title: Angiotensin II-induced relaxation of anococcygeus smooth muscle via desensitization of AT1 receptor, and activation of AT2 receptor associated with nitric-oxide synthase pathway.
abstract: We evaluated the role of receptor desensitization, activation of AT(2) receptors, and enzymatic degradation of angiotensin II (Ang II) by amino/neutral endopeptidases in rat anococcygeus smooth muscle (ASM) relaxation. Ang II (0.3 nM to 10 microM) produced contractions (E(max) = 21.50 +/- 5.73%) followed by passive relaxations (E(max) reduced to 9.08 +/- 2.55%). Contractions were inhibited (E(max) = 13.67 +/- 2.03%) by losartan (0.1 microM; AT(1) antagonist) but not by PD123,319 [S-(+)-1-([4-(dimethylamino)-3-methylphenyl]methyl)-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo(4,5-c)pyridine-6-carboxylic acid] (0.1 microM; AT(2) antagonist). Conversely, the passive relaxation was inhibited (E(max) = 18.00 +/- 3.45%) by PD123,319 but not by losartan. Ang II (0.3 microM to 100 microM) produced initial contractions (E(max) = 11.49 +/- 9.39%) followed by active relaxations [I(max) (maximum inhibition elicited by the agonist) = 47.85 +/- 4.23%] on strips precontracted by bethanechol (100 microM). A second administration of Ang II on the background of bethanechol (1 h later) resulted in stronger relaxations (I(max) = 64.03 +/- 5.47%) without the initial contractions. N(G)-Nitro-l-arginine methyl ester [nitric-oxide synthase (NOS) inhibitor], ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; guanylate cyclase inhibitor), PD123,319, and tetrodotoxin (neurotoxin) inhibited the relaxations. The presence of AT(1) and AT(2) receptors was confirmed by Western blot. Experiments with amastatin (1 microM) and thiorphan (1 microM), aminopeptidase, and neutral endopeptidase inhibitors, respectively, excluded the involvement of enzymatic degradation in Ang II-induced relaxation of ASM. In conclusion, the rat ASM relaxation by Ang II is the result of active and passive relaxations. The passive relaxation depends on desensitization of excitatory AT(1) receptors, and the active relaxation is mediated by stimulation of AT(2) receptors and activation of the neuronal NOS/soluble guanylate cyclase pathway.
authors.affiliation: Department of Medicine, Division of Gastroenterology & Hepatology, Jefferson Medical College, Thomas Jefferson University, 1025 Walnut Street, Room # 901 College, Philadelphia, PA 19107, USA.
authors.forename: Márcio A F
authors.initials: MA
authors.lastname: de Godoy
authors.forename: Ana Maria
authors.initials: AM
authors.lastname: de Oliveira
authors.forename: Satish
authors.initials: S
authors.lastname: Rattan
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000804:Angiotensin II / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D018826:CD13 Antigens; D004347:Drug Interactions; D043384:Glutamyl Aminopeptidase / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology; D019808:Losartan / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044140:Receptor, Angiotensin, Type 1 / Q000187:drug effects / Q000378:metabolism*; D044139:Receptor, Angiotensin, Type 2 / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D015244:Thiorphan / Q000494:pharmacology
chemical_list: C092006:7-Ala-angiotensin (1-7); D007093:Imidazoles; D010446:Peptide Fragments; D010455:Peptides; D011725:Pyridines; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D000804:Angiotensin II; C073402:PD 123319; C017759:9-(tetrahydro-2-furyl)-adenine; D013779:Tetrodotoxin; C016977:amastatin; D015244:Thiorphan; D019001:Nitric Oxide Synthase; D018826:CD13 Antigens; D043384:Glutamyl Aminopeptidase; D000225:Adenine; D019808:Losartan; D019331:NG-Nitroarginine Methyl Ester