Functional characterization of beta-adrenoceptors mediating relaxation in sheep gallbladder

The purpose of this study was to characterize beta-adrenoceptor subtype(s)) mediating relaxation in smooth muscle strips of the sheep gallbladder. Exp eriments were performed on isolated smooth muscle strips suspended in tissu e baths containing Krebs' solution. Isoprenaline (10(-8) M-10(-5) M) and sa lbutamol (10(-7) M-10(-4) M) produced concentration-dependent relaxation of carbachol (10(-7) M-3 x 10(-7) M) contracted smooth muscles of the sheep g all bladder. Isoprenaline-induced relaxation was significantly antagonized by propranolol with -logK(B) values of 7.81 +/- 0.11 (n = 7) and 7.73 +/- 0 .12 (n = 6) in the fundic and ductal strips respectively. Atenolol (10(-5) M), a selective beta(1), adrenoceptor antagonist, also significantly antago nized isoprenaline-induced relaxation with -logK(B) values of 5.82 +/- 0.11 and 6.09 +/- 0.09 in the fundic and ductal strips respectively. However, I CI 118551, a selective beta(1)-adrenoceptor antagonist, at concentrations u p to 10(-6) M had little or no effect on isoprenaline-induced relaxation in either of these preparations. BRL 37344A, a selective beta(2)-adrenoceptor agonist produced concentration-dependent relaxation of carbachol-precontra cted fundic and ductal strips. BRL 37344 was approximately 9-fold more pote nt in the ductal than fundic strips. In both preparations, BRL 37344-induce d relaxation was not significantly (p > 0.05) antagonized by propranolol (3 x 10(-7) M). This would confirm that the response was mediated via beta(3) -adrenoceptors. It was concluded that beta(1)- and beta(3)-adrenoceptors co exist in the sheep gallbladder and mediate smooth muscle relaxation. (C) El sevier, Paris.