ADRENALINE STIMULATED GLYCOGEN BREAKDOWN IN RAT EPITROCHLEARIS MUSCLES - FIBER-TYPE SPECIFICITY AND RELATION TO PHOSPHORYLASE TRANSFORMATION

The effect of adrenaline on glycogen breakdown in different skeletal m uscle fibre types was investigated in the epitrochlearis muscle in vit ro. Histochemical studies showed that adrenaline stimulated glycogen b reakdown in all three major fibre types, with a higher absolute glycog en breakdown in type IIB fibres compared to type IIA and type I fibres . In biochemical studies we found that the glycogenolytic rate decreas ed during prolonged incubation with adrenaline, although the percentag e phosphorylase in the a form and the concentration of glucose-6-phosp hate (G-6-P) remained high. In the dose response studies we found an E C(50) of 2.2 x 10(-8) M adrenaline for adrenaline stimulated glycogen breakdown, and an EC(50) of 2.0 x 10(-7) M for adrenaline stimulated a ccumulation of G-6-P, excluding G-6-P as the key inhibitor of phosphor ylase a activity.