Distinct long-term regulation of glycerol and non-esterified fatty acid release by insulin and TNF-alpha in 3T3-L1 adipocytes.
OBJECTIVE
Adipose tissue lipolysis plays a central part in total body fuel metabolism. Our study was to assess the long-term regulation of glycerol and non-esterified fatty acid (NEFA) release by insulin or TNF-alpha.


METHODS
Fully differentiated 3T3-L1 adipocytes were exposed for up to 22 h to insulin or TNF-alpha.


RESULTS
Long-term insulin treatment resulted in increased basal glycerol release, reaching sixfold at 22 h with 1 nmol/l insulin. Partial inhibition was observed by pharmacologically inhibiting phosphatidylinositol 3-kinase or the mitogen-activated kinase kinase--extracellular signal-regulated kinase cascades. This represented 50-60% of the response induced by 1 nmol/l TNF-alpha and approximately 40 % of the glycerol release maximally stimulated by isoproterenol (1 micromol/l, 30 min). The cellular mechanism seemed to be distinct from that of TNF-alpha: First, glycerol release in response to long-term insulin was progressive with time and did not display a lag-time characteristic of the effect of TNF-alpha. Second, pretreatment and co-treatment of the cells with troglitazone greatly inhibited TNF-alpha-induced glycerol release (128.5 +/- 10.2 to 35.4 +/- 2.1 nmol/mg protein per h) but not the effect of insulin, which was exaggerated. Third, hormone-sensitive lipase protein content was decreased (45 %) by TNF-alpha but not following long-term insulin. Finally, TNF-alpha was associated with NEFA release to the medium, whereas long-term insulin treatment was not. Moreover, glycerol release during isoproterenol-stimulated lipolysis was additive to the effect of long-term insulin, whereas NEFA release was inhibited by nearly 90 %. CONCLUSIONS INTERPRETATION: Contradictory to its short-term inhibitory effect, long-term insulin stimulates glycerol release with concomitant stimulation of NEFA re-esterification.
Rosenstock
M
M
The S. Daniel Abraham Center for Health and Nutrition, Department of Clinical Biochemistry, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
Greenberg
A S
AS
Rudich
A
A
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects* / Q000378:metabolism*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry; D002867:Chromones / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005230:Fatty Acids, Nonesterified / Q000378:metabolism*; D005419:Flavonoids / Q000494:pharmacology; D051275:Glucose Transporter Type 4; D005990:Glycerol / Q000378:metabolism*; D007328:Insulin / Q000008:administration & dosage / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D007700:Kinetics; D008066:Lipolysis / Q000187:drug effects; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D009004:Monosaccharide Transport Proteins / Q000032:analysis; D009025:Morpholines / Q000494:pharmacology; D009124:Muscle Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000032:analysis; D013844:Thiazoles / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage / Q000494:pharmacology*
D000318:Adrenergic beta-Agonists; D001786:Blood Glucose; D002867:Chromones; D004791:Enzyme Inhibitors; D005230:Fatty Acids, Nonesterified; D005419:Flavonoids; D051275:Glucose Transporter Type 4; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D009004:Monosaccharide Transport Proteins; D009025:Morpholines; D009124:Muscle Proteins; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; C495693:Slc2a4 protein, mouse; D013844:Thiazoles; D014409:Tumor Necrosis Factor-alpha; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D020928:Mitogen-Activated Protein Kinases; D005990:Glycerol; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one