Contraction Of Femoral Arteries Research Articles

Methylglyoxal-induced enhancement of uridine diphosphate-mediated contraction in rat femoral artery was due to activation of p38 MAPK and Syk tyrosine kinase

Although abnormalities of function in femoral artery, including aberrant vascular reactivity to various vasoactive mediators, are common in many chronic disorders including hypertension and diabetes, their inducible and/or progressive factors remain unclear. On the other hand, methylglyoxal (MGO), a highly reactive dicarbonyl compound, has been implicated in the pathogenesis of several chronic disorders. Although our previous studies demonstrated that uridine 5'-diphosphate (UDP)-induced contraction in the femoral artery is increased in hypertensive rat model, the direct relationship between MGO and UDP-mediated contraction is currently unknown in rat femoral artery. We therefore investigated the acute effect of MGO (4.2 × 10−4 M for 60 min) on UDP-induced contraction in the rat femoral artery. MGO amplified the UDP-induced contraction in the Wistar rat femoral artery. This augmented response was not abolished in all conditions, including nitric oxide synthase inhibition by L-NNA (10−4 M), cyclooxygenase inhibition by indomethacin (10−5 M), or endothelial denudation. Moreover, in the endothelium-denuded arteries, the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 (10−5 M) reduced the UDP-induced contraction in both control and MGO-treated groups, while MGO enhanced the p38 MAPK activation regardless of the UDP presence. Moreover, in the endothelium-denuded arteries, the Syk tyrosine kinase inhibitor piceatannol (10−5 M) reduced the UDP-induced contraction in both control and MGO-treated groups. These results suggest that MGO enhances UDP-induced contraction in rat femoral arteries and that this enhancement may be partly due to increases in the activities of Syk tyrosine kinase and p38 MAPK in femoral arterial smooth muscle.

Erratum to "Contribution of Ca2+-Dependent Cl- Channels to Norepinephrine-Induced Contraction of Femoral Artery Is Replaced by Increasing EDCF Contribution during Ageing".

[This corrects the article DOI: 10.1155/2014/289361.].

The enhancement of serotonin-induced contraction of rat femoral artery is mediated by angiotensin II release from intact endothelium

We have performed an in vitro study on isolated intact or denuded femoral artery (FA) of healthy, diabetic, and/or rats submitted to the FA occlusion. The aim was to determine the contribution of endothelium and endothelial dysfunction (ED) on serotonin-induced action in FA. Further, the contribution of angiotensin II and cyclooxygenase products of arachidonic acid was investigated. A marker of ED, vWF was measured in animal serum. Serotonin induced contraction-dependent contraction of isolated FA, which was increased in preparations with endothelium. Pathological conditions such as endothelial denudation, nicotine-induced ED, diabetes or occlusion of FA reduced serotonin-induced contraction. Comparable reduction of serotonin-induced contraction was achieved after inhibition of AT1 receptors with losartan in isolated FA with intact endothelium. Our results demonstrate that angiotensin II contributes to the enhancement of serotonin-induced contraction of femoral arteries with intact endothelium. This increase is attenuated by endothelium removal, nicotine treatment, vascular occlusion, and/or hyperglycemia.

The reversible P2Y12 antagonist ACT-246475 causes significantly less blood loss than ticagrelor at equivalent antithrombotic efficacy in rat.

The P2Y12 receptor is a validated target for prevention of major adverse cardiovascular events in patients with acute coronary syndrome. The aim of this study was to compare two direct‐acting, reversible P2Y12 antagonists, ACT‐246475 and ticagrelor, in a rat thrombosis model by simultaneous quantification of their antithrombotic efficacy and surgery‐induced blood loss. Blood flow velocity was assessed in the carotid artery after FeCl3‐induced thrombus formation using a Doppler flow probe. At the same time, blood loss after surgical wounding of the spleen was quantified. Continuous infusions of ACT‐246475 and ticagrelor prevented the injury‐induced reduction of blood flow in a dose‐dependent manner. High doses of both antagonists normalized blood flow and completely abolished thrombus formation as confirmed by histology. Intermediate doses restored baseline blood flow to ≥65%. However, ACT‐246475 caused significantly less increase of blood loss than ticagrelor; the difference in blood loss was 2.6‐fold (P < 0.01) at high doses and 2.7‐fold (P < 0.05) at intermediate doses. Potential reasons for this unexpected difference were explored by measuring the effects of ACT‐246475 and ticagrelor on vascular tone. At concentrations needed to achieve maximal antithrombotic efficacy, ticagrelor compared with ACT‐246475 significantly increased carotid blood flow velocity in vivo (P = 0.003), induced vasorelaxation of precontracted rat femoral arteries, and inhibited contraction of femoral artery induced by electrical field stimulation or by phenylephrine. Overall, ACT‐246475 showed a significantly wider therapeutic window than ticagrelor. The absence of vasodilatory effects due to high selectivity of ACT‐246475 for P2Y12 provides potential arguments for the observed safety advantage of ACT‐246475 over ticagrelor.

Contribution of Ca2+-Dependent Cl−Channels to Norepinephrine-Induced Contraction of Femoral Artery Is Replaced by Increasing EDCF Contribution during Ageing

The activation of Ca2+-dependent Cl− channels during norepinephrine-induced contraction of vascular smooth muscle was suggested to depolarize cell membrane and to increase Ca2+ entry. Hypertension and ageing are associated with altered Ca2+ handling including possible activation of Ca2+-dependent Cl− channels. Our study was aimed to determine Ca2+-dependent Cl− channels contribution to norepinephrine-induced contraction during hypertension and ageing. Norepinephrine-induced concentration-response curves of femoral arteries from 6- and 12-month-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were recorded using wire myograph. Pretreatment with Ca2+-dependent Cl- channel inhibitor indanyloxyacetic acid 94 [R(+)-IAA-94](IAA) attenuated norepinephrine-induced contraction in all groups, but relatively more in WKY than SHR arteries. The attenuation of norepinephrine-induced contraction after Ca2+-dependent Cl− channels blockade was partially reduced in 12-month-old WKY rats, but substantially diminished in 12-month-old SHR. IAA effect was enhanced after NO synthase inhibition but decreased by ageing. In 20-month-old WKY rats norepinephrine-induced contraction was not affected by IAA but was almost abolished after cyclooxygenase inhibition by indomethacin or niflumic acid. In conclusion, contribution of Ca2+-dependent Cl− channels to norepinephrine-induced contraction diminished with age, hypertension development, and/or NO synthesis inhibition. Ca2+-dependent Cl− channels are important for maintenance of normal vascular tone while their inactivation/closing might be a pathological mechanism.

Response of Rabbit Ear and Femoral Arteries to 5-Hydroxytryptamine During Cooling

Abstract The effects of cooling on the response of cutaneous and non-cutaneous arteries to 5-hydroxytryptamine (5-HT) were analysed. Segments 2-mm long from rabbit central ear (cutaneous) and femoral (non-cutaneous) arteries were prepared for isometric tension recording in an organ bath at 37 and 24°C (cooling). 5-HT (10−9-3 times 10−4 M) induced concentration-dependent contraction of the arteries. The sensitivity and maximal contraction of ear arteries and only the maximal contraction of femoral arteries to this amine were reduced at 24°C. Endothelium removal or pretreatment with the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester (l-NAME, 10−5 m) did not affect the response at 37°C but reversed the decreased sensitivity at 24°C in ear arteries, and neither procedure modified the reactivity at 24 or 37°C in femoral arteries to 5-HT. At both temperatures, the response of ear arteries to 5-HT was shifted to the right by phentolamine (10−6M) more than by the 5-HT antagonist, ketanserin (3 times 10−7M), and that of femoral arteries was shifted to the right by ketanserin or the 5-HT1/5-HT2 antagonist methysergide (3 times 10−7 M) more than by phentolamine, in arteries with and without endothelium. These data concur with the proposition that the contraction to 5-HT is mediated mainly by α-adrenergic receptors in ear arteries and mainly by 5-HT-ergic receptors in femoral arteries, and suggest that cooling reduces the sensitivity of cutaneous, but not of deep arteries to 5-HT, probably by endothelium-nitric oxide-dependent mechanisms.

Influence of calcium-dependent potassium channel blockade and nitric oxide inhibition on norepinephrine-induced contractions in two forms of genetic hypertension

The activation of Ca 2+-dependent K + channels (BK Ca) leads to the attenuation of vascular contraction. Our study aimed to evaluate BK Ca influence on norepinephrine (NE)-induced femoral artery contraction in two forms of genetic hypertension. NE dose-response curves were studied before and after BK Ca blockade or after combined blockade of BK Ca and NO synthase (NOS) in femoral arteries with intact endothelium from normotensive Wistar (WIS), hypertensive hereditary hypertriglyceridemic (HTG), or spontaneously hypertensive rats (SHR). NE-induced contractions of femoral arteries were augmented in both hypertensive strains compared with Wistar rats, but acetylcholine-induced relaxation was impaired in HTG only. The increase of basal vascular tone of isolated arteries after BK Ca blockade was similar in all rat strains, but subsequent NOS inhibition increased basal vascular tone more in vessels from both hypertensive rat strains. NOS inhibition increased sensitivity to NE in all strains, but BK Ca blockade in SHR only. Neither treatment enhanced maximal NE-induced contraction. NO-dependent attenuation of NE-induced contractions was greater in SHR than HTG or Wistar vessels, whereas large conductance Ca 2+-dependent K + channels may play a greater role in modulating vascular contraction in the severe form of hypertension.

Two isoforms of cyclooxygenase contribute to augmented endothelium-dependent contractions in femoral arteries of 1-year-old rats

The present experiments were designed to study the changes in endothelium-dependent contractions with aging. The rat femoral arteries of 20-week and 1-year-old rats with and without endothelium were suspended in organ chambers to record isometric tension. The production of oxygen-derived free radicals in the endothelium was measured with 2,7o-dichlorodihydrofluorescein diacetate (DCF) using confocal microscopy. Protein presences were determined by Western blotting. In the arteries from the 1-year-old rats, endothelium-dependent relaxations to A23187 were reduced, but the endothelium-dependent contractions to A23187 (in the presence of Nomega-nitro-L-arginine methyl ester hydrochloride [L-NAME; an inhibitor of nitric oxide synthase]) were augmented, demonstrating endothelial dysfunction with aging. Indomethacin normalized the responses, suggesting that a cyclooxygenase (COX)-dependent contraction is prominent in aging. The endothelium-dependent contractions were also prevented by terutroban (a blocker of thromboxane-prostanoid receptors), confirming the activation of thromboxane-prostanoid receptors on vascular smooth muscle. Valeryl salicylate and NS-398 (preferential inhibitors of COX-1 and COX-2, respectively) partially reduced the response, indicating that both COX-1 and COX-2 are involved. Western blotting confirmed the upregulation of both isoforms in the arteries of the 1-year-old rats. In the presence of L-NAME, A23187 increased the DCF fluorescence in the endothelium, demonstrating that the production of oxygen-derived free radicals contributes to endothelium-dependent contractions. The activity of catalase was reduced in the arteries with endothelium of 1-year-old rats, indicating that hydrogen peroxide is the likely mediator of increased oxidative stress in the aging endothelium. Endothelium-dependent contractions are augmented with aging. Oxidative stress potentiates the response, and both COX-1 and COX-2 are involved.

Oxygen‐derived free radicals mediate endothelium‐dependent contractions in femoral arteries of rats with streptozotocin‐induced diabetes

The present experiments were designed to study the contribution of oxygen-derived free radicals to endothelium-dependent contractions in femoral arteries of rats with streptozotocin-induced diabetes. Rings with and without endothelium were suspended in organ chambers for isometric tension recording. The production of oxygen-derived free radicals in the endothelium was measured with 2',7'-dichlorodihydrofluorescein diacetate using confocal microscopy. The presence of protein was measured by western blotting. In the presence of L-NAME, the calcium ionophore A23187 induced larger endothelium-dependent contractions in femoral arteries from diabetic rats. Tiron, catalase, deferoxamine and MnTMPyP, but not superoxide dismutase reduced the response, suggesting that oxygen-derived free radicals are involved in the endothelium-dependent contraction. In the presence of L-NAME, A23187 increased the fluorescence signal in femoral arteries from streptozotocin-treated, but not in those from control rats, confirming that the production of oxygen-derived free radicals contributes to the enhanced endothelium-dependent contractions in diabetes. Exogenous H2O2 caused contractions in femoral arterial rings without endothelium which were reduced by deferoxamine, indicating that hydroxyl radicals contract vascular smooth muscle and thus could be an endothelium-derived contracting factor in diabetes. The reduced presence of Mn-SOD and the decreased activity of catalase in femoral arteries from streptozotocin-treated rats demonstrated the presence of a redox abnormality in arteries from rats with diabetes. These findings suggest that the redox abnormality resulting from diabetes increases oxidative stress which facilitates and/or causes endothelium-dependent contractions.

The calcium ionophore A23187 induces endothelium‐dependent contractions in femoral arteries from rats with streptozotocin‐induced diabetes

To study the importance of endothelium-derived contracting factors (EDCFs) in arteries of rats with type I diabetes. Rat femoral arteries were collected four or twelve weeks after induction of diabetes with streptozotocin. Rings, with or without endothelium, were suspended in organ chambers for isometric tension measurement. COX protein levels were determined by Western blotting. Four weeks after the injection of streptozotocin, the endothelium-dependent relaxations (during contractions to phenylephrine) to A23817 were attenuated, but the endothelium-dependent contractions (quiescent preparations) to the ionophore were augmented. Indomethacin and S18886 prevented the endothelium-dependent contractions, while dazoxiben reduced them in rings from streptozotocin-treated rats, suggesting that thromboxane A2, activating TP- receptors, is involved. Twelve weeks after the injection of streptozotocin, the changes in endothelium-dependent relaxations and contractions to A23187 were even more noticeable. The protein expression of COX-1 was increased in femoral arteries of the diabetic rats. Valeryl salicylate and SC560 inhibited the contractions, suggesting that the EDCFs are produced by COX-1. At that time, a combination of S18886 with EP1-blockers was required to abolish the contractions, suggesting that the EDCFs involved act at both TP- and EP-receptors. Rings without endothelium from streptozotocin-treated rats exhibited a reduced maximal contraction to potassium chloride and U46619, combined with hyper-responsiveness to the latter, suggesting that more prolonged diabetes also alters the responsiveness of vascular smooth muscle. The production of EDCFs is progressively increased in the course of type I diabetes. Eventually, the disease also damages vascular smooth muscle.

Nifedipine-sensitive vascular reactivity of femoral arteries in WKY: the effect of pertussis toxin pretreatment and endothelium removal

Maintenance of norepinephrine (NE)-induced contraction is dependent on Ca(2+) influx through L-type voltage-dependent Ca(2+) channels (VDCC), which is opposed by nitric oxide. Adrenergic receptors are coupled with different G proteins, including inhibitory G proteins (Gi) that can be inactivated by pertussis toxin (PTX). Our study was aimed to investigate the effects of endothelium removal, PTX pretreatment and acute VDCC blockade by nifedipine on the contractions of femoral arteries stimulated by norepinephrine. We used 12-week-old male WKY, half of the rats being injected with PTX (10 microg/kg i.v., 48 h before the experiment), which considerably reduced their blood pressure (BP). Contractions of isolated arteries were measured using Mulvany-Halpern myograph. NE dose-response curves determined in femoral arteries from PTX-treated WKY rats were shifted to the right compared to those from control WKY. On the contrary, removal of endothelium augmented NE dose-response curves shifting them to the left. Acute VDCC blockade by nifedipine (10(-7) M) abolished all differences in NE dose-response curves which were dependent on the presence of either intact endothelium or functional Gi proteins because all NE dose-response curves were identical to the curve seen in vessels with intact endothelium from PTX-treated animals. We can conclude that BP reduction after PTX injection is accompanied by the attenuation of NE-induced contraction of femoral arteries irrespective of endothelium presence. Moreover, our data indicate that both vasodilator action of endothelium and Gi-dependent vasoconstrictor effect of norepinephrine operate via the control of Ca(2+) influx through VDCC.

Origin of ATP for Ca 2+ -induced contraction in the guinea-pig femoral artery

Previously, we have described differences between the rat proximal colon and femoral artery with respect to the role of ATP newly synthesized by creatine kinase. In the present study the role of newly synthesized ATP was studied in the guinea-pig femoral artery to examine species differences. In the alpha-toxin-permeabilized preparation of the guinea-pig femoral artery, the rapid Ca(2+)-induced contraction was suppressed when creatine kinase activity was inhibited. The contraction was restored completely by treatment with NaN(3), an inhibitor of ecto-ATPase, the enzyme that breaks down exogenous ATP. Thus, ATP newly synthesized by creatine kinase may have no role in contraction of the guinea-pig femoral artery. This is in marked contrast to the rat femoral artery, in which Ca(2+)-induced contractions are almost completely inhibited by inhibition of creatine kinase activity but only partly restored by NaN(3). To characterize the difference between the guinea-pig and rat tissue, the origin of ATP required for contraction was determined in intact preparations. Monoiodoacetic acid, an inhibitor of glycolysis, inhibited the high K(+)-induced contraction in the guinea-pig femoral artery more potently than in the rat tissue. In contrast, an inhibitor of mitochondrial respiration, carbonylcyanide p-(trifluoromethoxy)phenylhydrazone (FCCP), inhibited contraction in femoral arteries from rats, but not from guinea-pigs. These results suggest that contraction in the rat femoral artery is dependent largely on oxidative phosphorylation, while contraction in the guinea-pig tissue is dependent only on glycolysis. Because oxidative phosphorylation generates ATP and phosphocreatine, while glycolysis generates only ATP, the strong dependence of the contraction of the rat femoral artery on the oxidative phosphorylation is consistent with its dependence on ATP newly synthesized by creatine kinase from ADP and phosphocreatine, as previously shown. Thus, it is proposed that ATP, newly synthesized by creatine kinase, in addition to ATP generated by oxidative phosphorylation, is utilized for contraction in the rat femoral artery, while glycolysis produces sufficient ATP for contraction in the guinea-pig femoral artery.

Neuropeptide Y selectively potentiates alpha1-adrenoceptor-mediated contraction through Y1 receptor subtype in rat femoral artery.

The aim of this study was to investigate the synergism between neuropeptide Y and other vasoconstrictors (phenylephrine and serotonin) and which neuropeptide Y receptor subtype is responsible for the neuropeptide Y-induced potentiation. Exogenous neuropeptide Y (10 nM) potentiated alpha1-adrenoceptor-mediated (PE-induced) contraction in rat femoral artery permissively without its direct action, but not in the thoracic aorta. In contrast, neuropeptide Y produced no change in serotonin-induced contraction in both arteries. Increasing concentrations of neuropeptide Y caused dose-dependent potentiation of the phenylephrine-induced contraction in the femoral artery. This potentiation was blocked by a selective neuropeptide Y-Y1 receptor antagonist, BIBP3226 [(R)-N2-(diphenylacetyl)-N-[4-hydroxyphenyl)methyl]-argininamide] (1 microM). Semiquantitative reverse transcriptase polymerase chain reaction showed the selective expression of neuropeptide Y-Y1 receptor mRNA in the femoral artery. These findings indicated that the neuropeptide Y-induced selective potentiation of alpha1-adrenoceptor-mediated contraction is mediated through neuropeptide Y-Y1 receptor in rat femoral artery.

Coronary and femoral arterial contraction with high glucose, insulin, and glucose-insulin-potassium solution: effects of hypoxia

We studied whether the contractile responses to potassium chloride (KCI) of rat coronary and femoral arteries differ when perfused with solutions containing varying concentrations of metabolic substrates (glucose, oxygen, insulin) and whether these differences might explain some of the beneficial effects of glucose-insulin-potassium (GIK or polarizing) solution. We also studied the mediation of the endothelium on these effects. Contraction of femoral arteries decreased with low and high glucose while in coronary arteries it increased as the glucose concentrations rose. Endothelin receptor antagonists blocked this increase. The tension increase induced by insulin in both vessels was smaller in the coronary arteries. The ETA receptor antagonist PD51242 blocked most of the insulin effect in the coronary arteries, whereas in the femoral arteries this was blocked by the ET(B) receptor antagonist BQ788. Hypoxia blocked the constrictive responses to glucose and insulin of the coronary but not of the femoral arteries. GIK increased contractile force in hypoxic femoral arteries but reduced that in coronary arteries. The contractile response decreased by GIK in hypoxic coronary arteries was restored by N(G)-nitro-L-arginine methyl ester, suggesting mediation by nitric oxide. We conclude that in the presence of high glucose and/or insulin levels, coronary arteries respond to KCl differently from femoral arteries, their behavior during hypoxia might explain some of the beneficial effects of GIK.

Recombinant CRP induces increased release of ICAM and thrombomodulin, but not vWF or E selectin, from HUVECs

The activation of Ca2+-dependent K+ channels (BKCa) leads to the attenuation of vascular contraction. Our study aimed to evaluate BKCa influence on norepinephrine (NE)-induced femoral artery contraction in two forms of genetic hypertension. NE dose-response curves were studied before and after BKCa blockade or after combined blockade of BKCa and NO synthase (NOS) in femoral arteries with intact endothelium from normotensive Wistar (WIS), hypertensive hereditary hypertriglyceridemic (HTG), or spontaneously hypertensive rats (SHR). NE-induced contractions of femoral arteries were augmented in both hypertensive strains compared with Wistar rats, but acetylcholine-induced relaxation was impaired in HTG only. The increase of basal vascular tone of isolated arteries after BKCa blockade was similar in all rat strains, but subsequent NOS inhibition increased basal vascular tone more in vessels from both hypertensive rat strains. NOS inhibition increased sensitivity to NE in all strains, but BKCa blockade in SHR only. Neither treatment enhanced maximal NE-induced contraction. NO-dependent attenuation of NE-induced contractions was greater in SHR than HTG or Wistar vessels, whereas large conductance Ca2+-dependent K+ channels may play a greater role in modulating vascular contraction in the severe form of hypertension.

Arachidonate metabolites and serotonin contraction of femoral arteries from DOCA-salt hypertensive rats.

Serotonin stimulates phospholipase A(2)(PLA(2)) leading to the production of prostaglandin products, several of which are vasoconstrictors. We hypothesised that the elevated vascular responsiveness to serotonin in deoxycorticosterone acetate (DOCA)-hypertensive rats is due in part to augmented production of vasoconstrictor cyclooxygenase products (e.g. PGF(2)alpha). Denuded helical strips of femoral arteries from DOCA-salt hypertensive rats (SBP 183 +/- 7 mmHg) and normotensive control rats (SBP 115 +/- 2) were used in all experiments. EC(50) values for several agonists were significantly reduced in DOCA arteries compared with controls (in mu mol/L, control vs. DOCA): PGF(2)alpha (0.99 vs. 0.23), PGE(2) (0.72 vs. 0.22), arachidonate (1.52 vs. 0.73), serotonin (0.19 vs. 0.07), noradrenaline (0.029 vs. 0.013), KCl (40.1 vs. 27.0 mmol/L) and AlF(4) (2.3 vs. 1.4 mmol/L). Treatment with indomethacin (14 mu mol/L) inhibited the responses to serotonin in DOCA arteries (EC(50) values 0.07 untreated vs. 0.70) and eliminated the responses to arachidonate but did not affect KCl or AlF(4-)contractions. Cyclooxygenase inhibitors shifted concentration response curves to serotonin in sham and DOCA tissues equally. Thus increased sensitivity to serotonin in DOCA arteries persisted following cyclooxygenase blockade. Therefore, although arachidonate products contribute to the serotonergic contraction in femoral arteries, the augmented response in arteries from DOCA hypertensive rats is not due to increased production of or sensitivity to cyclooxygenase products. Furthermore,arachidonate metabolites do not contribute to the contraction induced by either AlF(4-)or KCl in this preparation.

α1-Adrenoceptor subtypes mediating contraction of the femoral artery in spontaneously hypertensive rats

alpha 1-Adrenoceptors (ARs) were divided into alpha 1H and alpha 1L subtypes by their different affinities for bunazosin or prazosin. alpha 1H-ARs were further subdivided into alpha 1A, alpha 1B, and alpha 1C subtypes. Therefore, this study was undertaken to determine which alpha 1-AR subtypes were involved in the activation of femoral artery preparations by alpha 1-AR agonists in spontaneously hypertensive rats (SHR). For comparison, aortic strips were also incorporated in the present study. In the presence of propranolol, deoxycorticosterone, and desipramine, norepinephrine (NE) contracted the vascular strips in a dose-dependent manner. Negative log EC50 values and maximum responses of NE-induced contraction of the SHR femoral artery were unchanged and increased, respectively, compared with those of Sprague-Dawley and Wistar-Kyoto rats (WKY). Contractile responses of the SHR aortae to NE were similar to those of the normotensive tissues. Schild plot data for alpha 1-AR antagonists indicated that alpha 1-AR subtypes mediating contraction of the aorta were homogeneous and had high affinities for bunazosin (pA2 9.4, alpha 1H subtype) and WB 4101 (pA2 9.3) and a low affinity for 5-methylurapidil (pA2 7.7). In the femoral artery, because Schild plots for bunazosin had slopes of less than 1.0, there were alpha 1H and alpha 1L subtypes. Bunazosin, at 10(-9) M, which could mask the alpha 1H subtype, yielded a Schild plot for bunazosin with a slope not different from unity and decreased the pA2 value for bunazosin (pA2 9.4 vs. 8.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Ryanodine-induced contraction in femoral artery from spontaneously hypertensive rats

The mechanismsof ryanodine-induced contractions were studied in strips of femoral arteries from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Ryanodine (30 nM to 30 μM) alone contracted arterial strips in a dose-dependent manner. The maximum contraction in SHR was about 5 times greater than that in WKY. SHR strips had about a 30 times lower threshold than WKY strips. Pretreatment with ryanodine caused a more potent dose-dependent inhibition of 10 mM caffeine-induced contraactions in SHR than in WKY. Ryanodine (10 μM) failed to contract SHR strips in a CaCl 2-free solution, whereas caffeine induced a transient contraction in the solution. Under the conditions that the sarcoplasmic reticulum was depleted of Ca 2+ by exposure of the strips to the CaCl 2-free solution, ryanodine caused a contraction in the presence of extracellular Ca 2+. Verapamil (1 nM to 1 μM) relaxed the strips precontracted with ryanodine in a dose-dependent manner. In WKY strips exposed to a 15 mM K + solution, ryanodine-induced contractions were potentiated and were not different from those of SHR strips in a normal K + (5.9 mM) solution. These results suggest that ryanodine contracts rat femoral arteries by promoting Ca 2+ influx through voltage-dependent Ca 2+ channels, ad that the ability of ryanodine to contract the arteries may depend on the state of the Ca 2+ channels.

Malfunction of arterial sarcoplasmic reticulum leading to faster and greater contraction induced by high-potassium depolarization in young spontaneously hypertensive rats.

The contribution of sarcoplasmic reticulum was studied with regard to the increase in arterial contraction induced by a high-potassium depolarization in spontaneously hypertensive rats (SHR). The 20 mmol/l potassium-induced contraction of femoral arteries was faster and greater in 6-week-old SHR than in age-matched normotensive Wistar-Kyoto (WKY) rats. Relaxation after washing the arteries with a Krebs solution was slower in SHR than in WKY rats. When the sarcoplasmic reticulum of SHR arteries had been depleted of calcium by caffeine in a calcium-free solution, the rate of high-potassium-induced contraction of the calcium-depleted SHR arteries was slowed, the same result as that with non-calcium-depleted WKY arteries. In ryanodine-treated arteries, the rate and magnitude of high-potassium-induced contraction were enhanced slightly in SHR and greatly in WKY rats, resulting in no final difference between SHR and WKY rats. Ryanodine slowed the relaxation rate in WKY rats but not in SHR. These results suggest that the diminution in ability of sarcoplasmic reticulum to sequester calcium may be responsible for the faster rate and greater magnitude of high-potassium-induced contraction with the slower relaxation in SHR arteries. We postulated that genetic malfunction of sarcoplasmic reticulum causes the increased contraction of arterial smooth muscle leading to the enhanced vasoconstriction and elevated blood pressure in SHR.

Differential effects of hypoxia upon contractions evoked by potassium and noradrenaline in rabbit arteries in vitro.

1. A study has been made on isolated sections of rabbit femoral, renal and saphenous arteries of the effects of graded hypoxia (reducing bath PO2 from 110 mmHg, normoxia, to 55, 23 and 6 mmHg) upon contractile responses evoked by noradrenaline (NA) and KCl to 80% of maximum. 2. Potassium-evoked contractions were not affected by moderate hypoxia but were reduced in all vessels to 70-80% of the control response in normoxia, by exposure to either PO2 23 or 6 mmHg. Potassium-evoked contractions were virtually abolished by Ca2(+)-free Krebs solution and greatly reduced by verapamil (10 microM), indicating that they relied upon influx of extracellular Ca2+. 3. By contrast, NA-evoked contractions were reduced in a graded fashion in all vessels by exposure to graded levels of hypoxia and at PO2 6 mmHg they were significantly more reduced than K(+)-evoked contractions. Noradrenaline-evoked contractions of femoral arteries were most affected, being reduced to 80% of control at PO2 55 mmHg, and to 28% and 6% of control at PO2 23 and 6 mmHg respectively. Contractions in renal arteries were least affected, being reduced to only 47% of control at PO2 6 mmHg. 4. Noradrenaline-evoked contractions were reduced, but not abolished, in Ca2(+)-free Krebs solution. In normoxia, they reached 42%, 35% and 25% of control responses in the presence of Ca2+ in femoral, renal and saphenous arteries respectively. The Ca2(+)-free responses of the femoral and saphenous arteries were significantly different, indicating that the femoral arteries were least dependent and saphenous most dependent on influx of extracellular Ca2+ for contraction. 5. Contractions evoked by NA in Ca2(+)-free Krebs solution were not significantly affected by PO2 55 mmHg. Those evoked in saphenous arteries were not affected by more severe hypoxia, but in renal arteries they were significantly reduced at PO2 23 mmHg, while in femoral arteries they were significantly reduced both at PO2 23 and at PO2 6 mmHg. 6. Verapamil produced changes similar to Ca2+ withdrawal. Contractions evoked by NA in the presence of verapamil were affected by hypoxia in a similar way to those evoked in the absence of Ca2+. 7. These results indicate that the inhibition of contraction induced by hypoxia is not simply dependent upon inhibition of Ca2+ influx. Instead, we propose that receptor-operated rather than voltage-operated processes are particularly vulnerable, there being inhibition of the components of contraction which are dependent on receptor-operated Ca2+ influx and release of intracellular Ca2+.