Difference in the potency of α2-adrenoceptor agonists and antagonists between the pithed rabbit and rat

J. M. Bulloch, J. R. Docherty, Nicholas Flavahan, J. C. McGrath, C. E. McKean

Research output: Contribution to journalArticle

Abstract

The subtypes of α-adrenoceptors which mediate pressor responses to sympathomimetic agonists or to nerve stimulation in pithed rabbits have been classified according to the effects of 'selective' agonists and a comparison has been made, for the α2-subtype, with corresponding responses in the rat. In the rabbit the dose-response curve for phenylephrine was shifted to the right in parallel by prazosin (1 mg kg-1) and was unaffected by rauwolscine (1 mg kg-1). The dose-response curve for noradrenaline was shifted to the right by prazosin (1 mg kg-1) and was shifted to a smaller extent by rauwolscine (1 mg kg-1) or imiloxan (10 mg kg-1). After rauwolscine, prazosin produced a rightward shift larger than when given alone. After prazosin, rauwolscine produced a rightward shift larger than when given alone. The responses to pressor nerve stimulation at low frequencies (<1 Hz) could be reduced by prazosin, rauwolscine or imiloxan but those at a higher frequency could be reduced only by prazosin. These results indicate that the responses to noradrenaline or to nerve stimulation are mediated by both α1- and α2-adrenoceptors. Low doses or frequencies have a proportionately greater component which is α2. Responses to noradrenaline after prazosin (1 mg kg-1), were sufficiently sensitive to rauwolscine to be considered as predominantly α2. A comparison was therefore made of such responses in the rat and rabbit. They were produced by a lower dose per unit body weight in the rat whereas this was less marked for the α2-adrenoceptor agonist guanabenz. In the rabbit they were more susceptible to blockade by rauwolscine but were less sensitive to Wy 26703 than in the rat. This demonstrates that the α2-adrenoceptors mediating pressor responses in vivo, like those in other tissues in vitro, are different in rat and rabbit, with regard to antagonists.

Original languageEnglish (US)
Pages (from-to)457-466
Number of pages10
JournalBritish Journal of Pharmacology
Volume91
Issue number3
StatePublished - 1987
Externally publishedYes

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Yohimbine
Prazosin
Adrenergic Receptors
Rabbits
Norepinephrine
Guanabenz
Sympathomimetics
Phenylephrine
Body Weight

ASJC Scopus subject areas

  • Pharmacology

Cite this

Difference in the potency of α2-adrenoceptor agonists and antagonists between the pithed rabbit and rat. / Bulloch, J. M.; Docherty, J. R.; Flavahan, Nicholas; McGrath, J. C.; McKean, C. E.

In: British Journal of Pharmacology, Vol. 91, No. 3, 1987, p. 457-466.

Research output: Contribution to journalArticle

Bulloch, J. M. ; Docherty, J. R. ; Flavahan, Nicholas ; McGrath, J. C. ; McKean, C. E. / Difference in the potency of α2-adrenoceptor agonists and antagonists between the pithed rabbit and rat. In: British Journal of Pharmacology. 1987 ; Vol. 91, No. 3. pp. 457-466.
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