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Upregulation of muscarinic receptors by long‐term nitric oxide inhibition in the rat ileum
Author(s) -
Bricola Alice AO,
Teixeira Simone A,
De Luca Iara MS,
Muscará Marcelo N,
Abdala Fernando MF,
Porto Catarina S,
Zanesco Angelina,
Antunes Edson,
De Nucci Gilberto
Publication year - 2003
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1046/j.1440-1681.2003.03807.x
Subject(s) - carbachol , ileum , muscarinic acetylcholine receptor , methacholine , endocrinology , medicine , chemistry , nitric oxide synthase , dissociation constant , receptor , nitric oxide , biology , respiratory disease , lung
Summary 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 N G ‐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 pEC 50 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 (K D ) and maximal number of binding sites (B max ) 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 B max for [ 3 H]‐quinuclidinyl benzilate of approximately 57% in the l ‐NAME treated group without any significant change in K D 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 µmol/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.