title: Three different vasoactive responses of rat tail artery to nicotine.
abstract: The vasoactive effects of nicotine on isolated rat tail artery tissues were studied. Nicotine transiently contracted rat tail artery tissues (EC50, 55.6 +/- 2 microM) in an extracellular Ca2+ dependent and endothelium-independent fashion. The blockade of alpha1-adrenoceptors, but not alpha2-adrenoceptors or P2X purinoceptors, inhibited the nicotine-induced contraction by 38 +/- 7% (p < 0.05). Nicotine (1 mM) depolarized membrane by 13 +/- 3 mV, but did not affect L-type Ca2+ channel currents, of the isolated rat tail artery smooth muscle cells. The phenylephrine-precontracted tail artery tissues were relaxed by nicotine (EC50, 0.90 +/- 0.31 mM), which was significantly inhibited after the blockade of nicotinic receptors. Simultaneous removal of phenylephrine and nicotine, after a complete relaxation of the phenylephrine-precontracted tail artery strips was achieved by nicotine at accumulated concentrations (> or =10 mM), triggered a Ca2+-dependent rebound long-lasting vasoconstriction (n = 20). This rebound contraction was abolished in the absence of calcium or in the presence of tetracaine in the bath solution. Pretreatment of vascular tissues with a nicotinic receptor antagonist did not affect the nicotine-induced vasoconstriction or nicotine withdrawal induced rebound contraction. The elucidation of the triphasic vascular effects of nicotine and the underlying mechanisms is important for a better understanding of the complex vascular actions of nicotine.
authors.affiliation: Department of Physiology, University of Saskatchewan, Saskatoon, Canada. wangrui@duke.usask.ca
authors.forename: R
authors.initials: R
authors.lastname: Wang
authors.forename: Z
authors.initials: Z
authors.lastname: Wang
mesh_terms: D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000502:physiology; D020746:Calcium Channels, L-Type / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D009478:Neuropeptide Y / Q000502:physiology; D009538:Nicotine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013623:Tail / Q000098:blood supply; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D020746:Calcium Channels, L-Type; D009478:Neuropeptide Y; D009538:Nicotine