Liver glycogen metabolism during short-term insulin-induced hypoglycemia in fed rats.
The activities of glycogen phosphorylase and synthase during infusions of glucagon, isoproterenol, or cyanide in isolated liver of fed rats submitted to short-term insulin-induced hypoglycemia (IIH) was investigated. A condition of hyperinsulinemia/hypoglycemia was obtained with an intraperitoneal injection of regular insulin (1.0 U kg(-1)). The control group received ip saline. The experiments were carried out 60 min after insulin (IIH group) or saline (COG group) injection. The rats were anesthetized and after laparotomy, blood was collected from the vena cava for glucose and insulin measurements. The liver was then infused with glucagon (1 nM), isoproterenol (2 microM), or cyanide (0.5 mM) during 20 min and a sample of the organ was collected for determination of the activities of glycogen phosphorylase and synthase 5 min after starting and 10 min after stopping the infusions. The infusions of cyanide, glucagons, and isoproterenol did not change the activities of glycogen synthase and glycogen phosphorylase. However, glycogen catabolism was decreased during the infusions of glucagon and isoproterenol in IIH rats, being more intense with isoproterenol (p < 0.05), than glucagon. It was concluded that short-term IIH promoted changes in the liver responsiveness of glycogen degradation induced by glucagon and isoproterenol without a change in the activities of glycogen phosphorylase and synthase.
Obici
Simoni
S
Department of Pharmacy and Pharmacology, State University of Maringá, PR, Brazil.
Lopes-Bertolini
Gisele
G
Curi
Rui
R
Bazotte
Roberto Barbosa
RB
D000818:Animals; D004789:Enzyme Activation / Q000187:drug effects; D005247:Feeding Behavior / Q000187:drug effects*; D005934:Glucagon / Q000008:administration & dosage / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D024981:Glycogen Phosphorylase / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism; D050261:Glycogenolysis / Q000187:drug effects; D006019:Glycolysis / Q000187:drug effects; D007003:Hypoglycemia / Q000139:chemically induced / Q000378:metabolism*; D066298:In Vitro Techniques; D007274:Injections, Intraperitoneal; D007328:Insulin / Q000008:administration & dosage* / Q000494:pharmacology*; D007545:Isoproterenol / Q000008:administration & dosage / Q000494:pharmacology; D019344:Lactic Acid / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008112:Liver Glycogen / Q000378:metabolism*; D008297:Male; D019289:Pyruvic Acid / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D007328:Insulin; D008112:Liver Glycogen; D019344:Lactic Acid; D019289:Pyruvic Acid; D005934:Glucagon; D024981:Glycogen Phosphorylase; D006006:Glycogen Synthase; D005947:Glucose; D007545:Isoproterenol