Characterization of postsynaptic α‐adrenoceptors in rat aortic strips and portal veins

Digges, K. G.; Summers, Roger J.

doi:10.1111/j.1476-5381.1983.tb10002.x

Cited by 95 publications

(35 citation statements)

References 30 publications

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“…Based upon the reported selectivity of the yohimbine diastereoisomers corynanthine and rauwolscine for a,-and a2-adrenoceptors, respectively (McGrath, 1982), our observations with these antagonists appear to confirm the view that the rat aorta contains only a,-adrenoceptors (Digges & Summers, 1983b), while the rabbit saphenous vein contains predominantly x2-adrenoceptors (Alabaster et al, 1985). The possible contribution ofa,-adrenoceptors to responses in the rabbit saphenous vein, as evidenced by the nonlinearity ofthe Schild plots for rauwolscine, appears to be minimal since the selective x,-adrenoceptor agonist McGrath, 1982) was markedly less potent than NA.…”

Section: Discussionsupporting

confidence: 70%

“…The pA2 values for the selective m,-antagonist corynanthine against NA of 7.74 or (-)-m-octopamine of 7.49 are similar in separate studies of rat aorta (7.35 for NA, Digges & Summers, 1983b) and anococcygeus (7.3 for NA, McGrath, 1984). This validates the use of the aorta and confirms that for phenylethanolamines its ml-adrenoceptor need not be considered unusual.…”

Section: Discussionsupporting

confidence: 63%

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Activities of octopamine and synephrine stereoisomers on α‐adrenoceptors

Brown¹,

McGrath

Midgley

et al. 1988

British J Pharmacology

100

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1 The activities of the (-)-and (+ )-forms of m-and p-octopamine and m-and p-synephrine on a,-adrenoceptors from rat aorta and anococcygeus and a2-adrenoceptors from rabbit saphenous vein were compared with those of noradrenaline (NA).2 The rank order of potency of the (-)-forms on cx,-adrenoceptors from rat aorta and a2-adrenoceptors was NA > m-octopamine = m-synephrine > p-octopamine = p-synephrine. The two m-compounds were 6 fold less active than NA on x,-adrenoceptors from rat aorta and 150 fold less active on x,-adrenoceptors. The two p-compounds were 1,000 fold less active than NA on both oqadrenoceptors from rat aorta and x2-adrenoceptors. The rank order ofpotency ofthe (-)-forms on oqadrenoceptors from rat anococcygeus was NA = m-synephrine > m-octopamine >p-octopamine = p-synephrine. m-Octopamine was 4 fold less active than NA and (-)-m-synephrine. The two pcompounds were 30 fold less active than NA. 3 The rank order of potency of the (+)-forms was NA>m-octopamine>m-synephrine>p-octopamine >p-synephrine on both a,-and M2-adrenoceptors. The potency ofeach ( + )-form was 1-2 orders of magnitude less than that of the (-) counterpart, the differences being greater for the stereoisomers of synephrine than for those of octopamine on both a,-and M2-adrenoceptors. 4 The yohimbine diastereoisomer antagonists, rauwolscine and corynanthine, were tested against (-)-NA and (-)-m-octopamine-induced contractions in both preparations. Based upon the known selectivities of these isomers for a-adrenoceptor subtypes, it is concluded that the rat aorta contains only a,-adrenoceptors while the rabbit saphenous vein possesses predominantly M2-adrenoceptors.5 Ligand binding data for the octopamine and synephrine stereoisomers at oq-and a2-binding sites from rat cerebral cortex was also obtained. (-)-Forms were more active than (+ )-forms. The rank order of affinity of the (-)-forms for both a,-and M2-binding sites was NA > m-octopamine = msynephrine >p-synephrine >p-octopamine. The relative affinities ofthe members ofthe series against a,-binding sites were very similar to their relative functional activities on rat aorta. However, the affinities of both m-and p-compounds relative to that of ( -)-NA were much greater at the x2-binding sites than were the relative activities in rabbit saphenous vein, possibly suggesting low intrinsic efficacy. Functional antagonist responses to NA by the (-)-octopamine and synephrines could not, however, be demonstrated on rat aorta or rabbit saphenous vein. 6 The activities of m-octopamine and m-synephrine were not significantly different from each other on either a,-adrenoceptors from rat aorta or x2-adrenoceptors; however, m-synephrine is more active than m-octopamine on a,-adrenoceptors from rat anococcygeus. Both m-octopamine and msynephrine can be considered to be naturally occurring x,-selective amines. However, if m-and poctopamine are co-released with NA in amounts proportional to their concentration, it is concluded that their activities on m,-and x2-adrenoceptors are too low to be ...

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Section: Discussionsupporting

confidence: 70%

Section: Discussionsupporting

confidence: 63%

Activities of octopamine and synephrine stereoisomers on α‐adrenoceptors

Brown¹,

McGrath

Midgley

et al. 1988

British J Pharmacology

100

View full text Add to dashboard Cite

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“…Ikunobu et al, (1990) [17] found that, yohimbine inhibited the blood vessels responses to adrenaline and phenylephrine. Moreover, yohimbine was found not significantly different than prazosin (a selective α 1 adrenoceptor antagonist) in inhibiting the effects of phenylephrine and noradrenaline on rat aortic strips [26].…”

Section: Discussionmentioning

confidence: 99%

Effects of methanolic extract of yohimbe bark (<i>Pausinystalia yohimbe</i>) on isolated rabbit aortic strip and rat uterus

Hassan¹,

Eldin²,

Ahmed³

et al. 2013

Health

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Background: Medicinal plants contain physiologically active principles that over the years have been exploited in traditional medicine for the treatment of various ailments. Objectives and Methods: This study aimed to investigate the effects of the methanolic extract of Pausinystalia yohimbe bark (5 mg/ml) on isolated rabbit aortic strip and rat uterus. Results: methanolic extract of P. yohimbe bark (5 mg/ml) produced relaxation of the phenylephrine precontracted-rabbit aortic strip. This relaxation may be resulted through nitric oxide (NO), since the pretreatment of the isolated rabbit aortic strip with methylene blue inhibited the NO-mediated relaxation. Moreover, the extract exhibited relaxation of rat uterine muscles, which appeared to be not mediated by activation of β 2 -adrenoceptors and/or H 2 receptors, since the relaxant effect continued even after the pretreatment of the tissue with propranolol and ranitidine respectively. Conclusion: The obtained results revealed that methanolic extract of P. yohimbe bark caused relaxation of both isolated rat uterus and rabbit aortic strip through facilitating the role of endogenous compounds such as NO.

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“…The high affinity of clonidine, as judged by pharmacological and radioligand binding studies led Ruffolo et al (1980) and Weiss et al (1983) to conclude that the rat aorta and tail artery contained c2-adrenoceptors. Other studies with rat aortic strips concluded that it contained a2-adrenoceptors although more than one subclass of a1-adrenoceptors may be present (Digges & Summers, 1983;Randriantsoa et al, 1981;Beckenringh et al, 1983). Thus, in view of the difficulty of demonstrating the presence of the two subtypes of a-adrenoceptors in vitro, it may be premature to attribute with certainty the responses of isolated aortic and carotid strips in this study to the activation of either al or o2-adrenoceptors.…”

Section: (C) Responses In Calcium-free Solution (Cfs)mentioning

confidence: 99%

Calcium‐dependence and antagonism of responses to α₁‐ and α₂‐adrenoceptor agonists in vascular tissues from hypertensive and normotensive rats

Rutledge

Swamy

Triggle

1984

British J Pharmacology

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Characterization of postsynaptic α‐adrenoceptors in rat aortic strips and portal veins

Cited by 95 publications

References 30 publications

Activities of octopamine and synephrine stereoisomers on α‐adrenoceptors

Activities of octopamine and synephrine stereoisomers on α‐adrenoceptors

Effects of methanolic extract of yohimbe bark (<i>Pausinystalia yohimbe</i>) on isolated rabbit aortic strip and rat uterus

Calcium‐dependence and antagonism of responses to α₁‐ and α₂‐adrenoceptor agonists in vascular tissues from hypertensive and normotensive rats

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Characterization of postsynaptic α‐adrenoceptors in rat aortic strips and portal veins

Cited by 95 publications

References 30 publications

Activities of octopamine and synephrine stereoisomers on α‐adrenoceptors

Activities of octopamine and synephrine stereoisomers on α‐adrenoceptors

Effects of methanolic extract of yohimbe bark (&lt;i&gt;Pausinystalia yohimbe&lt;/i&gt;) on isolated rabbit aortic strip and rat uterus

Calcium‐dependence and antagonism of responses to α1‐ and α2‐adrenoceptor agonists in vascular tissues from hypertensive and normotensive rats

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Product

Resources

About

Effects of methanolic extract of yohimbe bark (<i>Pausinystalia yohimbe</i>) on isolated rabbit aortic strip and rat uterus

Calcium‐dependence and antagonism of responses to α₁‐ and α₂‐adrenoceptor agonists in vascular tissues from hypertensive and normotensive rats