EXPRESSION OF BETA(1)- AND BETA(3)-ADRENERGIC-RECEPTOR MESSAGES AND ADENYLATE-CYCLASE BETA-ADRENERGIC RESPONSE IN BOVINE PERIRENAL ADIPOSE-TISSUE DURING ITS TRANSFORMATION FROM BROWN INTO WHITE FAT

Possible modifications of the beta-adrenergic effector system during t he development of bovine perirenal brown adipose tissue (BAT) in utero and its transformation into white-like adipose tissue after birth wer e studied. The parameters assessed were the level of expression of bet a(1)-, beta(2)- and beta(3)-adrenergic receptor (AR) mRNAs and the res ponse of the plasma-membrane adenylate cyclase to (-)-isoprenaline and to the beta(3)-agonist BRL, 37344. The beta(3)-AR mRNA was found to b e expressed very early in utero, i.e. before the third month of foetal life. Then it increased dramatically (9-fold) between month 6 of foet al life and birth. A high beta(3)-AR mRNA level was maintained after b irth up to an age of 3 months. After conversion of BAT into white-like adipose tissue, i.e. in the adult bovine, the beta(3)-AR mRNA express ion became small or not detectable, and the beta(1)-AR mRNA, which was expressed much less than the beta(3)-AR mRNA in foetal life, became p redominant. A response of the adenylate cyclase to (-)-isoprenaline wa s observed in foetal life (3.1-fold stimulation). It decreased after b irth (1.8-fold stimulation) and then remained constant until adulthood . A response to BRL 37344 was also observed in foetal life (1.8-fold s timulation). It was maintained after birth, but disappeared in the adu lt. A possible relationship between the beta-AR expression and the ade nylate cyclase response to (-)-isoprenaline on the one hand and the un coupling-protein expression on the other is discussed. The bovine migh t represent a good model to understand the transition from brown to wh ite fat in the human.