Effects of supranormal liver glycogen content on hyperglucagonemia-induced liver glycogen breakdown.
The purpose of the present study was to test the hypothesis that a higher hepatic glycogen level is associated with higher glucagon-induced hepatic glycogen depletion. Four groups of anesthetized rats received three injections (at times 0, 30, and 60 min) of glucagon (intravenously, 20 [microg/kg). Among these groups, hepatic glycogen levels had previously been manipulated either by an overloading diet (Fast-refed), a reduction in food intake (1/2-fast), or exercise (75 min of running, 26 m/ min, 0% grade). A fourth group had normal hepatic glycogen levels. A fifth group of rats was injected only with saline (0.9% NaCl). Liver glycogen concentrations were measured every 30 min during the course of the 90-min experiment, using liver samples obtained from the open liver biopsy technique. Plasma glucagon concentrations were significantly higher (P < 0.05) in the glucagon-injected groups than in the saline-injected group. As expected, liver glycogen levels were significantly higher (P < 0.01; 1.6-fold) in the Fast-refed group than in all other groups. Glucagon-induced decreases in liver glycogen concentrations were similar in Fast-refed than in normally fed and exercised rats when the overall 90-min period was considered. However, during the course of the last 30-min period, liver glycogen was significantly (P < 0.01) decreased only in the Fast-refed group. The Fast-refed, normally fed, and exercised groups had a similar glucagon-induced hyperglycemia that was significantly more elevated (P < 0.01) than glucose levels measured in the saline-injected group. Glucagon-induced reactive hyperinsulinemia was observed only in the Fast-refed and normally fed rats, and not in the exercised and 1/2-fast rats. It is concluded that supranormal levels of liver glycogen may be associated with a larger hyperglucagonemia-induced liver glycogen breakdown.
Bélanger
P
P
Département de Kinésiologie, Université de Montréal, Québec, Canada.
Couturier
K
K
Latour
M G
MG
Lavoie
J M
JM
D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D004837:Epinephrine / Q000097:blood; D005934:Glucagon / Q000097:blood* / Q000494:pharmacology; D007328:Insulin / Q000097:blood; D008112:Liver Glycogen / Q000378:metabolism*; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010805:Physical Conditioning, Animal; D051381:Rats; D017207:Rats, Sprague-Dawley
D001786:Blood Glucose; D007328:Insulin; D008112:Liver Glycogen; D005934:Glucagon; D009638:Norepinephrine; D004837:Epinephrine