Beta-endorphin infusion during exercise in rats does not alter hepatic or muscle glycogen.
The aim of this study was to determine whether beta-endorphin infusion influences liver or muscle glycogen concentration during exercise. Thirty-two rats (Harlan Co., IN, USA) with a body mass of 265-290 g were assigned at random to four groups, each of eight rats: (1) beta-endorphin infusion for 90 min at rest; (2) beta-endorphin infusion for 90 min while running on a rodent treadmill at 22 m x min(-1) and 0% grade; (3) saline infusion (0.9% NaCl) for 90 min at rest; and (4) saline infusion for 90 min while running on a rodent treadmill at 22 m x min(-1) and 0% grade. Beta-endorphin infusion elevated plasma beta-endorphin concentration by 2.5-fold at rest compared with saline infusion at rest, and by two-fold after exercise compared with saline infusion after exercise. Beta-endorphin infusion attenuated exercise-induced glucose concentration but did not alter the fasting hepatic glycogen concentration at rest or after exercise compared with saline infusion. Fasting hepatic glycogen decreased significantly as a result of 90 min of exercise independent of treatment. Deep intermedius muscle glycogen concentration at rest was similar after 90 min of both beta-endorphin and saline infusion and decreased significantly as a result of 90 min of exercise independent of treatment. Our results suggest that liver and muscle glycogenolysis is not responsible for the differences in plasma glucose with beta-endorphin infusion during exercise.
Jamurtas
A Z
AZ
Department of Physical Education and Sport Sciences, University of Thessaly, Trikala, Greece. ajamurt@pe.uth.gr
Goldfarb
A H
AH
Chung
S C
SC
Hegde
S
S
Marino
C
C
Fatouros
I G
IG
D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D005934:Glucagon / Q000097:blood; D006003:Glycogen / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010805:Physical Conditioning, Animal; D011897:Random Allocation; D051381:Rats; D001615:beta-Endorphin / Q000494:pharmacology*
D001786:Blood Glucose; D001615:beta-Endorphin; D006003:Glycogen; D005934:Glucagon