Hormone-sensitive Lipase and Monoglyceride Lipase Activities in Adipose Tissue

Abstract

Several workers (l-3) have reported that lipase activity assayed in homogenates of adipose tissue is increased by exposure of the tissue to epinephrine or to adrenocorticotropic hormone prior to homogenization. In general, the magnitude of the increases observed has been small compared to the large effects of these hormones on glycerol format,ion by the intact tissae. In studies of whole homogenates or complex fractions thereof, the possibility that several lipase activities are being simultaneously assayed cannot be ruled out. I f only one of these activities were responsive t,o hormonal stimulat,ion, the effects of a hormone on lipase activity as assayed would appear relatively small. The studies reported below were undertaken in an at,tempt to characterize and to study the hormone-sensitive lipase activity in adipose tissue without interference from other lipases. l3y devising suitable assay conditions, me have been able to measure a lipase activity that apparently reflects rather well the hormone-sensitive lipolytic activity of the intact tissue. In addition, we have investigated a lipase activity present in adipose tissue of both rats and rabbits which exhibits a marked specificity for hydrolysis of monoglycerides. Evidence indicating that this activity is distinct from the hormone-sensitive lipase activit’y and probably also from lipoprotein lipase is presented. Preliminary reports of this work have appeared (4-6).