Summary
Following i.v. bolus injections into pithed normotensive rats, the maximal diastolic pressor responses to B-HT 920 and B-HT 958 amounted to 115 and 35 mm Hg, respectively. Prazosin (0.1 mg/kg, i.v.,-15 min) was without effect on the log dose-pressor effect curve of B-HT 958, whereas yohimbine (1 mg/kg, i.v.,-15 min) shifted this curve about 30-fold to the right, showing the exclusive participation of α2-adrenoceptors in the vasoconstrictor response to B-HT 958. In doses of 10 and 30 mg/kg, B-HT 958 displaced the log dose-vasoconstrictor effect curve of B-HT 920 approximately 6- and 30-fold, respectively, to the right, illustrating the partial agonism of B-HT 958 at postjunctional vascular α2-adrenoceptors. Despite the marked difference in intrinsic activity of B-HT 920 and B-HT 958, the calcium entry blocker nifedipine exhibited a comparable inhibitory action on the vasopressor responses to both agonists. This finding indicates that partial and full agonism at vascular α2-adrenoceptors are not related to the susceptibility of the initiated pressor response to inhibition by calcium entry blockade.
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Wilffert, B., van Heiningen, P.N.M., Mathy, M.J. et al. Lack of relationship between intrinsic activity and susceptibility of pressor responses to blockade by nifedipine among the α2 agonists B-HT 920 and B-HT 958. Naunyn-Schmiedeberg's Arch. Pharmacol. 327, 90–92 (1984). https://doi.org/10.1007/BF00504998
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DOI: https://doi.org/10.1007/BF00504998