IN-VIVO QUANTIFICATION OF GLUCOSE-UPTAKE AND CONVERSION TO GLYCOGEN IN INDIVIDUAL MUSCLES OF THE RAT FOLLOWING EXERCISE

Glycogen depletion is thought to be a potent stimulus for the substant ially increased glucose fluxes observed in skeletal muscle following e xercise. The aim of this study was to establish the relationships betw een the glycogen mass and the rates of glucose uptake (R-g) and glucos e incorporation into glycogen (R,I,) in individual muscles of consciou s adult Wistar rats following moderate nonexhausting treadmill exercis e (15 m/min at a 10 degrees slope for 45 minutes, similar to 65% VO2ma x). Muscle glycogen content was determined at 0, 20, 45, 90, or 135 mi nutes following exercise and compared with Rb and R,I, measurements at matched times. Muscle types varied in the rate of glycogen resynthesi s, Glycogen depots of glycolytic muscle (white gastrocnemius) were sti ll significantly (P <.01) lower than preexercise levels after 135 minu tes; red oxidative muscles (soleus and red gastrocnemius) were essenti ally repleted by 90 minutes. Immediately following exercise, Rb and R, I, in red gastrocnemius and soleus were 42 +/- 4 and 42 +/- 5 and 36 /- 2 and 33 +/- 7 mu mol/(min.100 g), greater than the rates induced b y maximal insulin stimulation in previous studies. In red muscles, the re was a strong inverse relationship between R,I, and tissue glycogen content, consistent with a dominant role for the glycogen mass in the regulation of glycogen resynthesis, Copyright (C) 1998 by W.B. Saunder s Company.