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

Abstract

The intracellular level of 3'':5''-AMP (cyclic AMP) and its stimulation in vitro by norepinephrine [NE] 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 4-fold higher than in the white ones. Addition of NE in the incubation medium doubled the cyclic AMP content of white adipocytes from control or fluctuating-cold-adapted rats, and enhanced 4-fold in constant-cold-adapted rats. In brown adipocytes NE increased cyclic AMP levels in the 1st 2 groups, but had no effects in constant-cold-adapted rats. In the 2 tissues of control and fluctuating-cold-adapted rats the NE action was increased by phentolamine and decreased by propranolol. The lack of response to NE of brown adipocytes from constant cold-adapted rats was not due to the predominance of the .alpha. component of hormone receptors. Antilipolytic drugs (nicotinic acid, insulin and prostaglandin E2 [PGE2]) inhibited the action of NE on white adipocytes; only PGE2 had an effect on brown ones.