Pharmacological characterization of cellular mechanisms of the renal vasodilatory effect of nicotine in rats Mahmoud M. El-Mas ⁎, Sahar M. El-gowilly, Eman Y. Gohar, Abdel-Rheem M. Ghazal Department of Pharmacology, Faculty of Pharmacy, University of Alexandria, Alexandria, Egypt ABSTRACT ARTICLE INFO Article history: Received 13 October 2007 Received in revised form 12 February 2008 Accepted 23 April 2008 Available online 30 April 2008 Keywords: Nicotine Endothelium Nitrergic neurotransmission Perfused kidney Vasodilation Nitric oxide synthase K+ channels Nicotine causes vasodilation in the renal vasculature through as yet unidentified mechanism. This study investigated the role of endothelial and non-endothelial factors in the vasodilatory action of nicotine in the rat isolated kidney. Nicotine vasodilation in phenylephrine-preconstricted perfused kidneys was evaluated in the absence and presence of drugs that interfere with nitric oxide synthase (NOS), K + channels, cholinergic or adrenergic activity. Nicotine infusion (5 × 10 - 5 , 1 × 10 - 4 , and 5 × 10 - 4 M) produced concentration-dependent decreases in the renal perfusion pressure, which continued for 20 min with a peak depressor effect observed at approximately 3 min. Nicotine vasodilation was associated with increases in norepinephrine and NO metabolites (nitrite/nitrate, NOx) levels in the renal effluent. Chemical denudation of the endothelium with 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propane-sulfonate (CHAPS), or inhibition of NOS (N G -nitro-L-arginine, L-NNA), or guanylate cyclase (methylene blue) almost abolished the renal vasodilatory action of nicotine. Nicotine vasodilation was also significantly attenuated after selective blockade of ATP-sensitive (K ATP , glibenclamide) or inward rectifier (K ir , BaCl 2 )K + channels but remained unaltered after blockade of large-conductance calcium-activated (BK Ca , tetraethylammonium, TEA) or voltage-dependent (K v , 4-aminopyridine) K + channels. Hexamethonium (ganglionic blocker), propranolol (β-adrenceptor blocker), guanethidine (adrenergic neuron blocker), atropine (muscarinic antagonist) or the use of kidneys preconstricted with 80 mM KCl reduced the vasodepressor action of nicotine. Finally, exposure to diclophenac or neostigmine had no effect on nicotine vasodilation. Together, these findings implicate endothelial NOS and K ATP and K ir channels in the renal vasodepressor effect of nicotine. Further, the sympathetic-dependent NO-mediated neurogenic vasodilation apparently contributes, at least partly, to nicotine vasodilation. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Nicotine produces contrasting effects on vascular tone including vasodilation (Zhang et al., 1998; Lee et al., 2000), vasoconstriction (Marano et al., 1999; Ayajiki et al., 2002), biphasic effect (vasoconstric- tion & vasodilation) (Wang and Wang, 2000) or sometimes no effect on vascular tone (Mayhan, 1999). Variations in animal species, tissues, dose and duration of nicotine regimens are likely contributing factors to the divergent vascular effects of nicotine. The vasoconstrictor action of nicotine has been accounted for by sympathetic neural stimulation (Bultmann et al., 1991; Marano et al., 1999), endothelial dysfunction (Black et al., 2001; Feitelson et al., 2003), or the release of vasopressin (Groudine and Morley, 1996) or endothelin (Haak et al., 1994). Contradictory reports are available as regards cellular sites that mediate the vasodilator effect of nicotine. In the dorsal aorta of the giant shovelnose ray, the relaxant effect of nicotine was attenuated by endothelium removal and by indomethacin, suggesting the involve- ment of endothelial cyclooxygenase pathway in the nicotine response (Donald et al., 2004). In the smooth muscle cells of the rat tail artery, nicotine produced dual effects (increase or decrease) on K + currents depending on the concentration of the drug (Tang et al., 1999). This effect of nicotine was partly dependent on nicotinic receptors and also involved direct interaction with K + channels (Tang et al., 1999). In the cerebral artery of several animal species, nicotine causes vasodilation via the activation of presynaptic nicotinic receptors, particularly the α 7 -nicotinic acetylcholine receptor subtype, on adrenergic nerve terminals to release norepinephrine. The latter stimulates β 2 -adrenoceptors on neighboring perivascular nitrergic nerve terminals causing the release of nitric oxide and subsequent vasodilation (Zhang et al., 1998; Lee et al., 2000; Si and Lee, 2002). In support of this assumption were the observations that nicotine vasodilation is inhibited in arteries pretreated with (i) NOS or guanylate cyclase inhibitors, (ii) β-adrenoceptor or adrenergic neuron blockade or chemical sympathectomy, and (iii) tetrodotoxin (Zhang et al., 1998; Lee et al., 2000; Si and Lee, 2002). In effect, the presence of β 2 -adrenoceptors on nitrergic nerve terminals receives more support European Journal of Pharmacology 588 (2008) 294–300 ⁎ Corresponding author. Department of Pharmacology, Faculty of Pharmacy, Uni- versity of Alexandria, Alexandria, Egypt. Tel.: +20 2010 170 8620; fax: +20 203 487 3273. E-mail address: mahelm@hotmail.com (M.M. El-Mas). 0014-2999/$ – see front matter © 2008 Elsevier B.V. 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