Submitted on May 9, 2007
Accepted on November 5, 2007
Contrasting Effects of Exercise, AICAR and Increased Fatty Acid Supply on In Vivo and Skeletal Muscle Glucose Metabolism
Christian Rantzau1, Michael J. Christopher2, and Frank Peter Alford2*
1 Medicine (AH/NH), University of Melbourne, Melbourne, Victoria, Australia
2 Endocrinology/Diabetes, St Vincents Hospital, Fitzroy, Victoria, Australia
* To whom correspondence should be addressed. E-mail: frank.alford{at}svhm.org.au.
The increased energy required for acute moderate exercise by skeletal muscle (SkM) is derived equally from enhanced fatty acid (FA) oxidation (FAox) and glucose oxidation (Gox). Availability of FA also influences contracting SkM metabolic responses. Whole body glucose turnover and SkM glucose metabolic responses were determined in paired dog studies during: i) 30 min moderate exercise (VO2 max ~60%) test vs. 60 min low-dose 5-aminoimidazole-4-carboxamide-1-
-D-ribofuranoside infusion (AICAR); ii) an AICAR infusion vs. modest elevation of FA induced by a 150 min combined Intralipid / heparin (IL/hep) infusion; iii) an acute exercise test performed with vs. without IL/hep. The exercise responses differed from those observed with AICAR: plasma FA and glycerol rose sharply with exercise, whereas FA fell and glycerol was unchanged with AICAR; glucose turnover, and glycolytic flux (GFexog) doubled with exercise but rose only by 50% with AICAR; SkM glucose-6-phosphate rose and glycogen content decreased with exercise whereas no changes occurred with AICAR. The metabolic responses to AICAR vs. IL/hep differed: GFexog was stimulated by AICAR but suppressed with IL/hep; no changes in glucose turnover occurred with IL/hep. Glucose turnover responses to exercise were similar in the IL/hep and non-IL/hep, but SkM lactate and glycogen concentrations rose with IL/hep compared with exercise alone. In conclusion, the metabolic responses to acute exercise are not mimicked by a single dose of AICAR or altered by short term enhancement of fatty acid supply.
