Catecholamines lipolytic action

These drugs selectively reduce cardiostimulatory, vasodilating, broncholytic, and metabolic (glycogenolytic and lipolytic) action of catecholamines released from adrenergic nerve endings and adrenal glands. 

Growth hormone increases the sensitivity of the adipocyte to the lipolytic action of the catecholamines and decreases its sensitivity to the lipogenic action of insulin. These actions lead to the release of free fatty acids and glycerol into the blood to be metabolized by the liver. GH also decreases esterification of fatty acids, thereby reducing triacylglycerol synthesis within the fat cell. Recent evidence suggests that GH may impair glucose uptake by both fat and muscle cells by a postreceptor inhibition of insulin action. 

The adipose tissues of pig and guinea pig do not respond to the lipolytic action of the catecholamines and, in this respect, are comparable to those of duck and rabbit. Hamster adipose tissue is responsive to the lipolytic action of the catecholamines, but not to that of glucagon. In this respect the hamster pattern of response compares with that of the dog observed in our experiments, and with the pattern of human adipose tissue described by Rudman and Di Girolamo. ... 

THE LIPOLYTIC ACTION OF CATECHOLAMINES AND ACTH AND THE INTERACTION OF PROSTAGLANDIN E ... 

Fig. 4. Action of thyroid hormones on cyclic AMP production and degradation in the adipocyte. The response of the adipocyte to different lipolytic hormones (/3 catecholamines, ACTH and glucagon) is under thyroid hormone control both at the level of the receptor-adenylate cyclase complex and at the level of the phosphodiesterase. T, also regulates the expression of several key lipogenic enzymes.

AMP levels. In this tissue it has also been possible to show that the lipolytic effects of the catecholamines can be mimicked by the direct application of cyclic AMP or its dibutyryl derivative which penetrates into the tissue more readily. The actions of cyclic AMP appear to be due to a direct activation of the enzyme triglyceride lipase, which controls the rate-limiting step in fat break-down. Here again the evidence is strongly in favour of the view that the -actions of the catecholamines are mediated through a stimulation of adenyl-cyclase activity. 

---