HIGH PHYSIOLOGICAL LEVELS OF EPINEPHRINE DO NOT ENHANCE MUSCLE GLYCOGENOLYSIS DURING TETANIC STIMULATION

This study examined whether high physiological concentrations of epine phrine (EPI) would enhance muscle glycogenolysis during intense muscul ar contractions. Muscles of the rat hindlimb were perfused for 12 min at rest and 45 s of tetanic stimulation (1.0-Hz train rate, 100-ms tra in duration at 80 Hz) without EPI (control) or with 15 or 35 nM EPI. I n the EPI groups the muscles were perfused with EPI for the last 2 min of rest perfusion and throughout stimulation. Glycogenolysis in the w hite gastrocnemius, red gastrocnemius, plantaris, and soleus muscles d uring stimulation was unaffected by the presence of EPI in the perfusi on medium. In addition, muscle lactate and hindlimb lactate efflux wer e similar in EPI and control groups. It is concluded that EPI is not i mportant for enhancing glycogenolysis in rat muscles composed predomin antly of fast-twitch fibers during intense short-term tetanic stimulat ion.