Contrasting action of short- and long-term adrenaline infusion on dog skeletal muscle glucose metabolism.

There are important differences between the short- and long-term effects of adrenaline on determinants of glucose tolerance. To assess this metabolic adaptation at tissue level, the present study examined the effect of acute and prolonged in vivo elevation of adrenaline on glycogen metabolism and glycolysis in skeletal muscle. Adrenaline (50 ng.kg-1.min-1) was infused for 2 h or 74 h and the results compared with 1 h 0.9% NaCl infusion in six trained dogs. Muscle glycogen content was reduced by long-term adrenaline (161 +/- 17 vs NaCl 250 +/- 24 mumol/g dry weight; p less than 0.05) but not short-term adrenaline (233 +/- 21) indicating a sustained effect of adrenaline on glycogen metabolism. Acutely, glycogen synthase I was reduced (short-term adrenaline 12 +/- 6 vs NaCl 22 +/- 7 mumol glycosyl units.g-1.min-1; p less than 0.05) but returned to normal with prolonged adrenaline infusion (20 +/- 5). In contrast, Km for glycogen phosphorylase alpha was not changed acutely (short-term adrenaline 31 +/- 6 vs NaCl 27 +/- 7 mmol/l inorganic phosphate) but was reduced during long-term infusion (19 +/- 4; p less than 0.05 vs short-term adrenaline). Thus, with short- and long-term adrenaline infusion, there were different enzyme changes, although likely to promote glycogenolysis in both cases. In the glycolytic pathway the substrates glucose 6-phosphate and fructose 6-phosphate did not change significantly and hexokinase was not inhibited. Acutely, phosphofructokinase had reduced Vmax (short-term adrenaline 34 +/- 6 vs NaCl 44 +/- 5 U/g; p less than 0.05) but was still above the maximal operating rate in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)