A 48-hour lipid infusion in the rat time-dependently inhibits glucose-induced insulin secretion and B cell oxidation through a process likely coupled to fatty acid oxidation.
Short- and long-term effects of hyperlipidemia with elevated FFA on insulin secretion were investigated. Male Sprague-Dawley rats were fed ad libitum and additionally infused with Intralipid 10%, 1.0 ml/h. After 3 h of Intralipid the response to 27 mM glucose in isolated perfused pancreas was enhanced by 86%, P less than 0.02. After 6 h of Intralipid enhancement had subsided. After 48 h of Intralipid glucose-induced insulin release was inhibited by 49%, from 1950 +/- 177 microU/min after saline to 1003 +/- 232 microU/min after Intralipid, P less than 0.02. Inhibition was glucose-selective since responses to other secretagogues (1 mM 3-isobutyl-1 methylxanthine, 10 mM octanoate, or 5 mM alpha-ketoisocaproic acid) were unaffected as were pancreatic contents of insulin (2284 +/- 111 mU/pancreas after saline, 2566 +/- 131 mU/pancreas after Intralipid). In isolated islets from 48 h lipid infused rats production of [14-C]CO2 from D[U-14-C]glucose was decreased (P less than 0.02) in parallel with the insulin response to 27 mM glucose. Glucose-induced secretion was partially normalized by in vitro exposure to a carnitine palmitoyl-transferase I inhibitor (Etomoxir). Effects of a 48 h lipid infusion were also tested during hyperglycemia. Rats were infused with glucose, and hyperglycemia was enhanced by dexamethasone (25 micrograms/24 h). Hyperglycemia depressed glucose-induced secretion from perfused pancreas from 2072 +/- 22 microU/min after saline + dexamethasone to 1185 +/- 155 microU/min after glucose + dexamethasone, P less than 0.01). Intralipid, added to the latter protocol, further inhibited glucose-induced secretion to 437 +/- 87 microU/min, P less than 0.005. Hyperlipidemia is concluded to be associated with short term stimulation but long term inhibition of glucose-induced insulin secretion. Evidence indicates that inhibition depends on fatty acid oxidation, is coupled to decreased glucose oxidation and operates both during normo- and hyperglycemia.
Department of Endocrinology, Karolinska Hospital, Stockholm, Sweden.
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Sako
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Grill
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002334:Carnitine O-Palmitoyltransferase / Q000037:antagonists & inhibitors; D003907:Dexamethasone / Q000494:pharmacology; D004852:Epoxy Compounds / Q000494:pharmacology; D005217:Fat Emulsions, Intravenous / Q000494:pharmacology*; D005227:Fatty Acids / Q000378:metabolism*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005947:Glucose / Q000494:pharmacology*; D006943:Hyperglycemia / Q000097:blood; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains
D001786:Blood Glucose; D004852:Epoxy Compounds; D005217:Fat Emulsions, Intravenous; D005227:Fatty Acids; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D003907:Dexamethasone; D002334:Carnitine O-Palmitoyltransferase; D005947:Glucose; C054207:etomoxir; D015056:1-Methyl-3-isobutylxanthine