α2‐Adrenoceptor agonists enhance vasoconstrictor responses to α1‐adrenoceptor agonists in the rat tail artery by increasing the influx of Ca2+

Xiao, Xinyue; Rand, M. J.

doi:10.1111/j.1476-5381.1989.tb14635.x

Cited by 25 publications

(15 citation statements)

References 23 publications

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“…Agmatine by itself does not appear to have any direct postjunctional actions on the rat tail artery. Even though agmatine is a ligand at x2-adrenoceptors (Piletz et al, 1995) it failed to reproduce the responses associated with stimulation of these receptors including direct contraction or potentiation of the vasoconstriction elicited by stimulation of ax-adrenoceptor agonists (Xiao & Rand, 1989). The finding is in agreement with conclusions of Pinthong et al (1995) in the porcine palmar lateral vein.…”

Section: Discussionsupporting

confidence: 82%

“…However, agmatine did (Xiao & Rand, 1989). Agmatine slightly potentiated the contractile response to NA, although the differences were not statistically significant ( Figure Ic, Table 1).…”

Section: Resultsmentioning

confidence: 84%

“…This vessel has the advantages that the function of post-junctional a2-adrenoceptors in regulating arterial tone has been characterized (Medgett & Langer, 1984;Xiao & Rand, 1989), and its dense sympathetic innervation permits analysis of regulation of vascular contraction by pre-junctional receptors. We demonstrate that agmatine, while without a direct action upon vascular smooth muscle, can inhibit the neurogenically mediated contraction of the rat tail artery by activating prejunctional a2-adrenoceptors.…”

Section: Introductionmentioning

confidence: 99%

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Agmatine, an endogenous modulator of noradrenergic neurotransmission in the rat tail artery

González

Regunathan

et al. 1996

British J Pharmacology

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1 We investigated the vascular effects of agmatine (decarboxylated arginine), an endogenous ligand for x2-adrenoceptors and non-adrenoceptor imidazoline (I-) receptors, present in endothelium, smooth muscle and plasma, using the rat tail artery as a model. 2 While by itself agmatine (10 nM-1 mM) was without effect on isolated arterial rings, at the highest concentration used (1 mM) it slightly increased EC50 values for contractions elicited respectively by the xl-and x2-adrenoceptor agonists methoxamine and clonidine. 3 Agmatine (0.03-1 mM) produced a concentration-dependent transient inhibition of the contractions induced by transmural nerve stimulation (TNS; 200 mA, 0.2 ms, 1 Hz, 10 s). This effect was abolished by the CL2-adrenoceptor antagonists, rawolscine and idazoxan. 4 In the presence of rawolscine or idazoxan, agmatine produced a concentration-dependent delayed facilitation of TNS-induced contractions, which was prevented by cocaine. 5 Neither inhibitory nor potentiating actions were produced by agmatine on contractions induced by noradrenaline (NA) administration. 6 Agmatine did not directly affect [3H]-NA uptake in bovine cultured chromaffin cells. 7 Agmatine can regulate vascular function by two opposing actions at sympathetic nerve terminals, with different latencies: a transient inhibition of NA release mediated by prejunctional x2-adrenoceptors and a cocaine-sensitive delayed facilitation the mechanism of which is undetermined at present. 8 The results reveal the existence of a novel endogenous amine modulating NA release in the perivascular sympathetic terminals.

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Section: Discussionsupporting

confidence: 82%

“…However, agmatine did (Xiao & Rand, 1989). Agmatine slightly potentiated the contractile response to NA, although the differences were not statistically significant ( Figure Ic, Table 1).…”

Section: Resultsmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

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Agmatine, an endogenous modulator of noradrenergic neurotransmission in the rat tail artery

González

Regunathan

et al. 1996

British J Pharmacology

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“…Upon stimulation with noradrenaline, the arterial smooth muscle contracts in two phases: the initial phasic response followed by a sustained tonic response. In the absence of extracellular Ca 2+ , the tonic response to noradrenaline is abolished (Xiao and Rand 1989). Our results are consistent with the above rationale.…”

Section: Response To Noradrenalinesupporting

confidence: 94%

Application of real-time confocal microscopy to intracellular calcium ion dynamics in rat arterioles

Saino

Matsuura

Satoh

2002

Histochem Cell Biol

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The regulation of cytosolic Ca(2+) homeostasis is essential for cells, including vascular smooth muscle cells. Arterial tone, which underlies the maintenance of peripheral resistance in the circulation, is a major contributor to the control of blood pressure. Confocal microscopy was employed to study the alteration in intracellular calcium ion concentration ([Ca(2+)](i)) in arterioles (external diameters <100 microm) with respect to selected modifying reagents. 5-Hydroxytryptamine (1 microM), ATP (10 microM), and endothelin 1-3 (5 nM) elicited an increase in [Ca(2+)](i) in most arteriole smooth muscle cells. The [Ca(2+)](i) increase sometimes propagated in an intercellular manner. When noradrenaline (10 microM) was used as a stimulant, [Ca(2+)](i) increase was observed only in a portion of the smooth muscle cells. It was also noted that the reaction of these cells with respect to ATP is different between testis and brain arterioles; the [Ca(2+)](i) increase in testicular arterioles is dependent on Ca(2+) influx from extracellular space, whereas in cerebral arterioles it plays a role in both the influx of extracellular Ca(2+) and the release of Ca(2+) from intracellular stores (i.e., sarco/endoplasmic reticulum). These results indicate that arterioles in different tissues may differ greatly in their responses. Real-time confocal microscopy was found to be a useful tool for investigating the structural and functional changes in living tissues.

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“…Since the early peak is almost completely abolished by prazosin, the inhibition of early peak constriction by rauwolscine possibly indicates that there is synergistic interaction between a 1 -and a 2 -adrenoceptors, as suggested by Docherty (1998). a 2 -Adrenoceptors have been reported to enhance the effects of a 1 -adrenoceptors in a number of tissues, by activation of different mechanisms to increase the concentration of intracellular free Ca 2 þ , which triggers the contraction (Xiao & Rand, 1989;Bao et al, 1993;Docherty, 1998). It remains to be clarified in future studies whether a potentiating interaction between a 1 -and a 2 -adrenoceptor exists in the human gastroepiploic artery and whether a Ca 2 þ mechanism participates in this process.…”

Section: Fukui Et Al Neurotransmission In Human Arterymentioning

confidence: 99%

Neurogenic double‐peaked vasoconstriction of human gastroepiploic artery is mediated by both α₁‐ and α₂‐adrenoceptors

Fukui

Yang

Chiba

2005

British J Pharmacology

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1 The contribution of postjunctional P2X receptors and subtypes of a-adrenoceptors to vasoconstrictor responses following periarterial electrical nerve stimulation (PNS, 30 s trains of pulses at a frequency of 2, 4 or 8 Hz) was investigated in human gastroepiploic arteries. 2 The vasoconstrictor response to PNS at a stimulation of 4 or 8 Hz was a two-peaked response, whereas at a frequency of 2 Hz it appeared only as a late peak. All vasoconstrictions evoked by PNS were abolished by phentolamine, a nonselective a-adrenoceptor inhibitor, but not by a,b-methylene ATP, a P2X receptor-desensitizing agent. 3 The early peak to PNS at 4 or 8 Hz was abolished by prazosin, an a 1 -adrenoceptor antagonist, while the late one still remained, although it was markedly inhibited. The responses remaining after prazosin were blocked by rauwolscine. The vasoconstrictor response to PNS at 2 Hz was not affected by prazosin (0.1 mM), but was abolished by rauwolscine (0.1 mM), an a 2 -adrenoceptor antagonist. 4 OPC-28326(10 mM), a newly developed vasodilator, which preferentially exerts its antagonistic actions on the a 2B -and a 2C -adrenoceptors, significantly reduced the noradrenaline-induced vasoconstriction in the absence or presence of prazosin. OPC-28326 had a greater inhibitory effect on the late peak evoked by PNS than the early one. The neurogenic responses remaining after OPC-28326 were abolished by prazosin. 5 The present results suggest that sympathetic vasoconstriction of the human gastroepiploic artery is mediated by both a 1 -and a 2 -adrenoceptors postjunctionally, but not by P2X receptors. The a 2 -adrenoceptors may be preferentially activated at a low frequency of stimulation, which induces a constriction more slowly than that by a 1 -adrenoceptors. The existence of a 2 -adrenoceptors may cause an enhancement of a 1 -adrenoceptor-induced responses.

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α₂‐Adrenoceptor agonists enhance vasoconstrictor responses to α₁‐adrenoceptor agonists in the rat tail artery by increasing the influx of Ca²⁺

Cited by 25 publications

References 23 publications

Agmatine, an endogenous modulator of noradrenergic neurotransmission in the rat tail artery

Agmatine, an endogenous modulator of noradrenergic neurotransmission in the rat tail artery

Application of real-time confocal microscopy to intracellular calcium ion dynamics in rat arterioles

Neurogenic double‐peaked vasoconstriction of human gastroepiploic artery is mediated by both α₁‐ and α₂‐adrenoceptors

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α2‐Adrenoceptor agonists enhance vasoconstrictor responses to α1‐adrenoceptor agonists in the rat tail artery by increasing the influx of Ca2+

Cited by 25 publications

References 23 publications

Agmatine, an endogenous modulator of noradrenergic neurotransmission in the rat tail artery

Agmatine, an endogenous modulator of noradrenergic neurotransmission in the rat tail artery

Application of real-time confocal microscopy to intracellular calcium ion dynamics in rat arterioles

Neurogenic double‐peaked vasoconstriction of human gastroepiploic artery is mediated by both α1‐ and α2‐adrenoceptors

Contact Info

Product

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About

α₂‐Adrenoceptor agonists enhance vasoconstrictor responses to α₁‐adrenoceptor agonists in the rat tail artery by increasing the influx of Ca²⁺

Neurogenic double‐peaked vasoconstriction of human gastroepiploic artery is mediated by both α₁‐ and α₂‐adrenoceptors