Catecholamine stimulation of iodothyronine 5'-deiodinase activity in rat dispersed brown adipocytes.

We describe an in vitro system for evaluating the direct effects of catecholamines on the activity of the type II iodothyronine 5'-deiodinase in dispersed rat brown adipocytes. Incubation with norepinephrine or phenylephrine for 3-4 h causes up to a 5-fold increase in deiodinase activity in these cells. As found in vivo studies, the norepinephrine stimulation is blocked by coincubation with the alpha 1-adrenergic antagonist prazosin. The beta-adrenergic antagonist alprenolol either has no effect or increases stimulation by norepinephrine. These results suggest that beta-adrenergic agonists inhibit the activation or synthesis of the deiodinase in these cells.