title: Mechanism of halothane-induced inhibition of isoproterenol-stimulated lipolysis in isolated rat adipocytes.
abstract: The effect of halothane on isoproterenol-stimulated lipolysis was determined in isolated rat epididymal fat cells. The maximal lipolytic response (Emax) activated by isoproterenol was 350 +/- 61 nmol of glycerol/10(5) cells/hr with an EC50 of 5.1 X 10(-9) M. When the adipocytes were simultaneously bubbled with 2.5% halothane, the Emax decreased to 158 +/- 43 nmol of glycerol/10(5) cells/hr and the dose response curve for isoproterenol was shifted to the right (EC50 3.5 X 10(-8) M, p less than 0.05). When lipolysis was maximally stimulated with (-)-isoproterenol (10(-6)M), the inhibitory effect of halothane was found to be both dose dependent (IC50 approximately 2.5%, v/v) and reversible following washout. Neither the nonhydrolyzable cAMP analog, 8-(4-chlorophenylthio) adenosine 3',5'-cyclic monophosphate (2 X 10(-3)M), nor forskolin (10(-6) M) was able to normalize lipolysis in the presence of halothane. The activation of cAMP-dependent protein kinase (EC 2.7.1.37) activity by isoproterenol was not different in halothane-exposed cells when compared to unexposed cells. When control adipocytes were exposed to isoproterenol (10(-6) M), there was a 2.5-fold increase in the activity of hormone-sensitive lipase (EC 3.1.1.3) from 0.64 +/- 0.13 to 1.53 +/- 0.32 pkat (pmol/sec) per mg (p less than 0.005, n = 10). However, in the presence of halothane (2.5%, v/v) isoproterenol stimulation of hormone-sensitive lipase was attenuated by 50% to values of 1.06 +/- 0.23 pkat/mg (p less than 0.01, n = 10). Halothane had no direct inhibitory effect on hormone-sensitive lipase since this enzyme's activity was unaffected when homogenates of isoproterenol-stimulated control cells were incubated with halothane. These studies suggest that halothane impairs the activation of hormone-sensitive lipase by cAMP-dependent protein kinase and in this manner inhibits beta-adrenergic-stimulated lipolysis.
authors.affiliation: Department of Anesthesia, Stanford University School of Medicine, California 94305.
authors.forename: P G
authors.initials: PG
authors.lastname: Prokocimer
authors.forename: M
authors.initials: M
authors.lastname: Maze
authors.forename: R G
authors.initials: RG
authors.lastname: Vickery
authors.forename: F B
authors.initials: FB
authors.lastname: Kraemer
authors.forename: R
authors.initials: R
authors.lastname: Gandjei
authors.forename: B B
authors.initials: BB
authors.lastname: Hoffman
mesh_terms: D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006221:Halothane / Q000494:pharmacology*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D008049:Lipase / Q000032:analysis; D008066:Lipolysis / Q000187:drug effects*; D008297:Male; D011494:Protein Kinases / Q000032:analysis; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D011494:Protein Kinases; D008049:Lipase; D007545:Isoproterenol; D002118:Calcium; D006221:Halothane