title: Comparative effects of insulin and isoproterenol on lipoprotein lipase in rat adipose cells.
abstract: The effects of insulin and isoproterenol on lipoprotein lipase mass and enzyme activity were investigated in rat adipocytes. Cells were pulse labeled for 1 h with [35S]methionine to measure immunoprecipitable lipoprotein lipase. The results showed that 80% of the newly synthesized enzyme was membrane associated and 20% was secreted into the cell incubation medium. Enzyme activity was mainly associated with lipoprotein lipase secreted into the medium. A 10-min incubation with 10(-7) M insulin stimulated the secretion of lipoprotein lipase activity and the activity associated with adipocyte membranes. Conversely, 10(-6) M isoproterenol decreased the activity in all fractions. In addition, insulin increased lipoprotein lipase mass associated with cell membranes and decreased that in the incubation medium, whereas isoproterenol induced a decrease in both cell membranes and medium. Insulin and isoproterenol stimulated phosphorylation of lipoprotein lipase. These findings suggest that insulin stimulates the secretion of active lipoprotein lipase and a reuptake of inactive secreted enzyme, and isoproterenol decreases the activity by enzyme degradation. Moreover, because both agents stimulate phosphorylation of lipoprotein lipase, phosphorylation may play a role in the effect of insulin increasing enzyme activity, in secretion or reuptake, and in the effect of isoproterenol inducing degradation of lipoprotein lipase.
authors.affiliation: Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, La Plata, Argentina.
authors.forename: G E
authors.initials: GE
authors.lastname: Chiappe de Cingalani
authors.forename: J W
authors.initials: JW
authors.lastname: Goers
authors.forename: M
authors.initials: M
authors.lastname: Giannotti
authors.forename: C I
authors.initials: CI
authors.lastname: Caldiz
mesh_terms: D017667:Adipocytes / Q000187:drug effects* / Q000201:enzymology*; D000818:Animals; D007328:Insulin / Q000494:pharmacology*; D007545:Isoproterenol / Q000494:pharmacology*; D008071:Lipoprotein Lipase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008297:Male; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar
chemical_list: D007328:Insulin; D008071:Lipoprotein Lipase; D007545:Isoproterenol