Effects of epinephrine on glucose metabolism in contracting rat skeletal muscles

Abstract

The effects of epinephrine on glucose metabolism during contractile activity and insulin stimulation were investigated in fast-twitch (epitrochlearis) and slow-twitch (soleus) muscles from Wistar rats. All muscles were mounted on contraction apparatuses, and some muscles were stimulated electrically for 30 min in vitro. Glucose uptake and glucose phosphorylation were measured with 2-[1,2-3H(N)]deoxy-d-glucose and glucose transport with 3- O-[ methyl-3H]methyl-d-glucose.d-[1-14C]mannitol was used to correct for extracellular space. In epitrochlearis, both contraction and insulin increased glucose transport by threefold, and combined they showed an additive effect. Epinephrine (10−6 M) did not influence glucose transport across the membrane during contractile activity or insulin stimulation. In the absence of epinephrine, similar glucose phosphorylation was obtained during contraction and during insulin stimulation in epitrochlearis (∼12 mmol ⋅ kg dry wt−1 ⋅ 30 min−1). In the presence of epinephrine, 9.5 ± 0.6 mmol ⋅ kg dry wt−1 ⋅ 30 min−1 glucose was phosphorylated during contraction, whereas only 2.0 ± 0.3 mmol ⋅ kg dry wt−1 ⋅ 30 min−1 was phosphorylated during insulin stimulation ( P < 0.01), despite a similar glucose 6-phosphate concentration. Comparable results were obtained in soleus. In conclusion, our data suggest that epinephrine inhibits glucose phosphorylation much less during contraction than during insulin stimulation.