Adenosine 3',5'-cyclic phosphate, lipolysis and oxygen consumption in brown adipose tissue from newborn rabbits. Effect of cervical sympathectomy and of noradrenalin and theophylline in vitro, and the partial purification of an adenosine 3',5'-cyclic phosphate-dependent protein kinase.

Abstract

The rates of lipolysis and O 2 consumption and the concentration of cyclic AMP were measured in lipid-replete and lipid-depleted brown fat and isolate cells. A cyclic AMP-dependent protein kinase, with properties similar to those of other tissues, was partially purified. Noradrenalin caused an increase in the concentration of cyclic AMP which occurred before the fall in the concentration of ATP and was within the range that affected the activity of protein kinase. Theophylline potentiated the effect of noradrenalin upon lipolysis, the concentration of cyclic AMP and the rate of O 2 consumption in brown fat. Insulin and propranolol lowered the concentration of cyclic AMP in the presence of noradrenalin. There was a significant correlation between the concentration of cyclic AMP and submaximal lipolysis. Interruption of the cervical sympathetic nerve to brown fat prevented the increase in the concentration of cyclic AMP in the tissue when the animals were exposed to cold. Depletion of lipid from the tissue did not impair its ability to increase the concentration of cyclic AMP. It is concluded that cyclic AMP can mediate the effect of noradrenalin upon lipolysis in brown fat. The possibility that cyclic AMP also mediates at least some aspects of the stimulation of the heat production of the tissue is discussed.