Liver glucagon receptor binding properties: rapid changes with exercise and post-exercise

Abstract

The purpose of this study was to describe the effects of swimming exercise and post-exercise periods on liver glucagon receptor (GR) binding properties. Rats were randomly assigned to a rest control, a swimming exercise (90and 180-min) and post-exercise (60and 180-min) groups. Rats were sacrificed at the end of the exercise or the post-exercise periods, blood was sampled and liver was removed rapidly. Plasma membranes were purified from liver and saturation kinetics were obtained by incubation (10 mg of proteins/150 mL) with ()I-labeled glucagon at concentrations ranging from 0.15 to 3.0 nM for 30 min at 30°C. results: No changes were observed with blood glucose during exercise and post-exercise periods, even if hepatic glycogen concentrations were significantly depleted with both exercise and post-exercise periods. Saturating curve analysis indicated higher glucagon receptor density with exercise reaching after 180 min: Bmax = 8.19 ± 0.29 pmol/pg of proteins vs 3.09 ± 0.53 pmol/pg of proteins in liver from resting control (P < 0.05). The glucagon receptor density decreased in post-exercise to reach 4.46 ± 1.75 pmol/pg of proteins after 180 min of post-exercise. Moderate changes in glucagon receptor affinity were also observed in the exercise and post-exercise groups compared to the control group (Kd at 180 min exercise and post-exercise: 0.46 ± 0.05 and 0.17 ± 0.01 vs 0.33 ± 0.05 nM in the rest control group). At the pancreatic hormone levels, these binding properties changes were associated with an increase in glucagon/insulin ratio of x2.8 and x8.7 during 90 and 180 min exercise periods and x9.3 and x2.7 after 60 and 180 min postexercise periods vs the rest control group. conclusion: these results suggest that exercise and post-exercise episodes induced both changes in insulin and glucagon concentrations and rapid modification in glucagon receptor binding properties. Although the exact mechanisms remain unknown, there is no doubt that the liver adapt rapidly to exercise through modulation of GR binding characteristics. Funded by Natural Sciences and Engineering Research Council of Canada.