RT Journal Article SR Electronic T1 STUDY OF PHOSPHODIESTERASE INHIBITORS ON LIPOLYSIS, PHOSPHODIESTERASE ACTIVITY AND CYCLIC 3', 5'-ADENOSINE MONOPHOSPHATE LEVELS IN ISOLATED FAT CELLS JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 379 OP 385 VO 185 IS 2 A1 DONALD O. ALLEN A1 JULIA F. CLARK A1 JAMES ASHMORE YR 1973 UL http://jpet.aspetjournals.org/content/185/2/379.abstract AB Papaverine, 1-ethyl-4-(isopropylidenehydrazine)-1H-pyrazole-(3,4-b)-pyridine-5-carboxylic acid, ethylester-HCl (SQ 20,009) and theophylline were compared as phosphodiesterase inhibitors at two different substrate concentrations of cyclic 3' , 5'-adenosine monophosphate (cyclic AMP). At both concentrations of cyclic AMP, papaverine and SQ 20,009 were found to be more potent than theophylline. However, only theophylline was capable of stimulating lipolysis in the isolated fat cell preparation. All three compounds augmented the lipolytic response to both epinephrine and corticotropin. Theophylline alone was able to cause a small but significant increase in the intracellular levels of cyclic AMP in isolated fat cells whereas papaverine and SQ 20,009 were without effect. In addition, theophylline greatly augmented the ability of epinephrine to elevate cyclic AMP levels in fat cells whereas the other two compounds produced no change. Theophylline produced no stimulation in adipose tissue glycogen phosphorylase activity. In fact, high concentrations of this methylxanthine were inhibitory. These results demonstrate a lack of correlation between phosphodiesterase inhibition and stimulation of lipolysis or increases in tissue levels of cyclic AMP. It is concluded that great care should be taken in assuming that the effects of theophylline on adipose tissue metabolism are secondary to inhibition of cyclic nucleotide phosphodiesterase. © 1973 by The Williams & Wilkins Co.