Beta(3)-adrenoceptors mediate smooth muscle relaxation in the rat lower oesophageal sphincter.
1. The role of beta(3)-adrenoceptors in isoprenaline-induced relaxation of carbachol-precontracted ring segments of the rat lower oesophageal sphincter (LOS) was examined. 2. Isoprenaline (10(-8)M-10(-5)M) relaxed ring segments of the LOS in a concentration-dependent manner. Propranolol (10(-7)M) had very little antagonist effect on isoprenaline-induced relaxation. 3. Dobutamine (10(-7)M-10(-4)M), salbutamol (10(-7)-10(-4)M) and BRL 37344 (10(-8)-10(-5)M) also relaxed carbachol-contracted ring segments of the LOS in a concentration-dependent manner. The relaxant responses to these agonists were similarly not antagonized by propranolol (10(-7)M). 4. Cyanopindolol (10(-6)M), produced a parallel rightward displacement of isoprenaline, dobutamine, salbutamol and BRL 37344 concentration-response curves with similar potencies. The pKB values range from 7.3 +/- 0.1 to 7.7 +/- 0.2. 5. The relaxant effect of isoprenaline in the rat LOS was not inhibited by NG-nitro-L-arginine (L-NOARG; 3 x 10(-5)M), glibenclamide (10(-5)M) or tetraethylammonium (1 mM). 6. It was concluded that beta(3)-adrenoceptors mediate isoprenaline-induced relaxation in rat lower oesophageal sphincter and that activation of these receptors was not linked to either ATPase-, Ca(2+)-dependent K+ channels or to NO release.
Oriowo
M A
MA
Department of Pharmacology & Toxicology, Faculty of Medicine, Kuwait University, Safat, Kuwait.
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D004943:Esophagogastric Junction / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D004983:Ethanolamines / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D019335:Nitroarginine / Q000494:pharmacology; D026902:Potassium Channel Blockers; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*; D022702:Receptors, Adrenergic, beta-3
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D004983:Ethanolamines; D026902:Potassium Channel Blockers; D011943:Receptors, Adrenergic, beta; D022702:Receptors, Adrenergic, beta-3; D019335:Nitroarginine; C057368:BRL 37344; D002217:Carbachol; D011433:Propranolol; D007545:Isoproterenol