Sympathetic and parasympathetic nerves regulate postsynaptic alpha-2 adrenoceptor in salivary glands.
The effects of sympathetic denervation or parasympathetic decentralization on the inhibitory effects of postsynaptic alpha-2 adrenoceptors were studied in the submaxillary and the sublingual gland of the rat. Chronic sympathetic denervation enhanced by a factor of 10 the potency of clonidine to inhibit the secretory responses of the submaxillary gland to either norepinephrine or methacholine. In denervated glands, clonidine (1 microgram/kg), reduced markedly the response to norepinephrine, but potentiated this response in control glands. Blockade of postsynaptic alpha-2 adrenoceptors with idazoxan (3 micrograms/kg) enhanced the secretory responses of denervated glands to norepinephrine. Parasympathetic decentralization also potentiated the inhibitory effects of the alpha-2 agonists. In the submaxillary gland the potency of guanabenz to decrease the secretory response to methacholine was increased by a factor of 30. Supersensitivity to the inhibitory effects of clonidine was also observed in parasympathetically decentralized sublingual glands. Parasympathetic decentralization increased the maximum binding site of [3H]clonidine binding by about 50% in both the submaxillary and sublingual glands. No changes in KD were detected. This surgical procedure also increased the maximum binding site of [3H]prazosin binding in submaxillary glands. The present findings show clearly that interruption of either branch of the autonomic nervous system induces supersensitivity of the inhibitory response mediated through postsynaptic alpha-2 adrenoceptors. The enhanced inhibitory activity could mask alpha-1 adrenoceptor supersensitivity after postganglionic sympathetic denervation.
D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000502:physiology*; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012463:Saliva / Q000378:metabolism; D012469:Salivary Glands / Q000294:innervation / Q000502:physiology*; D013361:Sublingual Gland / Q000187:drug effects / Q000502:physiology; D013363:Submandibular Gland / Q000294:innervation / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology*
D008688:Methacholine Compounds; D011942:Receptors, Adrenergic, alpha; D016210:Methacholine Chloride; D003000:Clonidine; D009638:Norepinephrine; D011224:Prazosin