Abstract

The SS-enantiomer 3-(2-ethylphenoxy)-1-[(1S)-1,2,3,4-tetrahy dronaphth-1-ylaminol]-(2S)-2-propanol oxalate (SR 59230A) is proposed to be the first beta 3-adrenergic receptor antagonist. The present work shows that SR 59230A, unlike its inactive RR-enantiomer (SR 59483), antagonized a typical beta 3-adrenergic response in vitro, i.e., SR 58611A, the ethyl-[(7s)-7-[[(2R)-2-(3- chlorophenyl)-2-hydroxethyl]amino]-5,6,7,8-tetrahydronaphth- 2- yl]oxyacetate hydrochloride- or (-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one (CGP 12177)-stimulated synthesis of cAMP in rat brown adipose tissue membranes, with pKB values of 8.87 +/- 0.12 and 8.20 +/- 0.15. In addition, SR 59230A had no antagonistic effect on forskolin-induced cAMP accumulation in rat interscapular brown adipose tissue. SR 59230A, in contrast to the selective beta 1- and beta 2-adrenoceptor antagonists (+/-)[2-(3-carbamoyl-4-hydroxyphenoxy)-ethylamino]- 3-[4(1-methyl-4-trifluoromethyl-2-imidazolyl)-phenoxy]-2 propanol and erythro-(+/-)-1-(7-methylindan-4-yloxy)-3-isopropylaminob utan- 2-ol-hydrochloride did not counteract the cAMP production induced by (-)-isoprenaline or norepinephrine (NE) in rat brain areas rich in beta 1- or beta 2-adrenoceptors, such as frontal cortex and cerebellum. Moreover, in proliferating brown fat cells, in which the beta 1-adrenoceptor is the only beta-adrenergic subtype coupled to cAMP production, SR 59230A did not modify the production of cAMP induced by NE, whereas CGP 12177 did. In confluent brown fat cells, in which the beta 3-adrenoceptor is the functional beta-adrenergic subtype coupled to adenylyl cyclase, SR 59230A antagonized the NE-induced cAMP accumulation and glycerol release without affecting their basal values, whereas CGP 12177, which per se stimulated cAMP accumulation and glycerol release, did not change the NE-induced increase of either parameter. Finally, SR 59230A concentration-dependently counteracted the NE-stimulated synthesis of uncoupling protein gene in confluent brown fat cells, which is considered mainly a result of selective stimulation of beta 3-adrenoceptors. These results provide evidence that the new selective beta 3-adrenoceptor antagonist can contribute considerably to functional characterization of the beta 3-adrenoceptors.