Etomidate attenuates phenylephrine-induced contraction in isolated rat aorta

PURPOSE: A previous study has shown that etomidate inhibits the angiotensin II-induced calcium influx in rat aortic smooth muscle cells. The goals of our current in vitro study were to investigate the effect of etomidate on phenylephrine-induced contraction in rat aorta, and to elucidate the associated signalling pathway. METHODS: Endothelium-denuded aortic rings were suspended for isometric tension recording. Concentration-response curves for phenylephrine (10(-9) to 10(-6) M), 5-hydroxytryptamine (10(-7) to 10(-4) M) and potassium chloride (10 to 60 mM) were generated in the presence and absence of etomidate (5 x 10(-6), 3 x 10(-5), 5 x 10(-5) M). For the rings pretreated with verapamil (10(-5) M), the phenylephrine concentration-response curves were generated in the presence and absence of etomidate (5 x 10(-5) M). In the rings exposed to calcium-free isotonic depolarizing solution, the contractile response induced by the addition of calcium was assessed in the presence and absence of etomidate (5 x 10(-5) M). RESULTS: Etomidate (5 x 10(-5) M) produced a significant rightward shift in the concentration-response curves for phenylephrine, 5-hydroxytryptamine and potassium chloride. Etomidate (5 x 10(-5) M) did not alter phenylephrine-induced contraction in the rings pretreated with verapamil. Etomidate (5 x 10(-5) M) significantly attenuated the contractile response induced by the addition of calcium in the calcium-free isotonic depolarizing solution. CONCLUSION: The results suggest that etomidate, which exceeds the clinically relevant concentration, attenuates the phenylephrine-induced contraction by having an inhibitory effect on the calcium influx by blocking the L-type calcium channels in the rat aortic vascular smooth muscle.     

Diazepam attenuates phenylephrine-induced contractions in rat aorta

In this in vitro study we examined the effects of diazepam on a phenylephrine-induced contraction in rat aorta and determined the associated cellular mechanism focusing on the endothelium-derived vasodilators. The concentration-response curves for phenylephrine and potassium chloride were generated in the presence or absence of diazepam. Phenylephrine concentration-response curves were generated from the endothelium-intact rings pretreated independently with N(W)-nitro-L-arginine methyl ester, PK 11195, tetraethylammonium, and indomethacin in the presence or absence of diazepam. Diazepam (7 x 10(-7) M) attenuated the phenylephrine-induced contraction in the endothelium-intact rings, whereas a large dose (5 x 10(-6) M) of diazepam attenuated the phenylephrine-induced contraction in the aortic rings with or without the endothelium. A pretreatment with the N(W)-nitro-L-arginine methyl ester completely abolished the diazepam (7 x 10(-7) M)-induced attenuation of the phenylephrine concentration-response curve, as well as the diazepam (5 x 10(-6) M)-induced attenuation of the maximal contractile response to phenylephrine. The N(W)-nitro-L-arginine methyl ester (10(-4) M)-induced contraction was enhanced in the rings pretreated with diazepam (5 x 10(-6) M). These results indicate that a supraclinical concentration of diazepam attenuates phenylephrine-induced contraction by increasing endothelial nitric oxide activity and directly affecting vascular smooth muscle.     

Direct inhibition of rat detrusor muscle contraction by erythromycin

PURPOSE: Detrusor instability is a common problem in the elderly, which is usually treated with anti-cholinergic medication. This study investigates the effect of erythromycin on rat detrusor muscle contractile response to characterise its potential as an alternative inhibitor of bladder muscle contraction. MATERIALS AND METHODS: Strips of rat detrusor muscle were suspended in a perfusion organ bath. The contractile response to direct muscle stimulation, electrical field stimulation (EFS, 0.5-60 Hz), carbachol (10(-5) M), and potassium (10-80 x 10(-3) M) were determined before and after the addition of erythromycin (10(-4)-10(-3) M). The contractile response to carbachol (10(-5) M) in the presence of nifedipine (10(-8) or 10(-6) M) or in calcium-free Kreb's solution was also determined in the absence and presence of erythromycin. RESULTS: Erythromycin 5 x 10(-4) M inhibited the maximum contractile response to EFS, carbachol, and potassium by 38% (P < 0.01), 62% (P < 0.001), and 17% (P < 0.05), respectively, but did not significantly reduce the response to direct muscle stimulation. The atropine-resistant component of EFS-evoked contraction was inhibited by 19.5% (P < 0.01) in the presence of erythromycin. In calcium-free Krebs solution, the maximum contractile response to carbachol was reduced by 42% of control (P < 0.0001) and nifedipine 10(-8) M had no additional effect. When erythromycin 5 x 10(-4) M was added together with nifedipine 10(-8) M, the response to carbachol was inhibited by a further 25% (P < 0.005). CONCLUSIONS: Erythromycin inhibits rat detrusor muscle contraction through the inhibition of calcium influx and the modulation of intracellular calcium movement.     

The effects of alfentanil on cytosolic Ca(2+) and contraction in rat ventricular myocytes

Previous investigations of the effects of potent opioid analgesics on the heart have concentrated on effects on contraction magnitude and time course, but little is known about their effects on cytosolic Ca(2+) regulation in cardiac tissue. In this study, we sought to assess the effects of alfentanil on contractility and the cytosolic Ca(2+) transient in ventricular myocytes isolated from the rat ventricle by enzymatic dispersion. Cells were loaded with fura-2 and electrically stimulated at 1 Hz, and Ca(2+) transients and contractions were recorded optically at 30 degrees C. Alfentanil 10(-8) and 10(-7) M had no effect on the magnitude or time course of contraction or the cytosolic Ca(2+) transient. In contrast, 10(-6) M alfentanil induced a significant (P < 0.001) positive inotropic effect, increasing the mean (+/-SEM) unloaded shortening from 7.3 +/- 1.3 microm to 8.7 +/- 1.4 microm (an increase of 20%), with no change in the cytosolic Ca(2+) transient. Myofilament Ca(2+) sensitivity was significantly (P = 0.027) increased by 10(-6) M alfentanil but unaffected at 10(-7) M alfentanil. These data show that 10(-6) M alfentanil, a concentration close to the maximum clinical free plasma concentration, induced a positive inotropic effect due to sensitization of the myofilaments to Ca(2+) rather than to modified cytosolic Ca(2+) regulation. IMPLICATIONS: Alfentanil, at concentrations achieved in clinical practice, increased contraction in ventricular cells by a mechanism involving an increase in the sensitivity of the contractile apparatus to Ca(2+).     

A supraclinical dose of tramadol stereoselectively attenuates endothelium-dependent relaxation in isolated rat aorta

Tramadol, a combination of R(-) and S(+) enantiomers, inhibits both the acetylcholine-mediated response of muscarinic receptors and the muscarine-induced accumulation of cyclic guanosine monophosphate. Our goals in this in vitro study were to investigate the effects of tramadol on endothelium-dependent relaxation induced by acetylcholine, to determine whether this effect of tramadol is stereoselective, and to elucidate the associated cellular mechanism in rat aorta. In endothelium-intact rings precontracted with phenylephrine with or without naloxone, dose-response curves for acetylcholine, histamine, and calcium ionophore A23187 were generated in the presence and absence of tramadol (racemic, R(-) and S(+)). Sodium nitroprusside dose-response curves were generated in the presence and absence of racemic tramadol. Racemic tramadol (5 x 10(-5) 10(-4) M) attenuated acetylcholine-induced relaxation in the rings with or without naloxone. R(-) tramadol, 5 x 10(-5) M, attenuated acetylcholine-induced relaxation, whereas S(+) tramadol, 5 x 10(-5) M, did not. Racemic tramadol (10(-4) M) had no effect on dose-response curves for calcium ionophore A23187 or sodium nitroprusside. Taken together, these results indicate that tramadol, at a supraclinical dose (5 x 10(-5) M), stereoselectively attenuates endothelium-dependent relaxation via an inhibitory effect at levels proximal to nitric oxide synthase activation on a pathway involving nonspecific endothelial receptor activation.     

Direct effect of ropivacaine involves lipoxygenase pathway activation in rat aortic smooth muscle

Purpose

Ropivacaine is a long-acting amino-amide local anesthetic that induces vasoconstriction in vitro and in vivo. The aim of this study was to investigate the pathways involved in arachidonic acid metabolism associated with S-ropivacaine-induced contraction of rat aortic smooth muscle in vitro.

Methods

Rat thoracic aortic rings without endothelium were isolated and suspended for isometric tension recording. Cumulative dose–response curves were generated with concentrations of 10^?5 to 10^?3 M ropivacaine enantiomer in the presence or absence of quinacrine dihydrochloride, nordihydroguaiaretic acid, quinacrine dihydrochloride plus nordihydroguaiaretic acid, indomethacin, fluconazole, AA-861, and verapamil. The maximal S-ropivacaine-induced contractile response achieved at 3 × 10^?4 M was also assessed in aortic rings pretreated with normal or calcium-free Krebs solution.

Results

Ropivacaine enantiomers induced dose-dependent biphasic contractions in aortic rings. S-ropivacaine (10^?4, 3 × 10^?4 M) induced a stronger contraction than R-ropivacaine. Quinacrine dihydrochloride (2 × 10^?5, 4 × 10^?5 M) attenuated the S-ropivacaine-induced biphasic contraction in a dose-dependent manner. Indomethacin (3 × 10^?5, 6 × 10^?5 M), nordihydroguaiaretic acid (10^?5 M), and AA-861 (10^?5 M) also attenuated the S-ropivacaine-induced dose-dependent biphasic contraction, whereas fluconazole (3 × 10^?5) had no effect. Combined pretreatment with quinacrine dihydrochloride and nordihydroguaiaretic acid almost completely abolished the S-ropivacaine-induced contraction. S-ropivacaine-induced contractile responses were attenuated by verapamil (10^?5 M) and calcium-free Krebs solution.

Conclusion

S-ropivacaine induces dose-dependent biphasic contractions in rat aortic smooth muscle through a mechanism requiring extracellular calcium that is mediated by activation of the lipoxygenase pathway and, to a lesser extent, the cyclooxygenase pathway.     

Adenosine induces mesangial cell contraction by an A1-type receptor

Adenosine is known to decrease renal blood flow and glomerular filtration rate. We have tested the hypothesis that adenosine exerts contractile effects on mesangial cells. Furthermore, we have studied, using selective agonists and antagonists for adenosine, which kind of adenosine receptor, A1 or A2, is mainly implicated in this response. We also investigated whether calcium is involved in adenosine-induced mesangial cell contraction. Rat cultured mesangial cells were exposed to adenosine (10(-7) to 10(-3) M) and the contraction was measured as changes in planar cell surface area (PCSA). Adenosine induced a time- and dose-dependent reduction of PCSA. This reduction in PCSA was prevented by incubation with the A1 blocker PD116,948 but not with the A2 blocker PD115,199. Adenosine-5'-ethylcarboxamide (NECA), an A2 agonist, did not induce significant changes in PCSA whereas N6-S-1-methyl-2-phenylethyl adenosine (S-PIA), an A1 agonist, induced a dose-dependent decrease in PCSA. Adenosine-induced mesangial contraction was prevented by verapamil or by incubation in a calcium-free medium. These results suggest that adenosine induces a specific contraction of cultured rat mesangial cells that seems to be mediated by its binding to the adenosine A1-type receptor. This contraction seems to be dependent on the influx of extracellular calcium.     

Multiple-signaling pathways are involved in the inhibitory effects of galangin on urinary bladder contractility

AIMS: Flavonoids comprise a large group of natural polyphenolic compounds, which possess a wide spectrum of physiological and pharmacological effects. Recently, the flavonoid galangin was found to modulate smooth muscle contractility. The aim of the present study was to investigate the mechanism of actions of galangin on pig bladder smooth muscle and to characterize its potential as an alternative inhibitor of bladder smooth muscle contraction. MATERIALS AND METHODS: Strips of pig detrusor muscle were mounted in separate 6-ml organ baths containing Krebs solution. The contractile response to carbachol (10(-8)-10(-4)M), potassium (2x10(-2)-10(-1)M), and electrical field stimulation-EFS (2-32 Hz) were determined before and after the addition of galangin (3x10(-5)M). The contractile responses to carbachol in calcium-free Krebs' solution plus EGTA and L-type channel blocker were determined in the absence and presence of the flavonoid. Furthermore, the effect of galangin was also evaluated after the administration in the bath of a number of antagonists/inhibitors including a combination of propranolol, phentolamine, capsazepine, and verapamil. Student's t-test and one factor ANOVA were used to determine the statistical significance of the effects. RESULTS: Galangin inhibited the maximal contractile response to carbachol and potassium by 57.41% (P<0.01) and 33.52% (P<0.05), respectively. The maximum force of the carbachol-evoked contractions in calcium-free solution after incubation with galangin was 32% of the maximum initial force (Emax.initial: 5.8387+/-0.72 mN, Emax.Galangin: 1.9157+/-0.30 mN, P<0.01). The maximal contractile responses to EFS at 2, 4, 8, 16, and 32 Hz were reduced, compared to control, by 91.61% (P<0.01), 79.46% (P<0.01), 70.54% (P<0.01), 61.10% (P<0.01), and 9.8% (P>0.05), respectively. The inhibitory effect of galangin was unaffected by a combination of propranolol, phentolamine, and capsazepine (P>0.05). However, when verapamil was added to the medium, the inhibitory effects of galangin were partially blocked. CONCLUSIONS: Galangin, at high concentrations, exerts an inhibitory effect on pig bladder smooth muscle contractility through the inhibition of calcium influx and the modulation of intracellular calcium movement. Furthermore, we have demonstrated that the inhibitory effect of galangin involves, at least in part, L-type calcium channels pathways.     

山楂叶总黄酮对离体大鼠胸主动脉环功能的影响

目的 观察山楂叶总黄酮(HLF)对大鼠胸主动脉血管环的作用,并探讨其作用机制.方法 采用大鼠胸主动脉环张力测定法,观察HLF对高浓度KCl(6×10-2mol/L)和去甲肾上腺素(NE,1×10-6mol/L)预收缩的离体大鼠胸主动脉血管环作用;并观察左旋硝基精氨酸甲酯(L-NAME,1×10-5mol/L)和吲哚美辛(1×10-4mol/L)对其作用的影响.结果 HLF(5×10～50×10-3g/L)对高浓度氯化钾(KCl,6×10-2mol/L)预收缩的内皮完整或去内皮的血管环均无明显作用(P＞0.05);对去甲肾上腺素(NE,1×10-6mol/L)预收缩的血管环产生内皮依赖性的舒张作用(P＜0.01);HLF对NE预收缩血管的舒张作用能被L-NAME(1×10-5 mol/L)显著阻断(P＜0.01),而不能被吲哚美辛(1×10-4mol/L)阻断(P＞0.05).结论 HLF对胸主动脉血管有舒张作用,其机制可能是通过抑制受体操纵的钙通道(ROC)的激活而直接抑制细胞外钙内流降低细胞内Ca2+浓度而起作用的;HLF的内皮依赖性舒张作用可能与血管内皮一氧化氮(NO)合成有关.

Abstract：

Objective To investigate the effects and mechanisms of hawthorn leaf flavonoids (HLF) on isolated thoracic aorta in rats. Methods The tension of rat thoracic aorta tings was measured.The effects of HLF on the thoracic aorta preconstricted by potassium chloride ( KCl, 6 × 10-2 mol/L) and norepinephrine (NE, 1 × 10-6 mol/L), as well as the effects of L-nitro arginine methyl ester (L-NAME,1 × 10-5 mol/L) and indomethacin ( 1 × 10-4 mol/L) on the relaxation response of HLF were observed.Results HLF completely relaxed the constriction induced by NE ( 1 × 10 -6 mol/L) in endothelium-intact thoracic aorta ( P ＜ 0. 01 ), but had no effect on those preconstricted aorta rings by a high concentration of KCl (6 × 10-2 mol/L) in endothelium-intact and endothelium-denuded rat aorta (P ＞ 0. 05). The relaxation response of HLF was significantly inhibited by L-NAME (P ＜ 0. 01 ), but not by indomethacin (P ＞0. 05). Conclusion The vasorelaxation induced by HLF in rat aorta rings may involve the reduction of Ca2+ influx through the calcium channels operated by receptor (ROC). The endothelium-dependent relaxation of HLF may be related to the generation of nitric oxide (NO).     

Bupivacaine inhibits thromboxane A2-induced vasoconstriction in rat thoracic aorta

Plasma levels of thromboxane A2 (TXA2), an inflammatory mediator inducing platelet aggregation, bronchoconstriction, and vasoconstriction, are increased in the perioperative period. A major role in the pathogenesis of perioperative thromboembolic and ischemic syndromes is attributed to this prostanoid. Local anesthetics (LA) inhibit signaling of TXA2 receptors expressed in cell models. Therefore, we hypothesized that LA may inhibit vasoconstriction induced by the TXA2 analog U46619 in rat thoracic aorta. Rings (3-mm length) of the rat thoracic aorta were mounted in organ baths and isometric contractile force was measured. Rings, with or without endothelium, were incubated for 60 min in bupivacaine (10(-6) or 10(-5) M) or Krebs-Henseleit solution (control group) and subsequently exposed to cumulative concentrations of U46619 (10(-10) to 10(-6) M). The reversibility of the TXA2-induced vasoconstriction by bupivacaine was also studied. Pretreatment of rings with bupivacaine concentration-dependently diminished TXA2-induced contraction in rat aortic rings. We found no significant differences in relaxing effect of bupivacaine between rings with and without endothelium. Contraction in rings established with U46619 could not be reversed by cumulative concentrations of bupivacaine. Bupivacaine inhibited carbachol-induced vascular relaxation. This study provides experimental evidence that bupivacaine is an endothelium-independent inhibitor of TXA2-induced vasoconstriction of rat thoracic aorta.     

Inhibitory effect of tramadol on vasorelaxation mediated by ATP-sensitive K+ channels in rat aorta

PURPOSE: Tramadol produces a conduction block similar to lidocaine by exerting a local anesthetic-like effect. The aims of this in vitro study were to determine the effects of tramadol on the vasorelaxant response induced by the adenosine triphosphate-sensitive K(+) (K(ATP)) channel opener, levcromakalim, in an endothelium-denuded rat aorta, and to determine whether this effect of tramadol is stereoselective. METHODS: The effects of tramadol (racemic, R(-) and S(+): 10(-6), 10(-5), 5 x 10(-5) M), and glibenclamide on the levcromakalim dose-response curve were assessed in aortic rings that had been pre-contracted with phenylephrine. In the rings pretreated independently with naloxone, and glibenclamide, the levcromakalim dose-response curves were generated in the presence or absence of tramadol. The effect of tramadol on the dose-response curve of diltiazem was assessed. RESULTS: Racemic, R(-) and S(+) tramadol (10(-5), 5 x 10(-5) M) attenuated (P < 0.0001) levcromakalim-induced relaxation in the ring with or without naloxone in a dose-dependent manner. The magnitude of the R(-)-tramadol-induced attenuation of vasorelaxant response induced by levcromakalim was greater (P < 0.05) than that induced by S(+)-tramadol. Glibenclamide almost abolished the levcromakalim-induced relaxation. Tramadol, 5 x 10(-5) M, did not significantly alter the diltiazem-induced relaxation. CONCLUSION: These results suggest that a supraclinical dose (10(-5) M) of tramadol [racemic, R(-) and S(+)] attenuates the vasorelaxation mediated by the K(ATP) channels in the rat aorta. The R(-) tramadol-induced attenuation of vasorelaxation induced by levcromaklim was more potent than that induced by S(+) tramadol. This attenuation is independent of opioid receptor activation.     

Comparative Contractile Effects of Halothane and Sevoflurane in Rat Aorta

Background: Volatile anesthetic agents have been shown to have contractile effects in vascular tissues during specific conditions. This study compared contractile effects of halothane and sevoflurane in rat aorta treated with verapamil. This study also tried to elucidate the mechanism of the contraction.

Methods: Endothelium-denuded rat thoracic aorta was used for recording of isometric tension and measurement of influx of 45Ca2+. All experiments were performed in the presence of verapamil. In recording of tension, rings were precontracted with a submaximum dose of phenylephrine, followed by exposure to halothane or sevoflurane. For measurement of influx of 45Ca2+, rat aortic strips were exposed to phenylephrine and then to additional halothane or sevoflurane. Influx of Ca2+ was estimated by incubating the strips in 45Ca2+-labeled solution for 2 min.

Results: Halothane (0.5-4.0%) induced contraction in a dose-dependent manner, whereas sevoflurane (1-4%) had no effect on tension. Influx of 45Ca2+ was strongly enhanced by halothane at 1% and 2%, but only slightly at 4%, and was not affected by 1-4% sevoflurane. SK&F 96365, a blocker of voltage-independent Ca2+ channels, abolished contraction and influx of 45Ca2+ by 1% halothane. Depletion of Ca2+ from the sarcoplasmic reticulum with ryanodine or thapsigargin reduced the contraction induced by halothane at 4% but not that at 1% and 2%.     

Effect of etomidate on endothelium-dependent relaxation induced by acetylcholine in rat aorta

The goals of this in vitro study were to investigate effects of etomidate on endothelium-dependent relaxation induced by acetylcholine in rat aorta, and to elucidate the associated cellular mechanism. In endothelium-intact rings precontracted with phenylephrine 10(-6) M, dose-response curves for acetylcholine (10(-9) to 10(-5) M) and calcium ionophore (10(-9) to 10(-6) M) were generated in the presence and absence of etomidate (5 x10(-6) 10(-5) M). In endothelium-intact or -denuded rings precontracted with phenylephrine 10(-6) M, sodium nitroprusside (10(-9) to 10(-6) M) dose-response curves were generated in the presence and absence of etomidate (10(-5)M). Etomidate (5 x10(-6), 10(-5)M) produced a significant rightward shift in the dose-response curves induced by acetylcholine (receptor-mediated endothelium-dependent agonist) and calcium ionophore A23187 (non receptor-mediated endothelium-dependent agonist). Etomidate (10(-5)M) had no effect on sodium nitroprusside (endothelium-independent nitric oxide donor)-induced vasorelaxant response in both endothelium-intact and -denuded rings. These results indicate that etomidate at clinically relevant concentrations attenuates endothelium-dependent relaxation induced by acetylcholine by an acting at a site distal to the endothelial muscarinic receptor, but proximal to guanylate cyclase activation of vascular smooth muscle in rat aorta.     

L-type calcium channels involvement in aortic smooth muscle contraction as revealed by membrane potential and active force dynamics

Membrane potential (MP) is essential in smooth muscle (SM) contractile activity, mainly by its effect upon L-type Ca2+ channels. We simultaneously recorded SM isometric tension and MP in de-endothelised rat aorta rings and examined their submaximal activation by K+, norepinephrine (NE) or phenylephrine (PHE) and the influence of methoxyverapamil (D600). K+ -induced contraction strictly correlated with depolarization, while faster contractions induced by NE or PHE started and peaked with a less depolarized membrane. D600 completely relaxed K+ or NE contracted rings, time-correlated with full repolarization, but partially relaxed PHE-contracted rings, with partial repolarization, which did not precede relaxation. The observed MP and force dynamics support known mechanisms of action of the drugs used. L-type channels participate in the depolarizing and contractile effect of NE, as opposite to their minor involvement in the effects of PHE.     

Involvement of Ca2+ Sensitization in Ropivacaine-induced Contraction of Rat Aortic Smooth Muscle

Background: The mechanisms of amino-amide local anesthetic agent-induced vasoconstriction remain unclear. The current study was designed to examine the roles of the protein kinase C (PKC), Rho kinase, and p44/42 mitogen-activated protein kinase (p44/42 MAPK) signaling pathways in calcium (Ca2+)-sensitization mechanisms in ropivacaine-induced vascular contraction.

Methods: Endothelium-denuded rat aortic rings, segments, and strips were prepared. The cumulative dose-response relations of contraction and intracellular Ca2+ concentration to ropivacaine were tested, using isometric force transducers and a fluorometer, respectively. The dose-dependent ropivacaine-induced phosphorylation of PKC and p44/42 MAPK and the membrane translocation of Rho kinase were also detected using Western blotting.

Results: Ropivacaine induced a dose-dependent biphasic contractile response and an increase in intracellular Ca2+ concentration of rat aortic rings, increasing at concentrations of 3 x 10-5 m to 3 x 10-4 m and decreasing from 10-3 m to 3 x 10-3 m, with a greater tension/intracellular Ca2+ concentration ratio than that induced with potassium chloride. The contraction was attenuated in a dose-dependent manner, by the PKC inhibitors bisindolylmaleimide I and calphostin C, the Rho-kinase inhibitor Y 27632, and the p44/42 MAPK inhibitor PD 098059. Ropivacaine also induced an increase in phosphorylation of PKC and p44/42 MAPK, and membrane translocation of Rho kinase in accordance with the contractile responses, which were also significantly inhibited by bisindolylmaleimide I and calphostin C, Y 27632, and PD 098059, correspondingly.     

The effect of hemoglobin on vasodilatory effect of calcium antagonists in the isolated rabbit basilar artery.

The effect of hemoglobin on the vasodilatory effect of calcium antagonists was studied in isolated rabbit basilar arteries using an isometric tension measurement method. The ability of nimodipine to relax or inhibit contractions elicited by high K+ depolarization or serotonin (5-hydroxytryptamine, 5-HT) was investigated in control arterial rings and rings pretreated by hemoglobin. Hemoglobin (10(-6) and 10(-5) M) reduced the relaxation induced by nimodipine (10(-10) to 10(-8) M) in the rings contracted by 40 mM KCl. This reduction in relaxation was also observed with 3 x 10(-10) to 3 x 10(-9) M nicardipine, 3 x 10(-8) to 3 x 10(-7) M verapamil, and 10(-7) to 10(-6) M diltiazem. On the other hand, the effect of nimodipine was not influenced by endothelial removal or by pretreatment with 10(-5) M albumin or 10(-6) M prostaglandin F2 alpha. Hemoglobin restored the 10(-10) and 10(-9) M nimodipine-induced inhibition of the contraction elicited by CaCl2 (0.3 to 20 mM) in a K(+)-rich, Ca(++)-free solution. This restoration was greater at higher concentrations of CaCl2. Hemoglobin enhanced both the nimodipine-sensitive tonic phase and the less sensitive phasic phase of contractions produced by 10(-6) M of 5-HT. It abolished the inhibitory effect of 10(-8) and 10(-7) M nimodipine on the phasic contraction. Endothelial removal also enhanced both phases of the contraction, but did not abolish the effect of nimodipine. This study showed that the vasodilatory effect of calcium antagonists, especially nimodipine, on the vasoconstriction induced by other vasoactive substances decreased in the presence of hemoglobin.     

Comparative contractile effects of halothane and sevoflurane in rat aorta

BACKGROUND: Volatile anesthetic agents have been shown to have contractile effects in vascular tissues during specific conditions. This study compared contractile effects of halothane and sevoflurane in rat aorta treated with verapamil. This study also tried to elucidate the mechanism of the contraction. METHODS: Endothelium-denuded rat thoracic aorta was used for recording of isometric tension and measurement of influx of 45Ca2+. All experiments were performed in the presence of verapamil. In recording of tension, rings were precontracted with a submaximum dose of phenylephrine, followed by exposure to halothane or sevoflurane. For measurement of influx of 45Ca2+, rat aortic strips were exposed to phenylephrine and then to additional halothane or sevoflurane. Influx of Ca2+ was estimated by incubating the strips in 45Ca2+-labeled solution for 2 min. RESULTS: Halothane (0.5-4.0%) induced contraction in a dose-dependent manner, whereas sevoflurane (1-4%) had no effect on tension. Influx of 45Ca2+ was strongly enhanced by halothane at 1% and 2%, but only slightly at 4%, and was not affected by 1-4% sevoflurane. SK&F 96365, a blocker of voltage-independent Ca2+ channels, abolished contraction and influx of 45Ca2+ by 1% halothane. Depletion of Ca2+ from the sarcoplasmic reticulum with ryanodine or thapsigargin reduced the contraction induced by halothane at 4% but not that at 1% and 2%. CONCLUSION: Halothane is suggested to cause contraction by enhancing influx of Ca2+ via voltage-independent Ca2+ channels at concentrations up to 2% and by inducing release of Ca2+ at 4%. Sevoflurane (1-4%) is devoid of these contractile effects.     

Selective effects of alfentanil on nociceptive-related neurotransmission in neonatal rat spinal cord

We have examined the effects of alfentanil on nociceptive-relatedneurotransmission in isolated neonatal rat spinal cord, withparticular attention to acute tolerance. Electrical stimulationof a lumbar dorsal root was used to evoke the monosynaptic reflex(MSR), a slow ventral root potential (sVRP), and the dorsalroot potential (DRP). Alfentanil (0.5 nmol litre^–1 to1 µmol litre^–1) depressed sVRP area by a maximumof 85%; EC₅₀ was approximately 2 nmol litre^–1. The effectsof alfentanil were selective for very slow, metabotropicallymediated sVRP components compared with faster NM DA receptor-mediatedcomponents. The MSR was unaffected. Alfentanil depressed DRParea by a maximum of 50% at 1 µmol litre^–1. Naloxoneantagonized all alfentanil effects. Morphine depressed sVRParea with an approximate EC₅₀ of 90 nmol litre^–1, givingan alfentanil:morphine potency ratio of 45:1. The effects ofalfentanil on sVRP showed no biphasic time dependence up to60 min. Naloxone administered after alfentanil produced a significantrebound in sVRP area to a level of 143 (SD 21.3)% above control.Thus, in this study there was no evidence for acute tolerance,as measured by a decrease in effectiveness over time, but therewas evidence as measured by rebound following naloxone.     

Effect of mild hypothermia on the vascular actions of phenylephrine in rat aortic rings

Intraoperative mild hypothermia is common. We have investigated the effects of mild hypothermia (34 vs 38 degrees C) on phenylephrine--(10(- 8) to 10(-5) mol litre-1) induced contractions of rat aortic rings mounted for isometric tension recordings. A marked decrease in Emax (maximal tension) (P < 0.05) and significant increase in EC50 (phenylephrine concentration producing 50% of maximal tension) were observed at the lower temperature in endothelium intact rings, but there was no effect of temperature when the endothelium had been removed. The decreased contraction with hypothermia in the endothelium intact vessels was restored to 84% by administration of the nitric oxide synthase inhibitor L-NNA and a small additional amount of tone was restored in the presence of the cyclooxygenase inhibitor, indomethacin. We conclude that mild hypothermia markedly decreased phenylephrine-induced rat aortic contraction in vitro by endothelium dependent mechanisms, largely related to increased nitric oxide production or action.      

Involvement of alpha-receptors and potassium channels in the mechanism of action of sildenafil citrate

Modulation of the adrenergic activity and interfering with channels such as potassium channels may affect relaxation and contraction of the corpus cavernosum. Sildenafil is a selective phosphodiesterase-5 inhibitor, proven effective in treating erectile dysfunction.In this study, the effect of sildenafil citrate on alpha-receptors modulation and potassium channels was tested. The direct relaxant effect of sildenafil citrate was studied by measuring changes in isometric tension in isolated strips of rabbit corpus cavernosum and rat aortic ring precontracted with phenylephrine or KCl compared to that of diazoxide in the presence and absence of tetraethylammonium. The inhibitory effect of sildenafil on electrical field stimulation-induced contraction of rabbit corpus cavernosum and rat anococcygeus muscle was also studied compared to that of phentolamine. Muscle relaxant effect of sildenafil (1 x 10(-9)-1 x 10(-6) M on phenylephrine-precontracted rabbit corpus cavernosum strips was not attenuated by N(G)-nitro-L-arginine (3 x 10(-5) M). Cumulative addition of sildenafil (1 x 10(-9)-1 x 10(-6) M) and phentolamine (1 x 10(-9)-1 x 10(-6) M) to the organ bath dose-dependently inhibited electrical field stimulation-induced contraction of rabbit corpus cavernosum and rat anococcygeus muscle, with almost similar EC(50) values. Sildenafil (1 x 10(-7) M) also inhibited phenylephrine-induced contraction of rat aortic rings by 39.83+/-3.01%. In addition, tetraethylammonium (1 x 10(-3) M) significantly attenuated the muscle relaxant effect of sildenafil (1 x 10(-9)-1 x 10(-6) M) on phenylephrine-precontracted strips of rabbit corpus cavernosum.Sildenafil citrate is capable of producing cavernosal smooth muscle relaxation by an additional mechanism that may involve alpha-receptors and potassium channel opening.