Mechanism of vascular relaxation by cholinomimetic drugs with special reference to pilocarpine and arecoline.
ABSTRACT The muscarinic receptor-mediated and non-muscarinic vascular effects of cholinomimetic drugs used in glaucoma were quantified. On the isolated rat aorta, the vascular tone induced by phenylephrine is functionally antagonized by cholinomimetic drugs. Based on EC50, the relative order of potency for the endothelium-dependent vascular relaxation was acetylcholine (0.05 microM) 1 > (+/-)-methacholine (0.35 microM) 1/7 > carbachol (0.63 microM) 1/12 > (+/-)-aceclidine (1.26 microM) 1/25. The maximal effects of the four agonists varied between 82-87%. The muscarinic vascular relaxation of 0.03 microM to 100 microM pilocarpine was less than 15%. At high concentrations, pilocarpine had 1/20.000 the vascular activity of acetylcholine. Physostigmine failed to potentiate the vascular relaxation of exogenous acetylcholine, indicating the absence of acetylcholine esterase in the tissue. Arecoline, with an EC50 of 7.76 microM, was partly sensitive to the removal of the endothelium. Atropine treatment did not block the vascular effect of high concentrations of pilocarpine. Atropine, as expected, blocked the vascular effects of carbachol with K(B) = 3.2 nM. Pilocarpine produces vascular relaxation by its competition with spasmogens like phenylephrine, oxymetazoline, vasopressin or latanoprost. Arecoline also shares these properties with pilocarpine in the blood vessel. The molecular mechanism of the vascular effects as well as ocular clinical implications of cholinomimetic drugs is discussed.
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ABSTRACT: AIMS: Endothelial cells play a pivotal role in vascular intimal inflammation during cardiovascular diseases. The chemerin/ChemR23 system in endothelial cells is one of physiological mechanisms that regulate inflammatory responses. Our previous studies indicated that stimulation of non-neuronal muscarinic receptor (NNMR) improved endothelial dysfunction. However, the relationship between the chemerin/ChemR23 signaling axis and NNMR in endothelial cell is poorly understood. Here, we first investigated whether the modulation of chemerin/ChemR23 signaling axis is involved in NNMR-mediated endothelial protection. MAIN METHODS: Cultured rat aortic endothelial cells (RAECs) were used. The ChemR23 protein expression and chemerin secretion were measured using Western blot analysis. The gene expression level of ChemR23 was examined with reverse transcriptase PCR (RT-PCR). The production of nitric oxide (NO) was determined by a nitrate reductase assay kit. KEY FINDINGS: A sharp decline of chemerin secretion and ChemR23 protein/gene expression was observed in RAECs after exposed to homocysteine at concentration of 0.5mmol/L. Arecoline (10μmol/L) pretreatment increased ChemR23 protein expression as well as mRNA expression, and enhanced the secretion of chemerin. Arecoline could also reverse the decreased ChemR23 mRNA expression induced by uric acid, high glucose, or oxidized low-density lipoprotein. Furthermore, the modulation of arecoline on chemerin/ChemR23 signaling axis was absolutely abolished in the presence of the nonselective muscarinic receptors antagonist atropine 1μmol/L. Additionally, arecoline improved endothelial dysfunction by increasing the reduced NO production induced by uric acid, which was blocked by anti-ChemR23 antibody. SIGNIFICANCE: The chemerin/ChemR23 signaling axis participates in NNMR-mediated protection against endothelial dysfunction in cardiovascular system.Life sciences 11/2012; · 2.56 Impact Factor
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ABSTRACT: A simple and rapid high-performance liquid chromatographic–electrospray ionization (ESI) tandem mass spectrometric method has been developed for elucidation of the structures of the metabolites of arecoline in rat urine after administration of a single dose (20mgkg−1). The urine samples were purified on a C18 solid-phase extraction cartridge and analysis was then performed on a reversed-phase C18 column with 60:40 (v/v) methanol–0.01% triethylamine solution (2mmolL−1, adjusted to pH3.5 with formic acid) as mobile phase and detection by on-line MS–MS. Identification of the metabolites and elucidation of their structures were performed by comparing molecular masses (ΔM), retention-times, and product ion spectra with those of the parent drug. The parent drug arecoline, four phase-I metabolites, and one phase-II metabolite were identified in rat urine.Chromatographia 11/2006; 64(11):705-708. · 1.37 Impact Factor
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ABSTRACT: The main objective of this investigation was to compare the acetylcholine potentiating action of huperzine-A with acetylcholinesterase inhibitor physostigmine on the frog rectus abdominus muscle, rat phrenic nerve diaphragm preparation, guinea pig ileum and human iris sphincter muscle. In vitro on the frog rectus abdominus muscle, microM of each alkaloid, incubated for 10 min, shifted the acetylcholine concentration response curve to the left. At EC(50) level, physostigmine potentiated acetylcholine response by 4-fold. The potentiation by huperzine-A was 40-fold. The acetylcholine maximum effect, relative to the control, increased to approximately 130% by each alkaloid. Neurally mediated twitch contraction of the rat diaphragm, a skeletal muscle at 1 microM was also potentiated more by huperzine-A than that by physostigmine. Neuromuscular block by (+)-tubocurarine was reversed more easily by huperzine-A than that by physostigmine. On guinea pig ileum, a 30 nM concentration of each alkaloid incubated for 5 min potentiated acetylcholine (10 nM) by 42%, and 33% for huperzine-A and physostigmine respectively. The difference in potentiation between the alkaloids was not significant. At 300 nM of each alkaloid, intrinsic indirect contractions were observed on the ileum, where the rate of contraction by huperzine-A was faster than that by physostigmine. On the iris sphincter, huperzine-A and physostigmine produced a concentration-dependent effect. Maximum effect after each alkaloid was achieved at 30 microM. Potentiation of acetylcholine response by 0.3 microM huperzine-A after a 10-min incubation was greater than that achieved by physostigmine at an equivalent concentration on the contralateral iris sphincter. In summary, huperzine-A exhibits greater acetylcholine potentiating activity on vertebrate muscles than that produced by physostigmine. The results are discussed in relation to the potential therapeutic value of huperzine-A.Journal of Ocular Pharmacology and Therapeutics 05/2003; 19(2):135-43. · 1.42 Impact Factor