Relation between central sympathoinhibitory and peripheral pre- and postsynaptic alpha-adrenoceptors as evaluated by different clonidine-like substances in rats.
A series of 8 clonidine-like substances were tested in rats on central sympathoinhibition (heart rate decrease in vagotomized rats, D50 = dose which decreased heart rate by 50 beats/min), peripheral postsynaptic activity (blood pressure increase in spinal rats, PD30 = dose which increased blood pressure 30 mm Hg) and peripheral presynaptic activity (inhibition of tachycardia as elicited by electrical stimulation in the spinal canal of pithed rats, ID50 = dose which inhibited for 50%). The D50, PD30 and ID50 were converted in moles/kg and the negative logarithms thereof were correlated. There was a good correlation between the central effect (D50) and both peripheral effects (PD30 and ID50, respectively; r = 0.89 and 0.91, respectively) provided one drug with low lipoid affinity was omitted from calculation (St 600). There was also good correlation between both peripheral effects (PD30 and ID50; r = 0.94) and this could be extended to other imidazolines which are not acting centrally as antihypertensives (oxymetazoline, naphazoline, St 91, tramazoline; r = 0.90). The results were interpreted by (1) the agonistic activity of the clonidine-like drugs mainly at alpha 2-adrenoceptors and (2) the presence of alpha 2-adrenoceptors at peripheral presynaptic, peripheral postsynaptic as well as central cardiovascular sites.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D002490:Central Nervous System / Q000187:drug effects*; D003000:Clonidine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D051381:Rats; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011942:Receptors, Adrenergic, alpha / Q000032:analysis / Q000187:drug effects*; D012044:Regression Analysis; D013565:Sympatholytics / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D007093:Imidazoles; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D013565:Sympatholytics; D003000:Clonidine