Hormonal control of porcine adipose tissue fatty acid release and cyclic AMP concentration

Compared with adipose tissue from other mammals, porcine adipose tissue has stringent specificity for stimulation of lipolysis by analogs of norepinephrine. This study was to ascertain whether the specificity for control was reflected in the concentration of tissue cyclic AMP (cAMP). Adipose tissue slices were incubated and concentrations of tissue cAMP and free fatty acids (FA) released to the medium were measured. It was necessary to include theophylline in the incubation medium to be able to measure changes in cAMP concentration. Fatty acid release and cAMP production were increased most effectively by the beta-adrenergic agonists; isoproterenol, fenoterol, dobutamine and the mixed alpha- + beta-adrenergic agonist, epinephrine. Isoproterenol-stimulated FA and cAMP production both inhibited by the beta-adrenergic antagonist, propranolol. There was no evidence for alpha 2-adrenergic inhibition of lipolysis in porcine adipose tissue because clonidine (alpha 2-adrenergic agonist) did not lower isoproterenol-induced FA or cAMP levels and phentolamine, an alpha-adrenergic antagonist, did not increase epinephrine-stimulated FA release or cAMP generation. These results imply that the stringent specificity observed for stimulation of swine adipose tissue lipolysis resides in the beta-adrenergic receptor coupled to cAMP production.