BETA-3 ADRENOCEPTOR SELECTIVITY OF THE DIOXOLANE DICARBOXYLATE PHENETHANOLAMINES

The beta-1, beta-2 and beta-3 adrenergic properties of several benzodi oxole-containing phenethanolamines were determined in vitro in both fu nctional and binding assays. In addition, two of the compounds were ev aluated for their effects on radioligand binding and cyclic AMP (cAMP) production in stably transfected Chinese Hamster Ovary (CHO) cells ex pressing the cloned rat or human beta-3 adrenoceptor or the human beta -2 or beta-1 adrenoceptor. The (+/-)-R,R*-racemate, CL 314,514, and t he pure (-)-R,R enantiomer, CL 316,243, stimulated rat adipocyte lipol ysis (beta-3 effect) with EC(50) values in the low nanomolar range, wh ile having no effect on the rate of contraction of guinea pig atria (b eta-1 effect) and little or no ability to prevent the insulin-stimulat ed incorporation of [C-14]glucose into rat soleus muscle glycogen (bet a-2 effect) with concentrations as great as 100 mu M. The lack of beta -1 and beta-2 adrenergic activity was confirmed by the low affinity of the compounds for beta-1 or beta-2 adrenoceptors in plasma membranes from rat heart or rat soleus muscle, respectively. In CHO cells expres sing each human beta adrenoceptor subtype, CL 314,514 bound to beta-3- CHO cells with a K-i of 2 mu M and stimulated cAMP production with an activation constant (K-act) of 1 mu M, whereas it did not bind to eith er beta-1- or beta-2-CHO cells at 100 mu M. CL 316,243 bound to membra nes from rat beta-3-CHO cells with a K-i of 1 mu M and stimulated cAMP production in beta-3-CHO cells with a K-act of 0.7 nM. These results indicate that CL 314,514 and CL 316,243 are highly selective agonists for the beta-3 adrenoceptor and as such may be useful for the treatmen t of diabetes and obesity.