1987
DOI: 10.1111/j.1476-5381.1987.tb11237.x
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Difference in the potency of α2‐adrenoceptor agonists and antagonists between the pithed rabbit and rat

Abstract: 1 The subtypes ofa-adrenoceptors which mediate pressor responses to sympathomimetic agonists or to nerve stimulation in pithed rabbits have been classified according to the effects of 'selective' antagonists and a comparison has been made, for the xt2-subtype, with corresponding responses in the rat.2 In the rabbit the dose-response curve for phenylephrine was shifted to the right in parallel by prazosin (1 mg kg-') and was unaffected by rauwolscine (1 mg kg '). The dose-response curve for noradrenaline was sh… Show more

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Cited by 15 publications
(3 citation statements)
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“…Figure 4 shows that clonidine‐ (10 μg kg −1 min −1 ) induced inhibition of electrically induced vasodepressor responses (as compared to those during 15 μg kg −1 min −1 methoxamine; control responses), which remained unaltered in animals pretreated with 1 ml kg −1 saline (Figure 4a), was: (i) antagonized in animals pretreated with 300 μg kg −1 rauwolscine (Figure 4b), 300 and 1000 μg kg −1 BRL44408 (Figures 4d and e) or 10 and 30 μg kg −1 MK912 (Figures 4i and j); and (ii) resistant to blockade in animals pretreated with 100 μg kg −1 BRL44408 (Figure 4c), 3000 and 10000 μg kg −1 imiloxan (Figures 4f and g) or 3 μg kg −1 MK912 (Figure 4h). It must be emphasized that the doses of the above antagonists were high enough to completely block their respective α 2 ‐adrenoceptor subtypes in the cardiovascular system ( Bulloch et al ., 1987 ; Gavin and Docherty, 1996 ; Willems et al ., 2001 ; Cobos‐Puc et al ., 2007 ).…”
Section: Resultsmentioning
confidence: 99%
See 1 more Smart Citation
“…Figure 4 shows that clonidine‐ (10 μg kg −1 min −1 ) induced inhibition of electrically induced vasodepressor responses (as compared to those during 15 μg kg −1 min −1 methoxamine; control responses), which remained unaltered in animals pretreated with 1 ml kg −1 saline (Figure 4a), was: (i) antagonized in animals pretreated with 300 μg kg −1 rauwolscine (Figure 4b), 300 and 1000 μg kg −1 BRL44408 (Figures 4d and e) or 10 and 30 μg kg −1 MK912 (Figures 4i and j); and (ii) resistant to blockade in animals pretreated with 100 μg kg −1 BRL44408 (Figure 4c), 3000 and 10000 μg kg −1 imiloxan (Figures 4f and g) or 3 μg kg −1 MK912 (Figure 4h). It must be emphasized that the doses of the above antagonists were high enough to completely block their respective α 2 ‐adrenoceptor subtypes in the cardiovascular system ( Bulloch et al ., 1987 ; Gavin and Docherty, 1996 ; Willems et al ., 2001 ; Cobos‐Puc et al ., 2007 ).…”
Section: Resultsmentioning
confidence: 99%
“…Admittedly, clonidine can also interact with imidazoline receptors ( Eglen et al ., 1998 ), but rauwolscine does not block them at concentrations that completely antagonize α 2 ‐adrenoceptors ( Göthert et al ., 1999 ). On this basis, we investigated the role of the α 2A , α 2B and α 2C subtypes by using the antagonists BRL44408 (α 2A ), imiloxan (α 2B ) and MK912 (α 2C ) (Table 1) at doses high enough to completely antagonize their respective receptor subtypes ( Bulloch et al ., 1987 ; Gavin and Docherty, 1996 ; Willems et al ., 2001 ; Cobos‐Puc et al ., 2007 ). As BRL44408 (300 and 1000 μg kg −1 ) or MK912 (10 and 30 μg kg −1 ), but not imiloxan (3000 and 10000 μg kg −1 ), antagonized clonidine‐induced inhibition (Figure 4), the simplest interpretation of these findings is that α 2A (blocked by BRL44408) and α 2C (blocked by MK912), rather than α 2B , adrenoceptors could be involved.…”
Section: Discussionmentioning
confidence: 99%
“…This study also highlighted the difficulties encountered when analysing prejunctional effects of an antagonist like yohimbine, which is also active at postjunctional a2-adrenoceptors. It has been proposed that postjunctional a2-adrenoceptors occur in the vicinity of the postganglionic sympathetic varicosities in the vasculature in the pithed rabbit (McGrath et al, 1982;Bulloch et al, 1987) and the pithed rat . Vasoconstrictor responses of the rabbit ileocolic artery to exogenous NA are mediated exclusively by a1-adrenoceptors, since they are abolished by relatively low concentrations of prazosin but not attenuated by yohimbine (von Kugelgen & Starke, 1985;and present study).…”
Section: Discussionmentioning
confidence: 99%