title: Upregulation of muscarinic receptors by long-term nitric oxide inhibition in the rat ileum.
abstract: 1. The aim of the present study was to examine the effects of long-term nitric oxide (NO) blockade on contractions of the rat ileum induced by muscarinic agonists. 2. Male Wistar rats received the NO synthesis inhibitor NG-nitro-l-arginine methyl ester (l-NAME; 20 mg/rat per day) in drinking water for 7, 15, 30 and 60 days. Concentration-responses curves to methacholine and carbachol were obtained and pEC50 values were calculated. Saturation binding assays were performed in membranes prepared from rat ileum after 60 days of l-NAME treatment and the dissociation constant (KD) and maximal number of binding sites (Bmax) were determined by Scatchard analysis. 3. The NO synthase activity of the ileum was markedly reduced in all l-NAME-treated groups. At 60 days after l-NAME treatment, a significant increase in the potency of methacholine (fourfold) and carbachol (threefold) was observed. In binding studies, we found a significant increase in Bmax for [3H]-quinuclidinyl benzilate of approximately 57% in the l-NAME treated group without any significant change in KD values. The contractile response to methacholine was not modified by the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (3 micro mol/L). No morphological alterations in the rat ileum were observed in l-NAME-treated rats. 4. Our findings suggest that treatment with l-NAME for 60 days induces a marked increase in the potency of methacholine and carbachol, as well as an increase in receptor number in the rat ileum.
authors.affiliation: Department of Pharmacology, Faculty of Medical Sciences, UNICAMP, Campinas, Brazil.
authors.forename: Alice A O
authors.initials: AA
authors.lastname: Bricola
authors.forename: Simone A
authors.initials: SA
authors.lastname: Teixeira
authors.forename: Iara M S
authors.initials: IM
authors.lastname: De Luca
authors.forename: Marcelo N
authors.initials: MN
authors.lastname: Muscará
authors.forename: Fernando M F
authors.initials: FM
authors.lastname: Abdala
authors.forename: Catarina S
authors.initials: CS
authors.lastname: Porto
authors.forename: Angelina
authors.initials: A
authors.lastname: Zanesco
authors.forename: Edson
authors.initials: E
authors.lastname: Antunes
authors.forename: Gilberto
authors.initials: G
authors.lastname: De Nucci
mesh_terms: D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007082:Ileum / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009569:Nitric Oxide / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000096:biosynthesis*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*
chemical_list: D004791:Enzyme Inhibitors; D011976:Receptors, Muscarinic; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase