Control of fat cell phosphatidate phosphohydrolase by lipolytic agents

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Abstract
The Mg2+-dependent phosphatidate phosphohydrolase activity increased in the microsomal and decreased in the soluble fraction of isolated rat fat cells, which were incubated for short periods with the lipolytic hormones or agents, epinephrine, cAMP, theophylline and dibutyryl cAMP. ACTH increased the microsomal and soluble activity. The increases in microsomal activity ranged from 30-134% with epinephrine to .apprx. 200% with dibutyryl cAMP. The decreases in soluble activity were more modest. The effect of epinephrine was inhibited by the .beta.-adrenergic antagonist propranolol, while the .alpha.-antagonist phentolamine enhanced it. Apparently, the fat cell phosphatidate phosphohydrolase is controlled through the .beta.-adrenergic receptor and the activity of adenylate cyclase. Lipolysis, as measured by fatty acid release, was stimulated in a similar pattern as the microsomal activity, suggesting parallel activation of the hormone sensitive lipase and phosphatidate phosphohydrolase. Activation of this lipogenic enzyme by lipolytic stimuli may represent a mechanism in which fatty acid release from adipose tissue may be modulated, and intracellular fatty acid accumulation may be counteracted during accelerated lipolysis in adipose tissue.