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We aimed to determine whether an experimental model of hyperthyroidism could alter the function of sympathetic and nitrergic components of mesenteric innervation. For this purpose, male Wistar rats were divided into (1) control rats (CT) and (2) rats infused with L-Thyroxine (HT). Body weight gain and adipose tissue accumulation were lower in HT rats, while systolic blood pressure and citrate synthase activity in the soleus muscle were increased by HT. In segments from the superior mesenteric artery, the application of an electrical field stimulation (EFS) induced a vasoconstrictor response, which was lower in arteries from HT animals. The alpha-adrenoceptor antagonist phentolamine diminished EFS-induced vasoconstriction to a lower extent in HT arteries, while the purinergic receptor antagonist suramin reduced contractile response to EFS only in segments from CT. In line with this, noradrenaline release, tyrosine hydroxylase expression and activation and dopamine ß hydroxylase expression were diminished in HT. The unspecific nitric oxide synthase (NOS) inhibitor L-NAME increased EFS-induced vasoconstriction more markedly in segments from HT rats. NO release was enhanced in HT, probably due to an enhancement in neuronal NOS activity, in which a hyperactivation of both PKC and PI3K-AKT signaling pathways might play a relevant role. In conclusion, perivascular mesenteric innervation might contribute to reduce the vascular resistance observed in hyperthyroidism.

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This study was designed to investigate the vasorelaxant effects and underlying mechanism of isocorynoxeine (ICN), one of the indole alkaloids from Uncaria hooks, on isolated mesenteric arteries in vitro. The myograph system was applied for isometric tension recording in the vascular rings. ICN relaxed both endothelium-intact and endothelium-denuded rat vascular rings precontracted with phenylephrine or KCl in a dose-dependent manner. Propranolol, tetraethylammonium, BaCl2, and glibenclamide had no influence on the vasodilator effect of ICN on phenylephrine-primed vascular rings, while 4-aminopyridine decreased the maximum relaxation. Furthermore, ICN produced a significant drop in maximum response in the PE log concentration-response curve without shifting to the right. In the Ca2+-free Kreb's-Henseleit buffer, ICN inhibited the contraction in vascular rings evoked by PE, but not by KCl. The phasic contractions of segments in the Ca2+-free Kreb's-Henseleit buffer induced by CaCl2 were restrained by ICN, while contractions elicited by caffeine displayed no differences. Furthermore, the phasic vasodilation of ICN was significantly lower than controls when pretreated with nifedipine and heparin. Both BAYK8644- and PE-evoked responses were significantly inhibited in the presence of 100 µM of ICN in human vascular smooth muscle cells loaded with the fluorescent Ca2+ indicator Fluo-4-AM. All these results suggest that ICN act in an endothelium-independent manner on the mesenteric artery. Its mechanisms of vasorelaxant action were produced by the inhibition of L-type calcium channel-mediated external Ca2+ influx and α1A-adrenoceptor-mediated intracellular Ca2+ release in vascular smooth muscle cells, and the participation of the Kv channel.

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We aimed to determine the influence of nitrergic innervation function on the decreased mesenteric arterial tone induced by high levels of triiodothyronine (T3), as a model of acute thyroiditis, as well as the mechanism/s implicated. We analysed in mesenteric segments from male Wistar rats the effect of 10 nmol/L T3 (2 h) on the vasomotor response to electrical field stimulation (EFS) in the presence/absence of specific neuronal NOS (nNOS) inhibitor L-NPA, or superoxide anion scavenger tempol. Nitric oxide (NO) release was measured in the presence/absence of tempol or PI3K inhibitor LY294002. Superoxide anion and peroxynitrite releases, nNOS, PI3K, AKT and superoxide dismutase (SOD) 1 and 2 expressions, nNOS and AKT phosphorylation, and SOD activity were analysed. T3 decreased EFS-induced vasoconstriction. L-NPA increased EFS-induced vasoconstriction more markedly in T3-incubated segments. T3 increased NO release. Tempol decreased EFS-induced vasoconstriction and augmented NO release only in segments without T3. LY294002 decreased NO release in T3-incubated segments. T3 diminished superoxide anion and peroxynitrite formation, enhanced SOD-2 expression, nNOS and AKT phosphorylations and SOD activity, and did not modify nNOS, PI3K, AKT and SOD-1 expressions. In conclusion, these results show a compensatory mechanism aimed at reducing the enhanced blood pressure that appears during acute thyroiditis.

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The main purpose of this study was to compare in vitro pharmacological properties of human αCGRP (CGRP) and a recently discovered metabolically stable CGRP analogue, SAX, in isolated rat and human artery segments. In rat, CGRP and SAX induced similar vasodilatory responses in isolated mesenteric artery with the potency of SAX being lower than that of CGRP (vasodilatory pEC50 8.2 ±â€¯0.12 and 9.0 ±â€¯0.11, respectively). A corresponding difference in receptor binding affinity of SAX and CGRP was determined in rat cerebral membranes (pKi 8.3 ±â€¯0.19 and 9.3 ±â€¯0.14, respectively). CGRP and SAX-induced vasodilation was antagonised with similar potencies by the CGRP receptor antagonist BIBN4096BS supporting a uniform receptor population for the agonists. In human tissue, SAX and CGRP induced similar pharmacological responses with different potencies in subcutaneous artery (vasodilatory pEC50 8.8 ±â€¯0.18 and 9.5 ±â€¯0.13, respectively) and human recombinant receptors (cAMP signalling pEC50 9.1 ±â€¯0.16 and 10.2 ±â€¯0.19). Like in the rat mesenteric artery, both SAX and CGRP-responses were inhibited by the CGRP receptor antagonist BIBN4096BS with similar antagonistic potencies. In conclusion, all pharmacological characteristics of SAX and CGRP in human and rat sources points towards action via a uniform BIBN4096BS sensitive receptor population with the potency of SAX being 5-10 fold lower than that of CGRP.

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We previously reported that nerve growth factor (NGF) facilitated perivascular sympathetic neuropeptide Y (NPY)- and calcitonin gene-related peptide (CGRP)-containing nerves injured by the topical application of phenol in the rat mesenteric artery. We also demonstrated that mesenteric arterial nerves were distributed into tyrosine hydroxylase (TH)-, substance P (SP)-, and neuronal nitric oxide synthase (nNOS)-containing nerves, which had axo-axonal interactions. In the present study, we examined the effects of NGF on phenol-injured perivascular nerves, including TH-, NPY-, nNOS-, CGRP-, and SP-containing nerves, in rat mesenteric arteries in more detail. Wistar rats underwent the in vivo topical application of 10% phenol to the superior mesenteric artery, proximal to the abdominal aorta, under pentobarbital-Na anesthesia. The distribution of perivascular nerves in the mesenteric arteries of the 2nd to 3rd-order branches isolated from 8-week-old Wistar rats was investigated immunohistochemically using antibodies against TH-, NPY-, nNOS-, CGRP-, and SP-containing nerves. The topical phenol treatment markedly reduced the density of all nerves in these arteries. The administration of NGF at a dose of 20µg/kg/day with an osmotic pump for 7 days significantly increased the density of all perivascular nerves over that of sham control levels. These results suggest that NGF facilitates the reinnervation of all perivascular nerves injured by phenol in small resistance arteries.

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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.

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Endothelin-1 causes long-lasting contraction via endothelin type A receptor (ETAR) in isolated rat mesenteric arteries (RMA) that cannot be readily terminated by removing the agonist, or by adding the ETAR antagonist BQ123 or the NO donor sodium nitroprusside. It could be terminated by adding calcitonin-gene related peptide (CGRP), most likely because CGRP causes ET-1/ETAR dissociation. Here we investigated this phenomenon in human coronary microarteries (HCMA). We simultaneously verified the effects of CGRP in RMA and HCMA towards other vasoconstrictors, i.e., the α1-adrenoceptor agonist phenylephrine, the thromboxane A2 analog U46619 (9,11-dideoxy-11α,9α-epoxy-methano-prostaglandin F2α) and KCl. Long-lasting contraction (remaining after washing away the agonist) was observed for ET-1 in RMA, but not HCMA. Constrictions to phenylephrine, U46619 or KCl did not last upon washing. When added on top of ET-1-initiated contraction in RMA, CGRP effectively counteracted vasoconstriction, i.e., it caused full relaxation. Inhibitory effects of CGRP were also observed when briefly exposing RMA and HCMA to CGRP 1h before the addition of ET-1. Similar inhibitory effects of transient CGRP pre-incubation were seen towards phenylephrine, U46619 or KCl in RMA and HCMA. In conclusion, our data imply that CGRP, like ET-1, causes long-lasting effects that remain apparent up to 1h after its removal from the organ bath. Thus, in addition to the reported dissociation of ET-1/ETAR complexes, CGRP causes long-lasting non-selective arterial smooth muscle relaxation that may add to the neuropeptide being a physiological antagonist of arterial effects of ET-1. Long-lasting, washout-resistant ET-1/ETAR interaction does not occur in HCMAs.

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OBJECTIVES: To investigate the chemical composition and vasorelaxant effect of the essential oil of Lippia alba (EOLA) in rat mesenteric artery. MATERIAL AND METHODS: Chemical composition of EOLA was investigated by gas chromatography-mass spectrometry (GC/MS). Vasorelaxant effect was evaluated in vitro in rat superior mesenteric artery rings. RESULTS: GC/MS analysis revealed the presence of 19 compounds, with geranial (48.58%) and neral (35.42%) being the major constituents. In intact rings precontracted with phenylephrine (Phe: 1 µM), EOLA (100-1000 µg/mL) induced relaxation, where the maximal effect (Emax) was 110.8 ± 10.8%. This effect was not modified after endothelium removal (Emax = 134.8 ± 16.5%), after tetraethylammonium (TEA) (Emax = 117.2 ± 4.96%), or in rings precontracted with KCl (80 mM) (Emax = 112.6 ± 6.70%). In addition, EOLA was able to inhibit the contraction caused by CaCl(2) and produced a small but significant (P<0.05) additional effect (from 70.5 ± 3.4 to 105.3 ± 13.5%, n = 5) on the maximal relaxation of nifedipine (NIF: 10 µM). CONCLUSIONS: The results demonstrated that EOLA induces endothelium-independent vasorelaxation, which appears to be caused, at least in part, by blocking Ca(2+) influx through voltage-operated Ca(2+) channels.