The quantification of adrenergic receptor (AR) mRNAs is an important tool in the study of the physiological and pathophysiological regulation of these receptors. Alterations of the levels of these mRNA represent one of the many mechanisms that regulate receptor signaling (1,2). Such alterations can be triggered by stimulation of the receptors themselves, but also by a variety of other causes. In patients, reductions of receptor mRNA levels have been observed in response to treatment with receptor agonists; in pathophysiological states, the best-known example is the downregulation of cardiac β₁-ARs in heart failure. On the other hand, upregulation of receptor mRNAs has been observed in response to stimuli, such as corticosteroids and thyroid hormones.