title: beta-Adrenergic desensitization by chronic insulin exposure in 3T3-L1 cultured adipocytes.
abstract: Cultured 3T3-L1 cells provide a model system for studies of the long-term regulation of lipolysis. Insulin acutely inhibits isoproterenol-stimulated lipolysis primarily by decreasing the apparent affinity apparent Km for isoproterenol. In contrast, chronic insulin exposure inhibits lipolysis by a reduction in the maximal effect of isoproterenol Vmax. The decrease in Vmax can be observed with insulin concentrations that are as low as 10(-9) mol/L at the time of addition. The effect is stable to washing, and the cells' responsiveness to isoproterenol returns partially with continued culture. Chronic insulin exposure also markedly reduced dibutyryl-cAMP-stimulated lipolysis indicating an insulin-induced change distal to cAMP concentration in the cascade of reactions controlling lipolysis in these cells. Time course and insulin dose-response experiments indicate an additional proximal alteration. These results indicate that: (1) 3T3-L1 cells are a useful model for studying the long-term regulation of lipolysis. (2) Chronic insulin exposure inhibits lipolysis by a mechanism that differs from the acute effect of insulin. (3) The chronic effects of insulin may be mediated through changes at multiple levels in the lipolytic cascade.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000273:Adipose Tissue / Q000166:cytology* / Q000187:drug effects; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007328:Insulin / Q000494:pharmacology* / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology; D008066:Lipolysis / Q000187:drug effects*; D051379:Mice; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000502:physiology
chemical_list: D007328:Insulin; D011943:Receptors, Adrenergic, beta; D003994:Bucladesine; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D007545:Isoproterenol