Ca 2+] i, the contractile response to phenylephrine in WKY aorta was potentiated under acidic pH conditions. Acidic pH-induced inhibition of the contraction to phenylephrine was unaffected by iberiotoxin, 4-aminopyridine, and glibenclamide (Ca 2+-activated, delayed rectifier and ATP-sensitive K + channel inhibitors, respectively), in aortas from both Wistar and WKY. Decrease in extracellular pH was associated with a rapid fall in intracellular pH (pH i) and the intracellular acidification profile was not different in both strains. All these results show that acidic pH induces strain-specific inhibitory and excitatory effects on the contractile state of aortas from Wistar and WKY rats, respectively. The sustained and transient relaxant responses to acidic pH in Wistar and WKY aortas, respectively, are due to decrease in [Ca 2+] i levels, but this decrease in [Ca 2+] i is independent of the activation of K + channels.

A new view of K+ -induced contraction in rat aorta: the role of Ca2+ binding.

Strong, K+ -induced contractions of rat aorta in Ca-free, Mg-free media were not accompanied by increased intracellular calcium concentration, [Ca2+](i), whereas such contractions in the presence of the divalent cations were correlated with rising [Ca2+](i) as assessed by fura-2. At the same time, calcium channel blockers, a modulator of Ca2+-binding proteins, and a modulator of actin polymerization, inhibited all types of K+ -induced contractions. Increasing the K+ in isotonic medium evoked a rise of (45)Ca2+ binding to the plasma membrane of freshly isolated aortic cells. Although Ca2+ -dependent events underlie the mechanism of K+ -induced vascular contractions in both the presence and absence of Ca2+, in contrast to the view that [Ca2+](i) is a key regulator of excitation-contraction coupling in smooth muscle, we suggest that the modulation of Mg2+ -dependent Ca2+ binding, probably within/at the L-type calcium channel by K+, is a trigger for aortic contraction. This Ca2+ binding may then activate actin-myosin interaction.

Influence of Vascular Endothelium in Contraction Induced by Phorbol Ester in Renal Hypertensive Rats

Background and Objectives:The vascular endothelium plays an important role in circulation, by modulating the contractile responses of the arterial smooth muscle. This study was aimed at investigating the possible role of the endothelium in the contractile response to phorbol 12, 13-dibutyrate (PDB) in chronic two-kidney, one clip (2K1C) hypertensive rats. Materials and Methods:2K1C hypertension was induced by clipping the left renal artery of the study rats, with age-matched rats receiving a sham treatment, which served as controls. The thoracic aortae were mounted in tissue baths to measure the isometric tension. Results:The PDB showed a dosedependent contraction, with larger responses in the 2K1C hypertensive than the sham-clipped control rats. Nnitro-L-arginine (L-NNA) and methylene blue (MB) induced an increase in the tension in the presence of PDB, and the potentiating effects of L-NNA or MB were attenuated in the 2K1C rats as compared to the controls. Staurosporine, an inhibitor of protein kinase C, completely inhibited the contractile response to PDB, as well as enhancing the effects of L-NNA and MB. Removal of the endothelium abolished the contractile responses to LNNA and MB in both the 2K1C and control rats. The relaxation responses to acetylcholine in the aortic rings precontracted with PDB were also attenuated in the 2K1C rats, and L-NNA prevented the effect of the acetylcholine-induced relaxation. Indomethacin, glibenclamide and iberiotoxin did not affect the PDB responses in both the 2K1C and control rats. Conclusion:These results indicate the endothelium plays an inhibitory role against PDB-induced contraction in rat aortae, by releasing nitric oxide, and the inhibitory role of the endothelium is impaired in 2K1C renal hypertension. (Korean Circulation J 2003;33 (11):1036-1043)