Beta-Adrenergic receptor modulation of adipocyte metabolism and growth

β-Adrenergic receptor (βAR) agonists reduce body fat in mammals and birds. Synthetic lipid metabolism is decreased in βAR agonist-treated animals or in agonist-treated adipocytes in vitro. Degradative lipid metabolism is increased by βAR agonists in adipocytes in vitro and in vivo. The βAR agonist effects are blocked by βAR antagonists. In mammalian tissues, there are at least three distinct βAR subtypes; β-1 (β1AR), β-2 (β2AR), and β-3 (β3AR). Individual tissues have different proportions of subtypes. For example, greater than 85% of the βAR in rat heart is β1AR, in guinea pig lung is β2AR, and in rat adipose tissue is β3AR. Subtype distribution within a tissue varies with species (e.g., human heart has 65% β1AR and porcine adipocytes have less than 10% β3AR). There is species variation in the amino acid sequence of a βAR subtype. Thus, it is expected that some βAR agonists would have different effects in the same tissue in different species because of different βAR subtype distribution and(or) amino acid sequence. In support of these concepts, the