Respective degree of expression of beta(1)-, beta(2)- and beta(3)-adrenoceptors 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)-adrenoceptor mRNA, as determined by total RNA Northern blot analysis in newborn brown adipose tissue, were 28, 63 and 9% respectively of the total beta-adrenoceptor mRNA. 3 The beta(1)/beta(2)-adrenoceptors of human 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)-adrenoceptor 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 concentration of about 10 mu M. The K-d and B-max values of the brown adipose tissue membrane beta(3)-adrenoceptors were 87 nM and 167 fmol mg(-1) of proteins, respectively. A low affinity [H-3]-CGP 12177 binding site population was also detected in these membranes. 4 In human omental white adipose tissue, no beta(3)-adrenoceptor mRNA could be detected in total RNA Northern blots and the beta(1)- and beta(2)-adrenoceptor mRNAs represented 9 and 91%, respectively of the total beta-adrenoceptor mRNA, and no specific binding of [H-3]-SB 206606 could be measured.