CARTEOLOL IS A WEAK PARTIAL AGONIST ON BETA(3)-ADRENERGIC RECEPTORS IN BROWN ADIPOCYTES

The ability of the beta(1)/beta(2) partial agonist carteolol to act as an agonist on beta(3)-adrenergic receptors was investigated by studyi ng its ability to stimulate thermogenesis (oxygen consumption) in brow n fat cells isolated from hamsters. Carteolol was able to induce therm ogenesis, with an EC50 of 5 mu M, but it was only a partial (40%) agon ist. D,L-Propranolol had a pK(B) of 5.1 as an antagonist against carte olol in this system, indicating that the carteolol effect was probably mediated via beta(3)-receptors. Also in mouse and rat cells, carteolo l was a partial agonist with EC50 values around 1 mu M. Being a partia l agonist, carteolol acted as an antagonist against norepinephrine-, B RL-37344-, or CGP-12177-stimulate thermogenesis with a pK(B) of approx imate to 5. The partial agonist effects of carteolol are discussed in relation to the absence of agonist effect of this compound on guinea-p ig taenia cecum a-receptors and in relation to the possible plurality of beta(3)-receptors.