General Pharmacology-the Vascular System最新文献

Relaxations to acetylcholine and contractions to acetylcholine in the presence of the nitric oxide (NO) synthesis inhibitor (l-N^G-nitroarginine methyl ester, l-NAME) were studied in aortic rings from rabbits fed either a control or a diet containing 0.5% cholesterol+14% coconut oil for 14 weeks and treated or not with atorvastatin (2.5 mg kg⁻¹ day⁻¹). Rings were incubated with the endothelin (ET_A) receptor antagonist BQ123, and/or the thromboxane A₂ (TXA₂)/prostaglandin H₂ (PGH₂) receptor antagonist ifetroban. In rabbits, high cholesterol and triglyceride plasma levels were associated with intimal thickening and blunted acetylcholine-relaxation as compared with controls. By contrast, acetylcholine+l-NAME response was higher. Incubation with either ifetroban or BQ123 increased acetylcholine-relaxation in both diet groups and it reduced the constrictor response only in dyslipidemic rabbits. Removal of endothelium reduced acetylcholine+l-NAME contraction in dyslipidemic rabbits, although increased it in control animals. Atorvastatin treatment reduced plasma lipid levels and lesion size in dyslipidemic animals. Likewise, it prevented acetylcholine-relaxation reduction. In addition, atorvastatin reduced constrictor response in dyslipidemic rabbits but only in rings with endothelium. Incubation with either ifetroban or BQ123 did not further modify these responses in atorvastatin-treated animals in any group. These data suggest that ET and TXA₂ availabilities seem to participate in the endothelial dysfunction associated with dyslipidemia. Atorvastatin treatment reduces intimal thickening and improves endothelial dysfunction in rabbits. This effect seems to be a consequence of its ability to act on ET and TXA₂ systems.

Mechanism of acetylcholine (ACh)-induced dilatation was investigated in isolated perfused rat kidney. Under a constant flow of 8–10 ml/min, ACh (0.001–3 μg/0.1 ml) caused a dose-dependent decrease in perfusion pressure raised by submaximum concentration of phenylephrine (PE). ACh-induced dilatations were inhibited by atropine (10⁻⁶ mol/l), hexamethonium (10⁻⁴ mol/l), indomethacin (10⁻⁵ mol/l), methylene blue (10⁻⁵ mol/l), N^G-nitro-l-arginine (l-NOARG, 10⁻⁴ mol/l), tetrodotoxin (TTX, 10⁻⁶ mol/l), capsaicin (10⁻⁶ mol/l), and glibenclamide (10⁻⁵ mol/l). These results suggest that in the isolated perfused rat kidney, endothelium-derived hyperpolarizing factor (EDHF), nitric oxide (NO), and tachykinin neuromediators may play a role in ACh-induced dilatation via stimulation of guanylate cyclase and opening of ATP-sensitive potassium channels.

Acute S 22068 (24 mg/kg po) improved glucose tolerance and increased insulin sensitivity, assessed as the acute blood glucose response to exogenous insulin. The same acute dose did not stimulate insulin secretion or induce hypoglycemia in fed animals. Comparison of acute S 22068 to equipotent doses (with respect to effect on glucose tolerance) of gliclazide (2 mg/kg) and metformin (60 mg/kg) found S 22068 to be similar to metformin with respect to its effects on basal glucose levels (BGL) and insulin sensitivity. This also suggests that S 22068 acts by a mechanism which does not involve insulin release. Acute or sub-chronic S 22068 (14 days at 25 mg/day) had no effect on brown adipose tissue (BAT) or white adipose tissue (WAT) lipogenesis, an insulin-sensitive metabolic pathway.

Sub-chronic treatment with S 22068 did not alter body weight (BW) or food intake, and resulted in tolerance to its effects on glucose metabolism and insulin sensitivity. These findings suggest that S 22068 is similar in effect to metformin, and is not insulinogenic, in contrast to the sulfonylureas or putative I₃ imidazoline site ligands.

Lidocaine is a widely used local anesthetic agent. The aim of this work was to study the action of lidocaine on human red blood cells exposed to an oxidative stress in vitro. Blood was obtained from healthy volunteers. After separation from plasma, the erythrocytes were suspended in phosphate buffer. Oxidative stress was induced by incubation with a free radical generator, the 2,2′ azobis (2-amidinopropane) hydrochloride (AAPH). Erythrocytes were incubated with or without lidocaine at two concentrations (36.93 and 73.85 μM) and with or without AAPH (20 mM). Electron paramagnetic resonance (EPR) spectroscopy was performed to identify the free radical species generated by AAPH using the spin trap 5-5′-dimethyl-l-pyroline-N-oxide (DMPO). Different sets of experiments were run. Potassium efflux was measured by flame photometry in each group at time 0 min and every 30 min of the experiment for 2 h. Hemolysis was studied by the Drabkin method at increasing concentrations of AAPH (20, 50, and 100 mM) and with or without lidocaine (36.93 μM). The oxygen radical absorbance capacity (ORAC) was measured by using allophycocyanin (APC) as a fluorescent indicator protein, and the antioxidant capacity of lidocaine (36.93 μM) was studied by the analysis of fluorescence of the APC. AAPH was shown to produce alkoxyl free radicals. Oxidative stress induced a marked increase in the potassium efflux and the hemolysis that was AAPH dose-dependent. Lidocaine inhibited the potassium efflux and delayed the occurrence of hemolysis. Lidocaine did not show any antioxidant properties for the free radical species generated by AAPH. In this model, lidocaine protects erythrocytes against oxidative stress. This effect is not explained by a free radical scavenging property. The results may be of great interest in clinical practice such as intravenous regional anesthesia or the prevention of ischemia–reperfusion injury.

We examined endothelium-dependent relaxation in the aortas and renal arteries of Otsuka Long–Evans Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetes mellitus, in comparison with non-diabetic Long–Evans Tokushima Otsuka rats as controls. Acetylcholine-induced relaxation in both arteries was attenuated, and the attenuation was restored to the control level by indomethacin. The relaxation was inhibited completely in the aortas, but only partially in renal arteries by N^G-nitro-l-arginine methyl ester, and the degree of the latter inhibition was greater in OLETF rats than in the controls. The relaxation was inhibited by aminoguanidine in both arteries of OLETF rats but not in the controls. Serum NO₂ plus NO₃ levels significantly increased in OLETF rats. These results suggest that impairment of relaxation in OLETF rat arteries is due to increased release of contractile factors but not decreased release of nitric oxide.

(1) The role of L-type Ca²⁺ channels in the relaxation to nitric oxide (NO)-mediated MaxiK_Ca channel activation was examined in guinea pig aorta. (2) Acetylcholine (ACh) produced an endothelium-dependent relaxation of guinea pig aorta precontracted with noradrenaline (NA), which was abolished by an NO synthase inhibitor, N^G-nitro-l-arginine (l-NNA). (3) Both endothelium-dependent relaxation by ACh and endothelium-independent relaxation by an NO donor, (±)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide (NOR3), were strongly suppressed by a soluble guanylate cyclase (sGC) inhibitor, 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one (ODQ), suggesting that increased intracellular cGMP plays the key role in both responses. (4) ACh- and NOR3-induced relaxations were significantly suppressed by iberiotoxin (IbTX), a selective blocker of MaxiK_Ca channels. (5) ACh- and NOR3-induced relaxations were greatly attenuated when arteries were precontracted with high KCl instead of NA, supporting the idea that K⁺ channel activation mediates the relaxant responses. (6) NOR3-induced relaxations were not affected by a L-type Ca²⁺ channel blocker, diltiazem. Furthermore, endothelium-independent relaxation by a K_ATP channel opener, (+)-7,8-dihydro-6,6-dimethyl-7-hyroxy-8-(2-oxo-1-piperidinyl)-6H-pyrano[2,3-f]benz-2,1,3-oxadiazole (NIP-121) was not affected by diltiazem and nicardipine. (7) These findings suggest that blockade of L-type Ca²⁺ channels is not a major mechanism responsible for the vascular relaxation due to NO-mediated MaxiK_Ca channel activation in guinea pig aorta.

Contribution of sodium channels and sodium/hydrogen exchangers (NHEs) to sodium accumulation during ischemia in the ischemic/reperfused heart was examined.

Ischemia increased the myocardial sodium. Reperfusion elicited a further increase in the myocardial sodium, which was associated with little recovery of the left ventricular developed pressure (LVDP) of the perfused heart.

Treatment with tetrodotoxin or dimethylamirolide (DMA) dose-dependently attenuated the ischemia- and reperfusion-induced increase in myocardial sodium and enhanced the post-ischemic recovery of the LVDP.

There was an inverse relationship between the increase in myocardial sodium during ischemia and the post-ischemic recovery of the LVDP.

The myocardial sodium accumulation during ischemia is mainly attributed to sodium influx through sodium channels and NHEs.

Soluble guanylyl cyclase (sGC) is a heterodimeric enzyme (comprised of α and β subunits) that generates the intracellular second messenger cyclic guanosine monophosphate (cGMP) from guanosine triphosphate (GTP). cGMP is subsequently important for the regulation of protein kinases, ion channels, and phosphodiesterases. Since recent evidence has demonstrated that heterodimerization of the α/β subunits is essential for basal and stimulated enzymatic activity, the existence of several types of isoforms for each of the two subunits, along with their varying degrees of expression in different tissues, implies that multiple regulatory mechanisms exist for sGC. Yet, progress in studying and clarifying the regulatory processes that can alter sGC expression and activity has only slowly started being elucidated. In the following paper, we elaborate on sGC structure, function, and distribution along with recently described signaling pathways that modulate sGC gene expression.

Using vascular smooth muscle, we describe the actions of three pharmacological tools, cyclopiazonic acid (CPA), thapsigargin (TG) and 2,5-di-(tert-butyl)-1,4-benzohydroquinone (tBHQ), which are presumed to act as selective inhibitors of the sarco-endoplasmic reticulum Ca²⁺-ATPases (SERCAs). In porcine aortic smooth muscle microsomes two Ca²⁺-ATPase activities have been described, one vanadate-sensitive and one vanadate-resistant, representing the Ca²⁺-ATPase activities of the plasma membrane and SERCAs, respectively. In agreement, CPA, TG and tBHQ, in the concentration range 0.1 μM to 0.1 mM, dose-dependently inhibit the Ca²⁺-ATPase activity only in the vanadate-resistant microsomes. However, 0.1 mM tBHQ also significantly inhibited the Ca²⁺-ATPase activity of vanadate-sensitive microsomes. In rabbit aortic rings, all three SERCA inhibitors produced a dose-dependant inhibition of contractions evoked by 20 mM caffeine or 1 μM phenylephrine (PE) in a Ca²⁺-free physiological solution. However, in PE-contracted rings, tBHQ (≥30 μM) also significantly inhibited the ability of cromakalim to induce relaxation. In conclusion, the data suggest that CPA, TG and tBHQ can all act as selective SERCA inhibitors in both porcine and rabbit aortic smooth muscle. However, in contrast to CPA and TG, high concentrations of tBHQ can exhibit some nonspecific effects, which include inhibition of the plasma membrane Ca²⁺-ATPase and possibly K⁺ channels regulated by cromakalim.

This study tests the hypothesis that insulin-like growth factor 1 (IGF-1)-induced vasodilation is due to the stimulation of tyrosine phosphatase. Rat aortic segments (endothelium intact) were placed in muscle baths for force measurement. Segments were contracted to serotonin [5-hydroxytyptamine (5-HT), 10⁻⁷–10⁻⁵ M] before and after incubation with IGF-1 (10-100 nM; 90 min). IGF-1 caused a 20% inhibition of 5-HT-induced contractions. This inhibition was reversed by the tyrosine phosphatase inhibitors sodium orthovanadate and molybdate. Orthovanadate did not alter inhibitory properties of the calcium channel antagonist verapamil, suggesting that the phosphatase inhibitors were relatively specific. IGF-1-induced inhibition was not altered by blockade of nitric oxide synthase. Western blot analysis confirmed that the 5-HT-induced stimulation of tyrosine phosphorylation of the 42-kDa extracellular signal-regulated mitogen-activated protein kinase protein was reduced by IGF-1 (52% inhibition), an inhibition that was attenuated by orthovanadate. These data are consistent with the hypothesis that the vasodilator activity of IGF-1 is mediated by the activation of a tyrosine phosphatase.