Relationship between hormone-sensitive lipolysis and lipase activity in rat fat cells

An assay for total hormone-sensitive lipase (HSL) in rat fat cells was devised in which fat-associated HSL was solubilized with ether, and triolein or cholesteryloleate was used as substrate. Norepinephrine (NE) caused marked release of glycerol from fat cells but did not activate HSL as estimated using triolein or cholesteryloleate as substrate. Propranolol, a beta-blocker, inhibited NE-induced lipolysis in fat cells without a concomitant reduction in HSL activity. The antilipolytic action of insulin on NE-induced lipolysis could not be explained by a decrease in HSL activity. Neither ACTH-induced lipolysis in fat cells nor its inhibition by insulin was accompanied by matching fluctuations in HSL activity. These results indicate that neither NE and ACTH-induced lipolysis in fat cells, nor the antilipolytic actions of propranolol and insulin, involve fluctuations in HSL activity.