Effects of Lipolytic and Antilipolytic Drugs on Metabolism of Adenosine 3′: 5′‐Monophosphate in Brown Adipose Tissue of Cold Acclimated Rats

The intracellular level of adenosine 3′:5′‐monophosphate (cyclic AMP) and its stimulation in vitro by norepinephrine were studied in brown and white adipocytes from rats adapted to constant or fluctuating cold. Cold acclimatization had no effect on the basal cyclic AMP intracellular content in both tissues, but the level in brown adipocytes was four‐fold higher than in the white ones. Addition of norepinephrine in the incubation medium doubled the cyclic AMP content of white adipocytes from control or fluctuating‐cold‐adapted rats, and enhanced four‐fold in constant‐cold‐adapted rats. In brown adipocytes norepinephrine increased cyclic AMP levels in the first two groups, but had no effects in constant‐cold‐adapted rats. In the two tissues of control and fluctuating‐cold‐adapted rats the norepinephrine action was increased by phentolamine and decreased by propranolol. The lack of response to norepinephrine of brown adipocytes from constant cold‐adapted rats was not due to the predominance of the α component of hormone receptors. Antilipolytic drugs (nicotinic acid, insulin and prostaglandin E 2 ) inhibited the action of norepinephrine on white adipocytes; only prostaglandin E 2 had an effect on brown ones.