title: Effects of glucose infusion in exercising rats.
abstract: To determine whether feedforward control of liver glycogenolysis during exercise is subject to negative feedback by elevated blood glucose, glucose was infused into exercising rats at a rate that elevated blood glucose greater than 10 mM. Liver glycogen content decreased 22.4 mg/g in saline-infused rats compared with 13.6 mg/g in glucose-infused rats during the first 40 min of treadmill running (21 m/min, 15% grade). Liver adenosine 3',5'-cyclic monophosphate (cAMP) concentration was significantly lower in the glucose-infused rats during the exercise bout. The concentration of hepatic fructose 2,6-bisphosphate remained elevated throughout the exercise bout in glucose-infused rats but decreased markedly in saline-infused rats. Plasma insulin concentration was higher and plasma glucagon concentration lower in glucose-infused rats than in saline-infused rats during exercise. Early in exercise, liver glycogenolysis proceeds in the glucose-infused rats despite the fact that glucose and insulin concentrations are markedly elevated and liver cAMP is unchanged from resting values. These observations suggest the existence of a cAMP-independent feedforward system for activation of liver glycogenolysis that can override classical negative feedback mechanisms during exercise.
authors.affiliation: Department of Zoology, Brigham Young University, Provo, Utah 84602.
authors.forename: W W
authors.initials: WW
authors.lastname: Winder
authors.forename: J
authors.initials: J
authors.lastname: Arogyasami
authors.forename: H T
authors.initials: HT
authors.lastname: Yang
authors.forename: K G
authors.initials: KG
authors.lastname: Thompson
authors.forename: L A
authors.initials: LA
authors.lastname: Nelson
authors.forename: K P
authors.initials: KP
authors.lastname: Kelly
authors.forename: D H
authors.initials: DH
authors.lastname: Han
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D003345:Corticosterone / Q000097:blood; D000242:Cyclic AMP / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005934:Glucagon / Q000097:blood; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D007262:Infusions, Intravenous; D007328:Insulin / Q000097:blood; D007773:Lactates / Q000097:blood; D008099:Liver / Q000378:metabolism*; D008112:Liver Glycogen / Q000378:metabolism; D008297:Male; D005082:Physical Exertion; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D007773:Lactates; D008112:Liver Glycogen; D005934:Glucagon; D000242:Cyclic AMP; D005947:Glucose; D003345:Corticosterone