Beta1- and beta3-adrenoceptors mediate relaxation in ovine trachealis smooth muscle.
Isoprenaline (non-selective) and noradrenaline (beta1-selective) concentration-dependently relaxed ovine tracheal strips precontracted with carbachol. The pD2 values were 7.07 +/- 0.08 and 6.13 +/- 0.10 for isoprenaline and noradrenaline, respectively. In the same preparation, salbutamol either produced weak relaxation or in some cases, contractile responses indicating the presence of very little or no beta2-adrenoceptors in this preparation. Isoprenaline-and noradrenaline-induced relaxations were antagonized by propranolol and atenolol with pA2 values in the range reported in the literature for an action on beta1-adrenoceptors. ICI 118551 also antagonized isoprenaline- and noradrenaline-induced relaxation but at concentrations much higher than are required to block beta2-adrenoceptors, confirming that beta2-adrenoceptors do not contribute significantly to these responses. The selective beta3-adrenoceptor agonist, BRL 37344A produced concentration-dependent relaxation of tracheal strips. BRL 37344A was a full agonist producing 100% relaxation of carbachol-induced tone. BRL 37344A-induced relaxation was weakly antagonized by propranolol confirming an action, mainly, on beta3-adrenoceptors. Cyanopindolol antagonized isoprenaline-induced relaxation (in the presence of propranolol, 10(-7) M) with a pA2 value of 8.06 +/- 0.24. It was therefore concluded that beta1- and beta3-adrenoceptors mediated agonist-induced relaxation in sheep tracheal strips.
Mustafa
S M
SM
Department of Pharmacology and Toxicology, Faculty of Medicine, Safat, Kuwait.
Yousif
M
M
Cherian
A
A
Oriowo
M A
MA
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001262:Atenolol / Q000494:pharmacology; D004983:Ethanolamines / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D010869:Pindolol / Q000031:analogs & derivatives / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*; D018342:Receptors, Adrenergic, beta-1 / Q000187:drug effects / Q000502:physiology*; D022702:Receptors, Adrenergic, beta-3; D012756:Sheep; D014132:Trachea / Q000187:drug effects*
D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D004983:Ethanolamines; D011412:Propanolamines; D011943:Receptors, Adrenergic, beta; D018342:Receptors, Adrenergic, beta-1; D022702:Receptors, Adrenergic, beta-3; C026777:ICI 118551; C047975:cyanopindolol; D001262:Atenolol; C057368:BRL 37344; D011433:Propranolol; D010869:Pindolol