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 the development of bovine perirenal brown adipose tissue (BAT) in utero and its transformation into white-like adipose tissue after birth were studied. The parameters assessed were the level of expression of beta(1)-, beta(2)- and beta(3)-adrenergic receptor (AR) mRNAs and the response of the plasma-membrane adenylate cyclase to (-)-isoprenaline and to the beta(3)-agonist BRL, 37344. The beta(3)-AR mRNA was found to be expressed very early in utero, i.e. before the third month of foetal life. Then it increased dramatically (9-fold) between month 6 of foetal life and birth. A high beta(3)-AR mRNA level was maintained after birth 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 expression 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 predominant. A response of the adenylate cyclase to (-)-isoprenaline was observed in foetal life (3.1-fold stimulation). It decreased after birth (1.8-fold stimulation) and then remained constant until adulthood. A response to BRL 37344 was also observed in foetal life (1.8-fold stimulation). It was maintained after birth, but disappeared in the adult. A possible relationship between the beta-AR expression and the adenylate cyclase response to (-)-isoprenaline on the one hand and the uncoupling-protein expression on the other is discussed. The bovine might represent a good model to understand the transition from brown to white fat in the human.