Stimulation of Respiration in Brown Fat Cells by Epinephrine, Dibutyryl-3′,5′-adenosine Monophosphate, and m-Chloro(carbonyl Cyanide)phenylhydrazone

The addition of epinephrine to free brown fat cells obtained by collagenase digestion of rat dorsal interscapular brown adipose tissue concurrently stimulated fatty acid release and respiration after a lag period of about 20 sec. All the effects of epinephrine were mimicked by dibutyryl-3′,5′-AMP. m-Chloro(carbonyl cyanide)phenylhydrazone, a potent uncoupler of oxidative phosphorylation, stimulated respiration within 5 sec after its addition to fat cells. Epinephrine, theophylline, and dibutyryl-3′,5′-AMP also accelerated respiration in brown fat cells, and addition of m-chloro(carbonyl cyanide)phenylhydrazone with these lipolytic agents did not affect their action on lipolysis or respiration. However, if m-chloro(carbonyl cyanide)phenylhydrazone was added prior to the lipolytic agents, it blocked the stimulation of lipolysis and respiration by theophylline, catecholamine, or dibutyryl-3′,5′-AMP. The lipolytic action of these agents was also inhibited by cyanide. The addition of free fatty acid to the medium did not mimic the stimulation of respiration by catecholamines, despite the fact that at high concentrations of fatty acid the lipolytic action of epinephrine was abolished. All of these results suggest that respiration is coupled to phosphorylation under basal conditions in brown fat cells but that epinephrine stimulates the formation of cyclic AMP which mediates either a direct uncoupling action or an indirect one through stimulation of free fatty acid release.