Regulation of glycogen synthesis in rat skeletal muscle after glycogen-depleting contractile activity: effects of adrenaline on glycogen synthesis and activation of glycogen synthase and glycogen phosphorylase

We investigated the effects of insulin and adrenaline on the rate of glycog en synthesis in skeletal muscles after electrical stimulation in vitro. The contractile activity decreased the glycogen concentration by 62%. After co ntractile activity, the glycogen stores were fully replenished at a constan t and high rate for 3 h when 10 m-i.u./ml insulin was present. In the absen ce of insulin, only 65% of the initial glycogen stores was replenished. Adr enaline decreased insulin-stimulated glycogen synthesis. Surprisingly, adre naline did not inhibit glycogen synthesis stimulated by glycogen-depleting contractile activity. In agreement with this, the fractional activity of gl ycogen synthase was high when adrenaline was present after exercise, wherea s adrenaline decreased the fractional activity of glycogen synthase to a lo w level during stimulation with insulin. Furthermore, adrenaline activated glycogen phosphorylase almost completely during stimulation with insulin, w hereas a much lower activation of glycogen phosphorylase was observed after contractile activity. Thus adrenaline does not inhibit contraction-stimula ted glycogen synthesis.