Isometric contraction increases endothelial nitric oxide synthase activity via a calmodulin antagonist-sensitive pathway in rat aorta

In this work, the possibility that isometric contraction activates endothelial nitric oxide synthase (eNOS) in a calcium/calmodulin (Ca2+/CaM)-dependent manner was examined in rat thoracic aorta. Step-wise stable contractile responses (precontractions) to phenylephrine were obtained in endothelium-intact and endothelium-denuded aortic rings. The subsequent addition of the NO synthase inhibitor, N(G)nitro-l-arginine methyl ester (l-NAME), or the soluble guanylyl cyclase inhibitor, ODQ, further augmented precontractions in a concentration-dependent manner. The amplitude of l-NAME- and ODQ-induced increases in tone were dependent on the level of precontraction; the maximal increments for l-NAME and ODQ were observed in arteries precontracted with phenylephrine at 67% of its maximal effect. Likewise, in endothelium-intact non-contracted arteries, l-NAME and ODQ induced small but significant increases in tone. Neither l-NAME nor ODQ had any effect in endothelium-denuded preparations. In endothelium-intact aortic rings precontracted with high K+ solutions, l-NAME also elicited supplementary contractions dependent on precontraction level. The CaM antagonist, calmidazolium, inhibited in a concentration-dependent, noncompetitive, manner the effects of l-NAME on the tone of endothelium-intact phenylephrine-precontracted aortic rings. These results suggest that isometric contraction increases the activity of eNOS by means of the Ca2+/CaM complex in rat aorta.     

Angiotensin-(1-7) is involved in the endothelium-dependent modulation of phenylephrine-induced contraction in the aorta of mRen-2 transgenic rats

1. The contribution of the local vascular production of angiotensin-(1-7) [Ang-(1-7)] to the control of alpha-adrenergic-induced contractions in the aorta of Sprague-Dawley (SD) and TGR(mRen-2)27 [mRen-2] rats was studied. 2. In mRen-2 rats, contractile responses to phenylephrine were diminished as compared to control SD rats in endothelium containing but not in endothelium-denuded vessels. L-NAME increased contractile responses to phenylephrine in mRen-2 rats and, after nitric oxide synthase blockade, responses to phenylephrine became comparable in both strains. 3. Inhibition of angiotensin-converting enzyme (ACE) by captopril potentiated contractile responses in mRen-2 rats and diminished contractile responses in SD rats, both effects being dependent on the presence of a functional endothelium. The effect of captopril in mRen-2 rats was abolished in vessels pre-incubated with Ang-(1-7). 4. Blockade of Ang-(1-7) and bradykinin (BK) receptors by A-779 and HOE 140 respectively, increased phenylephrine-induced contraction in mRen-2, but not in SD rats. This effect was seen only in endothelium-containing vessels. 5. Angiotensin II AT(1) and AT(2) receptor blockade by CV 11974 and PD 123319 did not affect the contractile responses to phenylephrine in aortas of transgenic animals but diminished the response in SD rats. This effect was only seen in the presence of a functional endothelium. 6. It is concluded that the decreased contractile responses to phenylephrine in aortas of mRen-2 rats was dependent on an intact endothelium, the local release and action of Ang-(1-7) and bradykinin.     

Angiotensin AT(1) receptor phosphorylation and desensitization in a hepatic cell line. Roles of protein kinase c and phosphoinositide 3-kinase

Desensitization and phosphorylation of the endogenous angiotensin II AT(1) receptor were studied in clone 9 liver cells. Agonist activation of AT(1) receptors blunted the response to subsequent addition of angiotensin II. Partial inhibition of the angiotensin II-induced calcium response was observed when cells were pretreated with dibutyryl cyclic AMP, tetradecanoyl phorbol acetate (TPA), vasopressin, or lysophosphatidic acid. All of these desensitization processes were associated with receptor phosphorylation. Angiotensin II-induced AT(1) receptor phosphorylation was partially blocked by the protein kinase C inhibitor bisindolylmaleimide I and by phosphoinositide 3-kinase inhibitors (wortmannin and LY294002); the actions of these inhibitors were not additive. Pertussis toxin pretreatment of cells also partially inhibited angiotensin II-induced AT(1) receptor phosphorylation. TPA-induced AT(1) receptor phosphorylation was completely blocked by bisindolylmaleimide I. AT(1) receptor phosphorylation was also induced by vasopressin and lysophosphatidic acid, and these effects were partially inhibited by bisindolylmaleimide I. Angiotensin II increased Akt/PKB (protein kinase B) phosphorylation and protein kinase C membrane association. The effect on Akt/PKB phosphorylation was blocked by phosphoinositide 3-kinase inhibitors. These findings indicate that clone 9 cells exhibit both homologous and heterologous desensitization in association with AT(1) receptor phosphorylation. In these hepatic cells, angiotensin II-induced receptor phosphorylation involves pertussis toxin-sensitive and -insensitive G proteins, and is mediated in part through protein kinase C and phosphoinositide 3-kinase.     

Angiotensin II receptor mRNA expression and vasoconstriction in human coronary arteries: effects of heart failure and age

Angiotensin II is a potent vasoconstrictor that is implicated in the pathogenesis of hypertension, heart failure and atherosclerosis. In the present study, angiotensin II receptor mRNA expression levels were quantified by real-time polymerase chain reaction and the vasocontractile responses to angiotensin II were characterised by in vitro pharmacology in endothelium-denuded human coronary arteries. Angiotensin II type 1 (AT(1)) and type 2 (AT(2)) receptor mRNA expression levels were significantly down-regulated in arteries from patients with heart failure as compared to controls. The angiotensin II-induced vasoconstriction diminished with increasing age in patients with heart failure (r(2)=0.31, P<0.05). Also, the AT(1) receptor mRNA expression levels decreased with increasing age in patients with heart failure (r(2)=0.74, P<0.05), while no such correlation could be shown in the control group (r(2)=0.04, P=n.s.). The AT(2) receptor mRNA expression levels did not correlate with age in patients with heart failure or controls. In conclusion, the diminished angiotensin II vasoconstriction with age in heart failure patients is most likely due to a lower density of AT(1) receptors and may result from a longer period of exposure to heart failure in older patients.     

Are multiple angiotensin receptor types involved in angiotensin (1-7) actions on isolated rat portal vein.

Angiotensin (1-7) [Ang (1-7)] is a bioactive component of the renin angiotensin system. Ang (1-7) may interact with angiotensin type 1 (AT1) or type 2 (AT2) receptors and with Ang (1-7) - specific receptors. We examined the interactions between different doses of Ang (1-7) (1 nM-1 microM) and angiotensin II (Ang II) (10 and 100 nM) on isolated rat portal vein. In endothelium-denuded portal vein rings, Ang (1-7) inhibited contractile effects induced by Ang II. The effects of Ang (1-7) were modified by indomethacin, N(G)-nitro-L-arginine methyl ester (L-NAME), (D-Ala7)-Angiotensin (1-7) (H-2888) and losartan. Our results suggest that on rat isolated portal vein rings without endothelium, Ang (1-7) reduces Ang II-induced contractions by acting mostly on Ang (1-7) specific receptors, and this effect is mediated by vasodilatatory prostaglandins. At high concentrations, Ang (1-7) effects are mediated by AT1-receptors, though to a lesser extent than by Ang (1-7) specific receptors.     

The effect of nitric oxide synthase blockade on responses to morphine in rat aortic rings

1 It has been suggested that opioids may play an indirect role in the regulation of the peripheral circulation through the control of nitric oxide (NO) release in vascular tissue. The current study was undertaken to investigate the effect of nitric oxide synthase (NOS) blockade on responses to morphine in phenylephrine (PE)- or KCl-precontracted rat aortic rings. 2 Morphine (3 x 10(-8) - 3 x 10(-5) M) administration did not cause any significant effect on basal tonus of endothelium-intact or endothelium-denuded preparations. Morphine produced concentration-dependent relaxation responses in endothelium-intact as well as in endothelium-denuded rat aortic rings precontracted by PE or KCl. Removal of endothelium did not significantly alter the relaxation responses to morphine. 3 The relaxant responses to morphine were significantly and partially inhibited by pretreatment of tissues with naloxone (NAL, 3 x 10(-5) M) for 5 min. The inhibitory effect of NAL on relaxant responses to morphine in PE- or KCl-precontracted rings did not differ significantly between endothelium-intact and endothelium-denuded preparations. 4 Incubation of endothelium-intact or endothelium-denuded rat aortic rings with NOS inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME, 10(-4) M) for 20 min did not cause a significant inhibition on relaxation responses to morphine. 5 These findings confirmed the presence of opiate receptors in rat thoracic aorta, but suggested that mechanisms other than NO release play a role in the relaxant effect of morphine on rat aortic rings.     

Endothelium-dependent response of the rabbit aorta to femtomolar concentrations of angiotensin II.

Thirty-five percent of endothelium-intact rabbit aortic rings tested contracted biphasically to angiotensin II (AII). The threshold concentration in these rings varied, ranging from 10(-16) to 10(-12) M. The remaining 65% contracted monophasically with a range of threshold concentrations of 10(-11)-10(-8) M. All endothelium-denuded rings tested contracted monophasically with a threshold concentration of 10(-10)-10(-8) M. The contractions of both types of rings were inhibited by 1-sar-8-ala-angiotensin II, but not phentolamine or indomethacin, indicating that the contractions were not mediated by secondary agonists such as noradrenaline or arachidonic acid metabolites. Bioassay studies revealed that 10(-16) M AII released an endothelial factor that modulated the action of AII, converting the monophasic response of an endothelium-denuded ring to a biphasic response to AII (10(-16)-10(-7) M). The results demonstrate for the first time the endothelium-dependent response of an artery to femtomolar concentrations of AII and support the existence of arterial angiotensin receptors capable of being saturated by circulating levels of the hormone.     

Effects of metabolic inhibitors on endothelium-dependent and endothelium-independent vasodilatation of rat and rabbit aorta.

1. Basal release of endothelium-derived relaxing factor (EDRF) rendered endothelium-containing rings of rat aorta 4.7 fold less sensitive to the contractile actions of phenylephrine and depressed the maximum response when compared with endothelium-denuded rings. The responsiveness and maximum response to phenylephrine was, however, similar in rings of rabbit aorta with or without endothelium. 2. Rotenone (1 nM-0.1 microM), an inhibitor of oxidative phosphorylation, induced a profound, irreversible blockade of phenylephrine-induced tone in endothelium-containing and endothelium-denuded rings of rat aorta, but induced only slight inhibition of tone in rings of rabbit aorta. 3. 2-Deoxy glucose (10 mM), an inhibitor of glycolysis, had no effect on phenylephrine-induced contraction in endothelium-denuded rings of rat aorta, but inhibited reversibly the endothelium-dependent depression of contraction in endothelium containing rings. 2-Deoxy glucose had no effect on phenylephrine-induced contraction in rings of rabbit aorta with or without endothelium. 4. Rotenone (0.1 microM) inhibited acetylcholine-induced, endothelium-dependent relaxation of phenylephrine-contracted rings or rat and rabbit aorta. In endothelium-denuded rings of rat aorta, relaxation induced by glyceryl trinitrate of isoprenaline was also inhibited, but relaxation induced by 8-bromo cyclic GMP or dibutyryl cyclic AMP was not. Relaxation induced by verapamil on KCl-contracted, endothelium-denuded rings of rat aorta was also unaffected. 5. 2-Deoxy glucose (10 mM) inhibited acetylcholine-induced, endothelium-dependent relaxation of phenylephrine-contracted rings of rat and rabbit aorta.(ABSTRACT TRUNCATED AT 250 WORDS)     

Angiotensin II stimulates superoxide production via both angiotensin AT1A and AT1B receptors in mouse aorta and heart

The present study was conducted to determine the roles of angiotensin AT(1A) and AT(1B) receptors in angiotensin II-induced superoxide anion production in mouse aorta and heart. Superoxide anion production in aorta was determined by the lucigenin chemiluminescence method, and thiobarbituric acid reactive substances in heart tissues were measured by biochemical assay. The basal production rate of superoxide anion in aorta of wild type (WT) mice was significantly higher than in angiotensin AT(1A) receptor knockout (AT(1A) KO) mice. Angiotensin II (2.8 mg/kg/day, s.c. for 13 days) significantly increased superoxide anion production in aorta of both AT(1A) KO and WT mice. However, the superoxide anion production rate in aorta of angiotensin II-infused AT(1A) KO mice was significantly lower than in angiotensin II-infused WT mice. Valsartan (40 mg/kg/day in drinking water) prevented angiotensin II-induced superoxide anion production in aorta of WT and AT(1A) KO mice. Similarly, thiobarbituric acid reactive substances levels in heart tissues of angiotensin II-treated WT and AT(1A) KO mice were significantly higher than those in vehicle-infused WT and AT(1A) KO mice, respectively. Valsartan prevented angiotensin II-induced increases of thiobarbituric acid reactive substances levels in heart tissue of both WT and AT(1A) KO mice. These results indicate that angiotensin II stimulates superoxide anion production via both angiotensin AT(1A) and AT(1B) receptors, and that angiotensin AT(1A) receptors appear to play a predominant role in angiotensin II-induced superoxide anion production in mouse aorta and heart.     

An analysis of the inhibitory effects of prazosin on the phenylephrine response curves of the rat aorta

Summary On the endothelium-intact rat aorta some studies have shown prazosin to cause nonparallel rightward shifts of ₁-adrenoceptor agonist response curves. The aim of the present study was to analyze the inhibitory effect of prazosin on the phenylephrine responses of the endothelium-intact and endothelium-denuded rat aorta. Firstly I used phenoxybenzamine treatment to characterize the phenylephrine responses. The K_A values for phenylephrine were 0.13–0.18 M and 0.07–0.16 M in the endothelium-intact and endothelium-denuded rat aorta, respectively. In order to produce maximal responses of the endothelium-intact or — denuded preparation, phenylephrine had to occupy 95–99% of the ₁-adrenoceptors.Secondly I compared the inhibitory effects of phentolamine and prazosin on the endothelium-intact rat aorta. Phentolamine at 0.1 and 1 M caused parallel rightward shifts of phenylephrine response curves with no effect on phenylephrine maximal responses (phentolamine pA₂ = 7.9). The inhibitory effects of phentolamine were readily reversible. Prazosin at 0.1–10 nM caused nonparallel rightward shifts of the phenylephrine response curves with a depression of the maximal response. These inhibitory effects of prazosin were either irreversible or only very slowly reversible in drug-free solution and slowly reversible in the presence of phentolamine. Ninety min was required for the inhibitory effect of prazosin to reach equilibrium whereas phentolamine was at equilibrium after 45 min. Finally I have characterized the inhibitory actions of prazosin on the endothelium-denuded rat aorta. Prazosin caused parallel rightward shifts of phenylephrine response curves with no effect on phenylephrine maximal responses. The inhibitory effects of prazosin were at equilibrium after 45 min and were readily reversible.In conclusion prazosin is a readily reversible ₁-adrenoceptor antagonist in the endothelium-denuded but not in the endothelium-intact rat aorta. It seems likely that the endothelium accumulates or binds prazosin strongly so that the inhibitory action of prazosin is apparently slowly reversible in the endothelium-intact rat aorta.     

Effects of angiotensin II and its metabolites in the rat coronary vascular bed: is angiotensin III the preferred ligand of the angiotensin AT2 receptor?

Aminopeptidases metabolize angiotensin II to angiotensin-(2-8) (=angiotensin III) and angiotensin-(3-8) (=angiotensin IV), and carboxypeptidases generate angiotensin-(1-7) from angiotensin I and II. Angiotensin-converting enzyme (ACE) inhibitors and/or angiotensin II type 1 (AT1) receptor blockers affect the concentrations of these metabolites, and they may thus contribute to the beneficial effects of these drugs, possibly through stimulation of non-classical angiotensin AT receptors. Here, we investigated the effects of angiotensin II, angiotensin III, angiotensin IV and angiotensin-(1-7) in the rat coronary vascular bed, with or without angiotensin AT1 - or angiotensin II type 2 (AT2) receptor blockade. Results were compared to those in rat iliac arteries and abdominal aortas. Angiotensin II, angiotensin III and angiotensin IV constricted coronary arteries via angiotensin AT1 receptor stimulation, angiotensin III and angiotensin IV being approximately 20- and approximately 8000-fold less potent than angiotensin II. The angiotensin AT2 receptor antagonist PD123319 greatly enhanced the constrictor effects of angiotensin III, starting at angiotensin III concentrations in the low nanomolar range. PD123319 enhanced the angiotensin II-induced constriction at submicromolar angiotensin II concentrations only. Angiotensin-(1-7) exerted no effects in the coronary circulation, although, at micromolar concentrations, it blocked angiotensin AT1 receptor-induced constriction. Angiotensin AT2 receptor-mediated relaxation did not occur in iliac arteries and abdominal aortas, and the constrictor effects of the angiotensin metabolites in these vessels were identical to those in the coronary vascular bed. In conclusion, angiotensin AT2 receptor activation in the rat coronary vascular bed results in vasodilation, and angiotensin III rather than angiotensin II is the preferred endogenous agonist of these receptors. Angiotensin II, angiotensin III, angiotensin IV and angiotensin-(1-7) do not exert effects through non-classical angiotensin AT receptors in the rat coronary vascular bed, iliac artery or aorta.     

Vascular reactivity to various vasoconstrictor agents and endothelium-dependent relaxations of rat thoracic aorta in the long-term period of pinealectomy

In this study, the effects of reduced melatonin concentrations in the long-term period of pinealectomy on mean arterial blood pressure (BP) and vascular responses in isolated rat thoracic aorta were investigated. Rats were pinealectomized (Px) two months before the beginning of the studies. Rings of endothelium-intact and -denuded rat arteries were mounted in isolated tissue baths for the measurements of isometric contractile force. No significant difference was determined between the arterial BP of Px (88.1 +/- 1.9 mmHg) and control (83.8 +/- 1.2 mmHg) rats. All arteries isolated from control and Px rats showed essentially identical contractions in response to phenylephrine, serotonin, calcium, clonidine, vasopressin, and angiotensin-II. Only endothelin-1 (ET-1)-induced contractions in the endothelium-denuded vessels isolated from Px rats were found to be increased to some extent. Pinealectomy did not affect acetylcholine or sodium nitroprusside-induced relaxation in the rat aorta either. These data suggest that reduced melatonin levels two months after pinealectomy did not modify either the vascular reactivity to various vasoconstrictor agents except the partially increased contractile responses to ET-1 in the endothelium-denuded thoracic aortas of Px rats or the endothelium-dependent and -independent relaxations in rat thoracic aorta. Restoration of the increased vascular responses to some vasoconstrictor agents, which were reported previously, may be the reason of why the hypertension is temporary following pinealectomy.     

Pre- and postsynaptic inhibitory potencies of the angiotensin AT1 receptor antagonists eprosartan and candesartan

The aim of the present study was to determine the inhibitory potency of two selective angiotensin AT(1) receptor antagonists, eprosartan and candesartan, at the level of the sympathetic nerve terminal and the vascular smooth muscle. Male New Zealand White rabbits, weighing 2100-2550 g, were used. To study eprosartan and candesartan at the neuronal angiotensin AT(1) receptor, we investigated their influence on the angiotensin II-enhanced, electrical field stimulation-evoked sympathetic transmission in the rabbit isolated thoracic aorta in a noradrenaline spillover model. To study both antagonists at the vascular angiotensin AT(1) receptor, concentration-response curves for angiotensin II were constructed in the presence or absence of the two angiotensin AT(1) receptor antagonists. Angiotensin II (10 nM) caused a significant increase by 107+/-11.1% of the stimulation-evoked sympathetic outflow, which was concentration-dependently inhibited by both eprosartan (pIC(50) 7.91+/-0.12) and candesartan (pIC(50) 10.76+/-0.13). Angiotensin II (1 nM-0.3 microM) caused a concentration-dependent increase in contractile force (E(max) 20.62+/-2.24 mN, pD(2) 8.16+/-0.04). Both eprosartan (pA(2) 8.90+/-0.11, pIC(50) 8.87+/-0.12 (10 nM angiotensin II)) and candesartan (pD(2)' 10.80+/-0.13) counteracted the contractions evoked by cumulative concentrations of angiotensin II. Candesartan proved a more potent antagonist than eprosartan at both the pre- and postjunctional angiotensin AT(1) receptor. For eprosartan, vascular inhibitory concentrations were 10-fold lower than sympatho-inhibitory concentrations, whereas for candesartan, inhibitory concentrations at both sites were similar. The results may be explained by differences between the pre- and postjunctional angiotensin AT(1) receptor subtype.     

内吗啡肽抑制苯肾上腺素和血管紧张素Ⅱ诱导的离体大鼠胸主动脉环收缩

目的:研究吗啡、内吗啡肽-1和内吗啡肽-2对由苯肾上腺素(PE)和血管紧张素(Ang)Ⅱ诱导离体大鼠胸主动脉环收缩的抑制作用.方法:离体血管环张力试验.结果:与对照组相比,吗啡、内吗啡肽-1和内吗啡肽-2的预处理(0.1-10μmol/L)能明显降低由PE(0.1μmol/L)和Aug Ⅱ(1μmol/L)(P<0.01)诱导离体大鼠胸主动脉环的张力,但是不能减少去内皮血管的张力.纳络酮(1μmol/L)能部分阻断内吗啡肽-1和内吗啡肽-2的抑制作用(P<0.01),N~(ω)-nitro-L-arginine(10μmol/L)或血管环去内皮能完全阻断这种作用(P<0.01).结论:内吗啡肽-1和内吗啡肽-2通过纳络酮敏感方式抑制由PE和AngⅡ诱导的离体大鼠胸主动脉环收缩,这种抑制作用可能与血管内皮NO的释放有关.     

The actions of angiotensin II on the isolated portal vein of the rat

Isolated rat portal vein suspended in Krebs bicarbonate medium showed regular rhythmic activity and contracted in response to angiotensin II, noradrenaline, adrenaline, tyramine, acetylcholine, serotonin and histamine. Angiotensin II was 3–10 times as potent as noradrenaline on a weight basis. Responses to angiotensin II were unchanged in the presence of antagonists to these drugs, excepting high concentrations of phentolamine. Electrical stimulation or noradrenaline did not potentiate responses to angiotensin II; angiotensin II did not potentiate responses to noradrenaline. Angiotensin II acts directly on the smooth muscle of rat portal vein; its action is independent of noradrenaline. Spontaneous contractions and responses to angiotensin II and noradrenaline were transiently depressed and then potentiated in media made hyperosmolar by addition of NaCl, sucrose or urea. Responses were depressed in hypo-osmolar low NaCl solution but unaffected by isosmolar low NaCl. An increase of intracellular potassium concentration would not alone account for the entire effect of increased osmolarity.     

Does segmental difference in alpha 1-adrenoceptor subtype explain contractile difference in rat abdominal and thoracic aortae?

The cyclooxygenase inhibitor, indomethacin, depresses adrenergic agonist constriction of endothelium-denuded rat abdominal, but not thoracic, aorta. In order to explain this finding, we explored the possibility of segmental differences in the population of alpha 1-adrenoceptor (AR) subtypes. In endothelium-denuded tissues, phenylephrine elicited concentration-dependent contractions in the thoracic and abdominal aortic rings with potencies and maximal effects that, respectively, did not differ significantly (P > .05). Indomethacin (1 x 10(-5) M) inhibited phenylephrine-induced contractions only in abdominal aorta. The subtype-selective alpha 1D-AR antagonist, BMY 7378, was found to antagonize contractions to phenylephrine competitively in abdominal (pA2 8.44) and thoracic (pA2 8.56) aortic rings. These data are consistent with published alpha 1D-AR functional potency and clonal alpha 1D-AR binding affinity. In addition, cumulative concentration-contraction curves for phenylephrine were competitively antagonized in the rat abdominal and thoracic aortae by prazosin, 5-methylurapidil and WB 4101, with pA2 values of 9.39 and 9.61, 7.64 and 7.85, and 9.43 and 9.58, respectively. These compounds with varying degrees of subtype selectivity inhibited contractions of the thoracic and abdominal aortae with affinities consistent with those determined at the alpha 1D-AR subtype. The results of this study suggest that the contraction to phenylephrine of the rat abdominal and thoracic aorta is mediated via the same alpha 1D-AR subtype.     

Evidence for the presence of A(1) adenosine receptors in the aorta of spontaneously hypertensive rats.

1. Isolated aortic rings (endothelium-intact and -denuded) from spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats were used in this study to examine the vasoactive effects of various adenosine analogues. 2. In phenylephrine contracted aortic rings, concentration-response curves were constructed by cumulative additions (10(-11) - 10(-5) M) of (2S)-N(6)-[2-endo-Norbornyl] adenosine (ENBA), N(6)-cyclopentyladenosine (CPA), R-N(6)-(2-phenylisopropyl) adenosine (R-PIA), 2-p-(-2-carboxyethyl) phenethylamino-5'-N-thylcarboxamido adenosine (CGS-21680). 3. A non-specific adenosine receptor agonist 2-chloroadenosine (CAD) resulted in biphasic response with a small contraction at lower concentrations (10(-9) - 10(-8) M) followed by a significant relaxation at higher concentration in endothelium-intact SHR tissues, suggesting presence of both A(1) and A(2) adenosine receptors in SHR aorta. However, only relaxation was observed in WKY. 4. Contractile response in SHR had the following rank order of potency: ENBA>CPA>R-PIA>CAD. The relaxation response in SHR and WKY had the following rank order of potency: CGS 21680>CAD>R-PIA>CPA>ENBA. 5. Removal of endothelium abolished the adenosine analogue induced contractions in SHR aorta and attenuated the vasorelaxation responses in the WKY and SHR. 6. The contractile response in SHR was abolished by A(1) adenosine receptor antagonist N(6)-endonorbornan-2-yl-9-methyladenine (N-0861). A(2) adenosine receptor antagonist, 3,7-dimethyl-1-proparglyxanthine (DMPX) did not affect the contraction response of adenosine analogues. 7. Endothelium-dependent contractions elicited by A(1) receptor agonists were blocked by indomethacin and by free radical scavengers. 8. These data suggest that the contractile response to adenosine analogues in SHR aorta is probably mediated by free radicals which are generated through the increased cyclo-oxygenase activity occurring in the vascular endothelium of SHR but not the WKY rats.     

The renin-angiotensin system: current data

The renin-angiotensin system (RAS) is a major physiological regulator of vascular tone and is implicated in cardiovascular pathophysiology. More recently, basic research has however continuously extended our understanding of the complexicity of the systemic and tissular RASs. The peptid hormone, angiotensin II, acts primarily via type I (AT1) and type II (AT2) angiotensin receptors. Most, if not all, of the peripheral and central actions of angiotensin II, including vasoconstriction, renal salt and water retention, facilitation of sympathetic transmission, modification of vascular and cardiac structure, oxydative stress stimulation and proinflammatory action were all thought to be mediated by the angiotensin type 1 receptor, AT1. Angiotensin II/III exerts actions through the AT2 receptor, which are directly opposed to those mediated by the AT1 receptor. Most notably, proteolytic fragments of angiotensin II also have biological activity via ther own receptors: angiotensin-(1-7)/AT1-7 and angiotensin IV/AT4. They are vasodilators in many arterial beds. The identification of these angiotensins opens the way to develop new therapeutics.     

Angiotensin II Enhances Responses to Endothelin-1 in Bovine Bronchial Smooth Muscle

Summary: Angiotensin II and endothelin-1 are putative mediators in asthma. In this study we have examined the effect of angiotensin II on endothelin-1-induced contractions in bovine bronchi and the receptor types involved in the response to these agonists. Angiotensin II alone is very low in potency, producing only small contractions. In the presence of angiotensin II 10^-7 or 3 × 10^-7 M, contractions evoked by endothelin-1 were markedly enhanced. The AII₁-receptor antagonist, losartan, abolished this enhancement suggesting that angiotensin II exerts this effect via an AII₁-receptor. The contraction evoked by endothelin-1 is mediated via an Et_A-receptor subtype since the Et_A-receptor antagonist FR139317 attenuated the response. This is offset by an inhibitory Et_B-type receptor, resulting in a larger contraction when these receptors are desensitized. Indeed, the Et_B-receptor agonist sarafotoxin S6c reversed methacholine-evoked tone in a concentration-dependent manner. In conclusion, angiotensin II potentiates contractions evoked by endothelin-1 in bovine bronchi. This may be a mechanism by which angiotensin II—which has little activity in bronchi—may evoke substantial changes in airway tone. Angiotensin II evokes this potentiation via AII₁-receptors, whilst endothelin-1 evokes contraction via Et_A-receptors, an action which is offset by an inhibitory effect of Et_B-receptors.     

Angiotensin II-mediated cellular responses: a role for the 3'-untranslated region of the angiotensin AT1 receptor

We have previously demonstrated that Chinese hamster ovary (CHO) cells transfected with the angiotensin II AT1 receptor gene containing only the coding region, presented tachyphylaxis to the total inositol phosphate (InsPs) and Ca2+ responses mediated by angiotensin II and [2-lysine]angiotensin II ([Lys2]angiotensin II). Now we have evaluated the possible role of the 3'-untranslated region of the angiotensin AT1 receptor mRNA in modulating the angiotensin AT1 receptor-mediated cellular responses. The binding parameters, as well as the Ca2+ and InsPs responses induced by angiotensin II and [Lys2]angiotensin II were similar in cells transfected with the angiotensin AT1 receptor with or without the 3'-untranslated region sequence. In cells transfected with the receptor containing the 3'-untranslated region sequence, angiotensin II-induced Ca2+ and InsPs responses were desensitized by repeated stimulations, whereas [Lys2]angiotensin II caused desensitization of InsPs production but not of Ca2+ uptake in these cells. Our results suggest that the 3'-untranslated region plays a role in modulating cell signalling involved in the tachyphylaxis of angiotensin AT1 receptor-mediated Ca2+ responses.