General Pharmacology-the Vascular System最新文献

Adenosine (0.1–300 μM) induced concentration- and endothelium-dependent relaxation of rat renal artery (RRA). N^G-Nitro-l-arginine (l-NOARG, 10 μM) significantly reduced adenosine-elicited dilatation, but not the application of indomethacin (10 μM), ouabain (100 μM) or tetraethylammonium (TEA, 500 μM). In the presence of high concentration of K⁺ (100 mM) or glibenclamide (1 μM), adenosine-evoked relaxation was almost abolished. 8-(3-Chlorostyril)caffeine (CSC, 0.3–3 μM), a selective A_2A-antagonist, significantly reduced adenosine-evoked dilatation in a concentration-dependent manner (pA₂=7.29). Conversely, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10 nM), an A₁-antagonist, did not alter adenosine-induced relaxation. These results indicate that adenosine produces endothelium-dependent relaxation of isolated RRA. Dilatation evoked by adenosine is mediated by predominant releasing of endothelium-derived hiperpolarizing factor (EDHF) and also in one part of nitric oxide (NO) from endothelial cells. The obtained results also suggest that RRA response to adenosine is most likely initiated by activation of endothelial adenosine A_2A receptors.

KMCP-98 is a newly synthesized adenosine receptor agonist by alkylation at the 7-position of the xanthines nucleus. We first investigated the pharmacological activities of KMCP-98 under in vivo and in vitro conditions. Acute intravenous injection of KMCP-98 (1.0, 2.0 and 3.0 mg/kg) produced a temporary fall in blood pressure and heart rate, followed by a sustained fall in heart rate in pentobarbital-anesthetized Wistar rats. The hypotensive and bradycardiac responses were inhibited by pretreatment with an A₁ adenosine receptor antagonist 8-phenyltheophylline (8-PT, 0.5 mg/kg). Both KMCP-98 and adenosine (0.3–100 μM) produced negative inotropic activitity in isolated guinea pig left atria. The negative inotropic activity of KMCP-98 was significantly blocked by pretreatment with A₁ receptor antagonists 8-PT (10 μM) and xanthine amine congener (XAC, 10 μM), a nonselective adenosine antagonist theophylline (10 μM), a K⁺ channel blocker tetraethylammonium (TEA, 10 mM) and a K_ATP channel blocker glibenclamide (1 μM). KMCP-98 (0.03–30 μM) produced concentration-dependent relaxations in carbachol (1 μM) precontracted guinea pig tracheal smooth muscle. The trachea relaxant response of KMCP-98 was markedly inhibited by A₂, A_2a and A_2b adenosine receptor antagonists 3,7-dimethyl-1-propargylxanthine (DMPX, 10 μM), 8-(3-chlorostyryl)caffeine (CSC, 10 μM) and alloxazine (10 μM), respectively, the nitric oxide synthase (NOS) inhibitor l-NAME (100 μM) and also by TEA and glibenclamide. In addition, KMCP-98 (0.03–30 μM) elicited relaxant response in norepinephrine (3 μM) precontracted rat thoracic aorta in a concentration-dependent manner. The thoracic aorta relaxant response of KMCP-98 was also significantly inhibited by DMPX, CSC, alloxazine, l-NAME, TEA and glibenclamide. Furthermore, the binding characteristics of KMCP-98, adenosine and 5′-N-ethylcarboxaminoadenosine (NECA) were evaluated in [³H]DPCPX and [³H]CGS 21680 binding to rat cortex and striatum, respectively. The K_i values of KMCP-98 for predominate A₁ and A₂ adenosine receptor sites were 3908±952 and 158±10 nM, respectively. In conclusion, KMCP-98 was found to be a xanthine-based adenosine receptor agonist associated cardiac depression, tracheal and aortic smooth muscle relaxations.

This study tested whether (1) L-type Ca²⁺ channel blockade and extracellular Ca²⁺ removal prior to endothelin-1, as compared to during the endothelin-1 constriction, resulted in lesser inhibition, and (2) the reduced inhibition due to prior L-type Ca²⁺ channel blockade resulted from enhanced non L-type Ca²⁺-channel-dependent constriction. Pretreatment of rabbit basilar artery in vitro with 1 μM verapamil, an L-type Ca²⁺ channel blocker, inhibited 3, 10, 30, and 100 nM endothelin-1 constrictions to a lesser extent than verapamil addition during the plateau endothelin-1 constriction. Ni²⁺ (0.03 and 0.1 mM), a nonselective cation channel blocker, relaxed the plateau endothelin-1 constrictions in vessels pretreated with verapamil to greater magnitudes than vessels unexposed to verapamil. Extracellular Ca²⁺ removal prior to 10, 30, and 100 nM endothelin-1 also inhibited the endothelin-1 constrictions to smaller magnitudes than Ca²⁺ removal during the plateau endothelin-1 constrictions. These results suggest that the reduced inhibition of the endothelin-1 constriction following pretreatment with L-type Ca²⁺ channel blocker or Ca²⁺-free solution, as compared to addition of these agents during the endothelin-1 constriction, is the result of non L-type Ca²⁺ channel opening and enhanced Ca²⁺-independent constriction, respectively.

To examine the antioxidant effect of bilirubin (BR) on leukocyte, we treated leukocytes obtained from healthy subjects with an oxidant and various concentrations of BR. High concentrations of BR decreased thiobarbituric acid reactive substances (TBARS) and catalase activities, increased superoxide dismutase (SOD) activity, but had no effect on glutathione (GSH) concentration. Our results showed that under physiological conditions, BR has an antioxidant effect only in high concentrations.

It was found that the production of nitric oxide (NO) by RAW 264.7 macrophages stimulated with interferon-γ (IFN-γ) and lipopolysaccharide (LPS) could be markedly inhibited by the ethyl-acetate-soluble fraction of 80% aqueous methanolic extract of stem barks of Cudrania tricuspidata (EACT). Inhibition of NO production was achieved by reducing inducible nitric oxide synthase (iNOS) expression at protein and mRNA levels and by inactivating nuclear factor-κB (NF-κB), but not by inhibiting iNOS activity. Thus, further phytochemical and pharmacological studies may lead to isolation and structural identification of an inhibitor of iNOS from C. tricuspidata, which has been used as a traditional medicine for curing inflammation.

Dopamine (DA) in combination with iron (Fe²⁺) has been demonstrated to induce apoptosis in neuronal-like PC12 cells by an oxidative stress mechanism. To get a better insight of cell death and protective mechanisms in DA/Fe²⁺-induced toxicity, we investigated the effects of DA/Fe²⁺ and the antioxidant action of 17β-estradiol (E2) in peripheral blood lymphocytes (PBL). We found that DA/Fe²⁺-induces apoptosis in PBL via a hydrogen peroxide (H₂O₂)-mediated oxidative mechanism, which in turn triggers a cascade of molecular events requiring RNA and de novo protein synthesis. We have also demonstrated that E2 prevents significantly DA/Fe²⁺-induced apoptosis in PBL by directly inhibiting the intracellular accumulation of peroxides generated by DA/Fe²⁺-reaction. This protective activity is independent of the presence or activation of the estrogen receptors (ERs). These data further support and validate our previous hypothesis that DA/Fe²⁺/H₂O₂ could be a general mediator of oxidative stress through a common cell death mechanism in both neuronal and nonneuronal cells. These findings may be particularly relevant to the potential approaches to rescue and prolong the survival of neurons by estrogens in patients with Parkinson's disease (PD).

Corticotropin-releasing factor and urocortin belong to a hypothalamic peptide family thought to be important in appetite regulation. The present study compared the appetite-suppressant effect of subcutaneous urocortin in obese mice to its cardiovascular effects. Acutely, urocortin (100 nmol/kg iv) reduced blood pressure and increased heart rate in urethane anesthetized nonobese mice; effects similar to those produced by subcutaneous urocortin (10 and 100 nmol/kg sc) in nonobese and ob/ob mice. Over this same dose range (10–100 nmol/kg sc), urocortin dramatically inhibited food consumption in the ob/ob mouse. To determine if the acute hypotensive effect of urocortin (10 nmol/kg sc) in the ob/ob mouse persisted after repeated urocortin administration, animals were pretreated for 3 days with urocortin (10 nmol/kg sc) or vehicle. Following urocortin pretreatment, urocortin-induced hypotension was similar to the effect in vehicle pretreated mice. However, urocortin-induced appetite suppression was reduced following 3 days of pretreatment with urocortin (10 nmol/kg sc) to ob/ob mice. These data suggest that the hypotensive and appetite-suppressant effects of urocortin are mediated by different mechanisms and tolerance to the hypotension did not readily occur in obese animals.

Nitrated tyrosine, implicated in protein dysfunction, is increased in various tissues in association with diverse pathological processes. Angiotensin converting enzyme (ACE) is a luminal vascular endothelial enzyme whose dysfunction is an early sign of endothelial injury. ACE contains a tyrosine critical for its enzymatic activity. Others have shown that nitrite exacerbates the ACE dysfunction of cultured endothelial cells in contact with activated polymorphonuclear neutrophils (PMN). We hypothesized that exogenous nitrite would enhance endothelial ACE dysfunction associated with PMN activation in the isolated lung. Rats received lipopolysaccharide (LPS) 2 h prior to isolated lung perfusion with Ficoll containing buffer. Either formyl-Met-Leu-Phe (fMLP, 10⁻⁷ M) or phorbol myristate acetate (PMA, 10⁻⁷ M) was used to activate PMN in lungs treated or not treated with 300-μM nitrite. A first pass indicator dilution method and first order reaction kinetics were used to determine ACE activity, while lung Ficoll content served as an index of vascular permeability. Both fMLP and PMA decreased endothelial ACE activity and increased pulmonary artery pressure, edema and vascular permeability. Exogenous nitrate did not potentiate the decrease in ACE activity, the lung injury or nitrotyrosine immunoreactivity of lung homogenates. In contrast to observations in cultured endothelial cells, our findings in the whole lung are compatible with the speculation of others that the rat lung has an unidentified factor, which minimizes accumulation of nitrated proteins.

The present study was carried out to evaluate the relaxation induced by histamine in tail arteries of rats after chronic inhibition of nitric oxide (NO) synthesis with the inhibitor N^G-nitro-l-arginine methyl ester (l-NAME) compared to tail arteries of control rats. The maximum relaxation induced by histamine was greater in control (88.09% ±5.50, n=6) than in l-NAME arteries (47.33% ±6.40, n=6), although pD₂ values were not different between the two groups (control: 4.89±0.08; l-NAME: 4.81±0.10). After incubation with 100 μM l-NAME in vitro, the maximum relaxation induced by histamine was only reduced in the control arteries (44.93% ±2.35, n=6), whereas it had no effect on aortas of rats pretreated with this inhibitor. The incubation with 100 μM l-NAME had the same effect as endothelium removal in both arterial groups. Furthermore, the relaxation induced by histamine was unaffected by indomethacin. The combination of l-NAME and the histamine antagonist cimetidine completely abolished the relaxation induced by histamine in both arterial groups. These results show that when NO synthesis is impaired, the relaxation induced by histamine is endothelium independent, and when NO-synthase is active, the relaxation involves both NO released from endothelial cells and an endothelium-independent mechanism that is sensitive to cimetidine.

Spiradoline, an arylacetamide kappa (κ) opioid receptor agonist, produced a potent tonic block of rat neuronal (EC₅₀=34±5 μM) and heart (EC₅₀=183±13 μM) sodium channels and also blocked IFMQ3 mutant neuronal sodium channels (EC₅₀=130±34 μM) that lack fast inactivation when expressed in Xenopus oocytes. Spiradoline produced a hyperpolarizing shift in the voltage-dependence of sodium channel inactivation and exhibited a marked frequency-dependent component to blockade of sodium channels. The onset of open channel block of the IFMQ3 channel by spiradoline was best fit with a first-order blocking scheme, yielding an affinity constant of 116±33 μM. Thus, spiradoline blocks sodium channels by interacting with the major states of the channel which could result in local anesthetic action in nerves and antiarrhythmic action in the heart.