Effects of glucagon with or without insulin administration on liver glycogen metabolism.
Rats fed ad libitum were given insulin alone (4 U/kg), glucagon alone (25 micrograms/kg), or insulin and glucagon sequentially. Phosphorylase a and synthase R activities, hepatic glycogen, uridine diphosphoglucose, inorganic phosphate (Pi), and plasma glucose, lactate, glucagon, and insulin concentrations were determined over the subsequent 40 min. In separate animals, muscle extraction of 2-deoxy-D-[3H]glucose also was determined. After glucagon administration, glycogen phosphorylase a and plasma glucose were increased within 5 min. However, the glycogen concentration did not decrease for 20 min. Glucagon administration to rats pretreated with insulin stimulated a similar increase in phosphorylase a activity. Again, glycogen was not degraded for 20 min. After insulin only, glycogen concentration remained unchanged. Plasma glucose decreased as expected. In each group, muscle extraction of 2-deoxy-D-[3H]glucose increased compared with the controls (P < 0.05). In summary, glucagon and/or insulin administration did not stimulate significant glycogen degradation for 20 min, even though phosphorylase was activated. The mechanism remains to be determined.
Ercan
N
N
Metabolic Research Laboratory, Minneapolis Veterans Affairs Medical Center, Minnesota, USA.
Gannon
M C
MC
Nuttall
F Q
FQ
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D003847:Deoxyglucose / Q000378:metabolism; D005934:Glucagon / Q000378:metabolism / Q000494:pharmacology*; D006003:Glycogen / Q000378:metabolism*; D007328:Insulin / Q000097:blood / Q000494:pharmacology*; D008099:Liver / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D006005:Phosphorylases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D001786:Blood Glucose; D007328:Insulin; D006003:Glycogen; D005934:Glucagon; D003847:Deoxyglucose; D006005:Phosphorylases