title: Ouabain distinguishes between nicotinic and muscarinic receptor-mediated catecholamine secretions in perfused adrenal glands of cat.
abstract: 1. The effect of ouabain on catecholamine (adrenaline and noradrenaline) secretion induced by agents acting on cholinoceptors was studied in perfused cat adrenal glands. Acetylcholine (ACh) (5 x 10(-7) to 10(-3) M), pilocarpine (10(-5) to 10(-3) M) and nicotine (10(-6) to 5 x 10(-5) M) caused dose-dependent increases in catecholamine secretion. Both ACh and nicotine released more noradrenaline than adrenaline and the reverse was the case for pilocarpine. 2. Ouabain (10(-5) M) enhanced catecholamine secretion induced by ACh (10(-5) M), pilocarpine (10(-3) M) and nicotine (3 x 10(-6) M) during perfusion with Locke solution. The ratio of adrenaline to noradrenaline was not affected by ouabain. 3. In the absence of extracellular Ca2+, ACh and pilocarpine, but not nicotine, still caused a small increase in catecholamine secretions, which were enhanced by treatment with ouabain (10(-5) M) plus Ca2+ (2.2 mM) for 25 min. The effect of ouabain was much more significant on noradrenaline secretion than on adrenaline secretion. The enhanced response was blocked by atropine (10(-6) M) but not by hexamethonium (5 x 10(-4) M). 4. Nifedipine (2 x 10(-6) M) inhibited the responses to pilocarpine and nicotine. The treatment with ouabain (10(-5) M) reversed only the response to pilocarpine and resulted in a significant increase in the proportion of noradrenaline released. 5. It is suggested that ouabain enhances evoked catecholamine secretions by facilitating Ca2+ entry through nicotinic receptor-linked Ca2+ channels and by increasing the intracellular Ca2+ pool linked to muscarinic receptors.
authors.affiliation: Department of Pharmacology, Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yamada
authors.forename: Y
authors.initials: Y
authors.lastname: Nakazato
authors.forename: A
authors.initials: A
authors.lastname: Ohga
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000311:Adrenal Glands / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002415:Cats; D002851:Chromatography, High Pressure Liquid; D004837:Epinephrine / Q000378:metabolism*; D005260:Female; D008297:Male; D009538:Nicotine / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D010862:Pilocarpine / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000378:metabolism
chemical_list: D002121:Calcium Channel Blockers; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D010862:Pilocarpine; D010042:Ouabain; D009538:Nicotine; D000109:Acetylcholine; D009638:Norepinephrine; D004837:Epinephrine