title: Clonidine inhibits salivary secretion by activation of postsynaptic alpha 2-receptors.
abstract: The effects of clonidine on the submaxillary gland of the rat were studied. Doses ranging between 100 to 3.000 micrograms/kg produced a sustained secretory response which was blocked by 0.1 mg/kg of prazosin but not by 1 mg/kg of yohimbine. Clonidine 10 micrograms/kg markedly inhibited the salivation induced by noradrenaline, methacholine and substance P but not that induced by isoproterenol. The inhibition caused by the alpha 2-agonist was greater for noradrenaline than for either methacholine or substance P. Blockade of alpha 2 adrenoceptors with yohimbine (0.3 - 1 mg/kg) prevented the inhibition by clonidine of noradrenaline, methacholine and substance P induced salivation. On the other hand, prazosin 0.1 mg/kg did not modify the inhibition by clonidine of methacholine induced secretion. The results obtained indicate that clonidine exerts a dual effect on salivary secretion: at high doses it elicits salivation through activation of alpha 1-adrenoceptors; at the dose of 10 micrograms/kg clonidine activates alpha 2-adrenoceptors which inhibit the secretory response evoked through either muscarine, substance P and alpha 1-adrenoceptor agonists.
mesh_terms: D000818:Animals; D003000:Clonidine / Q000494:pharmacology*; D005260:Female; D008688:Methacholine Compounds / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D017981:Receptors, Neurotransmitter / Q000187:drug effects; D012472:Salivation / Q000187:drug effects*; D013363:Submandibular Gland / Q000294:innervation* / Q000378:metabolism; D013373:Substance P / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D008688:Methacholine Compounds; D011942:Receptors, Adrenergic, alpha; D017981:Receptors, Neurotransmitter; D015016:Yohimbine; D013373:Substance P; D003000:Clonidine; D009638:Norepinephrine