beta(1)- and beta(3)-adrenoceptors mediate relaxation in ovine trachealis smooth up muscle

1 Isoprenaline (non-selective) and noradrenaline (beta(1)-selective) concen tration-dependently relaxed ovine tracheal strips precontracted with carbac hol. The pD(2) values were 7.07 +/- 0.08 and 6.13 +/- 0.10 for isoprenaline and noradrenaline, respectively. In the same preparation, salbutamol eithe r produced weak relaxation or in some cases, contractile responses indicati ng the presence of very little or no beta(2)-adrenoceptors in this preparat ion. 2 Isoprenaline-and noradrenaline-induced relaxations were antagonized by pr opranolol and atenolol with pA(2) values in the range reported in the liter ature for an action on beta(1)-adrenoceptors. ICI 118551 also antagonized i soprenaline- and noradrenaline-induced relaxation but at concentrations muc h higher than are required to block beta(2)-adrenoceptors, confirming that beta(2)-adrenoceptors do not contribute significantly to these responses. 3 The selective beta(3)-adrenoceptor agonist, BRL 37344A produced concentra tion-dependent relaxation of tracheal strips. BRL 37344A was a full agonist producing 100% relaxation of carbachol-induced tone. BRL 37344A-induced re laxation was weakly antagonized by propranolol confirming an action, mainly , on beta(3)-adrenoceptors. Cyanopindolol antagonized isoprenaline-induced relaxation (in the presence of propranolol, 10(-7) M) with a pA(2)-value of 8.06 +/- 0.24. 4 It was therefore concluded that beta(1)- and beta(3)-adrenoceptors mediat ed agonist-induced relaxation in sheep tracheal strips.