Differential regulation of the expression of α1-adrenergic receptor subtype genes in brown adipose tissue

The physiological control of the expression of the genes for the α1-adrenoceptor subtypes was examined in rat brown adipose tissue by analysing Northern blots of poly(A)-enriched RNA with oligonucleotide probes. In control rats, α1B-receptor gene expression was much lower in brown adipose tissue than in liver, but the expression of both α1A and α1D was higher than in the heart, making brown adipose tissue one of the mammalian tissues with the highest expression of these subtypes. During acute exposure to cold, α1B-receptor gene expression was essentially unchanged, α1A-receptor gene expression was increased and α1D-receptor gene expression was transiently decreased. Noradrenaline injection could mimic these effects of acute cold exposure, indicating that the physiologically induced up- and down-regulations were due to the interaction of noradrenaline with cells within the tissue. In chronically cold-acclimated animals, α1B-receptor gene expression was decreased but that of the α1A-receptor gene remained at a level twice that of controls. α1D-Receptor gene expression was also somewhat decreased. It is suggested that the enhanced expression of the α1A-receptor gene explains the increased α1-receptor density in recruited brown adipose tissue reported previously. The intricate and differential regulation of α1-receptor gene expression and the markedly enhanced expression of the α1A-receptor may imply that α1-receptors are important for the recruitment process or for maintenance of the recruited state in this tissue.