title: Mechanisms of sympathetic enhancement and inhibition of parasympathetically induced salivary secretion in anaesthetized dogs.
abstract: 1. The effects of superimposed and continuous sympathetic nerve stimulation on submandibular parasympathetic salivation were investigated in anaesthetized dogs. 2. Superimposed sympathetic nerve stimulation (1-2 min) initially enhanced and later inhibited salivary secretion induced by parasympathetic nerve stimulation (2-8 Hz) in glands with uncontrolled blood supply or constant-flow vascular perfusion. Propranolol (0.05 mg kg-1, i.a.) did not affect the diphasic sympathetic action whereas phentolamine (0.1 mg kg-1, i.a.) abolished it. Prazosin (0.025 mg kg-1, i.a.) greatly lessened the initial enhancement while yohimbine (0.025 mg kg-1, i.a.) alleviated the late inhibition. 3. Salivary secretion, induced by parasympathetic nerve stimulation (4 Hz) or acetylcholine infusion (10 micrograms kg-1 min-1, i.a.), was abolished by atropine (0.05 mg kg-1, i.a.), increased by phenylephrine infusion (0.25 microgram kg-1 min-1, i.a.) and depressed by clonidine infusion (0.75 microgram kg-1 min-1, i.a.). Hexamethionium (12.5 mg kg-1, i.a.) abolished the nerve-induced secretion but had no effect on the acetylcholine-induced secretion. 4. Continuous background sympathetic nerve stimulation decreased parasympathetic nerve-induced salivary secretion in glands with uncontrolled blood supply or constant-flow vascular perfusion. 5. These results show that parasympathetic salivation can be modified by the sympathetic system at the postsynaptic level; enhancement is via alpha 1-adrenoceptors whereas inhibition is via alpha 2-adrenoceptors.
authors.affiliation: Department of Physiology, Faculty of Medicine, University of Hong Kong.
authors.forename: M A
authors.initials: MA
authors.lastname: Lung
mesh_terms: D058668:Adrenergic alpha-1 Receptor Antagonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004285:Dogs; D004558:Electric Stimulation; D005260:Female; D008297:Male; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D012039:Regional Blood Flow / Q000187:drug effects; D012472:Salivation / Q000187:drug effects / Q000502:physiology*; D013363:Submandibular Gland / Q000098:blood supply / Q000187:drug effects / Q000378:metabolism; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*
chemical_list: D058668:Adrenergic alpha-1 Receptor Antagonists; D058669:Adrenergic alpha-2 Receptor Antagonists