RESPECTIVE DEGREE OF EXPRESSION OF BETA(1)-ADRENOCEPTOR, BETA(2)-ADRENOCEPTOR AND BETA(3)-ADRENOCEPTOR IN HUMAN BROWN AND WHITE ADIPOSE TISSUES

1 The possible existence of a beta(3)-adrenoceptor in human brown and white adipose tissues was investigated by mRNA expression and binding studies. 2 The relative amounts of beta(1)-, beta(2)- and beta(3)-adre noceptor mRNA, as determined by total RNA Northern blot analysis in ne wborn brown adipose tissue, were 28, 63 and 9% respectively of the tot al beta-adrenoceptor mRNA. 3 The beta(1)/beta(2)-adrenoceptors of huma n brown adipose tissue plasma membranes were characterized using [H-3] -CGP 12177 as a ligand. Their K-d and B-max values were 1.9 nM and 156 fmol mg(-1) of membrane proteins, respectively. The beta(3)-adrenocep tor was characterized by use of the new specific radioligand [H-3]-SB 206606. The binding of this ligand was stereospecifically displaced by the active R,R- or the inactive S,S-enantiomer of BRL 37344 up to a c oncentration of about 10 mu M. The K-d and B-max values of the brown a dipose tissue membrane beta(3)-adrenoceptors were 87 nM and 167 fmol m g(-1) of proteins, respectively. A low affinity [H-3]-CGP 12177 bindin g site population was also detected in these membranes. 4 In human ome ntal white adipose tissue, no beta(3)-adrenoceptor mRNA could be detec ted in total RNA Northern blots and the beta(1)- and beta(2)-adrenocep tor mRNAs represented 9 and 91%, respectively of the total beta-adreno ceptor mRNA, and no specific binding of [H-3]-SB 206606 could be measu red.