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Objectives Aqueous extract of Moringa oleifera leaves (MOE) is a potent inducer of endothelium-dependent relaxation of mesenteric resistance arteries of rats induced to be hypertensive using Nω-nitro-L-arginine methyl ester (L-NAME). Hydrogen sulfide (H2S) has been shown to participate in endothelium-dependent relaxation of small resistance arteries. Therefore, this study aimed to investigate whether endothelial H2S-dependent signaling plays a role in the vasorelaxation in response to MOE. Methods Mesenteric arterial beds isolated from L-NAME hypertensive rats were set up in an ex vivo perfusion system for measurement of vasoreactivity. All experiments were performed in the presence of the nitric oxide synthase inhibitor, L-NAME (100 µM) and the cyclooxygenase inhibitor, indomethacin (10 µM) to prevent the formation of nitric oxide and prostanoids, respectively. Results In the presence of the nitric oxide synthase inhibitor, L-NAME and the cyclooxygenase inhibitor, indomethacin, the endothelium-dependent vasorelaxation induced by MOE (0.001–3 mg) was completely inhibited by DL-propargylglycine (100 µM), which inhibits the H2Sgenerating enzyme, cystathionine γ-lyase. This H2Sdependent response was reduced by the KATP channel blocker; glibenclamide (10 µM), the KCa channel blocker; tetraethylammonium (1 µM), and the myo-endothelial gap-junctional uncoupler; 18α-glycyrrhetinic acid (10 µM). In contrast, the muscarinic receptor antagonist, atropine (100 µM), did not affect the response to MOE. Conclusions The results may suggest that H2S is the likely mediator of endothelium-dependent relaxation in response to MOE in mesenteric arterial beds of L-NAME-induced hypertensive rats. MOE-induced H2S-dependent vasorelaxation involves activation of KATP and KCa channels and requires myo-endothelial gap-junctional communication.

Background Enhancing relaxation of resistance arteries and decreasing oxidative stress by using natural products are potential strategies for prevention and treatment of hypertension. Purpose This study investigated whether aqueous extract of Moringa oleifera leaves (MOE) could alleviate Nω-nitro- L -arginine-methyl ester (L-NAME)-induced high blood pressure via modulation of vascular function and antioxidant properties. Methods An experimental hypertensive model was established by administration of L -NAME (50 mg/kg/day) in drinking water to male Wistar rats for 3 weeks. Arterial pressure was measured indirectly by tail-cuff plethysmography and directly via femoral artery catheterization. Vasoreactivity of isolated rat mesenteric arterial bed was determined by the changes in perfusion pressure detected by a pressure transducer. Vascular superoxide anion (O2•−) production was determined by lucigenin-enhanced chemiluminescence. Other biochemical measurements including malondialdehyde (MDA) level, superoxide dismutase (SOD), and catalase (CAT) activities were measured by colorimetric assay. Results L-NAME-treated rats developed significantly increased blood pressure and heart rate. Concurrent oral treatment with MOE (30 and 60 mg/kg/day) could decrease the high blood pressure and tachycardia in a dose-dependent manner. MOE reduced the impairment of acetylcholine-induced relaxation and decreased the hyperreactivity of adrenergic-mediated contraction in response to periarterial nerve stimulation and phenylephrine in isolated mesenteric arterial beds. In addition, MOE exhibited antioxidant effects in the hypertensive rats, as indicated by suppression of vascular O2•− production, decrease of plasma and thoracic aorta MDA levels, and increase of antioxidant activities of SOD and CAT. Moreover, MOE (0.001–0.3 mg) produced a dose-dependent relaxation in methoxamine pre-contracted arterial beds isolated from L-NAME hypertensive rats, which was abolished by endothelium denudation. Conclusion These findings suggest that the antihypertensive effect of MOE in L-NAME-hypertensive rats may be mediated by alleviating vascular dysfunction and oxidative stress and promoting endothelium-dependent vasorelaxation. MOE may be potentially useful as a natural product against hypertension.

A mass of evidence has identified a promoting of nitric oxide (NO) production in endothelial cells using natural products as a potential strategy to prevent and treat hypertension. This study investigated whether the aqueous extract of Moringa oleifera leaves (MOE) could lower mean arterial pressure (MAP) and relax mesenteric arterial beds in rats via stimulating endothelium-derived NO production. Intravenous administration of MOE (1-30 mg/kg) caused a dose-dependent reduction in MAP in anesthetized rats. In rats pretreated with the NO-synthase inhibitor, Nω-nitro-L-arginine methyl ester (L-NAME, 30 mg/kg, i.v.), the effect of MOE on MAP was significantly reduced. MOE (0.001-3 mg) induced relaxation in methoxamine (10 μM) pre-contracted mesenteric arterial beds, which was abolished by endothelium denudation. This endothelium-dependent vasorelaxation was reduced by L-NAME (100 μM) or the NO-sensitive guanylyl cyclase inhibitor, 1H- [1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one (10 μM). In primary human pulmonary artery endothelial cells, MOE (3-30 μg/mL) induced NO production, which was inhibited by L-NAME (100 μM) pretreatment. These findings show that MOE stimulates the endothelium-derived NO release for driving its vasorelaxation to lower arterial blood pressure. These suggest the development of MOE as a natural antihypertensive supplement.

Nicotine has been shown to have neuroprotective and neurotrophic actions in the central nervous system. To elucidate the peripheral neurotrophic effects of nicotine, we determined whether nicotine affected the reinnervation of mesenteric perivascular nerves following a topical phenol treatment. A topical phenol treatment was applied to the superior mesenteric artery proximal to the abdominal aorta in Wistar rats. We examined the immunohistochemistry of the distal small arteries 7 days after the treatment. The topical phenol treatment markedly reduced the density of tyrosine hydroxylase (TH)-LI and calcitonin gene-related peptide (CGRP)-LI fibers in these arteries. The administration of nicotine at a dose of 3 mg/kg/day (1.5 mg/kg/injection, twice a day), but not once a day or its continuous infusion using a mini-pump significantly increased the density of TH-LI nerves without affecting CGRP-LI nerves. A pretreatment with nicotinic acetylcholine receptor antagonists hexamethonium, mecamylamine, and methyllycaconitine, but not dextrometorphan, canceled the TH-LI nerve reinnervation induced by nicotine. Nicotine significantly increased NGF levels in the superior cervical ganglia (SCG) and mesenteric arteries, but not in the dorsal root ganglia, and also up-regulated the expression of NGF receptors (TrkA) in the SCG, which were canceled by hexamethonium. These results suggested that nicotine exhibited neurotrophic effects that facilitated the reinnervation of adrenergic TH-LI nerves by activating α7 nicotinic acetylcholine receptor and NGF in the SCG.

Background and Purpose Previous studies have demonstrated that nicotine releases protons from adrenergic nerves via stimulation of nicotinic ACh receptors and activates transient receptor potential vanilloid-1 (TRPV1) receptors located on calcitonin gene-related peptide (CGRP)-containing (CGRPergic) vasodilator nerves, resulting in vasodilatation. The present study investigated whether perivascular nerves release protons, which modulate axon-axonal neurotransmission. Experiment Approach Perfusion pressure and pH levels of perfusate in rat-perfused mesenteric vascular beds without endothelium were measured with a pressure transducer and a pH meter respectively. Key Results Periarterial nerve stimulation (PNS) initially induced vasoconstriction, which was followed by long-lasting vasodilatation and decreased pH levels in the perfusate. Cold-storage denervation of the preparation abolished the decreased pH and vascular responses to PNS. The adrenergic neuron blocker guanethidine inhibited PNS-induced vasoconstriction and effects on pH, but not PNS-induced vasodilatation. Capsaicin (CGRP depletor), capsazepine and ruthenium red (TRPV1 inhibitors) attenuated the PNS-induced decrease in pH and vasodilatation. In denuded preparations, ACh caused long-lasting vasodilatation and lowered pH; these effects were inhibited by capsaicin pretreatment and atropine, but not by guanethidine or mecamylamine. Capsaicin injection induced vasodilatation and a reduction in pH, which were abolished by ruthenium red. The use of a fluorescent pH indicator demonstrated that application of nicotine, ACh and capsaicin outside small mesenteric arteries reduced perivascular pH levels and these effects were abolished in a Ca2+-free medium. Conclusion and Implication These results suggest that protons are released from perivascular adrenergic and CGRPergic nerves upon PNS and these protons modulate transmission in CGRPergic nerves.

Moxifloxacin, a 4th generation of fluoroquinolones, is a broad spectrum antibacterial agent against respiratory tract pathogens, including Gram-positive and Gram-negative bacteria, anaerobic bacteria and atypical respiratory tract pathogens. In order to evaluate the efficacy and safety of generic moxifloxacin products, the bioequivalence of these generic products with an approved reference formulation should be demonstrated. Thus, the aim of this study was to compare the rate and extent of absorption of a new generic film coated moxifloxacin tablet product (Rapiflox®, Atlantic Laboratories Corporation Ltd., Bangkok, Thailand) with that of a reference product (Avelox®, Bayer Health Care AG, Leverkusen, Germany) when given as a single dose. A crossover study was performed in 20 healthy Thai volunteers. The subjects received either a 400 mg tablet of the reference or test product after overnight fasting. Blood samples were collected at pre-dose (0 hour) and at 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 24 and 34 hours post-dose. Moxifloxacin plasma level was measured by a validated HPLC method with fluorescence detector. Pharmacokinetic parameters were calculated using a non-compartmental model. The geometric mean of maximum concentration (Cmax) of the test product was 4,069.64 ng/ml, with median time to achieve maximum concentration (tmax) at 2 hours (range 0.25 - 6.00 hours), while the geometric mean Cmax and median tmax of the reference product was 4,211.98 ng/ml and 2.00 hours (range 0.25 - 8.00 hours). Furthermore, the geometric means of AUC0-tlast and AUC0-∞ for the test product were 49,731.66 and 51,865.89 ng×h/ml while those of the reference product were 51,927.97 and 54,455.93 ng×h/ml. The geometric mean of the ratios of Test/Reference for the logtransformed Cmax, AUC0-tlast and AUC0-∞ of moxifloxacin and their 90% CIs were 96.62% (83.21 - 112.19%), 95.77% (87.07 - 105.34%) and 95.24 (86.52 - 104.85%), respectively. Therefore, it can be concluded that these two moxifloxacin tablet products were bioequivalent in healthy Thai volunteers under fasting condition.

This study examined the effect of Carthamus tinctorius (CT) extract plus captopril treatment on blood pressure, vascular function, nitric oxide (NO) bioavailability, oxidative stress and renin-angiotensin system (RAS) in N(ω)-Nitro-l-arginine methyl ester (l-NAME)-induced hypertension. Rats were treated with l-NAME (40 mg/kg/day) for five weeks and given CT extract (75 or 150 or 300 or 500 mg/kg/day): captopril (5 mg/kg/day) or CT extract (300 mg/kg/day) plus captopril (5 mg/kg/day) for two consecutive weeks. CT extract reduced blood pressure dose-dependently, and the most effective dose was 300 mg/kg/day. l-NAME-induced hypertensive rats showed abnormalities including high blood pressure, high vascular resistance, impairment of acetylcholine-induced vasorelaxation in isolated aortic rings and mesenteric vascular beds, increased vascular superoxide production and plasma malondialdehyde levels, downregulation of eNOS, low level of plasma nitric oxide metabolites, upregulation of angiotensin II type 1 receptor and increased plasma angiotensin II. These abnormalities were alleviated by treatment with either CT extract or captopril. Combination treatment of CT extract and captopril normalized all the abnormalities found in hypertensive rats except endothelial dysfunction. These data indicate that there are synergistic antihypertensive effects of CT extract and captopril. These effects are likely mediated by their anti-oxidative properties and their inhibition of RAS.

BACKGROUND AND PURPOSE 5-HT is taken up by and stored in adrenergic nerves and periarterial nerve stimulation (PNS) releases 5-HT to cause vasoconstriction in rat mesenteric arteries. The present study investigated whether PNS-released 5-HT stored in adrenergic nerves affects the function of perivascular calcitonin gene-related peptide-containing (CGRPergic) nerves. EXPERIMENTAL APPROACH Rat mesenteric vascular beds without endothelium and with active tone were perfused with Krebs solution. Changes in perfusion pressure in response to PNS and CGRP injection were measured before (control) and after perfusion of Krebs solution containing 5-HT (10 µM) for 20 min. Distributions of 5-HT- and TH-immunopositive fibres in mesenteric arteries were studied using immunohistochemical methods. KEY RESULTS PNS (1–4 Hz) frequency dependently caused adrenergic nerve-mediated vasoconstriction followed by CGRPergic nerve-mediated vasodilatation. 5-HT treatment inhibited PNS-induced vasodilatation without affecting exogenous CGRP-induced vasodilatation, while it augmented PNS-induced vasoconstriction. Guanethidine (adrenergic neuron blocker), methysergide (non-selective 5-HT receptor antagonist) and BRL15572 (selective 5-HT1D receptor antagonist) abolished inhibition of PNS-induced vasodilatation in 5-HT-treated preparations. Combined treatment with 5-HT and desipramine (catecholamine transporter inhibitor), but not fluoxetine (selective 5-HT reuptake inhibitor), did not inhibit PNS-induced vasodilatation. Exogenous 5-HT inhibited PNS-induced vasodilatation, which was antagonized by methysergide. In immunohistochemical experiments, 5-HT-immunopositive nerves, colocalized with adrenergic TH-immunopositive nerves, were observed only in 5-HT-treated mesenteric arteries, but not in control preparations or arteries co-treated with desipramine. CONCLUSIONS AND IMPLICATIONS These results suggest that 5-HT can be taken up by and released from adrenergic nerves in vitro by PNS to inhibit CGRPergic nerve transmission in rat mesenteric arteries.

A previous report showed that histamine in denuded mesenteric vascular beds produced a triphasic response; an initial small histamine H(2) receptor-mediated vasodilation, a transient histamine H(1) receptor-mediated vasoconstriction, and finally a long-lasting vasodilation. We further investigated the vascular effect of histamine in mesenteric preparations without an endothelium to clarify the possible involvement of perivascular nerves. Male Wistar rat mesenteric vascular beds without an endothelium were perfused with Krebs solution containing methoxamine to produce active tone and lafutidine to block histamine H(2) receptor-mediated vasodilation. Histamine (1-100μM) was perfused for 1min and perfusion pressure was measured with a pressure transducer. Histamine caused a biphasic vascular response; initial vasoconstriction followed vasodilation. Tetrodotoxin (a neurotoxin, 1μM) and procaine (a local anesthetic, 100μM) significantly inhibited the vasoconstriction and vasodilation. Ruthenium red (a transient receptor potential vanilloid 1 (TRPV1) antagonist, 1μM) also significantly inhibited both phases of the response. Pretreatment with capsaicin (a depletor of calcitonin gene-related peptide (CGRP)-containing nerves, 5μM) significantly inhibited the vasodilation without affecting the initial vasoconstriction. Both indomethacin (a cyclooxygenase inhibitor, 0.5μM) and seratrodast (a thromboxane A(2) receptor antagonist, 0.1μM) abolished the histamine-induced vasoconstriction and subsequent vasodilation. These results suggest that histamine-induced vasoconstriction and long-lasting vasodilation are mediated by activation of TRPV1 on capsaicin-sensitive and capsaicin-insensitive nerves. They also suggest that perivascular nerves and prostanoids, probably thromboxane A(2), are responsible for the vascular response to histamine.

Rat mesenteric arteries were maintained by both adrenergic vasoconstrictor nerves and calcitonin gene–related peptide (CGRP) vasodilator nerves. However, functions of these nerves in a pathophysiological state have not fully been analyzed. The use of disease models developed genetically in mice is expected to clarify neural function of perivascular nerves. Thus, we investigated basic mouse vascular responses. Mesenteric vascular beds isolated from male C57BL/6 mouse were perfused with Krebs solution and perfusion pressure was measured. Periarterial nerve stimulation (PNS, 8 – 24 Hz) induced frequency-dependent vasoconstriction, which increased flow rate–dependently. PNS-induced vasoconstriction was abolished by tetrodotoxin (neurotoxin) and guanethidine (adrenergic neuron blocker) and blunted by prazosin (α1-adrenoceptor antagonist). Injection of norepinephrine caused vasoconstriction, which was abolished by prazosin. In preparations with active tone, PNS (1 – 8 Hz) induced frequency-dependent vasodilation, which was inhibited by tetrodotoxin, capsaicin (CGRP depletor), and CGRP8-37 (CGRP-receptor antagonist). Injections of CGRP, acetylcholine, and sodium nitroprusside induced vasodilations. Vasodilator response to CGRP was inhibited by CGRP8-37. Immunohistochemical study showed innervation of tyrosine hydroxylase- and CGRP-immunopositive fibers in mesenteric arteries and veins. These results suggest that male mouse mesenteric vascular beds are useful for studying neural regulation of mesenteric arteries, which are innervated by adrenergic and CGRPergic nerves regulating vascular tone. Keywords:: adrenergic vasoconstriction, calcitonin gene–related peptide (CGRP), CGRPergic vasodilation, mesenteric vascular bed, perivascular innervation

The present study investigated whether histamine was taken up by perivascular adrenergic nerves and released by periarterial nerve stimulation (PNS) to induce vascular responses. In rat mesenteric vascular beds treated with capsaicin to eliminate calcitonin gene–related peptide (CGRP)ergic vasodilation and with active tone, PNS (1 – 4 Hz) induced only adrenergic nerve–mediated vasoconstriction. Histamine treatment for 20 min induced PNS-induced vasoconstriction followed by vasodilation without affecting CGRP-induced vasodilation. Chlorpheniramine, guanethidine, combination of histamine and desipramine, and endothelium-removal abolished PNS-induced vasodilation in histamine-treated preparations. These results suggest that histamine taken up by and released from adrenergic nerves by PNS causes endothelium-dependent vasodilation in rat mesenteric arteries. Keywords:: histamine, perivascular adrenergic nerve, rat mesenteric artery

We previously reported that chronic hyperinsulinemia and insulin resistance induced by fructose-drinking loading elicited hypertension associated with abnormal neuronal regulation of vascular tone in an in vivo study using pithed rats. Therefore, to further clarify the detailed mechanisms of perivascular nervous system malfunction induced by chronic hyperinsulinemia, we investigated the neurogenic vascular responses and distribution of perivascular nerves using mesenteric vascular beds isolated from fructose-loaded rats with hyperinsulinemia. Male Wistar rats (6 weeks old) received 15% fructose solution as drinking fluid for 10 weeks (fructose-drinking rats, FDR), which resulted in significant increases in plasma levels of insulin, the glucose-insulin index, blood norepinephrine (NE) levels and systolic blood pressure, but not blood glucose levels, when compared with normal water-drinking rats (control rats). In perfused mesenteric vascular beds of FDR, enhanced adrenergic nerve-mediated vasoconstriction with no effect on NE-induced vasoconstriction and decreased calcitonin gene-related peptide (CGRP)-containing nerve-mediated vasodilation with no effect on CGRP-induced vasodilation were observed. Immunohistochemistry studies showed increased density of neuropeptide Y immunopositive adrenergic fibers and reduced density of CGRP immunopositive fibers in mesenteric arteries of FDR. Furthermore, FDR showed decreased CGRP content in dorsal root ganglia. These findings suggest that dysfunction of the neuronal vascular control system resulting from abnormal innervation of mesenteric perivascular nerves induced by the hyperinsulinemic state is responsible for the development of hypertension in FDR.

Immunohistochemical study of rat mesenteric arteries showed dense innervation of adrenergic nerves, calcitonin gene-related peptide (CGRP)-containing nerves (CGRPergic nerves), nitric oxide-containing nerves (nitrergic nerves). Double-immunostaining revealed that most CGRPergic or nitrergic nerves were in close contact with adrenergic nerves. CGRPergic and transient receptor potential vanilloid-1 (TRPV1)-immunopositive nerves appeared in the same neurone. In rat perfused mesenteric vascular beds without endothelium and with active tone, perfusion of nicotine, or bolus injection of capsaicin and acetylcholine and periarterial nerve stimulation (PNS) lowered pH levels of out flowed perfusate concomitant with vasodilation. Cold-storage denervation of preparations abolished pH lowering induced by nicotine and PNS. Guanethidine inhibited PNS- and nicotine-, but not acetylcholine- and capsaicin-, induced pH lowering. Pharmacological analysis showed that protons were released not only from adrenergic nerves but also from CGRPergic nerves. A study using a fluorescent pH indicator demonstrated that nicotine, acetylcholine and capsaicin applied outside small mesenteric artery lowered perivascular pH levels, which were not observed in Ca(2+) free medium. Exogenously injected hydrochloric acid in denuded preparations induced pH lowering and vasodilation, which was inhibited by denervation, TRPV1 antagonists and capsaicin without affecting pH lowering. These results suggest that excitement of adrenergic nerves releases protons to activate TRPV1 in CGRPergic nerves and thereby induce vasodilation. It is also suggested that CGRPergic nerves release protons with exocytosis to facilitate neurotransmission via a positive feedback mechanism.

Objectives: To compare the bioavailability of two risperidone orodispersible tablet products, Risperidone 1 mg Mouth dissolving tablet, Ranbaxy (Malaysia) Sdn. Bhd., Malaysia, as a test product and Risperdal 1 mg Quicklet, Janssen Ortho LLC, Gurabo, Puerto Rico, as a reference product, in healthy male volunteers under fasting condition. Materials and methods: A randomized, 2-treatment, 2-period, 2-sequence, single dose, crossover with a washout period of 2 weeks, was conducted in 24 healthy Thai male volunteers. Blood samples were collected at 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 3.5, 4, 5, 6, 8, 10, 12, 24, 36, 48, 72 and 96 h following drug administration. Plasma concentrations of risperidone and 9-hydroxyrisperidone were determined using a validated LC-MS-MS method. The pharmacokinetic parameters of risperidone and 9-hydroxyrisperidone were determined using a non-compartmental model. Results: The geometric means ratios (%) and 90% confidence interval (CI) of the test and reference products for the log-transformed pharmacokinetic parameters, C max , AUC 0― t and AUC 0―∞ of risperidone were 104.49 % (92.79% ― 117.66%), 100.96 % (92.15% - 110.61 %) and 97.99 % (90.72% ― 105.85%). The 90% CI of geometric means ratios of the test and reference products for the log-transformed pharmacokinetic parameters, C max , AUC 0―t and AUC 0―∞ of 9-hydroxyrisperidone were 97.00%, 96.97% and 97.49%. Conclusions: The 90% CI for the geometric means ratios (test/reference) of the log-trasformed C max , AUC 0―t and AUC 0―∞ of risperidone and its major active metabolite were within the bioequivalence acceptance criteria of 80% - 125% of the US-FDA.

The rat mesenteric artery has been shown to be innervated by adrenergic vasoconstrictor nerves and calcitonin gene-related peptide (CGRP)-containing (CGRPergic) vasodilator nerves. The present study was designed to investigate the involvement of histamine H(3) receptors in the neurotransmission of perivascular adrenergic and CGRPergic nerves. The mesenteric vascular beds without an endothelium isolated from male Wistar rats were perfused with Krebs solution and perfusion pressure was measured. In preparations with resting tension, the selective H(3) receptor agonist (R)-α-methylhistamine (α-methylhistamine; 10-100nM) significantly reduced periarterial nerve stimulation (2-8Hz)-induced vasoconstriction and noradrenaline release in the perfusate without an effect on the vasoconstriction induced by exogenously injected noradrenaline (0.5, 1.0nmol). In preparations with active tone produced by methoxamine (2μM) and in the presence of guanethidine (5μM), the periarterial nerve stimulation (1, 2Hz)-induced vasodilator response was inhibited by α-methylhistamine (0.1-1μM) perfusion without affecting vasodilation induced by exogenously injected CGRP (5pmol). Clobenpropit (histamine H(3) receptor antagonist, 1μM) canceled the α-methylhistamine-induced decrease in the periarterial nerve stimulation-induced vasoconstriction and noradrenaline release and periarterial nerve stimulation-induced vasodilation. These results suggest that the stimulation of H(3) receptors located in rat perivascular nerves inhibits presynaptically the neurotransmission of not only adrenergic nerves, but also CGRP nerves, by decreasing neurotransmitters.

The present study investigated pharmacological characterizations of muscarinic acetylcholine receptor (AChR) subtypes involving ACh-induced endothelium-independent vasodilatation in rat mesenteric arteries. Changes in perfusion pressure to periarterial nerve stimulation and ACh were measured before and after the perfusion of Krebs solution containing muscarinic receptor antagonists. Distributions of muscarinic AChR subtypes in mesenteric arteries with an intact endothelium were studied using Western blotting. The expression level of M1 and M3 was significantly greater than that of M2. Endothelium removal significantly decreased expression levels of M2 and M3, but not M1. In perfused mesenteric vascular beds with intact endothelium and active tone, exogenous ACh (1, 10, and 100 nmol) produced concentration-dependent and long-lasting vasodilatations. In endothelium-denuded preparations, relaxation to ACh (1 nmol) disappeared, but ACh at 10 and 100 nmol caused long-lasting vasodilatations, which were markedly blocked by the treatment of pirenzepine (M1 antagonist) or 4-DAMP (M1 and M3 antagonist) plus hexamethonium (nicotinic AChR antagonist), but not methoctramine (M2 and M4 antagonist). These results suggest that muscarinic AChR subtypes, mainly M1, distribute throughout the rat mesenteric arteries, and that activation of M1 and/or M3 which may be located on CGRPergic nerves releases CGRP, causing an endothelium-independent vasodilatation.